llillliii 


j*r  -  -  v  v  , 
^v?':      :  Vvv, 


W*tm>Vyi 


tjmimjm^^m 

M^  &  WJ&A  „  ^  M  ffi  .A-jV^.  i  vW 


O 


"vg^vvvCv^ 

^^U-^vVV 


Ww   •;•;»• 


,vvyuw 


M&aw 


"tftu  m  -v'v- •** 

p^if*  w^ 


JWWVW  A          v  "    ;v^wv-          '  *vv**v*VV**w    vwv   v^.v  y^-J-  -vvWv,;\ 

f^f^SssS' 

'vv.^^,       ^-: 


yy^y; 


^P^i^te 

^VvWvJvN" 


. 


^y,xM-:- 


ORE-DEPOSITS. 


A    SEQUEL    TO   THE    SECOND    EDITION.   OF   "  THE    GENESIS    OF 

ORE-DEPOSITS,"  BY  FRANZ  POSEPNY  AND  OTHERS;   BEING 

A  COMPILATION   OF  CONTRIBUTIONS   TO   THIS    SCIENCE 

FROM    THE    TRANSACTIONS    OF    THE    AMERICAN 

INSTITUTE     OF     MINING     ENGINEERS,    WITH 

A  CRITICAL  INTRODUCTION  AND  SYNOPSIS. 


BY 


SAMUEL    FKANKLIN    EMMONS, 

Economic  Geologist  of  the  U.  S.  Geological  Survey. 


CONTAINING  ALSO  A  BIOGRAPHICAL  NOTICE  OF  MB.  EMMONS  BY  DR.  GEORGE 
F.  BKCKER  ;  A  BIBLIOGRAPHY  OF  THE  SUBJECT  BY  PROF.  JOHN  D. 
IRVING,   H.  D.  SMITH,  AND   H.  G.  FERGUSON  ;   AND  A 
PREFACE  BY  DR.  ROSSITER  W.  RAYMOND,  SEC- 
RETARY EMERITUS  OF  THE  INSTITUTE. 


NEW  YORK,  N.  Y. : 

PUBLISHED  BY  THE  DESTITUTE 

AT  THE  OFFICE  OF  THE  SECRETARY. 

1913. 


>«•**>•*  *  *::,  :  »  >>,« 


CONTENTS. 


PAGE 

Preface, v 

Introduction.     By  SAMUEL  FRANKLIN  EMMONS,         .        .        ...      vii 
Biographical  Notice  of  Samuel  Franklin  Emmons.  By  GEORGE  F.  BECKER,  xxix 


The  Genesis  of  Certain  Ore-Deposits.  By  S.  F.  EMMONS,  .  ...»  I 
Structural  Eelations  of  Ore-Deposits.  By  8.  F.  EMMONS,  2d 

Geological  Distribution  of  the  Useful  Metals  in  the  United  States.    By  S.  F. 
EMMONS.     Discussion,  by  JOHN  A.  CHURCH,  ARTHUR  WINSLOW,  S.  F. 

EMMONS,  and  WILLIAM  HAMILTON  MERRITT, 65 

The  Torsional  Theory  of  Joints.     By  GEORGE  F.  BECKER.     Discussion,  by 

H.  M.  HOWE,  R.  W.  EAYMOND,  C.  K.  BOYD,  and  GEORGE  F.  BECKER,      92 

The  Allotropism  of  Gold.     By  HENRY  Louis, 105 

The  Superficial  Alteration  of  Ore-Deposits.     By  K.  A.  F.  PENROSE,  JR.,     .     110 
Some  Mines  of  Rosita  and  Silver  Cliff,  Colorado.     By  S.  F.  EMMONS,         .     139 
The  Genesis  of  Certain  Auriferous  Lodes.     By  JOHN  K.  DON.     Discussion, 
by  JOSEPH  LE  CONTE,  S.  F.  EMMONS,  GEORGE  F.  BECKER,  ARTHUR  WIN- 
SLOW,  W.  P.  BLAKE,  and  J.  R.  DON, 162 

Influence  of  Country-Rock  on  Mineral  Veins.  By  WALTER  HARVEY  WEED,  216 
Igneous  Rocks  and  Circulating  Waters  as  Factors  in  Ore-Deposition.  By 

J.  F.  KEMP, 235 

A  Consideration  of  Igneous  Rocks  and  Their  Segregation  or  Differentiation 
as  Related  to  the  Occurrence  of  Ores.    By  J.  E.  SPURR.     Discussion, 

by  ALEXANDER  N.  WINCHELL, 251 

The  Chemistry  of  Ore-Deposition.   By  WALTER  P.  JENNEY.    Discussion,  by 

JOHN  A.  CHURCH, 305 

Ore-Deposits  near  Igneous  Contacts.     By  WALTER  HARVEY  WEED.     Dis- 
cussion, by  W.  L.  AUSTIN, 364 

Ore-Deposition  and  Vein-Enrichment  by  Ascending  Hot  Waters    By  WALTER 

HARVEY  WEED,     .  403 

Basaltic  Zones  as  Guides  to  Ore-Deposits  in  the  Cripple  Creek  District, 

Colorado.     By  E.  A.  STEVENS, 411 

The  Geological  Features  of  the  Gold- Production  of  North   America.    By 
WALDEMAR  LINDGREN.    Discussion,  by  WILLET  G.  MILLER,  and  W. 

L.  AUSTIN,     . 424 

Osmosis  as  a  Factor  in  Ore- Formation.  By  HAL  BERT  POWERS  GILLETTE,  450 
The  Ore-Deposits  of  Sudbury,  Ontario.  By  CHARLES  W.  DICKSON,  .  .  455 
The  Genesis  of  the  Copper- Deposits  of  Clifton- Morenci,  Arizona.  By 

WALDEMAR  LINDGREN, 517 

The  Copper-Deposits  at  San  Jose,  Tamaulipas,  Mexico.  By  J.  F.  KEMP,  557 
The  Magmatic  Origin  of  Vein-Forming  Waters  in  Southeastern  Alaska.  By 

ARTHUR  C.  SPENCER, 582 

Genetic  Relations  of  the  Western  Nevada  Ores.     ByJ.E.  SPURR,         .        .     590 
Are  the  Quartz- Veins  of  Silver  Peak,  Nevada,  the  Result  of  Magmatic  Seg- 
regation ?    By  JOHN  B.  HASTINGS, 621 

The  Occurrence  of  Stibnite  at  Steamboat  Springs,  Nevada.     By  WALDEMAR 

LINDGREN,     ....        .        .        .        ...        .        .        .        .     629 

(hi) 


IV  CONTENTS. 

PAGE 

A  Summary  of  Lake  Superior  Geology  with  Special  Reference  to  Recent 

Studies  of  the  Iron- Bearing  Series.  By  C.  K.  LEITH,  .  •  '  .  .  .  633 

The  Geological  Relations  of  the  Scandinavian  Iron-Ores.  By  HJALMAR 

SJOGREN,  .  .  . 657 

The  Formation  and  Enrichment  of  Ore-Bearing  Veins.  ( With  Supplementary 

Paper. )  By  GEORGE  J.  BANCROFT, 696 

The  Distribution  of  the  Elements  in  Igneous  Rocks.  By  HENRY  S.  WASH- 
INGTON,  729 

The  Agency  of  Manganese  in  the  Superficial  Alteration  and  Secondary  En- 
richment of  Gold-Deposits  in  the  United  States.  By  WILLIAM  H. 
EMMONS,  .  .  . 759 


Cognate  Papers,     . 829 

Bibliography  of  the  Science  of  Ore-Deposits.     By  JOHN  D.  IRVING,  H.  D. 

SMITH,  and  H.  G.  FERGUSON,        .       ....        ...        .        •         .  837 

Index,  .        . 929 

ERRATUM. 

Page  761,  footnote  s :  for  1904,  read  1894. 


PREFACE. 


AT  the  Chicago  meeting  of  the  Institute  in  1893,  a  remarka- 
bly suggestive  and  comprehensive  paper  on  the  Genesis  of 
Ore-Deposits,  by  Prof.  Franz  Posepny,  an  Honorary  Member  of 
the  Institute,  was  presented  and  discussed.  This  paper  com- 
prised the  substance  of  the  author's  teaching  on  the  subject  at 
the  Mining  Academy  of  Pribram.  It  was  translated  by  me 
from  the  German  manuscript,  and  that  translation,  printed  by 
the  Institute,  was  the  first  publication  in  any  language  of  this 
important  treatise.  I  returned  the  original  to  Germany,  where 
it  was  subsequently  published. 

Posepny's  paper  and  its  discussion,  as  contained  in  Vols. 
XXIII.  and  XXIV.  of  our  Transactions ,  aroused  wide-spread 
attention;  and,  in  1895,  were  reprinted  in  a  separate  volume. 
The  first  edition  of  this  volume  having  become  exhausted,  a 
second  and  revised  edition,  comprising  a  large  number  of  addi- 
tional papers  and  discussions,  was  issued  in  1902.  As  an 
indexed  compilation  of  material  scattered  through  our  Trans- 
actions, the  "  second  Posepny  book  "  proved  so  convenient  to 
instructors,  students,  and  practicing  experts  that  another,  of 
similar  character,  is  now  called  for. 

The  great  recent  progress  of  the  science  of  ore-deposits  has 
been  largely  due  to  the  labors  of  the  members  of  the  U.  S. 
Geological  Survey  and  to  their  cordial  co-operation  in  the 
work  of  the  Institute,  through  contributions  to  its  Transactions. 

It  was  in  this  spirit  of  co-operation  that  S.  F.  Emmons,  the 
distinguished  economic  geologist  of  that  Survey,  who  had  been 
since  1877  a  member,  and  thrice  during  that  period  a  Vice- 
President,  of  the  Institute,  consented  to  edit  the  present  vol- 
ume. This  generous  service  I  accepted  with  enthusiastic 
gratitude,  both  personal  and  official ;  for  it  relieved  me  from  a 
task  for  which  I  could  scarcely  find  the  necessary  surplus  time 
and  strength,  and  it  secured  the  performance  of  that  task  by 
more  competent  hands  and  with  far  greater  technical  authority. 

Mr.  Emmons  made  the  selection  and  arrangement  of  the 

(v) 


VI  PREFACE. 

papers  to  be,  in  whole  or  in  part,  republished  in  the  volume, 
and  wrote  the  introductory  and  the  supplementary  chapter,  thus 
finishing  all  the  work  which  he  had  undertaken,  except  that 
final  revision  of  the  proof-sheets,  which  every  author  or  editor 
claims  as  a  right  and  needs  in  self-protection.  But  it  was  ar- 
ranged between  us  that  I  should  relieve  him  of  the  details  of 
proof-reading,  beyond  his  approval  of  the  text  of  his  own  con- 
tributions; and  this  text  had  been  so  thoroughly  discussed 
between  us  as  to  make  any  further  change. of  it  by  him  highly 
improbable.  He  had  also  approved  the  Preface  which  I  pro- 
posed— and  which,  alas !  is  no  longer  appropriate. 

The  sudden  death  of  Mr.  Emmons  has  necessitated  two 
changes  in  this  book — the  sorrowful  preparation  of  a  new 
Preface,  and  the  introduction  at  the  beginning  of  a  Biograph- 
ical Notice  by  Mr.  George  F.  Becker,  his  life-long  friend  and 
colleague,  commemorating  the  work  of  our  lost  leader  and 
brother.  In  all  other  respects  the  volume  is,  as  it  would  have 
been  had  he  been  spared  to  enjoy  its  completion  and  publica- 
tion, the  work  of  Mr.  Emmons ;  and  I  cannot  but  feel  that  it 
will  constitute  a  fitting  memorial  of  him,  wrought  by  his  own 
hand.  Only  too  often,  death  interrupts  the  sculptor  at  his 
work ;  but  in  this  exceptional  instance,  the  Messenger  waited, 
and  the  message  was  no  peremptory  summons,  but  the  gentler 
call,  "  Finish  what  thou  art  doing :  then  come — and  rest !  " 

It  should  be  added  that,  not  wishing  to  alter  the  work  of  my 
friend,  I  have  left  the  limit  of  selection  where  he  left  it ;  and 
therefore  this  "  Emmons  volume  "  contains  no  reference  to  In- 
stitute papers  published  later  than  the  Bulletin  of  December, 
1910. 

Thanks  are  also  due  to  Prof.  John  D.  Irving,  of  the  Sheffield 
Scientific  School  of  Yale  University,  for  the  preparation,  at  Mr. 
Emmons's  request,  of  the  Bibliography  which  adds  to  the  value 
of  the  book  as  a  guide  to  further  study. 

ROSSITER  W.  RAYMOND, 

Secretary  Emeritus. 


INTRODUCTION. 

BY  SAMUEL  FRANKLIN  EMMONS. 

THE  great  demand  for  the  "  second  Posepny  book  "  on  The 
Genesis  of  Ore-Deposits,  published  by  the  Institute  in  1902,  has 
abundantly  demonstrated  that  such  volumes  fill  a  real  want 
on  the  part  of  members  of  the  Institute  and  others ;  and  it  has 
been  judged  advisable  to  prepare  another,  including  additional 
important  papers  on  this  subject,  which  have  been  published 
in  the  Transactions  of  the  Institute. 

That  this  volume  should  not  have  an  unwieldy  bulk,  it  has 
been  necessary  to  omit  from  it,  either  entirely  or  in  part,  papers 
which  are  more  descriptive  than  genetic,  and  to  select  only 
those,  the  subject  matter  of  which  in  great  part  contributes  to 
the  elucidation  of  general  questions  of  genesis.  A  list  of  con- 
tributions that  might  have  been  included,  except  for  this 
restriction,  with  a  brief  abstract  of  each,  will  be  found  at  the 
end  of  the  volume,  in  a  supplementary  chapter,  followed  by  a 
general  bibliography  of  the  publications  on  the  subject. 

The  arrangement  of  the  papers  is  in  general  chronological ; 
but  such  an  arrangement  is  necessarily  imperfect,  because  those 
in  the*  previous  volume  were  contributed  in  a  middle  period 
(1893  to  1901),  and  some  of  the  papers  now  published  were 
written  before,  but  the  greater  part  after,  those  dates. 

The  plan  followed  in  the  selection  of  contributions  was  to 
make  them  represent,  as  far  as  they  can,  the  progress  of  inves- 
tigation and  thought  on  the  subject  of  ore-genesis  in  the  40 
years  that  have  elapsed  since  the  organization  of  the  Institute 
in  1871.  The  papers  themselves  were  not,  however,  written 
for  any  such  purpose,  but  are  merely  a  set  of  facts  and  deduc- 
tions which  the  respective  authors  thought  worthy,  at  the  time 
they  were  written,  of  the  consideration  of  their  fellow-members ; 
and  since,  as  already  stated,  they  were  written  in  part  before, 
but  for  the  most  part  after,  those  in  the  previous  volume,  they 
do  not  present  a  consecutive  or  connected  whole,  but  rather  a 
disconnected  series,  which  needs  some  kind  of  running  commen- 
tary to  bind  them  together.  It  is,  therefore,  the  province  of 

(vii) 


Vlll  INTRODUCTION. 

this  introductory  chapter  to  indicate  in  a  general  way  the  pro- 
gress of  opinion  in  the  period  under  consideration,  and  to  show 
the  place  occupied  and  the  part  played  in  this  progress  by  the 
different  papers  in  this  book  and  its  predecessor. 

At  the  time  of  the  organization  of  the  Institute  in  1871 — 
and  indeed  for  many  years  after  that  time — so  little  was  defi- 
nitely known  as  to  the  processes  entering  into  the  formation 
of  metalliferous  deposits  that  purely  geological  criteria  were 
rarely  used  in  determining  the  value  of  an  ore-deposit,  or  the 
best  method  of  working  it.  In  reading  the  reports  of  the  min- 
ing engineers  of  those  periods,  one  feels  that  such  criteria  were 
either  entirely  neglected  or  mentioned  in  a  merely  perfunctory 
way.  The  quantity  and  value  of  ore  available  or  actually 
opened  were  determined;  but  for  the  estimation  of  its  prob- 
able extent  in  unexplored  ground,  such  estimates  as  were  made 
at  all  were  ordinarily  based  on  an  effort  to  prove  the  deposit  to 
be  a  "  true  fissure-vein,"  in  which  it  was  then  assumed  that  ore, 
must  extend  to  an  indefinite  depth,  with  possibilities  of  becom- 
ing richer.  Among  professional  geologists  there  was  no  well- 
defined  consensus  of  opinion  with  regard  to  the  genesis  of 
ore-deposits.  It  was  the  commencement  of  what  I  have  else- 
where l  called  the  period  of  verification,  when  the  abundant 
and  varied  speculations  and  hypotheses  of  the  pioneers  in  this 
department  of  study  were  about  to  be  brought  to  the  test  of 
practical  application  in  a  wide  field  of  newly-developed,  ore- 
deposits.  Their  minds  were  hence  in  the  waiting  or  tentative 
stage. 

Neither  Whitney,  who  was  the  greatest  American  authority 
of  his  time,  nor  his  European  contemporary,  Gotta,  who, 
through  Prime's  translation  of  his  well-known  Treatise  on  Ore- 
Deposits,  was  for  many  years  the  recognized  authority  in 
American  law-courts,  had  very  decided  opinions  on  the  subject 
of  ore-genesis.  In  their  publications  they  presented  with  con- 
siderable impartiality  the  various  views  proposed  by  earlier 
students,  leaving  it  to  their  readers  to  select  that  which  might 
seem  most  worthy  of  belief. 

It  is  difficult  for  the  geologist  of  the  present  day  to  realize 
the  condition  of  geological  belief  at  that  time,  since  a  very 

1  Theories  of  Ore-Deposition  Historically  Considered,  Bulletin  of  the  Geological 
Society  of  America,  vol.  xv.,  p.  18  (1903). 


INTRODUCTION.  IX 

great  part  of  his  fundamental  data  in  geology  is  the  result  of 
much  later  investigations.  It  was  the  discovery,  in  the  sixties, 
that  the  auriferous  slates  of  California  were  of  Jurassic  age, 
which  finally  negatived  Murchison's  dictum  that  gold  could  be 
found  only  in  Palaeozoic  rocks.  It  was  not  until  well  in  the 
eighties  that  microscopical  petrography  had  come  to  play  any 
essential  part  in  American  geological  investigations.  Before 
that,  it  was  only  personal  observation  underground,  supple- 
mented occasionally  by  a  few  laboratory  or  blow-pipe  tests,  that 
furnished  information  as  to  the  processes  going  on  in  the  earth 
during  ore-deposition;,  and,  as  all  ores  were  thought  to  be 
necessarily  the  filling  of  pre-existing  open  spaces,  evidence  of 
replacement  was  seldom  looked  for. 

Richthofen's  report  on  the  Comstock  lode,  in  1865,  may 
probably  be  regarded,  in  view  of  his  previous  career,  as  repre- 
senting the  most  advanced  and  best-founded  views  of  his  time. 
After  professional  study  of  the  metallic  deposits  of  Hungary, 
the  geological  relations  of  which  most  nearly  approach  those 
of  our  Cordilleran  system,  he  had  accompanied,  as  geologist, 
the  scientific  expedition  of  the  Austrian  government  in  its 
voyage  around  the  world,  and  had  remained  in  California  to 
take  part  in  Whitney's  survey  of  the  Sierra  Nevada.  His 
Natural  Classification  of  Eruptive  Rocks  had  been  a  great  step 
in  the  scientific  study  of  igneous  action,  and  was  generally  ac- 
cepted by  petrologists,  until  it  was  finally  superseded,  some  20 
years  later,  through  new  light  thrown  upon  the  subject  by  the 
modern  science  of  microscopic  petrography.  Richthofen  re- 
garded the  Comstock  lode  as  a  true  fissure-vein — that  is,  as  a 
result  of  dynamic  action,  cutting  through  different  varieties  of 
rock,  and  extending  to  indefinite  depth.  Its  mineral  contents 
he  believed  to  have  been  deposited  from  solution,  the  silica 
having  been  precipitated  in  a  first  stage,  and  the  metallic  min- 
erals introduced  in  a  second  stage,  after  the  fissure  had  been 
re-opened.  The  extensive  decomposition  of  the  adjoining 
country-rock  could  not,  in  his  opinion,  be  explained  by  ther- 
mal action  alone;  .and  he  therefore  assumed  that  a  process 
had  taken  place,  similar  to  that  observed  in  the  solfataras  of 
active  volcanoes,  which  he  therefore  called  "  solfataric  action." 
As  the  source  of  the  water  which,  acting  as  a  solvent,  had 
brought  in  the  chlorine,  fluorine,  and  other  vein-materials,  he 


X  INTRODUCTION. 

found  the  ocean  too  far  away,  and  therefore  resorted  to  the 
waters  of  the  Great  Basin,  which  have  a  composition  similar 
to  that  of  the  ocean.  These  he  assumed  to  have  descended  to 
the  heated  region,  where  their  chlorine  and  fluorine  had  be- 
come as  active  as  they  are  supposed  to  be  in  actual  solfataras. 
For  the  source  of  the  mineral  substances  he  says :  "  We  have 
to  look  to  the  action  of  these  elements  on  the  surrounding 
rocks,"  which  is  an  application  of  the  lateral-secretion  theory. 
It  is  noteworthy  that,  in  spite  of  his  characterization  of  the 
action  as  solfataric,  he  considers  the  waters  to  have  been  of 
meteoric  origin.  This  was  the  most  definite  scientific  opinion 
that  could  be  given  at  that  time  by  the  leading  economic  geolo- 
'gist  of  the  day.  What  the  average  mining  engineer  would 
say  is  illustrated  by  the  statement  of  A.  Sutro  in  the  same 
report,  which  was  evidently  a  paraphrase  of  Bichthofen's 
opinion,  put  in  terms  more  comprehensible  to  the  average 
layman.  Sutro  says :  "  The  Comstock  lode  is  a  true  fissure- 
vein  ....  through  which  open  fissure  ascended  steam 
and  vapors,  gases,  acids,  sulphur,  chlorine,  and  fluorine,  carry- 
ing with  them  silica  and  metallic  particles  in  a  volatile  form, 
which  in  course  of  untold  ages  gradually  filled  up  the  fissure, 
and,  after  undergoing  many  chemical  changes,  formed  what  is 
now  known  as  the  Comstock  lode." 

In  the  later,  more  detailed  and  exact,  study  of  the  Comstock 
by  King  and  Hague,  published  in  1870,  the  former  declines  to 
go  into  abstruse  speculation  as  to  the  genesis  of  the  metals,  it 
being  his  opinion  that,  in  the  existing  state  of  knowledge  with 
regard  to  ore-deposits,  such  speculations  were  more  or  less  futile, 
inasmuch  as  they  could  not  be  supported  by  facts.  It  was  in 
pursuance  of  this  idea  that,  on  assuming  the  Directorship  of 
the  newly  established  U.  S.  Geological  Survey  in  1880,  Mr. 
King  founded  the  Division  of  Mining  Geology,  to  which  about 
half  of  the  entire  appropriation  granted  by  Congress  was  al- 
lotted. To  Mr.  Becker  and  myself,  whom  he  placed  in  charge 
of  this  division,  he  pointed  out,  in  the  following  terms,  the  ulti- 
mate results  at  which  he  aimed : 

"  You  will  make  accurate,  detailed,  and  exhaustive  studies  of  the  Comstock, 
Eureka,  and  Leadville  districts  ;  and,  when  these  are  completed,  your  principal 
assistants  will  be  competent  to  undertake  similar  studies  of  other  important  mining- 
districts  for  which  the  necessary  money  will  be  furnished,  thus  successively  dupli- 


INTRODUCTION.  XI 

eating  the  field  of  work,  so  that  at  the  expiration  of,  say,  ten  years,  the  varied 
types  of  deposits  in  all  important  mining-districts  will  have  been  studied  ;  and  the 
many  phenomena  bearing  upon  the  genesis  of  ore-deposits  thus  accurately  deter- 
mined should  be  sufficient  for  a  new  theory  of  ore-deposits,  based  upon  facts  accu- 
rately determined  in  the  light  of  modern  geology  rather  than,  as  is  that  of  the 
present  day,  upon  theoretical  speculations." 

While  the  course  of  events  has  not  been  exactly  that  which 
Mr.  King  planned,  and  results  have  been  slower  in  coming, 
and  less  definite  and  decisive,  than  his  sanguine  temperament 
anticipated,  they  have  been,  nevertheless,  such  as  to  demon- 
strate the  wisdom  of  his  plan.  An  important  factor  has  been 
the  hearty  concurrence  and  aid  in  this  work  afforded  by  indi- 
viduals among  the  body  of  mining  engineers,  as  soon  as  the 
first  results  of  the  work  planned  by  Mr.  King  had  demonstrated 
the  immediate  and  practical  aid  to  mining  which  might  be 
afforded  by  a  knowledge  of  the  geological  relations  of  an  ore- 
body.  It  is  this  factor,  emphasized  by  Dr.  Raymond  in  his 
Preface,  which  is  especially  brought  out  in  the  present  volume. 

The  monographic  reports  of  mining-districts  by  the  U.  S. 
Geological  Survey  presented  all  the  facts  discernible  with  regard 
to  the  geological  relations  of  the  deposits  in  each  district,  with 
the  conclusions  that  might  be  drawn  for  that  special  district ; 
but  it  was  many  years  before  a  sufficient  number  of  districts 
had  been  studied  to  permit  any  generalization  applicable  to  all 
deposits.  These  were  naturally  first  formulated  by  the  geolo- 
gists actually  occupied  in  that  work,  and  were  mainly  published 
in  the  Transactions  of  this  Institute,  because  they  would  thus 
reach  a  wide  audience  of  working  mining  engineers,  and  lead 
them  to  contribute  facts  and  discuss  results.  Thus,  the  first 
two  papers  in  this  volume  present  conclusions  drawn  by  me 
from  the  early  years  of  my  work  on  mining-geology,  mainly  in 
Colorado. 

No.  1.  The  Genesis  of  Certain  Ore-Deposits.  By  S.  F.  Ernmons. 
This  paper  was  written  to  correct  certain  misapprehensions  by 
critics  of  my  views  as  given  in  the  Leadville  report.  The  theo- 
retical conclusions  therein  expressed  were  of  a  preliminary 
rather  than  final  nature.  The  more  important  of  these  con- 
clusions were : 

a.  As  to  the  manner  of  deposition :  that  ore-deposition  by 
replacement  or  metasomatism  is  not  confined  to  easily-soluble 


Xll  INTRODUCTION. 

rocks  like  limestone,  but  is  quite   common  in  vein-deposits, 
even  in  siliceous  crystalline  rocks. 

b.  As  to  genesis :  that  most  ore-deposits  are  genetically  con- 
nected with  eruptive  or  igneous  rocks ;  and, 

c.  As  to  the  source  of  the   metals :  that  for  ore-deposition 
from  percolating  waters  (assuming,  as  was  then  universal  among 
geologists,   that  practically  all  waters  circulating  within  the 
earth's  crust  are  of  meteoric  origin),  it  is  more  reasonable  to 
suppose  that  these  waters  derive  their  metallic  contents  from 
bodies  of  igneous  rocks  at  moderate  distances  from  the  de- 
posits than  from  the   unknown   depth  or  barysphere.      The 
main  reason  for  this  assumption  is,  that  the  hypothetical  bary- 
sphere (or  region  where  the  rocks  are  distinctly  heavier,  hence 
richer  in  heavy  metals,  than  those  that  come  under  observation) 
must  be  at  such  great  depths  within  the  crust  that  it  would 
have  been  beyond  the  reach  of  meteoric  water.     Furthermore, 
the  suggestions  of  Bischof  and  Sandberger  had  pointed  out  a 
means  of  verification  of  this  theory,  of  which  the  derivation 
from  unknown  depths  is  not  susceptible.     A  modification  of 
the  lateral-secretion  theory  much  broader  than  the  restricted 
one  put  forth  by  Sandberger  was  therefore  adopted  as  affording 
the  most  fruitful  field  for  further  investigation  and  verification. 

No.  2.  On  the  Structural  Relations  of  Ore-Deposits.  By  S.  F. 
Emmons.  This  presents  my  generalizations  on  the  geological 
character  of  the  channels  through  which  ore-bearing  solutions 
may  have  reached  the  loci  of  various  ore-deposits,  the  conclu- 
sions being  that  such  channels  have  mostly  been  produced  by 
dynamic  action  and  are  in  the  nature  of  actual  rock-fractures 
or  fault-fissures,  even  where  no  displacement  is  discernible. 

No.  3.  The  Geological  Distribution  of  the  Useful  Metals  in  the 
United  States.  By  S.  F.  Emmons.  As  here  presented,  this  is 
a  series  of  extracts  from  a  paper  presented  by  me  at  the  Chi- 
cago meeting  of  the  Institute  (1893),  containing  the  views  then 
entertained  as  to  the  genesis  of  the  respective  metals.  These 
views  were  still  tentative,  and  their  presentation  was  very  much 
in  the  nature  of  a  report  of  progress ;  since  the  special  studies 
of  mining-districts  made  by  the  U.  S.  Geological  Survey  had 
not  proceeded  with  the  rapidity  originally  contemplated,  and 
the  material  for  a  new  theory  of  vein-formation  was  still  far 
from  complete. 


INTRODUCTION.  Xlll 

No.  4.  The  Torsional  Theory  of  Joints.  By  George  F.  Becker. 
This  is  a  scientific  demonstration,  from  the  point  of  view  of 
terrestrial  physics,  of  the  laws  governing  rock-fractures,  which 
he  groups  under  the  term  of  "joints,"  giving  the  criteria  by 
which  the  effects  of  the  agencies  of  pressure,  tension,  or  torsion 
maybe  recognized.  While  the  term  "joints  "  is  applied  by 
him  to  those  partings  in  rocks  on  which  the  throw  is  not  appa- 
rent without  close  observation,  the  laws  governing  them  are 
applicable  to  the  larger  fractures  on  which  mineral  veins  have 
formed. 

Meanwhile,  an  important  contribution  to  genetic  investiga- 
tion had  been  made  by  the  Norwegian  geologist,  Vogt,  in 
demonstrating  by  microscopical  study  that  certain  titaniferous 
iron-deposits  of  Sweden  were  in  the  nature  of  concentrations 
taking  place  before  consolidation  in  the  fused  magma  of  an 
eruptive  rock,  on  the  principle  of  magmatic  differentiation 
recently  announced  by  leading  petrographers  to  account  for 
the  varying  composition  of  eruptive  rocks  in  a  given  region. 
Such  magmatic  concentration,  I  maintained,  would  furnish  a 
means  of  accounting  for  the  localization  of  great  mineral  de- 
posits in  limited  areas  or  mining-districts,  and  their  absence 
in  other  areas  where  eruptive  rocks  are  equally  abundant,  by 
the  assumption  that,  in  the  fused  magmas  from  which  the 
eruptive  rocks  of  the  mining-districts  had  been  formed,  there 
had  been  a  concentration  of  metallic  minerals  previous  to  con- 
solidation. In  so  far,  then,  a  fact  of  observation  had  been  con- 
tributed to  the  hypothesis  that  the  metals  of  ore-deposits  might 
more  probably  have  been  derived  from  bodies  of  igneous  rocks 
which  had  consolidated  near  enough  to  the  surface  to  be  within 
the  reach  of  meteoric  waters,  rather  than  directly  from  the 
unknown  depths  of  the  barysphere. 

Posepny's  well-known  paper  on  The  Genesis  of  Ore-Deposits, 
read  at  the  Chicago  meeting,  and  forming  the  leading  article 
in  the  first  and  second  "  Posepny  volumes,"  published  by  the  In- 
stitute, stated  the  strongest  argument  yet  presented  in  favor  of 
the  ascension  theory,  as  distinguished  from  Sandberger's  nar- 
row conception  of  the  lateral-secretion  theory ;  and  had  a  great 
influence  in  bringing  about  a  revolution  in  the  mind  of  the 
professional  public  against  lateral  secretion  in  general.  In  his 
advocacy  of  the  direct  derivation  of  the  metals  from  the  bary- 


XIV  INTRODUCTION. 

sphere,  Posepny  did  not,  however,  remove  the  objections 
present  in  the  minds  of  those  who  favored  the  broader,  or 
American,  conception  of  the  lateral-secretion  theory — namely, 
that  it  seems  physically  impossible  for  meteoric  waters  to  have 
penetrated  the  crust  to  the  depths  at  which  what  is  under- 
stood by  the  term  "  barysphere  "  can  be  supposed  to  exist.  He 
tacitly  assumes  that  all  waters  circulating  within  the  earth's 
crust  have  a  meteoric  origin,  and  makes  a  most  important  dis- 
tinction between  those  above  and  those  below  what  he  called 
the  ground-water  level,  which  is  assumed  to  correspond  to  the 
lower  limit  of  oxidation.  The  former,  called  vadose  waters, 
directly  descending  from  the  surface,  exert  an  oxidizing  or 
decomposing  action  on  already-existing  deposits.  The  waters 
below  the  ground-water  level,  or  the  deep-seated  waters,  are, 
according  to  him,  ascending,  and  were  the  vehicle  through 
whose  agency  the  metals  were  brought  up  from  the  barysphere 
and  originally  deposited.  He  did  not,  however,  enter  into  any 
explanation  of  the  method  by  which  he  conceived  these  waters 
to  have  gathered  up  their  metallic  contents ; — thus  leaving  this 
part  of  the  subject  as  indefinite  as  it  had  been  at  the  beginning 
of  the  period  now  under  consideration ;  for  Posepny  apparently 
did  not  attach  much  importance  to  Vogt's  idea  of  magmatic 
concentration. 

In  a  general  way,  therefore,  it  may  be  said  that  the  actual 
progress  in  verification  made  in  the  decade  prior  to  1893  had 
been  mainly  in  the  line  of  getting  a  more  accurate  knowledge 
of  the  structural  character  of  the  openings  in  which  ore-deposits 
are  formed,  of  the  channels  through  which  the  mineral-bearing 
solutions  reach  these  openings,  and  of  the  processes  involved 
in  their  deposition.  Some  important  published  results  of 
generalization  on  these  lines  had,  however,  not  appeared  in 
the  Transactions  of  the  Institute — such,  for  instance,  as  Becker's 
laboratory  experiments  on  the  natural  solvents  of  the  pre- 
cious metals,  and  his  studies  on  the  processes  of  vein-forma- 
tion in  actual  progress  at  Clear  Lake,  California,  and  Steam- 
boat Springs,  Nevada. 

These  phenomena,  as  more  or  less  susceptible  of  direct  ex- 
perimental investigation  and  verification,  and  also  as  having  a 
direct  practical  bearing  upon  the  actual  exploitation  of  ore- 
deposits,  were  naturally  those  which  first  occupied  the  attention 


INTRODUCTION.  XV 

of  investigators.  Speculations  with  regard  to  the  ultimate 
source  from  which  the  metals  have  been  derived,  dealing  largely 
with  deep-seated  phenomena  beyond  the  reach  of  actual  obser- 
vation, are  less  subject  to  direct  experimental  investigation,  and 
must,  therefore,  be  verified  by  indirect  or  inductive  reasoning. 
The  determination  of  facts  on  which  such  reasoning  could  be 
based  constitutes  an  increasingly  important  factor  in  the  pro- 
gress of  scientific  inquiry;  and  it  has  often  been  made  by 
geologists,  chemists,  or  physicists,  without  special  reference  to 
the  applicability  of  such  facts  to  the  science  of  ore-deposition. 
But  economic  geologists  and  mining  engineers,  while  directing 
their  attention  primarily  to  problems  subject  to  direct  proof, 
and  having  practical  bearing  upon  the  mining  industry,  have 
not  neglected  the  more  speculative  aspects  of  these  problems. 
The  succeeding  papers  of  the  series  contained  in  this  volume 
illustrate  this  proposition,  bearing  as  they  do,  in  their  treat- 
ment of  widely  various  subjects,  now  upon  one  and  now  upon 
another  branch  of  the  general  inquiry. 

No.  5.  The  Allotropism  of  Gold.  By  Henry  Louis.  This 
paper,  aside  from  its  practical  application  to  the  separation  of 
this  metal  from  its  ores,  records  facts  which  it  may  be  impor- 
tant to  bear  in  mind  in  studying  the  various  forms  of  the  oc- 
currence of  gold  in  nature. 

No.  6.  The  Superficial  Alteration  of  Ore-Deposits.  By  R.  A. 
F.  Penrose,  Jr.  This  paper,  though  originally  written  for  the 
Transactions,  was,  for  reasons  not  necessary  to  record  here, 
actually  published  elsewhere.  It  is  the  first  complete  treatise 
on  the  action  of  vadose  waters  on  ore-deposits.  It  has  been 
deemed  desirable  to  put  it  on  record  here,  because  it  was 
the  only  publication  extant  treating  of  that  subject  at  the 
time  of  the  announcement  of  the  important  doctrine  of 
secondary  sulphide  enrichment,  at  the  opening  of  the  next 
decade.  Although  the  author,  like  Posepny,  does  not  ex- 
plicitly make  the  ground-water  level  the  lowest  limit  of  the 
alteration  he  describes,  it  is  evident  from  the  context  that,  in 
common  with  other  economic  geologists  of  the  time,  he  regarded 
this  level  as  more  or  less  identical  with  that  at  which  oxida- 
tion ceases,  and  that  he  did  not  admit  the  feasibility  of  the 
actual  transference  of  oxidized  material,  during  such  alteration, 
below  that  limit. 


XVI  INTRODUCTION. 

No.  7.  Some  Mines  of  Rosita  and  Silver  Cliff,  Colorado.  By  S. 
F.  Emmons.  This  paper  gives  the  record  of  actual  observa- 
tion of  the  occurrence  of  vadose  and  deep-seated  waters  in 
one  and  the  same  mine  (the  Geyser),  separated  by  a  zone,  over 
500  ft.  thick,  of  perfectly  dry  rock,  where  observation,  as  well 
as  analysis,  gave  an  entirely  independent  source  for  each  of 
the  respective  kinds  of  water.  While  the  conclusions  drawn 
in  this  paper  are  based  on  the  then-prevailing  belief  that  all 
the  waters  circulating  within  the  earth's  crust  are  primarily  of 
meteoric  origin,  the  facts  recorded  have  an  .equally  important 
bearing  upon  the  recently-adopted  theory  of  the  magmatic 
origin  of  most  deep-seated  waters. 

No.  8.  The  Genesis  of  Certain  Auriferous  Lodes.  By  John  R. 
Don.  This  is  an  abstract  from  a  record  of  exhaustive  chemical 
research,  carried  on  for  seven  years  by  Dr.  John  R.  Don,  of 
New  Zealand,  into  the  possible  source  of  gold,  which  has  con- 
tributed most  important  chemical  data  to  the  general  subject 
of  genesis.  Dr.  Don's  analyses  confirm  the  statements  of  pre- 
vious investigators  as  to  the  presence  of  gold  in  extremely 
dilute  solution  in  the  waters  of  the  ocean ;  and  his  experiments 
render  it  highly  improbable  that  gold  can  have  been  precipi- 
tated so  as  to  form  a  part  of  sedimentary  rocks ;  thus  confirm- 
ing the  assumption  that  its  source  is  to  be  looked  for  in  igneous 
material.  In  igneous  rocks,  however,  he  determines  that  it  is 
not  contained  in  the  bisilicates,  but  is  necessarily  associated 
with  pyrite ;  and,  as  he  assumes  that  the  pyrite  is  a  later  intro- 
duction since  the  consolidation  of  the  rock,  he  concludes  that 
the  gold  could  not  have  been  derived  from  the  rocks  examined 
by  him,  but  must  have  been  precipitated  from  solutions  ascend- 
ing from  rocks  deeper  than  any  now  exposed  at  the  surface, 
without,  however,  concerning  himself  "  with  the  question 
whether  this  source  is  the  vague  bary sphere  with  its  somewhat 
apocryphal  contents  of  heavy  metals."  As  will  be  seen  from 
the  discussions2  of  this  paper,  Dr.  Don's  critics,  while  not  ques- 
tioning the  accuracy  of  his  determinations,  do  not  agree  on  all 
points  with  the  conclusions  that  he  saw  fit  to  draw  from  them, 
and  do  not  admit  that  the  impossibility  of  derivation  from 
igneous  rocks  is  conclusively  proved. 

2  This  volume,  pp.  202  to  215. 


INTRODUCTION.  XV11 

Chronologically,  the  next  steps  in  the  development  of  the 
theories  of  genesis  were  taken  at  the  Institute  meetings  of  1900 
and  1901,  at  Washington  and  Richmond,  respectively.  The 
papers  presented  at  these  meetings  were  of  the  greatest  and 
most  critical  importance  in  the  development  of  the  various 
stages  of  the  history  of  ore-genesis,  and  have  been  included  in 
the  already-published  volume,  together  with  the  treatise  of 
Posepny,  which  they  so  seriously  modify  and  in  some  respects 
even  negative.  Space  will  not  permit  a  characterization  of 
them  at  all  commensurate  with  their  importance ;  and  they  will 
only  be  referred  to  briefly,  in  such  a  way  as  to  give  each  of 
them  what  appears  to  be  its  proper  place  in  the  historical  de- 
velopment of  opinion. 

In  his  Principles  Controlling  Ore-Deposition,  Van  Hise  pre- 
sented a  philosophical  treatment  of  the  entire  question  of  un- 
derground circulation  as  applied  to  ore-deposits,  based  on 
experimental  data  with  regard  to  underground  circulation 
furnished  by  the  Water  Supply  Department  of  the  U.  .S.  Geo- 
logical Survey.  In  this  he  explained,  more  definitely  and  in 
greater  detail  than  had  hitherto  been  done,  the  manner  in 
which  surface-waters,  in  their  downward  course,  spread  over 
wide  areas  within  the  crust,  and,  as  they  turn  upward,  unite  in 
the  larger  trunk-channels  through  which  they  ascend  to  reach 
the  surface  again  at  some  outlet  or  point  of  run-off.  The  ele- 
ment of  lateral  movement  in  underground  circulation  was 
shown  to  be,  therefore,  much  larger  than  had  previously  been 
conceived.  Van  Hise  believed  that  the  descending  and  later- 
ally-moving waters  had  been  the  main  agents  in  taking  up 
metallic  minerals  from  the  rocks  through  which  they  passed, 
and  that  from  these  waters,  ascending  through  trunk-channels, 
the  greater  part  of  ore-deposition  had  taken  place.  He  believed 
in  a  ground-water  level,  but  held  that  downward-moving  and 
oxidizing  waters  might  penetrate  some  distance  below  this 
level,  and  that  when  such  mineral-charged  solutions  met  other 
similarly-charged  solutions,  ascending  along  trunk-channels, 
extraordinarily  rich  deposits  would  be  formed ;  whereas  below, 
in  the  trunk-channels,  the  ores  would  be  mainly  low-grade 
pyritous  ores. 

The  following  paper  in  the  second  Posepny  volume  contains 
my  announcement  of  the  important  doctrine  of  "  Sulphide 


XV111  INTRODUCTION. 

Secondary  Enrichment,"  which  I  had  really  discovered  through 
my  studies,  in  1896,  of  the  veins  of  Butte,  Mont.,  although  I 
had  withheld  its  formal  announcement,  that  I  might  test  the 
general  applicability  of  the  theory  by  the  study  of  other  de- 
posits, especially  those  of  copper,  in  which  the  results  are  more 
easily  observable  than  in  those  of  other  metals;  and,  further, 
in  order  to  investigate  the  chemistry  of  the  processes  involved; 
for,  according  to  the  generally-accepted  theory  of  a  universal 
underground  water-level,  descending  oxidized  solutions  would 
become  diluted  and  neutralized  on  reaching  this  underground 
sea,  so  as  to  lose  their  distinctive  characters.  As  explained  in 
this  paper,  I  do  not  believe  in  any  such  universal  level,  but 
hold  that  the  level  to  which  water  will  rise  in  a  given  mine  or 
district  is  dependent  on  the  structural  relations  in  that  particu- 
lar mine  or  district,  which  thus  constitutes  a  separate  and 
independent  hydrostatic  basin,  so  that  the  water-level,  at 
points  no  great  distance  apart,  may  be  respectively  much 
higher  or  lower. 

The  next  paper  in  the  second  Posepny  book,  by  W.  H. 
Weed,  on  The  Enrichment  of  Gold  and  Silver  Veins,  is  of  simi- 
lar import.  In  the  original  survey  of  the  Butte  district,  in 
1896,  Mr.  Weed  had  acted  as  petrologist  in  charge  of  surface- 
geology.  Having  listened  to  my  discussion  of  the  importance 
of  this  new  doctrine  of  enrichment  by  descending  waters  below 
the  ground-water  level,  Mr.  Weed  had  appreciated  its  signifi- 
cance, and,  unknown  to  me,  had  studied  its  working  in  gold- 
and  silver-mines,  principally  in  Montana — of  which  study  this 
paper  was  the  result.  He  announced,  for  the  winter  meeting 
of  the  Geological  Society  of  America,  an  article  on  this  gen- 
eral subject,  which- was  not,  however,  actually  read  at  the  meet- 
ing of  the  Geological  Society  in  December,  1899,  but  was  writ- 
ten for  that  meeting  at  the  same  time  that  I  was  preparing, 
for  the  Institute  meeting  of  February,  1900,  my  paper  on  The 
Secondary  Enrichment  of  Ore-Deposits. 

In  the  second  Posepny  volume,  these  contributions  on  sec- 
ondary enrichment  are  followed  by  a  very  important  paper  of 
Waldemar  Lindgren,  read  at  the  same  meeting,  and  entitled 
Metasomatic  Processes  in  Fissure- Veins.  This  is  a  most  exact 
and  philosophic  discussion  of  the  part  which  metasomasis  has 
played  during  ore-deposition  in  various  classes  of  deposits,  and 


INTRODUCTION.  XIX 

the  changes  thereby  brought  about  in  the  wall-rocks,  as  well 
as  in  the  veins  themselves.  Mr.  Lindg'ren  shows  this  process 
to  have  an  even  wider  field  of  application  in  ore-deposition 
than  had  been  assumed  by  me  in  the  early  eighties,  although 
at  that  time  my  assumption  was  regarded  as  extra-hazardous ; 
but  he  deprecates  the  exaggerated  importance  assigned  to  it  by 
some  over-zealous  supporters  of  the  metasomatic  theory. 

Able  discussions  of  all  these  papers  by  prominent  economic 
geologists,  European  as  well  as  American,  were  read  at  the 
succeeding  meeting  of  the  Institute  in  February,  1901,  at  Rich- 
mond, Va.,  and  are  incorporated  in  the  latter  part  of  the  second 
Posepny  volume,  together  with  two  papers,  which  pursued  a 
new  line  of  reasoning,  destined  to  have  a  most  important 
influence  on  the  whole  question  of  genesis,  and  to  set  it,  so  to 
speak,  on  a  new  basis.  These  were  the  paper  of  Prof.  J.  F. 
Kemp,  on  The  Role  of  the  Igneous  Rocks  in  the  Formation  of 
Veins,  and  that  of  Waldemar  Lindgren,  on  The  Character  and 
Genesis  of  Certain  Contact-Deposits.  Both  authors  protest 
against  what  they  regard  as  the  too  great  importance  assigned 
by  Van  Hise  and  others  to  the  agency  of  meteoric  waters  in 
vein-formation — Kemp  attacking  the  question  on  theoretical 
grounds,  and  Lindgren  bringing  practical  proofs  from  a  large 
and  increasingly-important  class  of  deposits  that  could  not 
have  been  formed  by  meteoric  waters. 

Kemp  enters  at  once  into  the  broad  question  of  the  adequacy 
of  meteoric  waters  to  do  what  had  been  claimed  for  them,  in 
bringing  vein-material  up  from  the  barysphere,  and  makes  a 
strong  argument  against  this  adequacy  and  in  favor  of  the  prob- 
. ability  that  not  only  the  vein-materials  themselves,  but  the 
waters  that  carried  them,  were  derived  from  igneous  rocks. 
A  significant  indication  of  the  inadequacy  of  meteoric  waters 
was  furnished  by  the  recently-observed  fact  that  the  rocks  at 
the  bottom  of  very  deep  mines  (1,000  m.)  are  nearly  or  abso- 
lutely dry.  The  evidence  that  water  in  quantity  could  have 
been  furnished  by  igneous  magmas  is  necessarily  indirect, 
but  was  strengthened,  a  short  time  after  the  publication  of 
these  papers,  by  the  conclusions  reached  by  Suess,  from  the 
prolonged  studies  that  had  been  made  of  well-known  Euro- 
pean thermals,  namely,  that  the  waters  of  many  thermal  springs 
.are  entirely  derived  from  cooling  igneous  magmas,  squeezed 


XX  INTRODUCTION. 

out,  as  it  were,  during  the  process  of  crystallization.  Such 
waters  having  never  before  appeared  at  the  surface,  Suess 
calls  them  "juvenile"  waters;  but  in  America  they  are  per- 
haps more  frequently  called  magmatic  waters.  Suess  admits, 
however,  that  the  waters  of  some  springs  are  entirely  of  mete- 
oric origin,  and  that  .others  probably  have  a  mixed  meteoric- 
magmatic  origin,  while  a  portion  only  are  exclusively  mag- 
matic. 

Lindgren's  paper  on  contact-metamorphism  was  also  a  protest 
against  the  extreme  views  of  Van  Hise  and  others,  through  its 
demonstration  that  deposits  of  this  class  must  have  been  formed 
by  direct  emanations  from  cooling  igneous  magmas  at  a  tem- 
perature above  the  critical  point  of  water,  and  hence  in  gaseous 
or  pneumatolytic  state.  He  expressed  the  belief  (which  he 
confirmed  later  by  actual  observation  in  nature)  that,  contrary 
to  the  statement  of  European  petrographers,  this  metamor- 
phism  involves  also  an  actual  transfer  of  material  from  the 
intruding  magma  to  the  invaded  rock.  When  he  wrote  this 
paper,  there  were,  it  is  true,  few  deposits  of  economic  impor- 
tance to  which  a  contact-metamorphic  origin  could,  with  cer- 
tainty, be  ascribed;  but  since  then,  as  their  characteristics  have 
become  better  known,  the  number  of  such  deposits  discovered 
has  been  so  greatly  increased  that  they  constitute  in  reality  the 
strongest  argument  in  favor  of  the  theory  of  the  magmatic  ori- 
gin of  vein-forming  waters. 

After  the  appearance  of  these  two  papers,  there  was  a  marked 
revival  of  discussion  on  the  ultimate  source  of  the  metals — 
the  question,  as  it  came  to  be  called,  of  "  meteoric  versus  mag- 
matic waters."  The  advocates  of  the  latter  origin  often  went 
further  than  either  Kemp  or  Lindgren  would  have  been  willing 
to  go,  in  assuming  it  as  proved  that  the  great  majority  of  ore- 
deposits  have  been  deposited  from  highly-heated  waters  of 
magmatic  origin — that  is,  waters  occluded  in  igneous  magmas, 
and  expelled  or  squeezed  out  of  them  during  the  process  of 
crystallization.  This  theory  has  the  great  merit  of  furnishing 
a  ready  explanation  for  many  facts  connected  with  ore-deposi- 
tion for  which  it  has  hitherto  been  difficult  to  account.  If,  for 
instance,  it  be  admitted  that  the  mineral-bearing  waters  are 
furnished  by  the  cooling  magmas,  it  is  no  longer  necessary  to 
assume  that  surface-waters  circulate  to  impossible  depths;  since 


INTRODUCTION.  XXI 

the  magmas  themselves,  which  have  unlimited  powers  of  pene- 
tration, may  have  risen  to  within  the  region  of  possible  circu- 
lation before  the  commencement  of  the  process  of  consolidation 
which  would  have  squeezed  out  the  mineral-bearing  waters. 
Some  conservative  minds  still  require  more  definite  proof  that 
magmas  contain  water  in  sufficient  quantity  to  fulfill  the  re- 
quirements of  this  hypothesis;  for,  while  petrographers  in 
general  admit  the  possibility  that  during  the  consolidation  of 
magmas  mineral  salts  may  have  been  pneumatolytically  forced 
into  the  adjoining  rocks,  many  of  them  doubt  lhat  such  consoli- 
dating magmas  are  of  themselves  capable  of  furnishing  the 
long-continued  supply  of  water,  carried  through  long  distances, 
which  seems  to  be  required  for  the  formation  of  certain  classes 
of  deposits.  Direct  proof  of  what  has  taken  place  at  such  great 
depths  cannot,  it  is  evident,  be  obtained.  It  is,  therefore,  all  the 
more  important  to  find  well-determined  facts  of  observation  or 
experiment  that  may  indirectly  contribute  to  this  end.  In  the 
later  portion  of  the  present  volume  will  be  found  many  papers, 
the  bearing  of  which  upon  questions  of  genesis  may  seem 
rather  remote,  but  which  have  been  selected  because  they  con- 
tain scientific  data  which  may  be  found  later  to  have  inductive 
value  in  testing  some  of  the  current  theories. 

Returning  from  this  discussion  of  previous  contributions, 
required  for  the  continuous  history  of  the  literature  of  the 
subject,  as  embodied  in  our  Transactions,  I  resume  the  con- 
sideration of  the  papers  contained  in  the  present  volume. 

No.  9.  The  Influence  of  Country-Rock  on  Mineral  Veins.  By 
W.  H.  Weed.  This  is  a  compilation  of  facts  bearing  on  the 
change  of  the  mineral  contents  of  vein-deposits  as  such  deposits 
pass  from  one  rock  into  another. 

No.  10.  Igneous  Rocks  and  Circulating  Waters  as  Factors  in  Ore- 
Deposition.  By  J.  F.  Kemp.  This  paper  continues  the  discus- 
sion of  the  connection  of  vein-forming  waters  with  igneous 
magmas,  giving  the  author's  reasons  for  thinking  that  Van 
Rise's  final  arguments,  as  presented  in  the  discussion  of  pre- 
vious papers,  failed  to  afford  an  adequate  explanation  of  vein- 
phenomena  through  the  agency  of  meteoric  waters  alone.  As 
will  be  observed,  he  inclines  to  the  view  that  ore-deposits  are 
likely  to  occur  where  some  intrusive  rock  charged  with  me- 
tallic material  has  entered  the  earth's  crust  and  imparted  its 


XX11  INTRODUCTION. 

material  to  up-rising  mineral  waters,  and  that  deposition  in 
such  cases  has  ceased,  not,  as  maintained  by  Van  Hise,  because 
of  cementation,  but  because  the  stimulating  cause — the  heat  of 
the  intruded  body — became  exhausted.  He  also  differs  with 
Van  Hise  with  regard  to  the  abundance  of  veins,  and  the  uni- 
versal and  uniform  occurrence  of  ground-water  within  the 
earth's  crust. 

No.  11.  A  Consideration  of  Igneous  Hocks  and  Their  Segrega- 
tion or  Differentiation  as  Related  to  the  Occurrence  of  Ores.  By  J. 
E.  Spurr.  This  *is  a  recapitulation  and  analysis  of  arguments 
recently  brought  forward  in  favor  of  what  may  be  called  a 
magmatic  theory  of  ore-genesis  and  of  the  facts  that  support  it, 
together  with  certain  views  peculiar  to  the  author,  especially 
with  reference  to  the  magmatic  origin  of  certain  gold-bearing 
quartz  veins.  His  final  conclusion  is  "  that  the  origin  of 
metal-producing  districts  as  contrasted  with  barren  districts  is, 
in  most  cases,  due  primarily  to  magmatic  segregation,  and  that 
an  important  class  of  ore-deposits  is  due  directly  to  this." 
Most  workable  deposits,  however,  he  admits  to  be  due  to  sub- 
sequent concentrations,  often  several  times  repeated,  through 
the  agency  of  water  acting  either  chemically  or  mechanically. 
Like  some  others,  Mr.  Spurr  has  in  this  paper  misconceived 
the  meaning  of  the  word  "  occlude,"  assuming  it  to  be  equiva- 
lent to  "  squeeze  out,"  whereas  it  really  means  to  "  shut  in  "  or 
"  absorb." 

No.  12.  The  Chemistry  of  Ore-Deposition.  By  W.  P.  Jenney. 
This  is  an  elaborate  compilation  of  data  with  regard  to  the 
influence  which  the  various  forms  of  carbon  found  in  the  rocks 
may  have  had  in  the  precipitation  of  the  metals  in  ore-deposits 
from  their  solutions,  supplemented  with  actual  observations  by 
the  author,  mainly  in  the  lead-zinc  deposits  of  Missouri  and  of 
Tintic,  Utah. 

The  reducing  power  of  organic  matter  of  any  kind  has  been 
recognized  from  the  earliest  conceptions  of  the  genesis  of  ore- 
deposits;  and  Dr.  Jenney  has  rendered  a  valuable  service  in 
showing  the  great  extent  to  which,  under  one  form  or  other,  it 
is  found  in  nature  in  connection  with  them.  There  will  proba- 
bly be  geologists  who  will  question  whether,  in  all  instances 
quoted  by  him,  this  has  been  'the  only,  or  even  the  main,  agent 
in  the  formation  of  the  sulphide-deposits  mentioned.  Its  action 


INTRODUCTION.  XX111 

is  unquestionably  reducing;  but  that  a  substance  has  been  re- 
duced implies  that  it  was  primarily  in  an  oxidized  condition. 
That  this  was  the  case  for  the  secondarily-enriched  material  is 
undoubtedly  true;  but  for  primary  mineral  deposits  the  as- 
sumption seems  hardly  authorized. 

No.  13.  Ore-Deposits  Near  Igneous  Contacts.  By  W.  H.  Weed. 
This  is  an  attempt  to  make  a  genetic  classification  of  ore-de- 
posits, the  majority  of  which  the  author  believes  to  be,  pri- 
marily, direct  emanations  from  igneous  bodies.  Such  attempts, 
when  conscientiously  and  thoroughly  made,  serve  a  useful 
purpose  in  bringing  together  for  discussion  the  evidence  in 
favor  of  the  views  advocated ;  but  it  is  questionable  whether 
this  classification  of  metamorphic  contact-deposits,  made  before 
there  has  been  time  for  accurate  and  extended  studies  of  any 
great  number  of  such  deposits,  has  really  advanced  our  knowl- 
edge of  them  to  any  considerable  extent;  for  it  means  the  es- 
tablishing of  a  standard  which  nature  is  expected  to  follow, 
whereas,  the  reverse  method  is  the  only  one  which  can  yield 
sound  and  permanent  results. 

No.  14.  Ore-Deposition  and  Vein- Enrichment  by  Ascending 
Hot  Waters.  By  W.  H.  Weed.  This  paper  treats  of  a  phase 
of  secondary  enrichment  which,  though  normally  included  in 
the  original  statement  of  this  theory,  had  thus  far  received  but 
little  attention — namely,  enrichment  by  ascending  waters,  or 
differential  deposition.  It  is  a  phase  which  is  less  susceptible 
of  actual  observation  or  demonstration  than  that  by  descending 
waters ;  hence  the  data  bearing  on  this  subject  which  Mr. 
Weed  has  here  gathered  are  of  great  importance,  and  deserve 
to  be  put  on  record. 

No.  15.  Basaltic  Zones  as  Guides  to  Ore-Deposits  in  the  Cripple 
Creek  District,  Colorado.  By  E.  A.  Stevens.  This  paper  pre- 
sents the  conclusions  of  the  author,  who  had  been  profession- 
ally connected  with  various  Cripple  Creek  mines,  with  regard 
to  the  effects  of  recent  dikes  upon  ore-concentrations  in  that 
district.  They  differ  in  some  respects  from  the  theories  pre- 
viously maintained,  and  may  not  be  confirmed  by  future 
studies ;  but  they  are  suggestive  and  worthy  of  consideration. 

No.  16.  The  Geological  Features  of  the  Gold- Production  of 
North  America.  By  W.  Lindgren.  The  portion  of  the  paper 
included  in  this  volume  presents  the  practical  application  of 


XXIV  INTRODUCTION. 

the  knowledge  with  regard  to  ore-deposition  thus  far  ob- 
tained on  this  continent,  and  a  classification  of  deposits  of 
gold,  primarily  by  relative  age  and  also  to  a  certain  extent  by 
method  of  genesis,  and  gives  the  practical  conclusions  as  to 
future  production  that  may  be  drawn  therefrom.  Coming 
from  one  so  well  qualified  for  the  task,  bqth  by  ability  and 
by  the  advantages  of  official  position,  as  Mr.  Lindgren,  these 
conclusions  may  be  considered  as  most  important  and  authori- 
tative. 

No.  17.  Osmosis  as  a  Factor  in  Ore- Formation.  By  H.  B.  Gil- 
lette. This  paper  discusses  a  force,  the  possible  importance  of 
which  in  the  process  of  ore-deposition  has  not  received  the  at- 
tention from  economic  geologists  in  general  which  it  seems  to 
deserve.  Already,  in  1892,  Dr.  George  F.  Becker3  had  called 
attention  to  the  possibility  that  osmosis  might  explain  the  dif- 
fering action  of  the  same  mineral-bearing  solutions  on  the  inte- 
rior of  a  vein  and  the  adjoining  wall-rock,  only  the  solutions 
of  the  gangue-materials  being  able  to  penetrate  the  latter. 
Later,  experimental  tests  were  made  by  Dr.  E.  A.  Schneider  * 
on  colloidal  sulphides  of  gold,  carrying  out  the  idea  in  a  modi- 
fied form.  Lindgren  has  practically  applied  it  in  his  discus- 
sion of  the  vein-deposits  of  Nevada  City  and  Grass  Valley, 
Cal.,6  and  of  Cripple  Creek,  Colo.6 

Mr.  Gillette  does  not  refer  to  these  earlier  investigations,  but 
makes  the  suggestion  that  metasomatic  replacement — for  in- 
stance, of  limestone  by  kaolin — is  a  physical  rather  than  a 
chemical  process,  and  that  for  every  particle  deposited  by 
crystallization  a  particle  of  country-rock  may  be  dissolved. 

No.  18.  The  Ore-Deposits  of  Sudbury,  Ontario.  By  C.  W. 
Dickson.  The  genesis  of  these  important  nickel-bearing  pyr- 
rhotite-deposits  has  been  the  subject  of  repeated  discussion 
ever  since  their  discovery.  The  most  contradictory  conclu- 
sions have  been  reached  by  different  geologists,  whose  acknowl- 
edged ability  entitled  them  to  equal  scientific  credence.  The 
view  expressed,  in  this  paper  differs  essentially  from  those  of 
the  majority  of  writers  on  the  subject,  especially  the  Canadians; 

3  Mineral  Resources  of  the  United  States,  p.  156(1892). 

*  Bulletin  No.  90,  U.  S.  Geological  Survey  (1892). 

5  Seventeenth  Annual  Report,  U.  S.  Geological  Survey,  Pt.  II.,  p.  183  (1896). 

6  Professional  Paper  No.  54,  U.  S.  Geological  Survey,  p.  229  (1906). 


INTRODUCTION.  XXV 

but  it  presents  the  result  of  most  careful  microscopic  study; 
and  the  paper  contains  so  full,  and  apparently  methodical,  a 
statement  of  previous  investigations,  not  only  of  these,  but  of 
cognate  deposits,  that  it  has  been  thought  best  to  give  it  in 
full,  since  the  facts  are  important  and  worthy  of  credence, 
whatever  may  be  the  reader's  opinion  of  the  conclusions 
reached  by  the  author.  Even  if,  as  claimed  by  some  of  those 
who  hold  the  opposite  view,  the  phenomena  here  presented 
are  found  in  'only  a  small  portion  of  the  area  exploited,  that 
fact  does  not  justify  their  being  disregarded.  A  preliminary 
magmatic  concentration  does  not  preclude  a  subsequent  con- 
centration by  some  form  of  metamorphic  action.  It  may  never 
be  possible,  where  both  these  processes  have  been  active,  to 
determine  the  exact  proportion  of  the  resulting  deposit  which 
may  be  due  to  either,  that  is,  which  played  the  greater  part  in 
its  formation ;  but  it  would  hardly  seem  proper  to  characterize 
a  deposit  as  a  magmatic  concentration  if,  it  has  been  brought 
to  its  present  condition  of  an  economically-workable  deposit 
through  the  agency  of  subsequent  aqueous  concentration. 

No.  19.  The  Genesis  of  the  Copper-Deposits  of  Clifton-Morenci, 
Arizona.  By  W.  Lindgren.  This  is  an  admirable  supplement 
to  his  earlier  paper  on  contact-metamorphism  in  the  previous 
volume.  It  contains  the  genetic  conclusions  derived  from  an 
actual  and  detailed  study  of  a  most  typical  group  of  contact- 
metamorphic  deposits,  in  which  he  has  been  able  to  verify  in 
nature  many  of  his  previous  theoretical  conclusions — notably 
that  of  the  actual  contribution  of  material  by  intruding  igneous 
magmas  to  the  intruded  rocks,  as  well  as  many  new  and  valu- 
able data  as  to  the  phenomena  of  contact-metamorphic  copper- 
deposits. 

No.  20.  The  Copper-Deposits  of  San  Jose,  Tamaulipas,  Mexico. 
By  J.  F.  Kemp.  This  is  a  description  of  contact-metamorphic 
deposits  of  copper  in  limestone  in  the  periphery  of  an  intrusion 
of  diorite-porphyry.  It  contains  a  discussion  of  the  chemical 
processes  by  which  the  lime  silicates,  mainly  garnets,  are 
formed,  and  of  the  origin  of  the  material  which  enters  into 
their  composition — whether  it  can  all  be  accounted  for  as 
originally  contained  in  the  limestone,  or  whether  some  portion 
must  have  been  added  during  the  intrusion  of  the  igneous 
magma.  This  paper  thus  forms  a  supplement  to  that  of  Mr. 


XXVI  INTRODUCTION. 

Lindgren  on  Clifton-Morenci,  and,  though  descriptive,  consti- 
tutes an  addition  to  our  knowledge  of  the  general  process  of 
contact-metamorphism. 

'No.  21.  Magmatic  Origin  of  Vein-Forming  Waters  in  South- 
eastern Alaska.  By  A.  C.  Spencer.  This  is  an  argument  in 
favor  of  the  magmatic  origin  of  vein-forming  waters  in  that 
region,  following  the  suggestion  of  Lindgren  that  the  gold- 
quartz  veins  of  Victoria,  Australia,  and  of  California,  have  been 
deposited  chiefly  by  water  originally  contained  in  a  granitic 
magma,  possibly  aided  to  a  certain  extent  by  atmospheric 
waters. 

No.  22.  Genetic  Relations  of  the  Western  Nevada  Ores.  By  J. 
E.  Spurr.  This  paper  ascribes  a  magmatic  origin  to  the  ore- 
bearing  waters  which  have  produced  the  gold-  and  silver-de- 
posits of  western  Nevada,  arid,  in  the  Silver  Peak  district,  even 
suggests  that  the  gold-bearing  quartz  veins  are  siliceous  phases 
of  the  cooling  alaskite. 

No.  23.  Are  the  Quartz  Veins  of  Silver  Peak,  Nevada,  the 
Result  of  Magmatic  Segregation  ?  By  J.  B.  Hastings.  This  is  a 
criticism  of  Mr.  Spurr's  views,  as  applied  to  the  Silver  Peak 
quartz  veins  in  the  foregoing  paper. 

No.  24.  The  Occurrence  of  Stibnite  at  Steamboat  Springs,  Nevada. 
By  W.  Lindgren.  This  is  a  record  of  recent  additional  experi- 
mental observations  by  the  author  on  the  processes  going  on 
at  Steamboat  Springs,  Nevada,  where  Becker  had  in  1885 
proved  that  metallic  sulphides  were  actually  being  deposited 
by  hot  thermal  waters.  It  is  interesting  as  noting  the  changes 
that  have  apparently  taken  place  in  the  deposits  within  16 
years. 

No.  25.  A  Summary  of  Lake  Superior  Geology  with  Special 
Reference  to  Recent  Studies  of  the  Iron-Bearing  Series.  By  C.  K. 
Leith. 

No.  26.  The  Geological  Relations  of  the  Scandinavian  Iron- 
Ores.  By  Hjalmar  Sjogren. 

These  papers,  Nos.  25  and  26,  contain  respectively  summa- 
ries, by  men  especially  well  equipped  for  the  purpose,  of  the 
geology  of  the  two  great  iron-ore  regions  of  the  world, — the 
Lake  Superior  region  of  North  America  and  the  Scandinavian 
peninsula  in  Europe.  While  not  primarily  genetic,  they  pre- 


INTRODUCTION.  XXV11 

sent  summaries  of  the  geological  relations  of  the  respective 
deposits  which  involve  a  discussion  of  their  genesis. 

It  is  interesting  to  contrast  the  broader  outlines  of  genesis  of 
these  two  greatest  known  concentrations  of  metallic  ores  in  the 
world.  They  both  occur  in  the  very  oldest  rock-series  that  have 
yet  come  under  observation  and  study,  and  are  themselves,  in  the 
main,  of  pre-Cambrian  age,  though  they  may  have  suffered  some 
further  concentration  in  more  recent  times.  They  are  consid- 
ered to  be  essentially  concentrations  by  oxide-laden  surface- 
waters  of  iron-material,  originally  disseminated  in  the  form  of 
carbonate,  silicate,  or  even  oxide,  in  the  beds  of  the  sedimentary 
series  in  which  they  occur,  and  are  thus  what  the  European  geolo- 
gists would  classify  as  sedimentary  in  origin.  It  is  true  that  these 
primary  constituents  are  considered  by  Van  Hise  to  have  been 
derived  in  a  last  analysis  from  decomposing  igneous  rocks,  out 
of  which  they  were  dissolved  or  abraded  by  sea-waters,  while 
the  actual  process  that  has  made  them  of  economic  value  has 
been  later  than  sedimentation,  and  entirely  independent  of  it. 

The  sedimentary  origin  formerly  maintained  for  a  large 
proportion  of  the  Scandinavian  ores  is  now  considered  to  be 
impossible,  since  metasomatism,  the  importance  of  which  has 
been  more  readily  recognized  by  the  Swedish  than  by  any  other 
European  geologists,  is  shown  to  be  the  process  by  which  they 
have  been  formed,  through  the  agency,  however,  of  deep-seated 
rather  than  surface-waters.  Although  the  Scandinavian  iron- 
deposits  are  here  divided  into  several  distinct  types,  they  are 
all  more  or  less  distinctly  connected  with  igneous  eruptives. 
Some  are  considered  to  be  magmatic  segregations ;  the  greater 
part  are  some  form  of  pneumatolytic  formation,  of  which  the 
extreme  type  is  the  contact-metamorphic  deposit  in  limestone. 
One  or  more  of  the  lime  silicates,  garnet,  amphibole,  etc.,  are 
very  common  associates  of  all  the  ores.  Secondary  alteration 
and  concentration  by  surface-water  is  considered  to  have  played 
but  a  very  subordinate  part,  if  any,  in  producing  the  present 
deposits. 

No.  27.  The  Formation  and  Enrichment  of  Ore-Bearing  Veins. 
By  George  J.  Bancroft.  This  is  a  discussion,  by  an  experienced 
mining  engineer,  from  the  point  of  view  of  his  own  personal 
observations  in  Western  mining-districts,  of  various  points  in 
the  theories  of  genesis  from  aqueous  solutions  presented  in 


XXV111  INTRODUCTION. 

the  previous  papers.  The  main  conclusions  peculiar  to  his 
point  of  view,  are  that  veins  are  formed  in  relatively  short 
periods,  and  from  rich  or  concentrated  solutions. 

No.  28.  The  Distribution  of  the  Elements  in  Igneous  Rocks.  By 
H.  S.  Washington.  This  is  a  discussion  of  the  relative  amount 
of  the  elements,  as  shown  by  the  improved  modern  methods  of 
rock-analysis,  that  go  to  make  up  the  ore-deposits  found  in  dif- 
ferent varieties  of  igneous  magmas.  From  the  point  of  view 
of  the  petrographer  and  chemist,  this  is  an  important  inquiry; 
and  though  at  present  it  yields  but  few  results  of  actual  eco- 
nomic bearing,  it  is  significant  of  what  may  be  expected  from 
further  research  along  these  lines.  It  is  noteworthy  that  while 
the  average  water-content  of  crystalline  rocks  is  not  over  2  per 
cent.,  this  percentage  may  be  carried  up  to  12  in  fresh  glassy 
lavas,  from  which  the  water  was  unable  to  escape,  owing  to  the 
rapidity  of  solidification. 

No.  29.  The  Agency  of  Manganese  in  the  Superficial  Alteration 
and  Secondary  Enrichment  of  Gold-Deposits  of  the  United  States. 
By  Prof.  "W.  H.  Emmons,  Copperhill,  Tenn.  This  paper  forms 
a  fitting  close  to  the  series.  It  is  a  thorough  examination  and 
discussion  of  the  doctrine  of  secondary  enrichment,  as  applied 
to  the  single  metal,  gold.  It  had  already  been  noticed  that 
there  are  gold-deposits  which  have  evidently  been,  and  others 
that  apparently  have  not  been,  enriched  by  surface  oxidizing 
waters.  The  author  and  his  assistants,  by  a  series  of  chemical 
experiments,  have  discovered  the  cause  of  this  difference,  and 
thus  contributed  an  important  scientific  addition  to  the  doctrine 
of  secondary  enrichment,  which,  in  practice,  should  enable  the 
mining  engineer  to  determine  whether  a  given  gold-deposit  is 
secondarily  enriched ;  whether  it  is  capable  of  producing  valu- 
able placers  by  disintegration ;  or  whether  neither  condition 
can  be  expected.  It  also  accounts  for  transfers  of  gold  from  a 
higher  to  a  lower  horizon  in  certain  classes  of  deposits.  This 
is  the  type  of  investigation  to  which  we  may  look  hereafter  for 
the  most  valuable  results  in  furtherance  of  the  science  of  ore- 
genesis. 


BIOGRAPHICAL  NOTICE  OF    SAMUEL  FRANKLIN" 

EMMONS. 

BY   GEORGE  F.    BECKER,  WASHINGTON,  D.   C. 

(San  Francisco  Meeting,  October,  1911.     Trans.,  xlii.,  643.) 

A  MERE  record  of  Emmons's  professional  career  would  very 
inadequately  represent  the  man.  That  he  was  eminent  we 
know,  and  our  successors  will  realize  in  due  time ;  but  they 
must  depend  upon  us  for  knowledge  of  a  singularly  wholesome, 
modest,  unselfish  personality,  and  of  a  character  that  did  honor 
to  a  profession  in  which  trustworthiness  is  indispensable. 
Those  members  of  the  Institute  who  met  Emmons  are  his 
friends,  and  I  never  knew  one  of  these  who  was  not  the  better 
for  that  friendship. 

Emmons  was  born  in  Boston,  Mar.  29,  1841,  the  son  of 
Nathaniel  H.  and  Elizabeth  (Wales)  Emmons,  and  was  named 
Samuel  Franklin  after  an  ancestor  who  was  of  the  same  family 
as  Benjamin  Franklin.  He  took  the  degree  of  Bachelor  of 
Arts  at  Harvard  in  1861,  and  soon  afterwards  went  abroad  to 
complete  his  education.  From  1862  to  1864  he  attended  the 
courses  at  the  ficole  Imperiale  des  Mines  at  Paris,  Elie  de 
Beaumont  and  Daubree  being  among  his  professors.  The 
year  1864-1865  he  spent  at  Freiberg  under  Cotta  and  other 
famous  teachers ;  after  which  he  spent  another  year  in  travel- 
ing through  Europe.  Like  many  other  renowned  geologists, 
he  approached  his  ultimate  profession  from  its  economic  side, 
and  was  thus  from  the  first  imbued  with  a  sense  of  high  re- 
sponsibility in  the  promulgation  of  scientific  opinions  or  con- 
clusions. With  hypotheses  which  were  interesting  merely 
because  they  were  ingenious  or  even  plausible,  he  would  have 
nothing  to  do. 

In  1867  he  joined  the  Geological  Exploration  of  the  Fortieth 
Parallel  at  its  organization  under  Clarence  King,  serving  at 
first  as  a  volunteer,  but  soon  receiving  a  regular  appointment. 
This  expedition  was  the  first  one  of  purely  geological  char- 
acter sent  out  by  the  United  States  government.  As  Emmons 
has  shown  in  his  admirable  presidential  address  on  "  The 
Geology  of  Government  Explorations,"  its  work  was  founded 

(  xxix  ) 


XXX          BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

on  a  complete  and  comprehensive  plan,  adopted  before  taking 
the  field,  and  systematically  followed  in  all  essential  features 
during  the  ten  years  of  its  existence.  This  plan  aimed  at  the 
highest  efficiency  compatible  with  prompt  completion.  It  was 
important  from  every  point  of  view  that  the  broad  outlines  of 
the  geology  and  mineral  resources  of  the  belt  of  country  to  be 
opened  up  by  the  completion  of  the  transcontinental  railway 
should  be  made  known  as  soon  as  practicable.  To  execute  a 
final,  detailed  survey  under  such  conditions  was  impossible ; 
and  for  this  reason  the  work  was  called  an  exploration,  but  as 
a  first  approximation  to  the  truth  the  intention  was  to  make  it 
irreproachable  in  methods  and  in  symmetry.  The  best  experts 
to  be  had  were  secured ;  contour-mapping  as  a  basis  for  geo- 
logical work  was  introduced  for  the  first  time  in  this  country  ;l 
and,  when  lithological  collections  had  accumulated,  a  well- 
known  European  petrographer  was  engaged  to  discuss  them 
by  the  new  microscopic  methods,  then  wholly  unfamiliar  to 
American  geologists.  Emmons's  associates  as  assistant  geolo- 
gists were  our  late  eminent  colleague  James  D.  Hague,  and  his 
brother,  Mr.  Arnold  Hague.  The  expedition  started  in  1867 
from  Sacramento  :  and  it  will  help  our  younger  brethren  to 
grasp  the  changes  which  have  taken  place  in  the  civilization 
of  the  West  to  be  reminded  that  an  escort  of  30  regular 
soldiers  was  needed  in  that  year  to  protect  the  civilians  from 
hostile  Indians. 

To  realize  how  hard  the  men  worked,  it  is  only  needful  to 
glance  at  the  Fortieth  Parallel  memoirs  and  maps,  but  shoot- 
ing was  an  available  recreation,  and  afforded  a  legitimate 
means  of  varying  a  monotonous  diet.  There  was  one  particu- 
larly good  bear-story  which  Dr.  Eaymond  has  recorded  in  his 
notice  of  King  in  Emmons's  own  words.2  Of  this  Dr.  Raymond 
writes  me  : 

11  King,  who  always  reaped  the  glory  which  his  splendid  audacity  deserved, 
killed  the  bear  ;  but  the  story  shows  that  Eramons  was  posted  at  the  other  end  of 
the  passage  where  the  wounded  bear  would  have  come  out,  if  King's  shot  in  the 
dark  had  not  been  fatal !  " 

One  of  the  rules  of  the  Fortieth  Parallel  Survey  was,  that  its 

1  Capt.  John  Mullan's  Keport  on  the  Construction  of  a  Military  Road,  1863, 
contained  contour  sketch-maps  surveyed  and  drawn  by  Theodore  Kolecki. 

2  Trans.,  xxxiii.,  633  (1902). 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.  XXXI 

members  should  be  as  civilized  as  practicable,  especially  at 
meals.  The  men  believed  in  a  good  and  varied  diet,  well- 
cooked  and  served;  and,  when  the  accounting-officers  of  the 
War  Department  demurred  at  passing  a  bill  for  currant-jelly, 
they  were  met  with  a  threat  to  charge  up  at  the  rate  of  beef 
the  venison  furnished  by  members  of  the  mess.  By  such 
means  the  geologists  preserved  both  their  digestion  and  their 
adaptability  to  social  life  at  centers  of  civilization,  in  which 
every  one  of  them  took  a  prominent  part  in  later  years. 

Two  episodes  in  the  history  of  the  Exploration  of  the  For- 
tieth Parallel  deserve  mention.  In  1870,  the  appropriation- 
bills  passed  too  late  for  a  regular  season  of  field-work,  and 
King  decided  on  an  examination  of  the  extinct  volcanoes  of  the 
Cascade  range.  He  and  Emmons  ascended  Mt.  Shasta,  and 
there  found  the  first  glaciers  recognized  within  the  limits  of 
the  United  States.  Later,  in  the  same  autumn,  Emmons  made 
the  ascent  of  Mt.  Rainier,  where  he  found  much  more  extensive 
glaciers,  which  he  has  very  graphically  described.  Emmons 
made  no  claim  to  the  first  ascent  of  this  great  peak,  recogniz- 
ing that  it  had  been  scaled  two  months  earlier  by  Gen.  Hazard 
Stevens;  but  our  colleague,  who  was  accompanied  by  Mr.  A. 
D.  Wilson,  was  the  first  to  bring  from  this  dormant  volcano 
valuable  information  on  its  topography,  geology,  and  glaciol- 
ogy.  During  the  same  season  Mr.  Arnold  Hague  ascended 
Mt.  Hood,  where  he  too  discovered  typical  glaciers. 

In  1872  Emmons  took  part  in  the  exposure  of  the  famous 
diamond  swindle.  Though  strong  efforts  were  made  to  keep 
secret  the  locality  of  the  alleged  diamond  "  discovery,"  King 
made  out  that  it  must  be  in  a  region  which  Emmons  had  sur- 
veyed. They  set  out  together  to  investigate,  and  Emmons  was 
able  to  lead  the  little  party  to  the  scene  of  the  crime  in  Ver- 
million  Creek  Basin,  Wyoming.  This  had  been  selected  by  the 
swindlers  because  it  was-  in  a  nearly  waterless  region,  from 
which  almost  any  expert  would  retreat  *at  the  first  possible 
moment.  A  great  financial  disaster  was  averted  by  the  detec- 
tion of  this  fraud,  and  it  is  doubtful  whether  King  could  have 
achieved  the  disclosure  without  Emmons's  knowledge  of  the 
country. 

In  King's  Exploration,  Mr.  Arnold  Hague  and  Emmons  had 
charge  of  the  descriptive  geology.  In  1870  Emmons  had  con- 


XXX11        BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

tributed  a  chapter  on  the  Toyabe  range  and  some  minor  notes 
to  Vol.  III.  (Mining  Geology).  With  these  exceptions,  and 
that  of  his  description  of  Mt.  Rainier,  all  his  work  on  that  sur- 
vey is  contained  in  Vol.  II.  (Descriptive  Geology),  printed 
in  1877,  and  containing  nearly  900  pages.  In  the  letter  of 
transmittal  by  the  authors  the  limitations  of  the  work  are  thus 
emphasized :  ^ 

"It  will  be  readily  understood  by  the  reader,  from  the  very  title  of  the  work, 
that  this  does  not  claim  to  be  a  systematic  survey  like  those  of  Europe,  based  on 
accurate  maps,  but  is  rather  a  geological  reconnaissance  in  an  unknown  and  often 
unexplored  region,  where  geology  and  topography  had  to  go  hand  in  hand,  and 
that  therefore,  while  details  were  often,  from  the  necessities  of  the  case,  somewhat 
neglected,  it  was  the  general  bearing  of  the  leading  geological  facts  that  was  most 
constantly  in  our  minds." 

Now-a-days,  I  suppose,  no  one  would  think  of  reading  this 
volume  through,  though  it  remains  an  important  book  of  refer- 
ence. In  1877,  however,  it  was  full  of  news,  and  Gerhard  vom 
Rath,  to  whom  geology  (directly  and  indirectly)  owes  so  much, 
told  me  in  1888  that  it  was  the  interest  the  Descriptive  Geology 
aroused  in  him  which  led  him  to  visit  the  United  States.  It 
was,  I  remember,  the  first  work  I  ever  reviewed ;  and  I  greatly 
enjoyed  the  task. 

In  accordance  with  the  plan  of  the  Exploration  of  the 
Fortieth  Parallel  all  the  men  had  constantly  to  guard  against 
two  temptations,  one  being  to  follow  out  their  problems  by  de- 
tailed studies  at  an  undue  expenditure  of  time,  and  the  other 
to  gain  time  by  slighting  important  matters  in  which  they 
might  happen  to  feel  relatively  slight  personal  interest.  There 
can  be  no  doubt  that  they  displayed  great  self-control ;  and  in 
my  opinion  the  result  was  an  unrivaled  model  of  a  preliminary 
survey  in  an  unknown  region. 

It  should  not  be  forgotten  that  the  topographic  and  the 
geologic  reconnaissances  were  executed  at  substantially  the 
same  time,  so  that  tfce  geologists  rarely  had  maps  in  the  field 
on  which  to  record  their  work.  This  involved  keeping  in 
mind  and  in  note-books  a  vast  number  of  detailed  observations 
systematically  co-ordinated  and  of  a  prescribed  standard  in  re- 
spect to  generality.  Ten  years  of  this  sort  of  thing  gave 
Emmons  an  unusual  command  of  details,  and  power  to  marshal 
them  mentally  without  extraneous  aid.  In  short,  it  was  the 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.       XXX111 

training  in  descriptive  geology,  as  he  practiced  it,  which  en- 
abled him  subsequently  to  deal  with  the  complexities  of  Lead- 
ville. 

With  the  completion  of  the  Descriptive  Geology  in  1877,  the 
connection  of  its  authors  with  the  Fortieth  Parallel  ceased. 
For  the  next  two  years,  Emmons  devoted  himself  to  a  cattle- 
ranch  near  Cheyenne.  The  country  was  still  unfenced,  and 
great  profits  were  possible  in  this  business,  while  the  active, 
out-door  life  suited  Emmons's  temperament  and  habits.  Even 
after  his  return  to  scientific  life,  he  retained  his  interest  in  this 
ranch  for  some  years,  and  kept  there  a  pack  of  Scotch  deer- 
hounds  with  which  he  hunted. 

In  March,  1879,  the  government  organizations  which  had 
been  carrying  on  geological  reconnaissances  were  merged  in 
the  present  United  States  Geological  Survey,  and  King  was 
appointed  Director,  taking  his  oath  of  office  on  May  24.  As  a 
matter  of  course,  a  position  was  offered  to  Emmons,  and  he 
qualified  on  August  24. 

In  the  autumn  of  that  year  King  summoned  Emmons  and 
me  to  Washington,  in  order  to  prepare  schedules  for  the  ex- 
amination of  the  precious  metals  industries  under  the  Tenth 
Census,  a  task  undertaken  by  the  Survey  as  a  matter  of  cour- 
tesy to  the  Census  Bureau  and  as  germane  to  its  own  office. 
As  soon  as  Emmons  arrived,  I  called  upon  him ;  and  when,  an 
hour  later,  King  entered  the  room  to  introduce  us,  we  were 
already  friends.  Such  we  always  remained  without  a  single 
misunderstanding. 

It  was  for  each  of  us  a  busy  and  interesting  period,  and  in 
later  years  a  favorite  subject  for  reminiscence.  Emmons, 
though  of  course  strong  on  general  geology  and  lithology, 
was  rusty  in  technical  mining  and  metallurgy,  which  I  had 
been  teaching;  and  while  I  had  a  considerable  familiarity  with 
ore-deposits,  my  knowledge  of  general  geology  and  lithology 
was  elementary.  Indeed,  on  joining  the  Survey,  I  had  stipu- 
lated with  the  Director  that  he  should  call  upon  me  only  for 
mining  and  metallurgical  reports.  Thus  the  preparation  of 
schedules  led  to  many  instructive  discussions,  carried  on  with 
the  utmost  freedom  and  good-will.  We  worked  hard  and 
long.  Wo  were  in  almost  daily  consultation  with  King,  who 
was  well  informed  on  the  whole  subject,  but  I  do  not  remember 


XXXIV       BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

that  he  ever  made  any  material  change  in  our  plans ;  and  we 
also  had  prolonged  sessions  with  Gen.  Francis  A.  Walker, 
Superintendent  of  the  Census,  who  was  thoroughly  agreeable 
and  agreeably  thorough. 

Life  was  not  all  work,  however.  John  Hay,  then  Assistant 
Secretary  of  State,  and  King  had  at  Wormley's  a  private  dining- 
room,  which  they  invited  Emmons  and  me  to  share  with  them. 
I  doubt  whether  there  ever  was  table-talk  more  brilliant  than 
that  to  which  we  listened  in  that  room.  Neither  Emmons 
nor  I  said  much,  but  we  egged  on  the  other  two,  and  laid  little 
plots  to  get  them  started  on  matters  we  desired  to  hear  dis- 
cussed. King  and  Hay  were  intimate  friends,  and  particularly 
well-fitted  by  differences  in  temperament  and  experience  to 
complement  one  another  in  conversation.  Though  Hay  rarely 
indulged  in  humor  and  was  not  a  man  of  buoyant  spirits,  he 
was  never  commonplace  or  ponderous.  He  was  gifted  with 
true  wit,  whose  gleams  showed  even  familiar  relations  in  new 
aspects  and  revealed  relationships  among  less  familiar  things. 
He  offered,  but  never  obtruded,  suggestive  reflections  grace- 
fully epitomized,  and  in  this  intimate  companionship  disclosed 
the  grasp  of  affairs  and  breadth  of  view  which  were  to  make 
him  a  great  Secretary  of  State.  As  for  King,  hear  Hay ! 

"  He  was  inimitable  in  many  ways  :  in  his  inexhaustible  fund  of  wise  and  witty 
speech  ;  in  his  learning,  about  which  his  marvellous  humor  played  like  summer 
lightning  over  far  horizons ;  in  his  quick  and  intelligent  sympathy,  which  saw 
the  good  and  amusing  in  the  most  unpromising  subjects ;  in  the  ease  and  airy 
lightness  with  which  he  scattered  his  jewelled  phrases  ;  but  above  all  in  his  aston- 
ishing power  of  diffusing  happiness  wherever  he  went."  3 

Had  these  wonderful  dinners  not  been  so  entertaining  they 
might  have  been  considered  as  equivalent  to  a  post-graduate 
course  in  liberal  education.  They  exerted  a  lasting  influence 
on  Emmons  and  me,  expanding  our  views  and  adding  symme- 
try to  our  standards  of  thought  and  achievement. 

It  was  while  we  were  engaged  on  the  Census  schedules  that 
King  completed  his  plans  for  the  investigation  of  ore-deposits, 
and  placed  the  work  in  our  charge  by  the  orders  quoted  in 
Emmons's  introductory  chapter  to  this  volume.  I  was  reluct- 
ant to  accept  the  responsibility,  and  I  should  have  persisted  in 

3  Clarence  King  Memoirs,  p.  131  (1904). 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.  XXXV 

refusing  it,  had  not  Ernmons  urged  me  to  make  the  attempfy 
assuring  me  in  the  kindest  manner  of  his  co-operation  and 
assistance,  so  far  as  circumstances  might  permit.  He  began  to 
cram  me  immediately;  and,  during  the  field-work  in  Leadville 
and  on  the  Com  stock,  we  were  in  constant  correspondence  on 
every  phase  of  both  problems. 

Early  in  1880,  each  of  us  had  to  select  and  instruct  a  staff  of 
young  mining  engineers  who  were  to  collect  the  statistics  and 
technological  data  under  the  Census,  while  at  the  same  time 
we  organized  and  commenced  our  ' geological  field-work;  in 
fact  Emmons  began  on  the  geology  of  Leadville  just  before  the 
New  Year. 

What  little  is  to  be  said  of  the  Census  work  may  be  said 
here,  although  it  was  not  completed  until  Emmons's  abstract  of 
his  Leadville  report  had  been  printed.  The  purpose  of  the 
Statistics  and  Technology  of  the  Precious  Metals  was  to  furnish 
mining-men  with  accurate  data  of  production  and  a  record  of 
technical  practice  in  the  year  1880,  together  with  such  an  out- 
line of  the  geology  of  the  mining-districts  as  could  be  prepared 
from  material  already  published,  supplemented  by  the  informa- 
tion derived  from  the  reports  and  collections  sent  in  by  the 
experts  in  the  field.  It  was  a  harassing  piece  of  work ;  and  it 
is  needless  to  say  that  some  districts  were  more  competently 
reported  than  others ;  but  under  the  circumstances,  and  on  the 
whole,  the  authors  were  fairly  satisfied  with  the  result.  Its 
value  would  have  been  enhanced  by  prompt  publication.  By 
working  at  night  and  on  holidays  the  manuscript  and  maps 
were  completed  and  transmitted  on  Feb.  8,  1883  ;  but  more 
than  a  year  elapsed  before  the  first  galley-proofs  reached  us ; 
and  in  the  meantime  the  maps  had  disappeared  from  the 
Census  Office.  I  remember  exactly  how  we  felt ! 

After  King  retired  from  government  work,  I  was  placed  in 
charge  of  the  Statistics  and  Technology  of  the  Precious  Metals, 
so  that  for  a  time  I  had  the  honor  of  counting  Emmons  nomi- 
nally as  my  assistant;  but  of  course  we  worked  together  as 
before,  and  no  question  of  subordination  was  allowed  to  arise. 
When  it  came  to  deciding  the  order  of  our  names  on  the  title- 
page,  however,  he  said  I  was  in  charge  and  should  come  first, 
while  I  maintained  that  he,  as  the  senior  and  more  experienced, 
should  take  precedence.  As  neither  would  be  convinced,  I 


XXXVI          BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

proposed  deciding  the  matter  by  the  turn  of  a  coin.  Thus  we 
settled  it,  standing  by  the  statue  of  Jackson,  in  the  city  of 
Washington.  He  won  the  toss  and  I  my  way.  -  > 

In  spite  of  the  labor  involved  in  gathering  statistics  under 
the  Census,  Emmons  pushed  the  examination  of  the  geology  of 
Leadville  so  energetically  that  he  was  able  to  close  his  office 
at  the  camp  on  Apr.  1,  1881,  and  to  transmit  his  Abstract  of 
a  Report  on  the  Geology  and  Mining  Industry  of  Leadville 
on  October  20  of  that  year.  This  abstract,  which  appeared  in 
the  Second  Annual  Report  of  the  Director  of  the  United  States 
Geological  Survey,  is  a  memoir  of  87  pages  and  contains  the 
principal  results  of  the  investigation.  The  publication  of  the 
Monograph  was  delayed  by  various  causes  till  1886;  but  his 
main  conclusions  were  not  changed  in  the  intervening  time.4 
In  the  field-work  he  was  assisted  by  Ernest  Jacob,  Whitman 
Cross,  and  W.  H.  Leffingwell  as  geologists,  and  by  W.  F. 
Hillebrand  and  Antony  Guyard  as  chemists. 

Emmons's  views  of  the  Leadville  ore-deposits,  up  to  the  time 
of  the  publication  of  his  Monograph,  may  be  condensed  into 
the  following  statement:  Prior  to  oxidation,  the  ores  consisted 
of  sulphides  of  lead  and  silver,  zinc  and  iron,  which  were  de- 
posited by  substitution  for  country-rock,  this  being  as  a  rule 
limestone  or  dolomite,  but  in  some  instances  siliceous  in  char- 
acter. The  ore  reached  the  deposits  as  hot  aqueous  solutions 
at  high  pressures,  and  came  from  above.  The  temperature 
was  due  to  the  depth  (about  10,000  ft.),  and  the  magmatic  beat 
of  the  intrusive  porphyries.  The  water  was  of  meteoric  origin 
and  derived  its  metallic  content,  perhaps  wholly  but  demon- 
strably  in  part,  from  masses  of  porphyry  which  were  not  neces- 
sarily in  juxtaposition  with  the  ore.  The  principal  deposition 
took  place  at  the  upper  .surf  ace  of  the  blue  Carboniferous  lime- 
stone.5 

Twenty-one  years  later  he  returned  to  the  subject  with  Mr. 
J.  D.  Irving  in  a  paper  on  the  Downtown  District ; 6  and  the 

4  In  the  Abstract  Emmons  regarded  the  ores  as  derived  from  the  porphyries, 
while  in  the  Monograph  he  considered  them  as  "mainly  "  derived  from  this  source. 

5  See  Abstract,  Second  Annual  Report,   U.  S.   Geological  Survey,  p.  234   (1882). 
Geology  and  Mining  Industry  of  Leadville,   p.  584  (1886).     Also,   Trans.,  xv., 
138  (1886-87). 

6  Bulletin  No.  320,  U.  S.  Geological  Survey  (1907). 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.       XXXVll 

only  important  change  he  was  obliged  to  make  was  an  addition 
rather  than  a  correction.  Developments  in  the  intervening 
decades  had  shown  that  many,  instead  of  few,  ore-bodies 
existed  within  the  mass  of  the  Carboniferous  limestone  (not 
merely  near  its  upper  surface),  and  also  in  the  Silurian  lime- 
stone. Meanwhile,  however,  the  subject  of  juvenile  or  mag- 
matic  waters,  first  investigated  by  Charles  Sainte-Claire  Deville 
and  other  French  savants,  had  been  actively  studied  and  dis- 
cussed, so  that  in  1907  questions  arose  as  to  the  possible  par- 
ticipation of  such  waters  in  the  genesis  of  the  Leadville 
deposits.  How  far  the  original  sulphides  at  Leadville  were 
deposited  from  juvenile  waters,  and  whether  instances  of  depo- 
sition as  a  feature  of  contact-metamorphism  were  to  be  found 
there,  were  still  unknown. 

This  paper  by  Emmons  and  Irving  was,  in  fact,  a  partial  ab- 
stract in  advance  of  a  monograph  by  the  same  authors,  in 
which  the  entire  Leadville  work  was  to  be  revised.  Fortu- 
nately the  volume  was  so  nearly  completed  before  the  senior 
author's  death  that  Mr.  Irving  is  in  a  position  to  finish  it 
within  a  few  months.  How  far  it  will  answer  the  questions 
which  were  still  open  in  1907,  I  do  not  know. 

Leadville  presents  the  most  intricate  problem  of  mining- 
geology  ever  attempted ;  for  the  structure  is  as  complex  as  the 
chemical  history  of  the  deposits.  Emmons  brought  to  the 
study  of  this  district  a  mind  trained  to  carry  a  vast  number  of 
observations  in  due  relation  to  one  another;  and  this  enabled 
him  to  execute  a  truly  monumental  work.  His  Monograph 
has  been  of  enormous  importance  to  miners,  for  experience 
has  shown  that  its  predictions  were  substantially  correct;  it 
has  been  of  material  advantage  to  the  Geological  Survey  as  an 
evidence  of  what  geology  can  do  for  industry ;  and  it  has  set 
an  example  to  younger  geologists  of  the  mode  of  treatment 
proper  to  such  a  problem.  The  revision  of  this  great  work 
after  the  lapse  of  30  years  worthily  closed  his  career. 

Having  concluded  that  the  Leadville  ores  were  deposited  by 
substitution,  mainly  for  limestone,  Emmons  was  led  to  study 
instances  of  the  replacement  by  ore  of  other  rocks.  Indeed, 
even  in  his  Leadville  Abstract  of  1882,  he  had  recognized 
limited  occurrences  of  ores  substituted  for  siliceous  rocks. 
Cases  of  this  kind  had  been  described  in  Europe  by  G-roddeck 


XXXV111       BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

I 

and  others;  but  in  this  country  only  the  native  copper  of 
Lake  Superior  had  been  recognized  as  pseudomorphic  by  Mr. 
Pumpelly.  Emmons  soon  found  abundant  evidence  capable 
of  interpretation  as  indicating  replacement  or  metasomatism  in 
a  wide  sense;  that  is  to  say,  he  found  much  ore  in  situations 
from  which  even  siliceous  rocks  or  minerals  had  been  re- 
moved. To  cover  them  all,  he  denned  metasomatism  as  an 
interchange  of  substances,  but  not  necessarily  molecule  by 
molecule. 

This  breadth  (perhaps  I  aught  to  say  looseness)  of  defini- 
tion was  unavoidable  unless  he  had  been  willing  to  postpone 
for  years  the  announcement  of  his  results ;  for  convincing  de- 
tailed proof  of  the  various  processes  active  in  the  alteration 
and  impregnation  of  wall-rocks  requires  prolonged  and  difficult 
chemical  and  microscopical  investigation.  Among  engineers 
the  idea,  new  to  many  of  them,  immediately  became  popular, 
too  popular,  in  fact;  and  at  one  period  there  was  danger  that 
all  deposits  would  be  set  down  without  due  proof  as  cases  of 
replacement.  Some,  however,  were  left  to  protest;  and,  after 
a  few  years,  the  matter  was  reduced  to  proper  proportions  by 
Mr.  Lindgren,7  who,  adopting  as  his  criterion  the  principle 
that  the  theory  of  substitution  of  ore  for  rock  is  to  be  accepted 
only  when  there  is  definite  evidence  of  pseudomorphic,  mo- 
lecular replacement,  worked  out  his  results  with  great  labor 
•and  discrimination.  There  can  be  little  doubt  that  as  geolog- 
ical chemistry  is  elaborated  the  importance  of  deposition  by 
substitution  will  be  still  further  recognized,  and  that  studies 
devoted  to  this  subject  will  shed  unexpected  light  on  geo- 
chemical  processes.8 

Secondary  enrichment  of  sulphide  ores  attracted  attention 

i   Trans.,  xxx.,  596  (1900). 

8  Among  the  very  first  observations  which  I  made  on  the  Comstock  lode  was, 
that  much  of  the  pyrite  in  the  wall-rock  was  pseudomorphic  after  ferromagnesian 
bisilicates.  (Geology  of  the  Comstock  Lode,  p.  210,  1882.)  Emmons's  studies  on 
replacement  led  me  to  examine  the  quicksilver-mines  very  closely  for  pseudo- 
morphic deposition  of  cinnabar.  In  spite  of  profound  alteration  of  wall-rock, 
attended  by  other  replacements,  I  found  no  instance  of  deposition  of  cinnabar  by 
substitution  for  carbonates  or  silicates.  These  facts  led  me  to  suggest  the  dia- 
lytic  or  osmotic  separation  of  ore-bearing  solutions,  a  hypothesis  which  is  thus 
indirectly  due  to  Emmons.  Geology  of  the  Quicksilver  Deposits  of  the  Pacific  Slope, 
p.  396  (1888),  and  Mineral  Resources  of  the  U.  S.  for  1892,  U.  S.  Geological  Survey, 
p.  156  (1893). 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.       XXXIX 

in  Europe  earlier  than  in  this  country.  The  relative  affinity  of 
the  metals  for  sulphur  was  investigated  as  long  ago  as  1837, 
by  E.  F.  Anthon,9  but  the  first  application  to  ore-deposits  with 
which  I  have  met  is  contained  in  Mr.  Joaquin  Gonzalo's  admi- 
rable monograph  on  Huelva,  issued  in  1888.  The  secondary 
deposits  of  chalcopyrite  (occasionally  accompanied  by  other 
copper-compounds),  and  galena,  as  they  are  found  at  Rio 
Tinto,  are  described  by  the  Spanish  geologist  as  occurring 
along  lithoclastic  fractures  in  the  mass  of  the  pyrite.  They 
are  attributed  to  a  process  of  segregation  within  the  mass  and 
to  the  reduction  of  sulphates  percolating  downward  from  the 
zone  of  oxidation.10  Mr.  J.  H.  L.  Vogt,  after  personal  exami- 
nation, entirely  assented  to  Mr.  Gonzalo's  views,  and  pointed 
out  subsequently  that  secondary  enrichment  is  the  true  mean- 
ing of  that  familiar  old  proverb:  Es  thut  kein  'Gang  so  gut, 
Er  hat  einen  eisernen  Hut.11 

Emmons's  own  studies  on  secondary  enrichment  were  begun 
at  Butte  in  1896;  and  he  freely  discussed  his  results  in  private, 
though  they  were  first  published  in  our  Transactions  in  1900. 
In  this  paper  he  quotes  from  that  of  Vogt,  issued  the  year 
before,  but  also  sets  in  order  a  long  series  of  observations  of 
his  own,  which  form  an.  extremely  important  contribution  to 
the  subject.  This  is  cognate  to  his  other  studies  on  replace- 
ment; for  his  idea  of  secondary  enrichment  might  be  para- 
phrased as  the  replacement  of  pyrite  by  the  sulphides  of  other 
metals,  especially  copper. 

The  idea  of  secondary  enrichment  was  in  the  air  at  the  close 
of  the  last  century,  and  had  been  very  distinctly  suggested  in 
this  country  (for  instance  by  Dr.  James  Douglas),  though  with- 
out sufficient  substantiation.  Almost  simultaneously  with  Em- 
mons's memoir  appeared  important  papers  by  Messrs.  Weed, 
Van  Hise,  and  Lindgren. 

It  is  not  needful  here  to  pass  in  review  all  of  Emmons's 
work.  A  full  list  of  his  papers  will  be  found  at  the  end  of  this 
notice.  All  of  them  are  as  conscientiously  elaborated  as  those 

9  Journal  filr  praktische  Chemie,  vol.  x. ,  p.  333  (1837).     See  also  E.  Schurmann, 
in  Leibig's  Annalen,  vol.  ccxlix.,  p.  326  (1888). 

10  Mem.  de  la  Comm.   del  Mapa  Geol6gica   de   Espana.     Descripcion  fisica, 
geologica  y  minera  de  la  provincia  de  Huelva,  por  Joaquin  Gonzalo  y  Tarin, 
pp.  217  to  220  et  passim  (1888). 

11  Zeitschrift  fur  praktische  Geologic,  pp.  241  10  254  (July,  1899). 


xl        BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

which  I  have  selected  for  mention  on  account  of  their  peculiar 
importance.  On  the  other  hand,  a  few  remarks  seem  appro- 
priate on  the  tendency  and  the  development  of  the  science 
which  he  so  admirably  represented. 

When  Clarence  King  planned  the  researches  of  the  U.  S. 
Geological  Survey  into  the  origin  and  nature  of  ore-deposits, 
and  placed  Emmons  and  me  in  charge  of  them,  no  one  of  us 
was  in  a  position  to  appreciate  the  multifariousness  and  intri- 
cacy of  the  facts  which  these  investigations  would  disclose ;  but 
before  King's  untimely  death,  the  vastness  of  the  task  was 
manifest,  as  well  as  the  necessity  for  improved  methods  of  in- 
vestigation and  for  experimental  researches  of  the  most  funda- 
mental character. 

More  than  half  of  the  great  amount  of  information  now 
available  to  mining-geologists  is  due  to  the  use  of  the  micro- 
scope, armed  with  which,  the  eyes  of  the  generation  now  pass- 
ing away  have  been  a  hundred  times  as  sharp  as  those  of  their 
predecessors.  But  the  microscope  is  not  merely  a  powerful 
magnifying-glass ;  it  is  an  instrument  of  moderate  precision, 
whose  use  has  familiarized  us  with  quantitative  measurement 
and  stimulated  us  to  demand  exact  methods  of  geological  in- 
vestigation. 

It  is  not  enough  to  know  the  facts,  for  these  alone  lead  only 
to  delusive  "  rules  of  thumb."  We  can  and  must  attain  a  com- 
prehension of  the  mechanical,  chemical,  and  thermal  processes 
which  underlie  the  formation  and  distribution  of  ores,  as  re- 
vealed not  only  by  the  microscope,  but  also  by  every  other 
available  method  of  research.  Many  of  the  problems  presented 
are  of  extraordinary  difficulty,  far  exceeding  in  this  respect 
most  of  those  undertaken  by  professional  physicists  and  chem- 
ists ;  but  they  are  not  insoluble ;  and  the  limits  of  our  knowledge 
are  extended  year  by  year. 

None  of  us  have  been  more  impressed  with  the  necessity  for 
such  researches  than  was  King,  or  even  Emmons,  who  regretted 
all  his  life  that  he  had  not  a  better  command  of  the  exacter 
sciences.  Let  me  pass  the  word  on  from  them  that  the  future 
of  the  science  of  ore-deposits  depends  on  investigations  of  the 
utmost  precision  into  the  fundamental  principles  of  geophysics. 
Physics  and  physical  chemistry  will  be  as  indispensable  to  the 
mining-geologist  of  the  future  as  mineralogy  to  the  petro- 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.         xli 

grapher  or  zoology  to  the  palaeontologist.  It  is  a  duty  which 
the  Institute  owes  to  its  founders,  its  members,  and  the  world, 
to  promote  and  foster  research  of  this  description;  to  advance 
as  rapidly  as  possible  the  day  when  mining-geologists,  no 
longer  groping,  will  comprehend  why  ore-deposits  are  what  we 
find  them  to  be. 

And  now  as  to  the  man  himself.  There  is  not  a  geological 
society  or  even  a  mining-camp  from  Arctic  Finland  to  the 
Transvaal,  or  from  Alaska  to  Australia,  where  Emmons's  name 
is  not  honored  and  his  authority  recognized ;  nor  is  there  a 
society  of  which  he  was  nominally  an  active  member  in  which 
he  was  not  really  active  and  efficient.  Thoroughness  and  good 
judgment  characterized  all  he  did.  He  had  a  very  high  sense 
of  responsibility  and  rarely  made  his  hypotheses  public ;  yet 
his  originality  has  enriched  the  science  to  which  his  life  was 
devoted.  In  private  life,  he  was  modest  to  the  point  of  diffi- 
dence, and  many  of  his  old  acquaintances  scarcely  knew  of  his 
distinction;  but  none  could  long  enjoy  his  acquaintance  with- 
out becoming  conscious  of  the  kindness  of  his  heart  and  the 
elevation  of  his  character.  He  would  not  have  known  how  to 
undertake  an  unworthy  action,  or  how  to  do  a  selfish  thing. 
His  published  investigations  will  live  on  as  sources  of  knowl- 
edge and  models  of  method ;  and  in  a  similar  circle  his  per- 
sonal example  will  continue  potent  for  good. 

Emmons  died  painlessly  and  unexpectedly  in  his  sleep  on 
Mar.  28,  1911,  the  eve  of  his  seventieth  birthday.  Thus  fitly 
ended  a  career  of  useful  labor  faithfully  performed. 


Among  the  societies  to  which  Emmons  belonged,  none  ap- 
pealed to  him  more  than  the  American  Institute  of  Mining 
Engineers.  He  joined  us  in  1877,  was  three  times  Vice-Presi- 
dent, contributed  many  papers  to  the  Transactions,  and  was 
always  ready  to  assist  in  organizing  our  meetings.  He  was 
also  a  member  of  the  National  Academy  of  Sciences,  the 
American  Philosophical  Society,  the  American  Academy  of 
Arts  and  Sciences,  the  Washington  Academy  of  Sciences,  the 
Geological  Society  of  London,  the  Geological  Society  of  Amer- 
ica, the  International  Congress  of  Geologists,  and  the  Colorado 
Scientific  Society.  He  was  elected  an  honorary  member  of  the 


xlii        BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

Societe  Helvetique   des  Sciences  Naturelles,  and  received  the 
degree  of  Doctor  of  Sciences  from  Harvard  and  Columbia. 


LIST  OF  SCIENTIFIC  PUBLICATIONS  OF  SAMUEL  F.  EMMONS. 

1870.  Geology  of  Toyabe  Range. 

U.  S.  Geol.  Exploration  of  40th  Parallel.  Vol.  III.  Mining  In- 
dustry. Chap.  VI,  sect.  II,  pp.  340-348,  with  colored  geological 
map. 

Geology  of  Philadelphia  or  Silver  Bend  region. 

Ibid.,  chap.  VI,  sect.  II,  pp.  393-396. 

Geology  of  Egan  Canon  District. 

Ibid.,  chap.  VI,  sect.  VI,  pp  445-449. 

1871.  Glaciers  of  Mt.  Rainier. 

Amer.  Jour.  Sci.,  3d  ser.     Vol.  I,  pp.  161-165. 

1877.     The  Volcanoes  of  the  U.  S.  Pacific  Coast. 

Address  delivered  at  Chickering  Hall,  N.  Y.,  Feb.  6,  1877.  Jour. 
Amer.  Geogr.  Soc.  Vol.  IX,  1876-'7,  pp.  44-65. 

1877.     Descriptive  Geology  of  the  40th  Parallel. 

U.  S.  Geol.  Exploration  o£  40th  Parallel.  Vol.  Ill  (with  Arnold 
Hague).  4to,  pp.  850,  with  26  plates  and  atlas  of  11  maps  and  2 
section  sheets,  colored  geologically. 

1882.     Abstract  of  Report  on  Geology  and  Mining  Industry  of 
Leadville,  Colo. 

U.  S.  Geol.  Survey.  Second  Ann.  Report.  Pp.  203-290,  with  geo- 
logical colored  map  and  sections. 

1882.  The  Mining  Work  of  the  U.  S.  Geological  Survey. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  X,  pp.  412-425. 

1883.  Geological  Sketch  of  Buffalo  Peaks. 

U.  S.  Geol.  Survey,  Bulletin  No.  1,  pp.  11-17. 

1883-4.     Opportunities  for  Scientific  Research  in    Colorado. 
Presidential  addresses. 

Proc.  Colo.  Sci.  Soc.     Vol.  I,  pp.  1-12  and  57-61. 

1883.  Ore-Deposition  by  Replacement. 

Proc.  Phil.  Soc.  Wash'n.     Vol.  VI,  p.  32. 

1884.  What  Is  a  Glacier  ? 

Proc.  Phil.  Soc.  Wash'n.     Vol.  VIE,  p.  37. 

1885.  Statistics  and  Technology  of  the  Precious  Metals. 

Tenth  Census  Reports.  Vol.  XIII  (with  G.  F.  Becker)  ;  Gov't  4to, 
541  pages.  (Submitted  in  1883.) 

1886.  Geology  and  Mining  Industry  of  Leadville,  Colo. 

U.  S.  Geol.  Survey,  Monograph  XII,  779  pages  and  45  plates,  with  atlas 
of  35  sheets  of  maps  and  sections  colored.  (Submitted  in  1885.) 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

1886.     Genesis  of  Certain  Ore-Deposits. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XV,  pp.  125-147. 

1886.  Notes  on  Some  Colorado  Ore-Deposits. 

Proc.  Colo.  Sci.  Soc.     Vol.  II,  pp.  85-105. 

1887.  On  the  Origin  of  Fissure  Veins. 

Ibid.,  Vol.  II,  pp.  187-202. 
1887.  On  Glaciers  in  the  Rocky  Mountains. 

Ibid.,  Vol.  II,  pp.  211-227. 
1887.  Preliminary  Notes  on  Aspen,  Colo. 

Ibid.,  Vol.  II,  pp.  251-277. 

1887.     Submerged  Trees  of  the  Columbia  River. 

Science.     Vol.  XX,  pp.  156-157. 

1887.  Notes  on  the  Geology  of  Butte,  Mont. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XVI,  pp.  49-62. 

1888.  Structural  Relations  of  Ore-Deposits. 

Ibid.,  Vol.  XVI,  pp.  804-839.* 
Same  translated  into  French  by  R.  A.  Bergier. 

Re>ue  Universelle  des  Mines.     Tome  X,  3me  ser.,  34me  ann.,  p.  130. 
Liege  et  Paris,  1890. 

1888.  On  Geological  Nomenclature. 

Rep.  ,of  Am.  ComHe  Intern.  Congress  of  Geologists,  pp.  58-61. 

1889.  On  Orographic  Movements  in  the  Rocky  Mountains. 

Bull.  Geol.  Soc.  Am.     Vol.  I,  pp.  245-286. 

1890.  Age  of  Beds  in  the  Boise  River  Basin,  Idaho. 

Proc.  Bost.  Soc.  Nat.  Hist.     Vol.  XXIV,  pp.  429-434. 
1890.     Notes  on  Gold-Deposits  of  Montgomery  County,  Md. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XVIII,  pp.  391-411. 

1892.     Fluorspar-Deposits  of  Southern  Illinois. 
Ibid.,  Vol.  XXI,  pp.  31-53. 

1892.  Faulting  in  Veins. 

Eng'r'g  and  Min'g  Journal.     Vol.  LIII,  pp.  548-549. 

1893.  Compte  Rendu  de  la  5me  Session  du  Congres  Geologique 

Internationale  (Editor). 

Gov't  Printing  Office.     529  pages,  21  plates,  39  figures. 

1893.     Geological  Distribution    of  the  Useful   Metals  in  the 
United  States. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXII,  pp.  53-95. 

1893.     Genesis  of  Ore-Deposits  (discussion). 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXIII,  pp.  597-602. 

1893.     Progress  of  the  Precious  Metal  Industry  in  the  U.  S. 

U.  S.  Geol.  Survey.     Mineral  Resources  for  1902,  pp.  46-94  ;  also  in 
Report  of  the  Director  of  the  Mint  for  1893,  pp.  117-141. 


xllV       BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

1894.     Geological  Guide  Book  to  the  Rocky  Mountains. 

John  Wiley  &  Sons,  New  York. 

1894.     Geology  of  Lower  California  (with  G.  P.  Merrill). 

Bull.  Geol.  Soc.  Am.     Vol.  V,  pp.  489-514. 

1894.  Geology  and  Mineral  Resources  of  the  Elk  Mountains, 

Colo. 

U.  S.  Geol.  Survey.     Folio  9.     Explanatory  text. 

1895.  Geology  of  the  Mercur  Mining  District,  Utah. 

U.  S.  Geol.  Survey.     16th  Ann.  Keport,  pp.  349-369. 

1896.  Geological  Literature  of  the  South  African  Republic. 

Journal  of  Geology.     Vol.  4.  pp.  1-22. 

1896.     Some  Mines  of  Rosita  and  Silver  Cliff,  Colo. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXVI,  pp.  773-823. 

1896.     The  Mines  of  Custer  County,  Colo. 

U.  S.  Geol.  Survey.     17th  Ann.  Report,  par*  II,  pp.  411-472. 

1896.  Geology  of  the  Denver  Basin  in   Colorado  (with  W. 

Cross  and  G.  E.  Eldridge). 

U.   S.  Geol.  Survey,   Monograph    XXVII,  4to,  526   pages,  with  31 
plates,  1 02  figures. 

1897.  The  Geology  of  Government  Explorations  (Presidential 

address  before  the   Geological    Society  of    Wash- 
ington, December,  1896). 

Science,  n.  s.     Vol.  V,  pp.  1-15  and  42-51. 

1897.     Economic  Geology  of  the  Butte  District,  Mont. 

U.  S.  Geol.  Survey.     Folio  No.  38.     Explanatory  text. 

1897.     Physiography  of  the  West  Coast  of  Peru,  S.  A. 

Science,  n.  s.     Vol.  V,  p.  889. 

1897.  The  Origin  of  Green  River. 

Science,  n.  s.     Vol.  VI,  pp.  19-21. 

1898.  Geology  of  the  Ten-mile  District,  Colorado. 

U.  S.  Geol.  Survey.     Geol.  Atlas  of  the  U.   S.,   Folio  No.  48.    Ex- 
planatory text. 

1898.     Map  of  Alaska  :  Its  Geography  and  Geology. 

U.  S.  Geol.  Survey.     44  pages  and  geol.  maps.     Special  report  to  the 
Fifty-fifth  Congress,  2d  session. 

1898.     Geology  of  the  Aspen  Mining  District,  Colorado. 

U.  S.  Geol.  Survey,  Monograph  XXX f,  pp.  xvn-xxxu.      Introduc- 
tion. 

1898.     Dr.  Don's  Paper  on  the  Genesis  of  Certain  Auriferous 
Lodes  (discussion). 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXVIF,  p.  993. 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS.        xlv 

1898.     A  Century  of  Geography  in  the  United  States. 

Science,  n.  s.     Vol.  VII,  p.  677. 

1898.  Geological  Excursion  Through  Southern  Russia. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXVIII,  pp.  3-23. 

1899.  Plutonic  Plugs  and  Subtuberant  Mountains. 

Geol.  Soc.  Wash'n,  and  abstract  in  Science,  n.  s.     Vol.  X,  pp.  24-25. 

1900.  Secondary  Enrichment  of  Ore-Deposits. 

Trans.  Am.   Inst.    Mg.  Eng'rs.     Vol.   XXX,   pp.    177-217.      Ibid., 
Genesis  of  Ore-Deposits  (1902),  pp.  199-204,  433-473,  756-762. 

1900.  Review  of  Kemp's  Ore  Deposits  of  the  United  States. 

Science,  n.  s.     Vol.  XI,  pp.  503-505. 

1901.  The  Delamar  and  Horn-Silver  Mines  :    Two  types  of 

ore-deposits  in  the  deserts  of  Nevada  and  Utah. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXXI,  pp.  658-683. 

1901.     The  Sierra  Mojada  and  its  Ore-Deposits  (discussion). 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXXI,  pp.  953-959.     Mexican 
volume  XXXII,  pp.  566-567. 

1901.  Clarence  King — A  Memorial. 

Eng.  and  Mg.  Jour.     Vot  73,  pp.  3-5.     Dec.  28,  1901. 

1902.  Biography  of  Clarence  King. 

Amer.  Jour.  Sci.,  4th  ser.     Vol.  13,  pp.  224-237. 

1902.     The  U.  S.  Geol.  Survey  in  its  Relation  to  the  Practical 
Miner. 

Eng.  and  Mg.  Jour.    Vol.  74,  p.  43. 

1902.     Sulphidische  Lagerstatten  vom  Cap  Garonne. 

Zeitsch.  f.  Prak  Geol.     Vol.  X,  p.  126. 

1902.     On  the   Secondary  Enrichment  of   Ore-Deposits  (dis- 
cussion). 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXXIII,  p.  1058. 

1902.  On  the  Hydrostatic    Level  Attained   by  the    Ore-De- 

positing Solutions  in  Certain  Mining  Districts  of 
the  Great  Salt  Lake  Basin  (discussion). 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXXIII,  p.  1062. 

1903.  Reminiscences  of  Clarence  King. 

Trans.  Am.  Inst.  Mg.  Eng'rs.     Vol.  XXXIII,  pp.  633-634,  636-638, 
643. 

1903.     Drainage  of  the  Valley  of  Mexico.  % 

Geol.  Soc.  Wash'n,  and  Science,  n.  s.     Vol.  17,  p.  £09. 

1903.     Little  Cottonwood  Granite  Body  of  the  Wasatch  Moun- 
tains. 

Am.  Jour.  Sci.,  4th  ser.     Vol.  XVI,  pp.  139-147. 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

1903.  Contributions   to   Economic   Geology,  1902  (introduc- 

tion). 

U.  S.  Geol.  Survey,  Bull.  No.  213,  pp.  15-30  ;  also  94-98. 

1904.  Theories  of  Ore  Deposition,  Historically  Considered. 

Bull.  Geol.  Soc.  Am.  (Presidential  address).  Vol.  15,  pp.  1-28  ;  also 
Eng.  and  Mg.  Jour.  Vol.  77,  pp.  117,  157,  199,  237  ;  also  Smith- 
sonian Report  for  1904. 

1904.     Contributions    to  Economic    Geology,    1903.      Metal- 
liferous Ores. 
U.  S.  Geol.  Survey,  Bull.  No.  225,  pp.  18-24. 

1904.  Economic  Resources  of  the  Northern  Black  Hills,  by 
J.  D.  Irving,  with  contributions  by  S.  F.  Emmons 
and  T.  A.  Jaggar,  Jr. 

U.  S.  Geological  Survey,  Prof.  Paper  No.  26.     222  pp. 

1904.     Clarence  King,  geologist. 

[In  the  Century  Association,  New  York.  King  Memorial  Committee. 
Clarence  King  Memoirs.  The  Helmet  of  Mambrino.  N.  Y.  and 
London.  ] 

1904.  Occurrence  of  Copper  Ores  in  Carboniferous  Limestone 
in  the  Region  of  the  Grand  Canon  of  the  Colorado. 

Abstract :  Science,  n.  s.     Vol.  XX,  pp.  760-761. 

1904.  The  Virginius  Mine. 

Eng.  and  Mg.  Jour.     Vol.  LXXVII,  p.  311. 

1905.  Investigation  of  Metalliferous  Ores. 

U.  S.  Geol.  Survey,  Bull.  No.  260,  pp.  19-27. 

1905.  Copper  in  the  Red  Beds  of  the  Colorado  Plateau 
Region . 

U.  S.  Geol.  Survey,  Bull.  No.  260,  pp.  221-232. 

1905.     The  Cactus  Copper  Mine,  Utah. 

U.  S.  Geol.  Survey,  Bull.  No.  260,  pp.  242-248. 

1905.     Contributions  to  Economic  Geology,  1904. 

In  U.  S.  Geol.  Survey,  Bull.  No.  260. 

1905.  Economic  Geology  of  the  Bingham  Mining  District, 

Utah,  by  J.  M.  Boutwell ;  with  a  section  on  areal 
geology  by  Arthur  Keith,  and  an  introduction  on 
general  geology  by  S.  F.  Emmons. 

IT.  S.  Geological  Survey,  Prof.  Paper  No.  38.     413  pp. 

1906.  What  is  a  Fissure  Vein  ? 

Econ.  Geol.     Vol.  I,  No.  4,  pp.  385-387. 

1906.  A  Map  and  a  Cross  Section  of  the  Downtown  District 
of  Leadville,  Colo. 

Abstract :  Science,  n.  s.     Vol.  XXIII,  pp.  816-817. 


BIOGRAPHICAL    NOTICE    OF    SAMUEL    FRANKLIN    EMMONS. 

1906.     Useful  Definitions. 

Min.    and   Sci.    Press.     Vol.    XCIII,    pp.   355-356  ;    proper  use  of 
mining  terms.     Min.  World.     Vol.  XXV,  No.  24,  p.  715. 

1906.     Los  Pilares  Mine,  Xacozari,  Mexico. 

Econ.  Geol.     Vol.  I.,  No.  7,  pp.  629-643  ;  Abstract :   Eng.  and  Min. 
Jour.     Vol.  LXXXII,  pp.  1066-1067. 

1906.  Contributions  to  Economic  Geology,  1905 ;  Investiga- 

tion of  Metalliferous  Ores. 

U.  S.  Geol.  Survey,  Bull.  No.  285,  pp.  14-19. 

1907.  Biographical  Notice  of  George  H.  Eldridge. 

Trans.  Am.  Inst.  Min.  Eng'rs.     Vol.  XXXVII,  pp.  339-340. 

1907.     Uinta  Mountains. 

Geol.  Soc.  Amer.,Bull.     Vol.  XVIII,  pp.  287-302. 

1907.     The  Downtown  District  of  Leadville,  Colo.,  by  S.  F. 

Emmons  and  J.  D.  Irving. 
U.  S.  Geol.  Survey,  Bull.  No.  320.     75  pp. 
1907.     Geological  Structure  of  the  Uinta  Mountains. 

Abstract :  Science,  n.  e.     Vol.  XXV,  pp.  767-768. 

1907.     Investigations  of  Metalliferous  Ores. 
U.  S.  Geol.  Survey,  Bull.  No.  315,  pp.  14-19. 
1907.     Suggestions  for  Field  Observations  of  Ore  Deposits. 

Min.  and  Sci.  Press.     Vol.  XCV,  pp.  18-20. 

1907.     Biographical  Memoir  of  Clarence  King,  1842-1901. 

Head  before  the  Nat.   Acad.  Sci.,  Apr.   23,   1903.     Nat,  A  cad.  Sci., 
Biog.  Mem.     Vol.  VI,  pp.  25-55. 

1909.  Development  of  Modern  Theories  of  Ore  Deposition. 

Min.  and  Sci.  Press.     Vol.  XCIX,  pp.  400-403. 

1910.  Economic  Geology  in  the  United  States. 

Mining  World.     Vol.  XXX,  pp.  1209-1211.     June  26,  1909  •    Cana- 
dian Min.  Inst.  Jour.     Vol.  XII,  pp.  89-101. 

1910.     Cananea  Mining  District  of  Sonora,  Mexico. 

Econ.  Geology.     Vol.  V,   No.  4,  pp.    312-366.     Abstract :  Eng.  and 
Min.  Jour.     Vol.  XC,  pp.  402-404. 

1910.     The  Cobalt  Mining  District  of  Ontario. 

Abstract :  Science,  n.  s.     Vol.  XXXI,  p.  517. 

1910.     Criteria  of   Downward  Sulphide  Enrichment  (discus- 
sion). 
Econ.  Geology.     Vol.  V,  No.  5,  pp.  477-479. 


No.  1. 

The  Genesis  of  Certain  Ore-Deposits. 

BY   S.    F.    EMMONS,*  WASHINGTON,    D.    C.      . 

(Bethlehem  Meeting,  May,  1886.     Tram.,  xv.,  125.) 

IN  a  report  upon  the  geology  of  Leadville  and  vicinity, 
which  is  still  in  the  hands  of  the  Public  Printer,  I  have  given, 
at  some  length,  my  conclusions  as  to  the  genesis  of  the  remark- 
able silver-lead  deposits  of  that  region,  and  the  data,  gathered 
during  a  long  and  careful  consideration,  upon  which  my  views 
were  founded.  In  the  brief  abstract  of  this  report,  published 
in  1881,  the  bare  conclusions  are  given,  with  but  few  of  the 
facts  upon  which  they  were  founded.  Since  that  time,  these 
conclusions  have  been  variously  criticised,  and  it  has  even  been 
assumed  that  the  views  I  expressed  with  regard  to  these  de- 
posits were  intended  as  a  theory  of  ore-deposits  in  general. 

Had  my  final  report  been  printed,  no  such  misconception 
could  have  occurred;  for,  in  that  I  explicitly  disclaim  any  in- 
tention of  general  application  of  the  theories  there  presented. 
Even  in  the  abstract  I  am  unable  to  find  any  statements  which 
would  justify  such  a  conclusion. 

Since  my  Leadville  work,  however,  I  have  had  further  op- 
portunities of  examining  ore-deposits,  and  have  given  the  gen- 
eral subject  much. thought  and  study,  and,  as  a  result,  I  have 
made  .in  my  own  mind  certain  generalizations,  which,  I  am 
conscious,  need  the  test  of  a  far  greater  number  of  practical 
applications  than  I  have  yet  been  able  to  make,  but  which,  I 
think,  it  may  be  well  to  present  to  the  members  of  the  Insti- 
tute as  suggestive,  that  their  own  observations  may  further 
prove  or  disprove  them.  I  shall  use  my  Leadville  observations 
and  the  criticisms  which  have  been  made  upon  them  as  a  sort 
of  text  for  my  remarks. 

The  salient  facts,  which  I  thought  to  have  determined  with 
regard  to  the  Leadville  deposits,  which,  as  is  well  known,  are 
silver-lead  deposits  in  a  dolomitic  limestone,  overlain  and  in 

*  U.  S.  Geological  Survey. 
1 


2  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

part  also  traversed  by  various  bodies  of  porphyry,  are  the  fol- 
lowing : 

1.  That  they  were  deposited  from  aqueous  solutions. 

2.  That  they  were  originally  deposited  as  sulphides,  at  a 
great  depth  below  the  rock-surface  (probably  10,000  ft);  that, 
by  subsequent  dynamic  movements  and  by  erosion,  they  have 
been  brought  to  their  present  position  near  the  surface,  and  that, 
through  secondary  alteration  by  surface-waters,  they  have  been 
changed  to  oxides,  carbonates,  and  chlorides. 

3.  That  the  process  of  deposition  was  a  metasomatic  inter- 
change between  the  minerals  brought  in  in  solution  and  the 
limestone — that  is,  that  they  were  not   deposited  in  already 
existing  open  cavities,  but  gradually  replaced  the  limestone, 
from  the  channels  through  which  they  reached  it  outward. 

4.  That  the  solutions  or  ore-currents  reached  the  present 
locus  of  the  deposits  directly  from  above  and  not  from  below. 

5.  That,  whatever  may  have  been  the  ultimate  source  from 
which  the  mineral  components  of  the  deposits  came,  the  ob- 
served facts  point  to  the  neighboring  eruptive  rocks  as  the 
immediate  source  from  which  they  were  derived  by  the  ore- 
bearing  solutions  which  deposited  them  in  their  present  locus. 

I  will  take  up  these  propositions  in  the  above  order,  and, 
after  discussing  the  criticisms  which  have  been  made  upon 
them,  see  how  far  they  may  be  applicable  to  other  deposits 
than  those  of  Leadville. 

1.  That  the  vast  majority  of  ore-deposits  have  been  deposited 
from  solutions,  seems  to  be  now  so  generally  admitted  as  to 
require  no  further  discussion  here.  This  view  is  held  by  most 
all  American,  English  and  German  geologists,  while  the 
French  may  be  considered  to  be  those  who  still  cling  to  the 
sublimation  theory  in  the  modified  form  which  is  based  on  the 
remarkable  synthetic  experiments  of  Senarmont,  Daubree,  and 
others.  But,  as  one  of  their  number  admits,1  this  is  practically 
only  a  variety  of  the  solution  theory,  which  assumes  that  pres- 
sure and  heat,  sufficient  to  vaporize  water,  are  necessary  to 
bring  about  a  solution  of  the  metallic  minerals.  That  many 
deposits  have  been  formed  under  conditions  of  great  heat  and 
pressure  is  most  probable ;  that  heat  and  pressure  greatly 


A.  De  Lapparent,  Traite  de  Geologic,  p.  1170  (1883). 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  3 

increase  the  solvent  power  of  percolating  waters  is  evident; 
but  that  heat  and  pressure  are  an  absolutely  essential  condition 
of  mineral  solution  cannot  be  maintained,  since  we  see  in 
nature  many  instances  of  mineral  solution  and  deposition 
under  ordinary  pressure  and  by  comparatively  cold  waters. 

2.  That  the  Leadville  ores  were  originally  deposited  in  the 
form  of  sulphides,  and  that,  therefore,  they  would  be  found  in 
that  condition,  when  explorations  should  have  been  pushed  in 
depth  beyond  the  oxidizing  action  of  surface-waters,  was  as- 
sumed  by   indirect   reasoning   at    the    time   my   abstract   was 
written,  since  at  that  time  no  sulphide  deposits  had  been  found 
on  the  so-called  "  contact "  in  the  region.     Explorations  made 
since  that  time  have  abundantly  proved  the  correctness  of  the 
assumption.     An  interesting  description  of  some  of  the  more 
important  sulphide  bodies,  and  of  a  previously  undiscovered 
fault,  was  read  at  the  Chattanooga  meeting  by  F.  T.  Freeland.2 

That  metallic  deposits,  with  the  single  exception  of  tin-ores, 
pass  into  sulphides  or  some  allied  combination  in  depth  has 
been  so  generally  observed,  that  it  has  almost  come  to  be  an 
axiom  in  vein-geology  that  original  deposition  must  have  been 
in  this  form.  Some  supposed  exceptions  have  been  observed; 
but  the  distinction  between  an  original  and  a  secondary  de- 
posit is  often  so  delicate  that  it  requires  a  most  thorough  and 
searching  examination  to  determine  the  point  satisfactorily. 
The  determination  beyond  the  shadow  of  a  doubt  of  an  origi- 
nal deposit  of  these  metals  in  an  oxidized  form  would  be  of 
the  utmost  interest  to  science. 

3.  That  the  process  of  ore-deposition  at  Leadville  was  a 
metasomatic 3  interchange  between  the  material  of  the  country- 
rock  and  the  minerals  brought  in  in  solution  by  the  ore-cur- 
rents, is  a  point  upon  which  I  particularly  desired  to  insist, 
because  it  is  either  tacitly  or  explicitly  assumed  by  most  text 
books  that  all  ore-deposits  in  limestones  are  the  filling  of  pre- 
existing cavities.     This  assumption,  like  the  one  that  fissure- 
veins  were  once  open  cavities  reaching  to  an  indefinite  depth, 
is,  it  seems  to  me,  the  result  of  generalizations  upon  too  few 


2  Trans.,  xiv.,  181  (1885-86). 

3  By  metasomatic  interchange,  I   understand  an  interchange  of  substances,  but 
not  necessarily  molecule  by  molecule  in  such  a  manner  as  to  preserve  the  original 
structure,  form,  or  volume  of  the  substance  replaced. 


4  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

facts.  The  facts  that  support  it  (the  arrangement  of  the  ore 
in  layers  parallel -to  the  walls  of  the  body,  etc.)  are  so  striking 
in  the  few  cases  where  they  have  been  observed,  that  they 
have  received  universal  mention,  while  the  far  more  numerous 
cases,  where  no  such  evidence  of  pre-existing  cavity  is  found, 
have  remained  in  most  instances  without  comment,  as  regards 
this  question. 

Professor  Le  Conte*  quotes  me  as  saying  that  the  ore  at 
Leadville  was  "  accumulated  in  hollowed-out  channels  in  the 
limestone,"  evidently  assuming  this  as  so  much  of  a  foregone 
conclusion  that  he  had  not  thought  it  necessary  to  read  my 
statement  of  the  diametrically  opposite  conclusion  at  which  I 
had  arrived.  Now,  I  not  only  distinctly  stated  that  I  believed 
the  ore  was  not  deposited  in  already  hollowed-out  channels  or 
pre-existing  cavities,  but  I  mentioned  that  the  caves,  which 
are  so  characteristic  of  limestone  formations,  were  at  Leadville 
formed  after  the  deposition  of  the  ore.  I  laid  stress  upon  the 
relation  of  these  caves  to  those  bodies,  not  because  it  was  the 
only  or  even  the  main  proof  of  the  statement  I  made,  but  be- 
cause I  thought  it  would  appeal  to  those  who  consider  all  lime- 
stone deposits  as  filling  cavities  hollowed  out  by  surface-waters. 
The  most  convincing  proof  of  the  statement  to  my  own  mind 
is,  that,  in  a  prolonged  study  of  the  various  deposits,  I  found 
no  single  fact  to  furnish  any  evidence  that  the  ore  was  depos- 
ited in  an  open  cavity ;  and  I  hold  that,  in  such  a  case,  the 
burden  of  proof  lies  on  the  side  of  those  who  uphold  the  open- 
cavity  theory.  There  is,  however,  a  consideration  which  can 
be  briefly  stated  and  which  affords  conclusive  evidence,  if  no 
other  were  present;  namely,  that  the  deposits  were  originally 
iormed  at  a  depth  of  about  10,000  ft.  below  the  surface  and 
before  the  strata  were  disturbed,  and  that,  therefore,  surface- 
waters  could  not  have  reached  their  locus  to  hollow  out  such 
cavities. 

I  find  it  difficult  to  understand  Professor  dewberry's  criti- 
cisms of  my  views  on  this  point.  In  the  first  place,  he  makes 
what  seems  to  me  a  totally  unwarranted  assumption,  that  I 
consider  that  the  Leadville  deposits  were  formed  by  surface- 
waters.  Then,  in  presenting  his  own  views  on  the  formation 

4  American  Journal  of  Science,  Third  Series,  vol.   xxvi.,  No.   151,  p.  18  (July, 

1883). 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  5 

of  the  Leadville  deposits,  he  says,  "  they  were  deposited  by 
substitution/'5  and  afterwards  remarks  that  the  fact  that  caves 
in  the  limestone  cut  across  the  ore-bodies  "  has  no  bearing  on 
the  question." 

In  a  former  article,  The  Origin  and  Classification  of  Ore- 
Deposits,6  his  meaning  is  less  ambiguous,  and  I  shall  take 
this  opportunity  of  criticising  him  in  turn.  One  of  the  divi- 
sions of  ore-deposits  there  given  by  him  is  "  chambers  or 
pockets  in  limestone,"7  of  which  he  says:  "From  a  study  of 
them  I  have  been  led  to  add  them  to  the  catalogue  of  forms  of 
ore-deposit  as  a  distinct  and  important  addition  to  those  given 
by  other  writers."  As  examples,  he  quotes  the  Eureka,  Rich- 
mond, Emma,  Flagstaff,  Kessler,  and  Cave  mines,  and  (with 
the  modification  of  their  contact-character)  the  Leadville  ore- 
bodies,  of  which  he  says  they  were  "  undoubtedly  accumu- 
lated in  vacant  spaces  formed  by  the  solution  of  the  limestone." 
The  formation  of  the  chambers  in  which  he  considers  these 
deposits  were  formed,  he  compares  to  that  ot  the  Mammoth 
Cave,  saying,  "  We  must  conclude  that  the  chambers  were 
formed,  like  modern  caves,  by  surface-water."  He  then  makes 
the  following  deductions  as  to  the  probable  extent  of  such 
deposits  :  "  They  will  not  be  found  to  extend  to  so  great  depth 
as  the  ore-bodies  of  fissure-veins,  since  the  excavation  of  the 
limestone,  if  produced  by  atmospheric  water,  must  be  confined 
to  the  zone  traversed  by  surface-drainage."  He  does  not  ex- 
plicitly state  what  he  considers  to  be  the  distinctive  character 
of  his  important  addition  to  the  classification  of  ore-deposits, 
the  want  of  information  in  regard  to  the  true  nature  of  which, 
he  says,  "  has  led  to  much  litigation  and  heavy  losses  in  mining." 
He  surely  cannot  mean  the  irregular  form  of  deposits  in  lime- 
stone, for  this  has  been  recognized  from  the  very  earliest  days 
of  mining,  and  has  formed  an  important  element  in  the  classi- 
fication of  most  writers  on  ore-deposits.8  It  would  seem,  there- 

5  The  Deposition  of  Ores.    School  of  Mines  Quarterly,  vol.  v.,  No.  4,  p.  341,  et  seg. 
(May,  1884). 

6  School  of  Mines  Quarterly,  vol.  i.,  No.  3,  pp.  87  to  104  (Mar.,  1880). 

7  This  division  lias  been  literally  adopted  by  J.  Arthur  Phillips,  in  his  Treatise 
on  Ore-Deposits  (1884). 

8  A  criticism  of  this  claim  of  novelty  may  be  found  in  the  Engineering  and  Mining 
Journal,  vol.  xxx. ,  No.  1,  p.  1  (July  3,  1880). 


6  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

fore,  that  this  distinctive  character  must  consist  in  their  having 
been  hollowed  out  originally  by  surface-waters. 

Surface-waters,  as  I  understand  the  common  use  of  the  term, 
means  those  waters  which  have  so  recently  left  the  surface  as 
to  still  retain  constituents  common  to  waters  now  found  at  or 
near  the  surface  (free  carbonic  and  organic  acids,  chlorides, 
etc.),  and  which  exert  an  oxidizing  action ;  and  from  the  above 
quotations  this  would  seem  to  be  his  interpretation  of  the  term 
also.  Moreover,  to  dissolve  out  caves  like  the  modern  caves 
there  should  be  a  comparatively  free  flow  of  water  and  ready 
drainage  to  carry  off  the  dissolved-out  material,  which  could 
only  be  found  at  comparatively  shallow  depths.  The  waters 
which  percolate  through  rocks,  even  at  the  greatest  known 
depths,  may  in  one  sense  be  considered  surface-waters;  but 
at  a  certain  depth  below  the  surface  these  waters  will  have  lost 
their  free  carbonic  and  organic  acids  and  have  become,  so  to 
speak,  saturated  and  only  able  to  dissolve  out  by  actual  inter- 
change of  their  constituents  with  those  of  the  rock  through 
which  they  pass ;  in  other  words,  no  longer  capable  of  leaving 
open  caves.  What  this  depth  is,  I  am  not  yet  prepared  to  say. 
It  would  differ  greatly  under  varying  local  conditions.  It  would 
probably  correspond  with  what  is  known  as  the  "  water-level  " 
in  Western  mines,  which  is  not  generally  below  a  thousand 
feet. 

Now  Professor  dewberry's  theory,  or  the  one  he  here  adopts, 
for  it  can  hardly  be  considered  original  with  him,  involves  a 
sort  of  see-saw  movement  for  the  rocks  inclosing  each  deposit, 
which,  though  not  impossible,  seems  from  a  geological  stand- 
point highly  improbable.  He  admits,  with  other  geologists, 
that  the  original  deposits  were  in  the  form  of  sulphides,  and 
that  the  oxidized  condition,  in  which  the  ores  he  speaks  of  are 
now  found,  is  due  to  the  action  of  surface-waters ;  hence,  as 
originally  deposited,  they  must  have  been  below  the  reach  ot 
surface-waters.  But  the  cavities  in  which  they  were  deposited 
were  formed  by  surface-waters ;  hence,  the  rocks  inclosing  the 
ore-deposits  must  have  been  once  so  near  the  surface  as  to  have 
been  hollowed  out  by  these  waters ;  then  have  been  depressed 
beyond  their  reach,  so  that  the  ore-bearing  solutions  which 
deposited  their  contents  in  the  caves  were  protected  from 
oxidizing  action,  and  then  again  raised  to  their  present  position, 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  7 

where  the  surface-waters  have  changed  their  sulphides  to 
oxides,  and  hollowed  out  a  new  set  of  caves.  When  I  say 
raised  and  depressed,  I  mean  not  necessarily  actual  but  only 
relative  movement,  as  referred  to  the  surface  of  the  earth ;  this 
surface  might  itself  have  been  raised  by  the  accumulation  of 
deposits  over  the  rocks,  and  these  accumulations  again  re- 
moved by  erosion,  so  that  the  result  would  be  accomplished 
without  actual  movement  of  the  inclosing  rock. 

In  such  an  assumption,  I  hold,  one  is  not  justified,  unless  he 
can  find  some  evidence  of  it  in  the  geology  of  the  region  in- 
volved. In  Leadville  there  is  none.  The  rocks  inclosing  the 
ore-deposits  were  never  so  near  the  surface  as  they  are  now, 
and  dynamic  action  and  erosion  have  gradually  raised  them 
from  the  depth  of  about  10,000  ft.,  at  which  the  original  sul- 
phide deposits  were  formed.  The  same  is  true  in  a  general 
way  of  the  other  examples  quoted  by  Professor  Newberry — the 
original  deposits  were  deep  seated,  and,  though  the  geology  of 
the  districts  has  not  yet,  in  all  cases,  been  studied  in  sufficient 
detail  to  afford  as  good  estimates  as  to  the  depth  of  the  original 
deposition  as  at  Leadville,  there  is  no  evidence  of  any  such 
relative  oscillations  as  his  theory  would  involve. 

The  practical  application  made  by  Dr.  Newberry,  though  a 
logical  deduction  from  his  theory,  viz.,  that  deposits  in  lime- 
stone must  be  limited  in  depth  to  the  zone  traversed  by  surface- 
drainage,  and  therefore  of  less  value  than  fissure- veins,  illustrates 
the  danger  of  a  priori  reasoning  in  geology,  since  it  not  only 
leads  to  geological  improbabilities,  but  gives  the  influence  of 
his  name  to  a  dangerous  popular  fallacy  already  too  current 
among  miners.  I  have  shown  in  my  Leadville  work  not  only 
that  the  geological  conditions  there  are  such  as  to  preclude  the 
possibility  of  the  formation  of  caves  by  surface-waters  prior  to 
the  original  ore-deposition,  but  that,  in  extent  and  in  the  quan- 
tity of  ore  contained  in  it,  the  Blue  limestone,  which  may  in 
one  sense  be  regarded  as  a  sort  of  horizontal  vein,  exceeds  any 
known  fissure-vein,  not  even  excepting  the  famous  Comstock 
lode.  At  Eureka,  which  is  Professor  Newberry's  typical  ex- 
ample, the  exhaustive  studies  of  J.  S.  Curtis,  who  came  to  the 
work  with  a  priori  views  similar  to  those  entertained  by  Pro- 
fessor Newberry,  have  shown  not  only  that  the  ores  were  not 
originally  deposited  in  open  caves,  but  that  caves  formed  by 


8  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

surface- waters  become  less  frequent  in  depth,  and  have  nearly 
disappeared  at  1,000  ft.  from  the  surface.  As  the  workings  in 
this  district  are  being  rapidly  deepened,  a  practical  illustration 
of  the  depth  at  which  cave-formation  by  surface-waters  is  still 
possible  will  soon  be  furnished.  It  will  also  be  seen  whether 
ore-deposition  in  this  region  stops  at  the  limits  of  cave-forma- 
tion. Even  should  it  be  found  to  do  so,  however,  it  would 
merely  show  a  local  coincidence,  and  not  a  logical  conse- 
quence. 

The  possible  application  of  the  theory  of  the  formation  of 
ore-deposits  by  replacement  or  substitution  is  almost  unlimited, 
and  the  limits  of  its  actually  demonstrated  application  are 
being  every  day  extended,  not  only  by  studies  of  new  districts, 
but  by  more  careful  arid  unbiased  studies  of  old  districts  in 
which  a  different  method  of  formation  had  previously  been 
determined  upon. 

The  process  is  most  readily  conceivable  in  the  case  of  easily- 
soluble  rocks,  like  limestone  and  dolomite ;  and,  in  point  of 
fact,  it  is  found  that  these  rocks  are  the  favorite  receptacle  of 
metallic  deposits  in  mining-regions  where  the  ores  occur  in 
the  later  stratified  rocks,  among  which  calcareous  beds  are 
abundant.  It  is  also  possible  that  in  the  older  and  more  crys- 
talline rocks,  where  the  calcareous  beds  are  of  limited  extent, 
metallic  deposits  occurring  in  large  masses,  like  those  of  iron, 
may  have  so  completely  replaced  the  calcareous  material  that 
little  or  no  trace  of  it  remains.  The  old  theory  that  iron-ores 
in  the  crystalline  rocks  are  of  eruptive  origin  is  generally 
abandoned  at  the  present  day.  The  few  geologists  who  still 
maintain  this  origin  for  individual  deposits  are  doubtless  in- 
fluenced in  their  opinion  by  respect  for  views  formerly 
advanced ;  while  among  those  who  come  to  the  study  with  a 
mind  free  from  preconceived  ideas,  and  who  push  their  exami- 
nations with  sufficient  thoroughness  and  detail,  I  have  known 
of  none  of  late  years  who  have  adopted  the  eruptive  theory. 
The  most  striking  instance  that  has  come  to  my  notice  is  that 
of  the  famous  specular  iron-ores  of  the  island  of  Elba,  which, 
when  I  was  a  student,  were  held  as  the  most  typical  example 
of  eruptive  or  sublimation  deposits.  These  deposits  were 
visited  by  the  most  prominent  geologists  of  Europe;  but, 
among  them,  Vom  Rath,  in  1870,  was  the  first  to  doubt  the 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  9 

eruptive  origin  of  the  ores,  which  he  showed  in  certain  por- 
tions was  impossible.  The  island  has  been  systematically 
studied  and  mapped  by  the  Geological  Survey  of  Italy ;  and  B. 
Lotti,  the  geologist  in  charge  of  this  work,  after  a  careful 
study  of  all  the  evidence  and  of  the  views  held  by  those  who 
have  gone  before  him,  but  whose  observations  were  necessarily 
less  complete  and  exact  than  his  own,  decides  that  they  must 
have  been  formed  by  replacement.  The  following  is  a  literal 
translation  of  his  conclusions  : 

"  We  may  therefore  reasonably  conclude  that  the  iron- 
deposits  of  Elba  and  their  analogues,  both  of  iron  and  of  other 
metals,  on  the  neighboring  continent  (excepting  those  con- 
nected with  the  serpentines)  are  formed  by  aqueous  solutions 
of  the  metals,  which  found  an  easier  passage  for  their  subterra- 
nean circulation,  and  perhaps  also  for  reaching  the  surface, 
between  rock-masses  of  different  nature,  and  deposited  the 
metallic  minerals  which  they  held  in  solution  when  they  met 
favorable  conditions ;  that  is,  either  in  proximity  to  the  surface 
or  in  contact  with  calcareous  rocks  with  which  an  interchange 
of  materials  took  place,  and  this  in  conformity  with  the  law 
that  the  more  easily  soluble  minerals  are  replaced  by  those 
that  are  less  soluble.  If  the  waters  contained,  besides  the 
bicarbonate  of  iron,  sulphydric  acid  also,  there  resulted  a  pre- 
cipitate of  sulphide  of  iron."9 

As  a  reaction  against  the  eruptive  theory,  it  has  been  re- 
cently held 10  that  all  deposits  of  iron  of  whatever  age  have 
been  formed,  like  the  bog  ores  now  forming,  by  surface-pre- 
cipitation, and  that  they  were  therefore  actual  sedimentary 
beds  originally,  but  in  many  cases  have  been  altered  by  later 
metamorphism.  This  going  to  the  other  extreme  is,  it  seems 
to  me,  as  dangerous  as  the  former  a  priori  reasoning;  and,  as 
I  read  the  descriptions  of  many  of  our  iron-deposits,  such  a 
contemporaneous  sedimentary  origin  for  them  would  be  im- 
possible. 

The  theory  of  the  formation  of  ore-deposits  by  replacement, 
as  opposed  to  that  by  the  filling  of  pre-existing  cavities,  may, 
however,  be  applied  to  deposits  in  rocks  which  are  not  so 


9  Descrizione  Geologica  deW  /so/a  d'  Elba,  p.  232  (1886). 

10  J.  S.  Newberry,  The  Genesis  of  Our  Iron-Ores,  School  of  Mines  Quarterly,  vol. 
ii.,  No.  1,  pp.  1  to  17  (Nov.,  1880). 


10  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

readily  soluble  as  limestone,  in  which  cases  the  percolating 
solutions  would  have  first  attacked  the  relatively  more  soluble 
among  their  constituents.  Very  many  so-called  fissure-veins 
in  crystalline  rocks  are  formed  by  percolating  waters,  circulat- 
ing along  joints,  shrinkage-cracks,  fault-planes,  or  zones  of 
crushed  rock,  which  have  filled  the  interstitial  spaces  and  re- 
placed the  materials  of  the  adjoining  country-rocks  to  a  greater 
or  less  extent  by  the  materials  they  held  in  solution,  but  are 
not  the  filling  of  any  considerable  open  cavities. 

The  comb-structure  of  veins,  on  which  the  early  geologists 
founded  their  theory  that  a  vein  was  necessarily  the  filling  of 
a  pre-existing  open  cavity,  is  of  comparatively  rare  occurrence. 
As  early  as  1869  Richard  Pearce  observed  in  the  classic  veins 
of  Cornwall  that  the  gangue-material,  instead  of  being  a  foreign 
material  brought  from  a  distance,  was  the  more  or  less  com- 
pletely altered  country-rock,  and  his  views  have  been  con- 
firmed and  further  illustrated  by  the  investigations  of  C.  Le 
Neve  Foster,  his  successor  in  that  district.  The  evidence 
obtained  by  my  own  observations,  together  with  the  data 
gathered  during  the  investigation  of  the  precious-metal  de- 
posits of  the  Rocky  mountains  under  the  Tenth  Census,  led 
me  to  conclude  that  the  majority  of  the  deposits  there  are  such 
replacement-deposits ;  and  I  have  not  yet  seen  satisfactory  evi- 
dence of  a  deposit  which  consists  essentially  of  the  filling  of 
any  considerable  pre-existing  cavity  by  foreign  material. 
Cracks  or  fissures  must  undoubtedly  have  existed,  which  de- 
termined the  concentration  of  mineral  solution  along  their 
course;  but  whether  such  cracks  were  to  any  great  extent 
fault-planes,  whose  movement  might  have  left  large  open 
spaces  between  the  irregularities  of  their  walls,  seems  ques- 
tionable. The  Comstock  vein  occupies  a  fault-plane,  and  its 
ore  fills  the  interstitial  spaces  in  the  crushed  material  between 
the  walls,  but  there  was  no  filling  of  a  pre-existing  open  cavity, 
as  I  understand  it.  In  Leadville  one  of  the  most  noticeable 
facts  is  that  the  fault-planes,  which  may  be  supposed  to  reach 
to  great  depths,  have  been  found  barren  of  ore  except  by  sec- 
ondary infiltration  from  surface-waters,  or  as  attrition-material 
from  pre-existing  deposits,  when  the  fault-line  cut  across  such 
deposits. 

In  this  connection  I  would  remark  that  it  seems  to  me  that 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  11 

the  idea  that  a  fissure-vein  necessarily  extends  to  an  indefinite 
depth  is  another  popular  error,  and  not  founded  on  good  geo- 
logical reasoning.  Whatever  the  nature  of  the  fissure  along 
which  the  deposit  has  taken  place,  whether  fault-plane,  joint, 
or  shrinkage-crack,  there  must  be-  some  mutual  relation  be- 
tween its  horizontal  and  its  vertical  dimensions.  In  other 
words,  the  study  of  structural  geology  shows  that  the  length  of 
such  a  fissure  or  crack  must  bear  some  proportional  relation 
to  its  extent  in  depth,  and  the  probability  is  that  the  latter 
must  be  less  than  the  former.  Now  veins  can  generally  be 
traced  continuously  for  an  extremely  limited  distance;  the 
Comstock,  which  is  probably  one  of  the  longest  known,  is 
traced  only  about  20,000  ft.,  and  those  which  exceed  1,000  or 
2,000  ft.  are  comparatively  rare.  As  yet  there  are  not  suffi- 
cient data  for  establishing  any  numerical  ratio  between  the 
depth  and  the  length  of  mineral  veins ;  I  would  suggest  to  my 
fellow-engineers  that  they  make  notes  on  this  relation,  when- 
ever opportunities  present  themselves.  It  may  be  said  that 
this  is  not  likely  to  have  much  practical  value,  since  the  depth 
from  which  the  ore  may  be  profitably  extracted  is  likely  to  be 
much  less  than  the  deduced  depth  of  the  fissure.  The  question 
has  a  bearing,  however,  upon  that  of  the  source  from  which 
the  ore  was  derived ;  and  any  fact  that  contributes  to  a  more 
accurate  knowledge  of  the  origin  and  manner  of  formation  of 
ore-deposits  has  practical  value,  since  it  enables  the  mining 
engineer  to  make  a  more  accurate  forecast  of  the  probable 
form  and  extent  of  any  individual  deposit  beyond  the  limits  ot 
exploration. 

4.  In  regard  to  the  direction  from  which  the  ore-bearing  so- 
lutions reach  the  locus  of  the  deposits,  the  brief  statement  made 
in  my  abstract  that  "  they  came  from  above,"  should  perhaps 
have  been  accompanied  by  some  qualifying  explanation.  In 
making  the  statement,  I  had  in  mind  the  common  explanation 
offered  in  regard  to  ore-deposits,  that  "they  came  from  below," 
a  statement  which  is  more  readily  made  by  those  who  have  not 
examined  the  deposits  of  which  they  speak  or  write,  than  by 
those  who  have,  since  they  are  not  under  the  necessity  of  ex- 
plaining observed  facts  in  accordance  with  this  hypothesis. 
The  prevalence  of  this  theoretical  method  of  explaining  the 
formation  of  any  ore-deposit  is  due  probably  to  the  great  plau- 


12  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

sibility  of  the  theory  generally  advanced  for  the  formation  of 
fissure-veins — namely,  that  the  metallic  contents  of  the  solu- 
tions were  taken  up  by  waters  under  conditions  of  great  heat 
and  pressure  (therefore,  probably  at  great  depths),  and  that  as 
these  solutions  approached  the  surface,  with  consequent  de- 
crease of  heat  and  pressure,  the  solvent  power  of  the  water 
decreased  also,  and  their  metallic  contents  were  gradually  de- 
posited all  along  the  walls  of  the  channel  through  which  they 
were  ascending.  ~No  exception  can  be  taken  to  this  theory,  as 
a  theory;  but  before  accepting  it  as  of  universal  application,  it 
is  important  to  see  whether  it  accords  with  observed  facts; 
and,  as  Leadville  presented  a  case  where  it  unquestionably  did 
not  so  accord,  I  made  the  statement  as  concise  and  as  strong  as 
possible,  to  counteract  the  effect  of  the  "  coming-from-below  " 
explanation  which  would  undoubtedly  be  offered. 

Such  a  one  is  that  made  by  J.  Alden  Smith,11  which  has  also 
been  quoted  by  J.  Arthur  Phillips  in  his  Treatise  on  Ore-Deposits, 
"  that  the  ore-deposits  of  this  district  came  from  below  through 
fissures  originating  in  the  granitic  rocks,  and  extending  up- 
wards penetrated  the  limestones  and  quartzites  to  the  contact 
with  the  overlying  porphyry ;  that  these  fissures  lead  to  many 
bedded  veins  in  the  limestone  and  quartzite,  and  to  contact- 
veins  of  more  or  less  value  between  the  formations  last  men- 
tioned, and  between  those  and  the  granitic  formation ;  and  that 
these  fissures  and  deposits  will  be  extensively  and  profitably 
worked  for  centuries  after  the  contact-deposits  now  operated 
are  exhausted." 

A  statement  like  the  above,  coming  from  one  whose  views 
would  be  accepted  as  of  scientific  value,  might  cause  much  use- 
less expenditure  of  money  in  prospecting  before  it  was  dis- 
covered that  the  essential  facts,  upon  which  it  would  appear  to 
be  founded,  existed  only  in  the  imagination  of  the  writer.  In 
Leadville,  no  ore-bearing  fissures  extending  downward  from 
the  deposits  have  yet  been  found.  The  facts  observed  during 
my  examination,  and  by  those  who  have  studied  the  region 
since,  show  that  the  solutions  must  have  penetrated  the  lime- 
stone from  its  contact  with  the  porphyry,  which  is  generally  its 
upper  surface,  and,  therefore,  downward.  An  apparent  excep- 

11  Report  on  the  Resources  of  Colorado,  p.  64  (1883). 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  13 

tion  to  this  state  of  things  is  found,  as  pointed  out  by  Charles 
M.  Rolker,12  on  Fryer  hill,  where,  according  to  him,  unreplaced 
dolomite  sand  forms  the  roof  of  the  deposit  over  large  areas, 
and  is  not  found  under  it.  I  am  ready  to  admit,  for  the  sake 
of  argument,  the  truth  of  this  statement  for  the  upper  part  of 
the  Blue  limestone  or  ore-horizon,  which  is  included  in,  or  both 
overlain  and  underlain  by,  porphyry.  The  lower  sheet  of  Blue 
limestone,  however,  which  has  porphyry  on  its  upper  surface 
alone,  is,  as  far  as  observed,  replaced  only  on  that  upper  sur- 
face. The  exception  is,  however,  in  this  case  only  apparent, 
and  does  not  militate  against  my  supposition.  According  to 
this,  the  intrusion  of  the  porphyry  bodies  opened  channels 
along,  and  in  some  cases  across,  the  sedimentary  beds ;  more- 
over, observation  shows  that  these  porphyry  bodies  admit  the 
percolation  of  water  freely  in  every  direction  through  their 
mass,  whereas  the  limestones  are  comparatively  impermeable 
except  along  joint-  or  fracture-planes.  Thus,  the  contact  be- 
tween porphyry  and  limestone  would,  everywhere,  be  a  prin- 
cipal water- channel;  and  this,  in  the  greater  part  of  the  region, 
is  at  the  lower  surface  of  the  former  and  the  upper  surface  of 
the  latter;  but  where,  as  on  Fryer  hill,  the  limestone  is  in- 
closed in  porphyry,  it  might  be  attacked  from  either  surface. 
I  can  offer  no  direct  reason  for  the  irregular  way  in  which  com- 
paratively unaltered  remnants  of  dolomite  are  left  on  Fryer 
hill ;  but  it  seems  no  more  abnormal  than  the  irregular  distri- 
bution of  the  rich  ore  within  the  mass  of  vein-material,  or  the 
fact  that,  in  some  places,  there  is  no  ore  at  all  at  the  contact. 
I  cannot  quite  agree,  however,  with  Mr.  Rolker's  opinion  as  to 
the  persistence  of  the  dolomite  sand  in  the  roof  of  the  ore-body. 
His  observations  in  the  Chrysolite  ground  would  naturally  have 
been  more  thorough  than  mine ;  but,  if  my  memory  does  not 
deceive  me,  unreplaced  dolomite  occurs  there  under,  as  well  as 
over,  the  ore-body,  as  it  certainly  does  in  the  Little  Chief, 
Virginius,  and  other  claims.  It  is  to  be  remarked  further  that, 
as  the  rich  ore-bodies  are  found  mostly  in  the  upper  part  of  the 
ore-horizon,  the  upper  surface  has  been  far  more  thoroughly 
explored  than  the  lower,  and  much  unreplaced  limestone  may 
exist  at  this  lower  surface  which  has  not  yet  been  found. 

12  Notes  on  the  Lead ville  Ore-Deposits,  Trans.,  xv.,  273  (1886-87). 


14  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

It  is  hardly  possible  to  establish  a  priori  any  general  direction 
for  the  flow  of  underground  waters  at  considerable  depths  below 
the  earth's  surface.  In  the  distinctly  stratified  rocks,  which 
form  the  immediate  surface,  and  in  which  they  may  flow  with 
comparative  freedom,  they  obey,  within  certain  limits,  the  laws 
of  hydrostatic  pressure ;  but,  at  the  great  depths  at  which  the 
Leadville  deposits  were  formed,  their  flow  must  have  been  very 
slow, — a  percolation  or  mere  capillary  circulation,  for  the  most 
part.  It  may  be  assumed,  in  general,  that  cold  waters  would 
have  a  general  downward  tendency  under  the  influence  of 
gravity,  while  superheated  waters  would  under  certain  condi- 
tions be  forced  upward;  but  the  movement  would  not  neces- 
sarily be  vertical  in  either  direction  at  any  given  point.  In  the 
present  state  of  geological  science,  it  is  not  possible  to  predi- 
cate for  any  given  point  within  the  earth's  crust  that  the  flow 
of  underground  waters  must  be  either  upward,  downward,  or 
sideways.  There  is  an  a  priori  possibility  of  either  direction ; 
and  the  most  probable  one  in  any  particular  region  must  be 
determined  by  an  actual  study  of  the  geological  conditions  at 
that  point.  For  this  reason,  it  seems  to  me,  the  student  of 
ore-deposits  should  divest  himself  as  soon  as  possible  of  any 
preconceived  bias  in  favor  of  the  old  schools  of  ascensionists, 
descensionists,  or  lateral  secretionists,  as  the  true  theory,  when 
arrived  at  by  actual  investigation,  will  probably  not  correspond 
exactly  to  the  theoretical  views  of  either  school,  and  the  time 
given  to  arguments  in  favor  of  the  exclusive  correctness  of  one 
over  the  other  is  more  or  less  wasted. 

In  his  admirably  written  paper  on  The  Genesis  of  Metallifer- 
ous Veins,13  Prof.  Joseph  LeConte,  after  combating  the  lateral- 
secretion  views  of  Dr.  F.  Sandberger,  says  that  the  latter's  idea 
of  the  ascensionists'  theory  is  a  misconception,  adding ;  "  Now, 
I  am  sure  that  no  one,  in  this  country  at  least,  holds  to  any 
such  view.  All  speculators  on  this  subject,  I  think,  now  hold 
that  the  mineral  contents  of  veins  are  wholly  derived  by  leach- 
ing from  the  rocks  forming  the  fissure-walls.  The  ascension 
theory  (if  we  use  that  name  at  all)  as  properly  understood,  i.e., 
the  theory  which  connects  vein-formation  with  solfataric  action, 
is  wholly  a  levigation  theory.  According  to  this  theory,  as  I 

13  American  Journal  of  Science,  Third  Series,  vol.  xxvi.,  No.  151,  pp.  1   to  19 
(July,  1883). 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  15 

understand  it,  the  vein-matters,  including  the  metallic  ores,  are 
not  derived  from  an  unknown  mysterious  region  of  volcanic 
fires,  but  are  gathered  by  leaching  from  the  whole  wall-rock 
from  top  to  bottom  of  the  fissure,  but  mainly  from  the  deeper 
parts;  because  these  are  under  heavy  pressure  and  superheated. 
Subterranean  waters,  gathering  soluble  matter  from  wide  areas 
and  great  thicknesses  of  rock,  find  their  way  into  fissures,  and 
these  then  become  the  natural  channel  back  to  the  surface  from 
which  they  came."  With  these  views  of  Dr.  Le  Conte,  as  with 
the  rest  of  his  article,  I  agree  in  most  respects,  while  differing 
with  him  as  to  their  application,  and  as  to  some  of  his  geological 
facts  and  reasonings,  as  will  be  seen  later. 

The  direction  taken  by  the  ore-currents  in  any  given  case  in 
bringing  the  material  of  ore-deposits  to  their  present  position 
could  be  readily  determined,  if  the  source  were  known  from 
which  these  materials  were  derived.  Perhaps  even  less  than 
the  direction  of  the  currents  is  this  source  susceptible  of  direct 
and  positive  proof;  but  its  probable  location  may  be  established 
by  inductive  reasoning,  and  indirect  or  even  negative  evidence 
may  be  furnished  by  actual  demonstration,  which  may  in  time 
raise  this  probability  very  nearly  to  practical  certainty. 

5.  I  stated  in  the  abstract  of  my  report  on  Leadville  that  the 
contents  of  the  ore-deposits  were  derived  from  the  neighboring 
eruptive  rocks.  By  "  neighboring  eruptive  rocks,"  I  do  not 
mean  that  they  must  necessarily  be  in  actual  contact  with  the 
ore-bodies;  they  may  be  at  some  distance  from  the  bodies, 
provided  there  is  no  impassable  barrier  to  prevent  the  passage 
of  solutions  from  one  to  the  other.  From  a  theoretical  point 
of  view,  it  is  evident  that  the  absolute  distance  is  not  essential, 
since  all  theories  of  derivation  of  the  contents  of  ore-deposits 
involve  a  greater  relative  distance  of  the  source,  than  that  which 
would  derive  them  from  the  bodies  of  rock  in  the  vicinity,  even 
if  not  at  absolute  contact.  Le  Conte's  ascension  theory,  quoted 
above,  supposes  vein-materials  to  have  been  derived  from  the 
rocks  adjoining  the  fissure  at  some  indefinite  depth,  where 
pressure  and  heat  were  abundant.  These  were  present  here: 
the  pressure,  that  of  10,000  ft.  of  superincumbent  strata;  the 
heat,  that  of  immense  bodies  of  slowly-cooling  eruptive  rock; 
only  the  fissure,  which  his  theory  conceives,  was  wanting. 

Something  analogous  to  this  fissure  might  be  conceived,  if 


16  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

the  Blue  limestone,  which  is,  in  one  sense,  the  matrix  of  the 
principal  ore-bodies,  had  occupied  a  vertical  instead  of  the 
more  nearly  horizontal  position  that  it  does.  At  the  time  the 
Leadville  deposits  were  originally  formed,  it  was  a  practically 
unbroken  horizontal  bed,  more  or  less  replaced  by  deposits  of 
ore  along  its  upper  surface  and  extending  through  joint-cracks 
at  varying  distances  into  its  mass  and  in  some  few  cases  reach- 
ing to  its  base.  If  the  dynamic  action  by  which  the  Mosquito 
range  was  uplifted,  instead  of  compressing  the  sedimentary 
strata  and  their  included  eruptive  sheets  into  a  series  of  folds, 
and  fracturing  and  displacing  them  by  faults,  had  simply 
uptilted  the  whole  into  a  vertical  position,  we  should  then  have 
had,  in  the  place  of  the  fissure,  a  great  vertical  limestone  zone 
with  ore  evidently  brought  in  by  solutions  acting  from  one  side 
or  wall  only.  It  would  then  seem  most  natural,  in  searching 
for  a  source  from  which  the  metallic  contents  had  been  derived, 
to  investigate  the  rocks  on  that  side.  The  advantage  of  the 
present  over  such  a  condition  of  things  is,  that  the  search, 
instead  of  being  necessarily  confined  to  rocks  adjoining  a  very 
limited  upper  portion  of  the  supposed  fissure,  can  be  carried 
on,  not  only  among  the  various  rocks  adjoining  the  whole  area 
of  ore-deposition,  but  for  a  considerable  distance  beyond  that 
area. 

Search  for  the  source  of  the  vein-materials  of  the  Leadville 
deposits  was  carried  on  by  subjecting  the  various  country-rocks 
to  delicate  chemical  tests,  in  order  to  ascertain  the  presence  or 
absence  in  them  of  the  most  characteristic  components  of  the 
vein-materials,  gold,  silver,  lead,  and  baryta.  In  selecting  spe- 
cimens for  testing,  those  were  chosen  which  came  from  points 
so  far  removed  from  any  known  deposit  that  there  could  be  no 
suspicion  that  the  materials  found  might  be  infiltrations  from 
such  deposits.  Among  the  specimens  of  eruptive  rocks,  the 
freshest  and  least  altered  were  naturally  selected,  since  decom- 
position might  be  expected  to  have  acted  on  such  basic  con- 
stituents first.  None  of  the  above  substances  were  found  in 
the  specimens  of  sedimentary  rock  tested;  and  the  tests  of 
eruptive  rock  were,  therefore,  multiplied,  as  much  as  the  time 
which  could  be  allotted  to  their  special  investigation  would 
permit.  The  greatest  number  of  tests  were  those  made  in  the 
dry  way  for  minute  traces  of  gold  and  silver,  for  the  reason 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  17 

that  these  could  be  made  with  far  greater  rapidity,  and  con- 
sequently in  greater  number  in  a  given  time,  than  in  the  wet 
way.  After  considerable  experiment  with  methods  and  mate- 
rials, it  was  found  possible  to  determine  in  this  way  with  accu- 
racy 0.005  oz.  per  ton,  or  0.000017  per  cent,,  of  silver,  an 
amount  which  it  wrould  have  required  an  enormous  amount  of 
concentration  to  detect  in  the  wet  way. 

The  results  may  be  briefly  stated  as  follows :  Baryta  was 
found  in  all  four  specimens  of  eruptive  rock  tested  for  this 
substance;  lead  in  14  out  of  17  specimens  tested;  and  silver 
in  32  out  of  42  specimens  tested.  It  is  to  be  remarked  that 
the  negative  results  do  not  necessarily  mean  an  absence  of  the 
substance  in  question,  but  only  that  the  amount  is  less  than  the 
process  employed  could  detect;  so  that  where  lead  is  found  in 
a  rock  it  is  probable  that  it  contains  silver  also,  but  in  rela- 
tively small  amount.  As  the  medium  percentage  of  lead  oxide 
in  the  above  tests  is  0.0032,  if  this  lead  oxide  contained  40  oz. 
of  silver  per  ton,  the  percentage  of  the  latter  in  the  rock  would  be 
within  the  limit  of  accuracy  given  above  for  our  determination 
of  silver,  and  could  not  have  been  detected  by  the  methods 
employed.  Several  hundred  assays  for  silver  were  made,  the 
results  of  which  correspond  in  general  to  those  given  above, 
but  possible  sources  of  error  were  found  in  some,  and  the  42 
represent  the  residue,  which  had  been  confirmed  as  accurate 
by  repeated  tests,  after  all  containing  any  possible  source  of 
error  had  been  eliminated. 

It  may  be  said  that  these  results  do  not  necessarily  prove 
that  the  materials  of  the  Leadville  deposits  were  derived  from 
these  eruptive  rocks,  and  not  from  some  unknown  bodies  of 
rock  still  richer  in  these  materials  at  unknown  depths.  Abso- 
lute proof,  as  I  have  already  said,  could  not  be  expected,  espe- 
cially as  against  an  unknown  quantity  whose  resources,  being 
unknown,  are  in  one  sense  unlimited,  but  this  evidence  shows 
a  possibility  which,  combined  with  all  the  other  facts  that  bear 
on  this  question  in  this  particular  district,  amounts  to  a  very 
strong  probability.  The  quantities  of  vein-constituents  found, 
though  minute,  are  quite  sufficient  when  one  realizes  what 
vast  bodies  of  eruptive  rock  still  exist  there,  and  reflects,  more- 
over, that  probably  a  very  much  larger  amount  was  present 
when  the  deposits  were  formed,  but  has  since  been  removed 


18  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

by  erosion.  As  against  the  probability  that  the  materials  were 
derived  from  eruptive  rocks  below,  there  is  the  evidence  af- 
forded by  the  geological  structure  of  the  region  that  the 
greater  mass  of  eruptive  bodies  coming  under  observation  are 
above  the  Blue  limestone,  which  is  only  400  ft.  above  the 
Archaean,  and  that  these  eruptive  rocks  came  up  through  the 
Archaean  in  extremely  narrow  channels  or  dikes,  and  only  spread 
out  in  large  bodies  after  reaching  the  sedimentary  strata  above  ; 
therefore,  that  in  all  probability  there  are  no  large  bodies  of 
eruptive  rock  beneath,  until  the  far-distant  sources  of  these 
rocks  are  reached ;  further,  that  the  Archaean  rocks,  as  far  as 
tested,  were  not  found  to  contain  these  substances. 

The  criticisms  that  have  been  made  upon  this  part  of  my  con- 
clusions are  mostly  general  rather  than  special.  Mr.  Rolker 
maintains  that  the  overlying  White  porphyry  (felsite)  should  be 
stained  by  basic  sulphate  of  iron,  if  the  vein-materials  had 
been  derived  from  it,  and  says,  "  against  Mr.  Emmons's  analy- 
sis of  the  felsite  stand  other  analyses  which  did  not  find  any 
lead  or  silver  in  it  (L.  D.  Ricketts)."  To  this  I  answer,  the  ex- 
traction of  such  minute  traces  of  metallic  minerals  by  percolat- 
ing waters  would  not  necessarily  leave  any  staining  visible  to  the 
naked  eye,  since  the  minerals  themselves  are  rarely  visible,  even 
under  the  microscope.  Moreover,  I  do  not  maintain  that  they 
came  from  the  White  porphyry  alone — there  are  other  bodies 
of  porphyry  from  which  they  could  have  been  derived ;  and 
this  porphyry  is  so  universally  decomposed,  as  shown  by  mi- 
croscopic examination,  that  it  is  difficult  to  see  what  all  of  its 
original  constituents  were.  Out  of  11  specimens  of  it,  included 
in  the  above-quoted  tests,  only  three  yielded  silver,  a  far 
smaller  proportion  than  that  of  the  other  varieties  of  eruptive 
rock,  which  were,  as  a  rule,  less  decomposed.  Still,  as  Mr. 
Rolker  himself  suggests,  this  may  merely  prove  that  its  me- 
tallic contents  had  been  leached  out.  As  for  the  counterproof 
of  other  analyses,  Mr.  Ricketts  himself  says  explicitly,14  that 
he  made  no  study  of  the  question  of  the  source  of  the  mate- 
rial, and  the  fact  that  his  single  analysis  of  White  porphyry 
gives  no  lead  or  silver  may  simply  prove  that  he  did  not  make 
the  special  test  for  these  materials  on  the  large  amount  of  rock 


The  Ores  of  Leadville,  p.  46  (1883). 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  19 

which  is  necessary  in  order  to  detect  them.  He  adds  that  his 
analysis  "  showed  scarcely  a  trace  of  sulphur,  though  the  rock 
at  one  time  certainly  contained  much  iron  pyrites." 

Dr.  dewberry's  criticisms  on  my  conclusions  are  entirely 
vitiated  by  his  complete  misapprehension  of  my  views.  He 
assumes  that  I  would  derive  the  ores  from  superficial  igneous 
rocks,  through  the  agency  of  surface-waters ;  but  since  I  my- 
self do  not  believe  that  they  could  have  been  formed  either  by 
surface-waters  or  from  recent  or  superficial  igneous  rocks,  it 
would  seem  unnecessary  to  refer  to  his  objections  to  that  view 
in  the  special  case  of  Leadville.  I  will  merely  say  that  the 
theory  which  he  proposes  as  a  substitute  for  mine,  "  that  the 
plane  of  contact  between  the  limestone  and  porphyry  has  been 
the  conduit  through  which  heated  mineral  solutions  coming 
from  deep-seated  and  remote  sources  have  flowed,  removing 
something  from  both  the  overlying  and  underlying  strata," 
etc.,15  is  one  which  he  himself  would  probably  reject,  if  he  had 
had  as  good  an  opportunity  of  examining  the  geological  struc- 
ture of  the  region  and  the  relation  of  the  ore-bodies  to  the  sur- 
rounding rocks  as  I  have  had. 

It  may  not  be  amiss  to  call  attention  to  the  fact  that  Pro- 
fessor Newberry  has  similarly  misapprehended  Mr.  Becker's 
views  as  to  the  genesis  of  the  ores  of  the  Comstock  lode.  To 
him  Professor  Newberry  attributes  the  hypothesis  that  the  Com- 
stock ores  were  leached  from  the  hanging-wall  by  cold  sur- 
face-waters. Becker's  memoir  contains  no  such  statement. 
On  the  contrary,  he  maintains  at  length  that  the  ore  was  ex- 
tracted from  the  hanging-wall  by  rising  waters  of  very  high 
temperature,  and  charged  with  solvents,  acting  at  considerable 
pressures. 

As  regards  the  general  derivation  of  the  vein-materials  from 
eruptive  rocks,  it  will  perhaps  be  wise  to  state  explicitly  what 
I  do  think  at  the  present  time,  reserving  the  right  to  modify 
my  views  if  I  see  fit,  as  I  gain  a  wider  and  more  exact  knowl- 
edge of  the  ore-deposits  of  the  world.  I  consider  that  at  the 
present  time  neither  I  nor  any  one  else  is  in  possession  of 
accurate  geological  knowledge  of  a  sufficiently  large  number 
of  ore-deposits  to  justify  the  formulation  of  that  knowledge 

15  School  of  Mines  Quarterly,  vol.  v.,  No.  4,  p.  341  (May,  1884). 


20  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

into  a  universally  applicable  theory  of  the  formation  of  ore- 
deposits.  Ore-deposits  occur  in  nature  under  such  varied  con- 
ditions, moreover,  that  it  seems  doubtful  if  any  one  theory  of 
their  formation  will  be  found  applicable  to  all  of  them,  and 
probably  the  final  theory  will  be  an  alternative  one.  As  one 
of  these  alternatives,  the  derivation  from  bodies  of  eruptive 
rock  in  the  vicinity  of  the  deposits  seems  to  have  in  its  favor 
more  evidence,  both  direct  and  indirect,  than  any  other  now 
offered. 

As  indirect  evidence,  European  geologists  have  long  re- 
marked that  regions  rich  in  ore-deposits  have,  in  the  majority 
of  cases,  been  regions  of  long-continued  eruptive  activity.  This 
association,  or  coincidence,  if  such  it  may  be  considered,  is  still 
more  striking  in  this  country ;  but  it  is  to  be  remarked  that  it 
is  wTith  the  older  and  generally  intrusive  rocks  of  eruptive 
origin  that  valuable  ore-deposits  are  most  frequently  associated, 
while  they  are  rare  when  these  rocks  only  form  surface-flows 
or  are  outpourings  of  actual  volcanic  vents.16  dewberry17 
brings  forward  the  latter  fact  as  argument  against  the  deriva- 
tion of  vein-materials  from  superficial  igneous  rocks,  and  as  such 
it  is  certainly  valid ;  but  the  greater  part  of  our  ore-deposits 
are  evidently  of  deep-seated  and  not  of  superficial  formation. 
I  have  no  evidence  to  prove  whether  recent  lavas  are  poorer  in 
vein-materials  than  the  older  intrusive  rocks  or  not;  nor  is 
that  an  essential  point,  since  it  is  evident  that  they  have  been 
subjected  to  the  leaching  process  for  but  a  comparatively  short 
time ;  that  the  surface-waters  which  reach  them  have  neither 
the  heat,  pressure,  nor  chemical  solvents  that  render  the  action 
of  deep-seated  waters  more  energetic,  and  therefore  that  con- 
centrations of  vein-materials  in  ore-deposits  from  them  could 
not  be  expected  to  be  as  frequent  or  as  considerable  as  those  in 
the  older  and  deep-seated  rocks. 

Professor  ISTewberry  is  inclined  to  doubt  the  frequency  of  the 
association  of  eruptive  rocks  and  ore-deposits,  and  says  in  re- 
gard to  the  mineral  belt  of  the  Far  West,  "  the  great  majority 
of  veins  are  not  in  immediate  contact  with  trap  rocks,  and  they 
could  not  therefore  have  furnished  the  ores."  As  to  the  im- 


6  Tenth  Census,  vol.  xiii.,  p.  63  (1880). 
17  The  Deposition  of  Ores,  School  of  Mines  Quarterly,  vol.  v.,  No.  4  (May,  1884). 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  21 

mediate  contact  of  trap  rock  with  these  veins,  I  do  not  feel  that 
I  have  sufficient  data  to  contradict  his  statement,  although  I 
am  equally  confident  that  it  is  not  justified  by  accurate  statis- 
tical knowledge  on  his  part.  But  the  statement  is  liable  to 
mislead,  in  that  the  reader  might  be  led  to  infer  that,  in  the 
instances  he  gives,  eruptive  rocks  do  not  occur  in  the  vicinity 
of  the  deposits,  whereas  I  am  qualified,  from  my  own  observa- 
tion and  from  knowledge  gained  during  my  investigations 
under  the  Tenth  Census,  to  state  that  this  inference  would  be 
diametrically  opposed  to  the  facts.  Not  only  are  there,  in  each 
of  the  11  districts  he  mentions,  known  developments  of  erup- 
tive rock  in  the  vicinity  of  the  deposits,  but  in  seven  of  these 
districts  there  are  important  mines — some  of  which  he  has 
quoted  by  name  in  his  list — in  which  eruptive  rocks  form  one 
or  both  walls  of  the  deposits. 

Professor  Le  Conte,  on  the  other  hand,  not  only  admits  the 
frequency  of  the  association  of  great  eruptive  activity  with  ore- 
deposition,  but  also  the  possible  derivation  of  the  vein-materials 
from  eruptive  rocks.  His  view  on  this  subject,  which  resem- 
ble's  the  Scotch  verdict  "  not  proven,"  is,  "  not  that  igneous 
rocks  alone  supply  the  materials,  but  rather  that  igneous  action 
supplies  the  heat  necessary  for  solution."  He  afterwards  ad- 
mits that  heat  is  not  in  all  cases  necessary  for  solution.  As 
Professor  Le  Conte's  views  may  be  taken  as  a  fair  representa- 
tion of  the  best  speculative  theories  on  the  subject  of  ore-depo- 
.sition  at  the  present  day,  it  may  be  assumed  that  there  are  no 
good  a  priori  grounds  against  the  derivation  of  vein-materials 
from  eruptive  rocks ;  and  it  remains  to  consider  what  direct 
evidence  there  is  in  its  favor.  Before  doing  this,  I  wish  to 
advert  to  a  geological  question,  as  regards  which  I  do  not  agree 
with  Le  Conte's  implied  ideas.  He  says  :  "  We  never  see  any 
stratified  rock  that  has  not  been  igneous  rock  nor,  I  believe, 
any  igneous  rock  that  has  not  become  so  by  refusion  of  strati- 
fied rocks."  This  statement  might  be  admitted  as  applied  to 
the  earlier  stages  of  the  earth's  history  when  its  first  crust  was 
forming,  and  yet  doubted  in  such  a  practical  application  to  the 
sedimentary  rocks  now  found  on  the  surface,  as  is  made  by 
Professor  dewberry  when  he  says : 1S  "  All  the  knowledge  we 

18  Deposition  of  Ores,  p.  337. 


22  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

have  of  the  subject  justifies  the  inference  that  most  of  the  igne- 
ous rocks  which  have  been  poured  out  in  our  Western  Terri- 
tories are  but  fused  conditions  of  sediments  which  form  the 
substructure  of  that  country,  .  .  .  and  it  is  possible  and  even 
probable  that  the  rocks  composing  the  volcanic  ridges  are 
but  phases  of  the  same  materials  that  form  the  sedimentary 
chains." 

The  estimated  aggregate  thickness  of  sediments  above  the 
Archaean  varies,  roughly  stated,  from  60,000  to  100,000  ft.,  but, 
owing  to  frequent  elevations  and  subsidences,  the  series  is 
probably  never  found  complete  at  any  one  point,  and  it  may  rea- 
sonably be  doubted  if  the  thickness  of  sediments  accumulated 
at  one  time  and  place  over  the  Archaean  ever  reached  even  the 
lowest  of  the  above  figures.  But,  by  the  agencies  of  dynamic 
action  and  erosion,  geologists  have  been  enabled  to  study  not 
only  these  great  thicknesses  of  overlying  sediments,  but  great, 
though  unknown,  thicknesses  of  the  Archaean  formations  be- 
neath ;  yet,  nowhere  in  the  vast  portions  of  the  earth's  crust 
that  have  already  been  examined  has  any  evidence  of  the  fusion 
of  sedimentary  rocks  into  an  igneous  magma  been  found.  For 
this  reason  it  seems  to  me,  and  I  believe  I  express  the  senti- 
ments of  the  majority  of  geologists  who  have  made  a  study  of 
eruptive  phenomena,  that  Professor  dewberry's  inference  is 
not  justified  by  the  knowledge  we  at  present  possess,  and  that 
the  region  of  fusion  whence  igneous,  rocks' may  be  supposed  to 
be  derived,  must  be  relegated  to  greater  depths,  and  beyond- 
the  reach  of  the  actual  sediments  which  we  can  now  observe  on 
the  surface. 

The  theory  that  vein-materials  have  been  derived  from  ad- 
joining rocks  is  by  no  means  a  new  one.  Both  Breithaupt  and 
Cotta  admitted  the  probability  of  such  derivation,  provided 
only  the  existence  of  the  vein-materials  could  be  proved,  while 
Bischof  not  only  strongly  upheld  the  theory,  but  by  chemical 
investigation  actually  detected  the  earthy  or  gangue-material 
of  veins  in  the  neighboring  country-rocks.  Acting  on  Bischof 's 
suggestion,  and  employing  methods  which  enabled  him  to 
detect  minute  traces  of  material  in  the  separate  constituents  of 
rocks,  Sandberger  has  been  investigating  for  many  years  past 
the  country-rocks  of  European  mining-districts.  He  finds  that 
the  basic  silicates  of  the  crystalline  country-rocks  (metamor- 


THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS.  23 

phic  or  eruptive)  contain  ,the  same  metals  as  are  found  in  the 
neighboring  deposits,  and  hence  concludes  that  the  materials 
of  the  latter  were  derived  from  the  former.19  The  investiga- 
tions of  country-rocks,  carried  on  by  Mr.  Becker  and  myself  at 
"Washoe  and  Leadville  respectively,  were  in  the  same  line  of 
research,  although  when  they  were  undertaken  we  had  not  the 
advantage  of  Sandberger's  experience,  and  our  methods  differed 
somewhat  from  his,  owing  to  the  peculiar  circumstances  under 
which  each  inquiry  was  conducted.  Our  results  in  either  case 
showed  at  least  a  possibility  of  the  derivation  of  the  materials 
from  the  eruptive  country-rocks,  which  the  geological  condi- 
tions heightened  to  a  probability.  Since  that  time,  I  have 
carried  on  similar  investigations,  with  some  improvements  in 
methods  suggested  by  experience,  on  the  country-rocks  of  other 
districts,  notably  those  of  Ten-Mile  and  Silver  Cliff,  Colo.,  which 
have  been  in  the  main  confirmatory  of  those  obtained  at  Lead- 
ville. Although  the  work  thus  far  done  in  this  line  covers  but 
a  small  portion  of  the  field  of  investigation,  it  affords  valuable 
indications  from  which  one  necessarily  draws  conclusions,  and 
which  certainly  point  a  way  for  further  research  that  promises 
to  be  fruitful  in  results.  The  conclusions  that  I  have  reached 
thus  far  are,  that  the  vein-materials  are  probably  derived  from 
country-rocks  in  the  neighborhood  of  the  deposits,  though  they 
are  not  necessarily  in  absolute  contact,  and  it  may  even  happen 
that  they  cannot  be  seen  at  the  surface.  And  the  chemical 
tests  thus  far  made  show  that  the  eruptive  rocks  rather  than 
the  sedimentary  are  the  more  likely  to  carry  the  materials  from 
which  the  vein-materials  have  been  derived.  I  am  by  no 
means  prepared  to  say  that  eruptive  rocks  will  everywhere  be 
found  to  be  the  source  of  the  vein-materials;  indeed,  it  would 
seem  that  there  are  many  deposits  where  this  would  be  impos- 
sible ;  and  yet  it  often  happens  that  the  published  descriptions 
of  such  deposits  are  not  sufficiently  complete  or  exact  to  enable 
us  to  form  a  decided  opinion  one  way  or  the  other. 

Professor  dewberry  considers20  that  an  unanswerable  argu- 
ment against  the  theory  of  lateral  secretion  is  furnished  by  the 
great  diversity  of  character  exhibited  by  different  sets  of  fis- 

19  Untersmhungen  uber  Erzgcinye  (1882). 

20  School  of  Mines  Quarterly,  vol.  v.,  No.  4,  p.  334  (May,  1884). 


24  THE    GENESIS    OF    CERTAIN    ORE-DEPOSITS. 

sure-veins  which  cut  the  same  country-rock.  It  seems  to  me 
that  a  certain  amount  of  diversity  might  be  allowed  in  different 
sets  of  veins  in  the  same  belt  of  rock,  without  disproving  the 
theory  as  I  understand  it;  first,  because  the  derivation  is  not 
confined  to  the  immediate  wall-rock;  secondly,  because  obser- 
vation shows  that  such  accessory  or  accidental  constituents  as- 
these  vein-materials  may  vary  very  greatly  in  the  same  body  of 
rock;  and  thirdly,  because  the  determining  cause  of  precipi- 
tation or  deposition  might  differ  in  the  different  sets  of  fissures, 
so  as  to  produce  a  difference  in  the  character  of  deposition  from 
one  and  the  same  solution.  Dr.  dewberry  does  not  state 
directly  how  great  a  diversity  he  considers  necessary  to  prove 
his  argument;  but  the  only  instance  in  which  he  actually  cites 
the  character  of  the  ores  has  been  unfortunately  chosen  for  this 
purpose.  It  is  that  of  the  Humboldt,  the  Bassick,  and  the 
Bull-Domingo  mines,  near  Rosita  and  Silver  Cliff,  which,  he 
says,  "  are  veins  contained  in  the  same  sheet  of  eruptive  rock, 
but  the  ores  are  as  different  as  possible."  In  point  of  fact,  the 
Bull-Domingo  deposit  occurs  in  Archaean  gneiss,  while  the  Bas- 
sick and  Humboldt  bodies  are  in  separate  and  distinct  bodies 
of  andesite,  evidently  belonging  to  different  outflows. 

To  summarize  the  above  somewhat  discursive  remarks :  The 
present  tendency  of  the  results  reached  by  careful  and  well- 
authenticated  determinations  of  the  origin  and  manner  of  for- 
mation of  ore-deposits  is  in  favor  of  a  continually  increasing 
applicability  of  the  following  conditions : 

That  they  are  deposited  from  solutions  made  by  percolating 
waters. 

That  the  deposition  takes  place  very  rarely  in  actually  open 
cavities,  but  most  frequently  by  a  metasomatic  interchange,  or 
by  replacement  of  the  more  soluble  or  more  accessible  portions 
of  a  rock  or  members  of  a  rock-series. 

That  these  solutions  do  not  necessarily  come  directly  upward, 
but  simply  follow  the  easiest  channels  of  approach. 

That  these  materials  are  not  immediately  derived  from  sources 
at  some  unknown  depth,  but  from  neighboring  bodies  of  rock 
within  limited  and  conceivable  distances. 

That  where,  as  is  so  often  the  case,  ore-deposits  are  associated 
with,  or  in  the  vicinity  of,  bodies  of  eruptive  rock,  especially 


THE    GENESIS   OF    CERTAIN    ORE-DEPOSITS.  25 

the  older  intrusive  rocks,  there  is  a  reasonable  probability  that 
their  materials  have  been  derived  from  these  rocks. 

In  order  to  accumulate  facts  upon  which  to  form  any  well- 
grounded,  broad  generalization  upon  these  very  important  sub- 
jects, we  need,  on  the  part  of  mining  engineers,  an  almost  in- 
definite multiplication  of  such  papers  as  those  of  Messrs. 
liicketts,  Freeland,  and  Rolker  on  the  Leadville  mines,  giving 
facts  in  the  minute  detail  which  can  only  be  arrived  at  by  long 
personal  observation  and  study.  Such  papers  should,  as  far  as 
possible,  be  based  upon  authoritative  determinations  of  geo- 
logical structure  of  the  region  where  the  mines  occur,  and  such 
determinations  it  seems  to  be  the  proper  province  of  a  govern- 
mental geological  survey  to  furnish,  as  private  individuals  can- 
not be  expected  to  have  the  extended  field-experience,  or  to  be 
able  to  carry  out  the  costly  investigations  which  they  necessa- 
rily involve. 


26  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 


No.  2. 
Structural  Relations  of  Ore-Deposits. 

BY  S.   F.    EMMONS,   WASHINGTON,   D.    C. 

(Boston  Meeting,  February,  1888.    Trans.,  xvi.,  804.) 

4 

' '  The  obscurity  which  still  veils  from  us  the  true  nature  of  veins  will  become 
more  and  more  cleared  up  when  they  can  be  considered  in  connection  with  the 
geological  structure  of  the  regions  in  which  they  occur."  1 

THESE  words,  according  to  Lossen,  the  biographer  of  the 
late  Dr.  A.  vori  Groddeck,  of  Clausthal,  were  the  last  received 
by  him  from  that  eminent  man,  perhaps  the  most  far-sighted 
and  carefully  progressive  of  recent  writers  on  ore-deposits. 
They  seem  to  me  to  form  a  fitting  'text  for  what  I  am  about  to 
say ;  since  I  find  that  many  of  the  conclusions  at  which  I  have 
arrived  by  my  own  study  of  the  structural  relations  of  ore- 
deposits,  or,  in  other  words,  of  the  structural  and  dynamic 
geology  of  the  regions  in  which  they  occur  in  this  country, 
Jiave  been  similarly  determined  by  him  within  recent  years  in 
Europe,  and  especially  in  his  home  field  of  work,  the  Harz. 

I  shall  not  enter  upon  a  detailed  account  of  how  far  other 
workers  may  have  arrived  at  similar  conclusions  with  myself, 
since  these  questions  of  priority  are  of  little  interest,  except  to 
those  immediately  concerned;  but  will  briefly  present  the 
methods  by  which,  in  my  work  in  this  country,  I  have  arrived 
at  certain  generalizations,  and  will  point  out  the  practical 
bearing  which  they  may  have  upon  the  work  of  mining 
engineers. 

In  my  first  thorough  and  systematic  examination  of  an  im- 
portant group  of  ore-deposits,  viz.,  that  of  Leadville,  Colo.,  I 
was  enabled,  through  the  generous  facilities  afforded  me  by 
the  then  Director  of  the  Geological  Survey,  Clarence  King,  to 


1  "Das  Dunkel,  welches  uns  die  wahre  Natur  der  Giinge  noch  immer  verhiillt, 
wird  sich  mehr  und  liiehr  lichten  wenn  sie  im  Zusammenhang  mit  dem  geognos- 
tischen  Ban  der  Gegenden,  in  denen  sie  auftreten,  betrachtet  werden  konnen." 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  27 

make  a  most  elaborate  and  detailed  study  of  the  geology,  not 
only  of  the  immediate  vicinity  of  the  mines,  but  of  the  adjacent 
mountain  regions,  based  upon  accurate  topographical  and  un- 
derground maps,  and  thereby  to  determine  the  structural  rela- 
tions of  these  ore-bodies  with  an  exceptional  degree  of  detail 
and  accuracy.  The  inductions  based  upon  these  structural 
relations  have  now  borne  the  test  of  seven  years  of  active  ex- 
ploration by  a  most  energetic  and  enterprising  mining  commu- 
nity, and  their  substantial  accuracy  has  been  so  abundantly 
proved  as  to  afford  an  excellent  practical  illustration  of  the 
importance,  in  this  class  of  deposits,  of  the  structural  study. 

In  entering  upon  this  work,  I  was,  I  must  admit,  far  from 
familiar  with  all  that  had  been  written  upon  the  theory  of  ore- 
deposits,  and  I  purposely  refrained  from  reading  up  upon  the 
subject  until  my  field-work  was  completed,  in  order  to  avoid 
the  danger  of  any  unconscious  bias  which  might  influence  my 
interpretation  of  the  facts  of  nature.  It  was  commonly  said 
at  that  time  of  the  Leadville  deposits  "that  they  went  contrary 
to  all  the  theories  of  geologists."  Such  statements  are  in 
general,  I  find,  liable  to  originate  in  a  misapprehension,  either 
of  the  true  conditions  which  prevail  at  the  locality  in  question, 
or  of  what  are  the  best  geological  theories.  In  this  case 
I  found,  in  two  respects  at  least,  that  the  process  of  ore-deposi- 
tion at  Leadville  was  not  in  accordance  with  the  most  widely 
accepted  theories  upon  the  subject.  First,  they  were  not  the 
filling  of  pre-existing  open  cavities  or  caves  in  the  limestone, 
but  had  been  formed  by  a  gradual  replacement  of  the  rock- 
material  by  the  substances  brought  in  by  the  ore-bearing  solu- 
tions. Secondly,  these  solutions  did  not  come  directly  from 
below,  as  seemed  to  be  considered  a  necessary  condition  for 
the  deposition  of  ores,  but  in  this  case  could  be  proved  to  have 
reached  the  immediate  locus  of  deposit  from  above. 

As  I  pointed  out  in  a  paper  read  before  the  Institute  two 
years  since,2  in  stating  the  results  I  had  arrived  at  in  regard  to 
the  genesis  of  the  Leadville  deposits,  I  made  no  claim  of  pre- 
senting any  complete  general  theory  or  classification  of  ore- 
deposits  at  that  time,  nor  have  my  observations  been  suffi- 
ciently wide  to  enable  me  to  do  so  now.  I  did,  however,  con- 

2  This  volume,  pp.  1  to  25  ;  Trans.,  xv.,  125  (1886-87). 


28  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

elude,  as  a  result  of  my  investigations,  that  existing  theories 
and  classifications  were  inadequate  to  account  for  the  various 
forms  under  which  ores  are  found  in  nature,  and  that  this  in- 
adequacy arose  probably  from  the  want  of  some  common  un- 
derlying genetic  basis.  Far  too  few  of  the  descriptions  of 
ore-deposits  in  various  parts  of  the  world,  upon  which  the 
existing  theories  have  been  founded,  are  based  upon  accurate 
determinations  of  their  structural  relations.  I  have,  therefore, 
been  emboldened  to  assume  that,  by  giving  more  attention  to 
these  structural  relations  than  has  hitherto  been  done,  many 
existing  uncertainties  might  be  cleared  up,  and  perhaps,  in 
time,  a  rational  or  natural  classification  of  ore-deposits  might 
be  formed.  In  the  paper  above  mentioned  I  stated  the  conclu- 
sions I  had  been  enabled  to  form  from  my  Leadville  and  later 
studies  in  regard  to  the  genesis  of  certain  ore-deposits,  mainly 
those  in  limestone,  and  touched  lightly  on  their  probable  appli- 
cation to  what  are  known  as  fissure-veins,  of  which  I  had,  up 
to  that  time,  had  but  limited  opportunities  of  personal  observa- 
tion. Since  then,  however,  especially  during  the  past  summer, 
I  have  visited  many  so-called  fissure-deposits  of  great  variety 
of  type,  and  during  these  visits  I  have  been  so  struck  with  the 
uniform  occurrence  of  certain  elementary  structural  conditions 
that  I  have  ventured  to  make  some  preliminary  generalizations 
based  upon  them,  that  seem  likely  to  find  a  very  wide  practical 
application,  and  to  furnish  a  basis,  with  modifications  that  may 
be  afterwards  introduced  as  a  result  of  wider  observation,  for 
a  general  classification  of  ore-deposits.  Whether  this  prove  to 
be  the  case  or  not,  it  seems  that  this  method  of  regarding  ore- 
deposits,  while  I  can  hardly  claim  for  it  much  that  is  absolutely 
new,  has  the  merit  of  being  a  simple,  rational  method,  which 
obviates  many  of  the  uncertainties  and  misapprehensions, 
especially  in  practical  application,  that  constantly  arise  from 
the  more  complicated  existing  systems. 

Preliminary  Statements. — The  ore-deposits  which  I  propose  to 
consider  are  original  or  primary  deposits  that  have  been  formed 
later  than  the  inclosing  rock.  They  exclude,  therefore,  second- 
ary deposits,  whether  of  mechanical  or  detrital  origin,  like 
placers,  or  of  chemical  origin,  like  bog  iron-ores,  which  result 
from  the  superficial  leaching  of  other  deposits.  They  also  ex- 
clude deposits,  such  as  beds  of  coal,  gypsum,  and  the  like, 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  29 

which  have  been  deposited,  so  to   speak,  contemporaneously 
with  the  inclosing  rock. 

Even  with  these  exclusions  they  include  practically  all  the 
workable  primary  deposits  of  useful  metals;  for  I  have  yet  to 
see  such  deposits  which  can  be  proved  to  have  been  formed 
contemporaneously  with  the  inclosing  rocks.  It  is  possible 
that  in  some  cases,  as  Irving  holds  with  regard  to  the  Lake 
Superior  iron-deposits,  there  was  an  original  nucleus  of  ore  con- 
temporaneously precipitated  with  the  sediments  which  formed 
the  rocks,  but  which  has  been  added  to  to  such  an  extent  by 
percolating  solutions  replacing  the  adjoining  portions  of  the 
inclosing  rocks,  that  the  present  ore-body  is  practically  a  later- 
formed  deposit. 

I  believe,  with  Pumpelly,  Posepny,  and  others,  that  all  our 
workable  deposits  of  the  useful  metals  are  the  result  of  a  pro- 
cess or  series  of  processes  of  concentration  or  aggregation  of 
material  previously  disseminated  in  a  minute  form  through  the 
mass  of  the  rocky  crust  of  the  earth. 

With  regard  to  these  deposits  there  are  certain  elementary 
postulates,  which  at  the  risk  of  apparent  unnecessary  repetition 
from  former  papers  I  think  it  best  to  briefly  enumerate. 

1.  That  these  deposits  were  formed  from  aqueous  solutions. 
In  other  words,  they  have  been  gathered  up  by  waters  contain- 
ing varying  substances  in  solution,  and  percolating  through  the 
earth's  crust,  and  again  deposited  in  their  present  concentrated 
form  under  a  change  of  conditions  which  favored  precipitation 
rather  than  solution. 

It  seems  hardly  necessary  at  the  present  day  to  bring  for- 
ward any  arguments  in  favor  of  the  aqueous  deposition  of  ores 
as  opposed  to  the  notion  of  an  eruptive  origin,  which  at  the 
best  has  been  a  theoretical  view  not  founded  upon  carefully 
and  critically  determined  facts;  but  if  there  exist  any  linger- 
ing doubts  in  any  mind  as  to  the  capability  of  solutions  to  take 
up  and  redeposit  the  various- minerals  found  in  our  ore-deposits 
I  would  recommend  a  perusal  of  Daubree's  recent  voluminous 
work  upon  subterranean  waters.3 

2.  That,  under  given  conditions  of  heat  and  pressure,  all  sub- 
stances are  more  or  less  permeable  to  water.     Hence  we  are 

*Les  eaux  souterraines  ct  V  epoque  actuelle  et  aux  epoques  anciennes  (1887). 


30  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

justified  in  assuming  that,  at  sufficient  depths  within  the  earth's 
crust,  waters  circulate  through  or  permeate  all  rocks,  even 
those  apparently  impermeable,  and  thus  may  dissolve  out 
minute  quantities  of  the  more  readily  attackable  materials 
within  their  mass,  and  remove  them  to  some  other  place.  It 
is  evident,  however,  that  these  waters  will  constantly  tend  to 
concentrate  in  such  portions  of  the  rocky  mass  as  offer  a  more 
ready  passage  or  flow,  and  that  during  such  passage  or  flow 
they  will  seek  relief  from  heat  or  pressure,  and  hence  come 
into  differing  conditions  which  may  favor  precipitation,  deposi- 
tion, or  chemical  interchange  of  the  materials  they  carry  in 
solution. 

Among  the  determining  causes  of  solution  and  of  precipita- 
tion or  deposition,  the  chemical  forces  undoubtedly  play  an  im- 
portant part.  The  capacities  of  various  alkaline  solutions  to 
take  up  metallic  minerals,  especially  when  hot,  and  the  condi- 
tions of  diminished  heat  and  pressure,  or  of  dilution,  which 
would  favor  precipitation  of  these  minerals,  present  an  extremely 
interesting  and  important  subject  of  discussion;  but  it  is  one 
that  would  take  too  much  time  to  treat  within  the  limits  of 
this  paper.  I  shall,  therefore,  confine  myself  as  far  as  possible 
to  the  mechanical  or  structural  conditions  which  would  favor 
ore-deposition  ;  in  other  words,  consider  what  are  the  natural 
water-channels  within  the  earth's  crust,  and  what  forms  of  ore- 
deposits  such  water-channels  will  give  rise  to,  when  the  chemical 
and  other  conditions  are  such  as  to  favor  a  deposition  of  valu- 
able minerals  in  workable  quantity  by  them. 

3.  A  further  postulate,  which  I  insist  on  the  more  strenu- 
ously for  the  reason  that  in  former  times  the  opposite  view  has 
been  so  almost  universally  held  among  writers  on  ore-deposits- 
is  that  a  large  pre-existing  open  cavity  is  not  a  necessary  con, 
dition  for  ore-deposition.  In  other  words,  that  ore-deposits 
are  to  a  large  extent  the  actual  replacement  of  the  country- 
rock  by  vein-materials,  and  that  the  filling-up  by  these  materials 
is  rather  that  of  interstitial  spaces  than  of  what  might  properly 
be  considered  open  cavities.  I  by  no'  means  deny  that  a  cer- 
tain limited  amount  of  unoccupied  space  may  have  existed  in 
the  water-channel  previous  to  the  ore-deposition,  but  I  wish  to 
remove  the  tendency  to  misapprehension  caused  by  the  previ- 
ously-conceived view,  under  which,  for  instance,  one  might 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  31 

regard  the  whole  width  of  an  8-ft.  vein  as  material  brought  in 
from  a  foreign  source,  when  in  point  of  fact  more  than  7  ft.  of 
it  might  be  more  or  less  completely  altered  or  replaced  coun- 
try-rock, and  less  than  a  foot  (and  this  not  in  one  body)  rep- 
resent spaces  actually  filled  in.  I  can  even  conceive  of  cases 
of  veins  showing  what  is  supposed  to  be  the  comb-structure, 
from  which  the  idea  of  the  pre-existing  open  space  was  origin- 
ally derived,  where  this  structure  is  produced  by  sheeting  of 
the  country-rock,  the  different  sheets  being  replaced  by  differ- 
ent mineral  combinations,  as  will  be  explained  later  on. 

Let  us  consider,  then,  what  would  be  the  natural  and  most 
readily  available  channels  which  wTould  tend  to  collect  the 
waters  circulating  within  the  earth's  crust,  and  constitute  their 
primary  water-courses. 

It  is  evident  that  the  nearest  analogy  to  the  flow  of  under- 
ground waters  which  can  actually  come  under  our  observation 
will  be  found  in  the  flow  of  springs,  especially  thermal  springs. 
A  study  of  the  phenomena  connected  with  spring-action  and 
deposition,  such  as  has  been  made  by  Daubree  in  his  valuable 
work  above  cited,  materially  aids  our  conceptions  of  what  may 
have  taken  place  in  the  deeper-seated  channels  which  have 
been  in  former  geological  periods  the  scene  of  ore-deposition. 

One  must  beware  of  following'this  analogy  blindly,  however, 
and  bear  in  mind  that  most  ore-deposits  must  have  been  formed 
at  considerable  depths  below  the  surface,  and  brought  to  the 
comparatively  short  distance  from  that  surface  which  they  now 
occupy  by  upheaval  and  erosion. 

An  instance  of  the  errors  into  which  one  may  be  otherwise 
led  is  afforded  by  a  paper  read  before  the  Institute  two  years 
since  by  Prof.  T.  B.  Comstock,4  ori  The  Geology  and  Vein- 
Structure  of  Southwestern  Colorado. 

Owing  to  the  vagueness  of  Mr.  Comstock's  statements,  and 
his  many  misconceptions  of  geological  facts,  we  cannot  always 
be  sure  of  his  meaning;  but  from  a  careful  consideration  of 
this  paper  I  infer  that  he  considers  the  head  of  Red  Mountain 
creek  in  that  region,  which  he  calls  a  crater-like  depression,  to 
be  an  extinct  geyser-basin,  and  that  the  ore-deposits  opened 
by  the  mines  now  worked  there  have  been  formed  by  geysers. 


Trans.,  xv.,  218  to  265  (1886-87). 


32  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

Now  a  geyser,  as  its  name  implies,  is  a  spring  which  violently 
ejects  its  waters  into  the  atmosphere,  and  hence,  even  more 
than  other  springs,  is  essentially  a  surface-phenomenon. 

As,  since  the  ore-deposits  of  Red  Mountain  basin  were  formed, 
something  like  2,000  ft.  in  thickness  of  rock-material  has  been 
eroded  away  to  form  the  basin,  it  is  evident  that  they  could 
not  have  been  formed  by  a  geyser,  nor  can  it  be  determined  at 
the  present  day  whether  geysers  ever  existed  there  or  not. 
Apparently  Professor  Oomstock  has  thought  to  find  a  resem- 
blance between  certain  rounded  ridges  of  light-colored  rock 
near  these  mines  and  the  mounds  formed  by  deposits  from  the 
springs  in  the  Yellowstone  Park.  Instead,  however,  of  being 
surface-deposits,  they  are  simply  portions  of  the  andesitic  coun- 
try-rock from  which  acid  waters  have  removed  the  basic  con- 
stituents, perhaps  depositing  a  certain  amount  of  silica  in  their 
place;  the  resulting  quartzose  masses,  offering  greater  re- 
sistance to  the  disintegrating  effect  of  atmospheric  agents  and 
to  erosion  than  the  surrounding  rocks,  have  been  left  as  inound- 
like  ridges  protruding  above  the  general  surface,  more  or  less 
independent  of  the  natural  drainage-channels. 

There  are  abundant  mounds  formed  by  deposits  from  springs 
in  the  vicinity  of  Red  mountain,  but  they  consist  mainly  of 
bog  iron,  and  are  formed  by  oxidizing  surface-waters  passing 
through  and  decomposing  bodies  of  sulphides  of  the  metals, 
whose  action  is  quite  distinct  from,  and  in  some  sense  the  re- 
verse of,  those  which  originally  formed  these  bodies.  It  would 
seem  almost  unnecessary  to  insist  on  this  distinction,  but  I 
recall  the  description  given  me  of  similar  deposits  in  the  Red- 
well  basin  in  the  Gunnison  region  by  J.  K.  Hallowell,  who 
claimed  as  exact  a  knowledge  of  the  geology  of  that  district  as 
Professor  Comstock  does  of  the  San  Juan  region.  According 
to  him,  galena  and  pyrite  can  be  found  in  actual  process  of 
formation  there  at  the  present  day.  On  personal  examination, 
I  found  that  a  bog  iron-deposit  had  been  formed  throughout 
the  debris  filling  the  bottom  of  this  ancient  glacier-basin,  and 
in  one  place  rested  directly  on  the  outcrop  of  a  vein  carrying 
pyrite,  galena  and  other  sulphurets.  Owing  to  the  extremely 
decomposed  condition  of  the  country-rock  of  this  vein  where 
the  bog  iron  rested  on  it,  Mr.  Hallowell  had  evidently  con- 
cluded that  it  formed  part  of  the  spring-deposit,  failing  to 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  33 

recognize  the  dividing-line  between  recent  deposit  and  original, 
though  decomposed,  rock-formation. 

Although,  in  studying  a  given  deposit,  it  is  not  safe  to  assume 
that  there  has  been  a  spring  at  that  particular  spot,  from 
whose  waters  it  was  deposited,  it  is  evident  that  the  under- 
ground flow  of  waters  which  formed  ore-deposits  would  have 
followed  similar  laws  to  those  which  regulate  the  flow  of  water 
now  appearing  at  the  surface  as  springs. 

Natural  Water- Channels. — From  the  study  of  the  flow  of 
spring-water,  three  principal  structural  conditions  may  be  con- 
ceived which  would  produce  natural  water-passages  in  the  rocks 
which  form  the  earth's  crust : 

1.  Sedimentation  or  bedding. 

2.  Intrusion  of  eruptive  masses. 

3.  Dynamic    movements   producing   fractures    across  rock- 

masses  of  differing  origin  or  composition. 

1.  From  the  first  of  the  above  causes,  by  the  deposition  of 
alternating  strata  of  varying  degrees  of  permeability,  or  by 
successive  flows  of  igneous  rocks,  natural  channels  will  be  af- 
forded parallel  to  the  stratification  or  bedding-planes,  and  more 
or  less  coincident  with  them  according  to  the  nature  of  the  ma- 
terial of  which  the  bounding  beds  are  formed.  This  is  proved 
by  the  fact  that  where  such  strata  or  beds  are  inclined  or  pli- 
cated, and  afterwards  eroded  so  that  their  edges  outcrop, 
springs  will  be  found  along  such  outcrops  where  they  are  at  a 
lower  level  than  the  general  mass  of  the  strata,  or  artificial 
springs  may  be  produced  by  artesian  borings  which  fulfill  the 
necessary  hydrostatic  conditions.  It  is  hardly  necessary  to 
quote  instances  of  flow  of  spring-waters  under  the  simple  con- 
ditions of  alternating  strata  of  permeable  and  impermeable 
sedimentary  rocks.  The  evidences  of  water-passage  between 
flows  of  eruptive  rock  are  well  shown  in  Idaho  and  eastern 
Oregon,  where  whole  rivers  disappear  beneath  the  great  lava- 
flows  that  cover  such  immense  areas  of  surface,  and  reappear 
.at  some  lower  level  at  the  bounding-plane  between  the  succes- 
sive flows,  evidently  having  sunk  through  some  natural  frac- 
ture and  followed  a  more  permeable  bed  of  mud  or  breccia, 
such  as  is  generally  found  alternating  with  the  beds  of  solid 
Java. 

These  primary  water-channels  along  bedding-planes  may 

3 


34  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

be  interrupted  by  either  of  the  two  other  causes  mentioned 
above. 

2.  Eruptive  dikes  or  cross-cutting  intrusive  bodies  of  any 
form  may  interpose  relatively  impermeable  masses  across  their 
course,  or  intrusive  bodies,  running  parallel  with  the  bedding, 
may  render  the  plane  of  contact  a  more  ready  water-passage 
than  it  otherwise  would  have  been.     Thus  in  regions  of  erup- 
tive activity,  springs,  especially  thermal  springs,  are  generally 
found  along  the  outcrop  of  the  contact  of  the  later  eruptives 
with  the  rocks  through  which  they  have  passed. 

3.  The  interruptions  to  these  primary  water-channels  result- 
ing from  the  varied  forms  of  rock-fracture  caused  by  dynamic 
movements  are  so  manifold  and  numerous  that  it  is  not  always 
possible  to  trace  back  to  cause  from  effect.     Frequently  springs 
issue  from   the   outcrops  of  fault-planes;    and,  when   crossed 
underground,  the  latter  are  generally  found  to  be  water-bear- 
ing.    It  is  easy  to  conceive  that  where  a  series  of  beds,  includ- 
ing certain  permeable  or  water-bearing  strata,  are  broken  or 
displaced  by  fault-movements,  the  current  along  the  permeable 
strata  may  be  interrupted.     On  the  other  hand,  the  passage  of 
water  along  this  new  water-channel  may  not  be  continuous  to 
the  surface,  but  may  only  follow  it  until  it  meets  another  per- 
meable stratum  and  turn  off  again  along  that  in  a  manner  similar 
to  the  well-known  occurrence  in  artesian  wells,  where,  if  the 
bore-hole  be  not  protected  by  a  water-tight  casing,  the  water 
rising  from  some  deeper  bed  may  gradually  be  dissipated  in 
other  permeable  beds  passed  through  by  the  drill,  between  the 
water-bearing  bed  and  the   surface,  and  the   surface-flow  be 
finally  lost  altogether. 

It  is  evident  that  the  greater  number  of  underground  water- 
channels,  though  perhaps  not  those  carrying  the  largest 
volumes  of  water,  will  be  afforded  by  the  multitudinous 
fractures  in  the  crystalline  or  eruptive  rocks  and  in  the  older 
and  more  metamorphosed  sedimentary  strata.  In  one  sense 
these  might  be  made  to  include  the  contact-channels  along 
dikes  and  intrusive  bodies  of  eruptive  rock  also  ;  for  it  is  prob- 
able that  such  bodies,  when  forced  up  from  below,  have  fol- 
lowed some  previously- determined  fracture  or  natural  division- 
plane. 

Before  proceeding  to  consider  how  far  the  origin  of  various 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  35 

types  of  ore-deposits  may  be  ascribed  to  the  passage  of  mineral- 
bearing  waters  along  one  or  more  of  the  above  natural  water- 
channels,  I  will  mention  another  possible  class  of  division- 
planes  in  rocks  which  have  been  considered  by  some  as  the 
origin  of  mineral-bearing  fissures,  but  to  which,  so  far  as  I 
know,  that  of  springs  has  never  been  ascribed.  These  are  con- 
traction-planes or  joints.  The  most  evident  examples  of  them 
are  naturally  found  in  eruptive  rocks,  notably  the  prismatic 
joints  of  more  recent  eruptives.  It  is  possible  that  the  divi- 
sion-planes which  tend  to  separate  most  eruptive  rocks  into 
parallelopipedic  fragments  may  have  been  originally  determined 
by  contraction  of  the  mass,  but  it  is  probable  that  the  actual 
fracturing  along  these  planes  was  produced  by  dynamic  move- 
ments. Whether  sedimentary  rocks  contract  after  deposition 
from  the  expulsion  of  the  water  they  must  have  contained  when 
forming  the  sea-bottom,  may  be  considered  an  open  question. 
One  thing  is  evident :  that  contraction-planes  must  be  confined 
to  one  rock-mass  or  bed,  and  cannot  cross  several  of  them,  as 
do  most  mineral-bearing  fissures.  It  is  also  evident  that,  as 
contraction-planes  alone,  there  would  have  been  no  movement 
or  pressure  along  them.  Hence  planes  where  evidences  of 
movement  or  pressure  are  found  cannot  result  from  contraction 
alone.  For  these  reasons,  and  the  further  one  that  I  have 
never  yet  found  ore-bodies  deposited  on  planes  which  I  could 
feel  assured  were  the  result  of  contraction  alone,  I  think  it  safe 
to  leave  contraction-planes  out  of  consideration  for  the  present, 
at  least. 

Ore-Deposits  Along  Bedding-Planes. — The  greater  part  of  our 
ore-deposits  are  found  in  mountainous  regions  where  eruptive 
and  dynamic  action  has  been  most  energetic;  consequently, 
deposits  resulting  from  the  flow  of  water  along  bedding-planes 
alone,  unconnected  with  the  other  classes  of  water-channels, 
form  but  a  small  proportion  of  the  whole.  There  are,  more- 
over, other  conditions  than  the  simple  readiness  of  flow  of 
water  that  come  into  play.  It  is  apparent  that  deposition  will 
take  place  more  readily  from  a  comparatively  sluggish  than 
from  a  rapid  flow ;  hence  conditions  that  tend  to  retard  the  flow 
or  cause  a  partial  stagnation  at  a  given  point  will  favor  pre- 
cipitation at  that  point.  Such  would  be  the  actual  contact  of 
an  impervious  stratum,  e.g.,  a  bed  of  clayey  material,  with  a 


36  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

readily  pervious  one  like  a  loose  sandstone.  Again,  in  pli- 
cated strata,  points  where  by  sharp  folding  the  beds  are  more 
closely  compressed  together — as  on  the  side  of  the  fold — than 
at  other  points,  are  often  found  to  carry  larger  bodies  of  ore. 
The  chemical  composition  of  the  different  beds  is  also  a  most 
important  factor ;  so  much  so  that  in  regions  like  the  Ten-Mile 
district,  where  thin  beds  of  limestone  are  found  scattered 
through  considerable  thicknesses  of  sandstone  and  shales,  the 
ore  of  the  so-called  bedded  deposit  is  almost  exclusively  con- 
fined to  the  more  readily  attackable  limestone.  The  term 
"  bedded  vein "  or  "  deposit,"  as  derived  from  von  Cotta's 
Lagergang  (literally,  bed-vein),  might  be  objected  to  as  seeming 
to  imply  that  the  ore  was  deposited  contemporaneously  with 
the  inclosing  beds,  and  for  this  reason  the  less  concise  term, 
"  deposit  along  bedding-planes,"  would  be  preferable.  Where 
the  deposit  occurs  at  the  junction  of  two  beds  of  very  dissimi- 
lar composition,  like  limestone  and  quartzite  or  slate,  it  is  often 
called  a  contact-deposit,  but  it  seems  that  this  term  should  be 
confined  to  those  of  the  next  class,  contact-deposits  with  rocks 
not  of  contemporaneous  formation. 

Instances  of  deposits  of  this  class  that  occur  to  me  are  those 
of  the  Ten-Mile  region,  the  Eed  Cliff  region,  and  others  in 
Colorado,  which  are  mostly  along  the  bedding-planes  between 
limestones  and  argillaceous  beds,  though  at  Red  Cliff  some  are 
found  in  quartzites.  The  iron-ore  beds  in  the  Silurian  rocks 
of  the  Appalachians  are  probably  of  this  class,  for  Prime  re- 
ports that  he  finds  evidence  that  they  are  the  replacement  of 
the  limestone  rock,  hence  cannot  have  been  formed,  like  bog 
iron-deposits,  contemporaneously  with  the  inclosing  rocks,  as 
dewberry  maintains.  They  are  not  necessarily  confined  to  the 
immediate  bedding-plane,  but  in  a  porous  rock  may  spread 
through  the  mass,  like  those  of  Silver  Reef,  where  precipita- 
tion has  been  probably  induced  by  the  presence  of  some  re- 
ducing-agent  of  organic  origin.  The  copper-deposits  of  Mans- 
feld  in  the  Harz,  and  the  lead-deposits  of  Commern  in  the 
Eifel,  may  be  found  to  belong  to  the  same  class,  though  they 
have  generally  been  considered  to  be  of  contemporaneous  origin 
with  the  inclosing  Triassic  beds. 

It  will  be  evident  a  priori  that  mineral  currents  following 
stratification-planes  cannot  be  considered  as  necessarily  coming 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  37 

from  below,  as  has'  been  assumed  by  many  to  be  the  universal 
direction  of  such  currents.  As  I  have  shown  in  a  former 
paper,5  the  direction  of  flow  of  underground  waters  cannot  be 
determined  beforehand  for  a  given  point;  as  this  flow  is  a 
circulation,  its  direction  may  vary  according  to  the  local  con- 
ditions which  would  govern  it.  As  far  as  my  observations  go, 
in  deposits  from  currents  following  stratification-planes  the 
waters  have  sunk  into  the  bed  from  its  upper  surface  as  if 
under  the  influence  of  gravity. 

Deposits  Along  Contact- Planes. — Mineral-bearing  solutions 
gathering  in  or  flowing  along  the  planes  of  contact  of  eruptive 
bodies  with  rocks  through  which  they  have  been  forced  would 
have  a  tendency  to  deposit  their  contents  along  such  planes, 
whatever  the  direction  of  their  flow.  If  they  were  ascending 
currents,  it  may  be  conceived  that  they  were  coming  from  a 
hotter  region,  or  from  the  vicinity  of  a  larger  and  not  so  thor- 
oughly cooled  mass  of  igneous  rock,  where  their  solvent  power 
was  greater,  to  a  cooler  region,  in  which  this  solvent  power 
would  be  relatively  less.  If  lateral  or  descending  flows,  gather- 
ing from  the  mass  of  one  of  the  walls  of  the  fissure,  precipitation 
might  be  induced  from  the  solutions  thus  brought  in  by  a 
retardation  or  temporary  stagnation  of  the  flow,  by  dilution 
through  mixing  with  other  waters  already  circulating  in  the 
fissure,  or  by  some  chemical  interchange  resulting  from  contact 
with  the  other  wall,  if  a  rock  of  different  chemical  composition 
from  that  through  which  the  solutions  had  been  passing.  For 
these  reasons  it  seems  advisable  to  distinguish  such  deposits 
from  those  along  stratification-planes  on  the  one  hand,  or  along 
rock-fractures  on  the  other,  even  in  those  cases  where  the  con- 
tact-plane may  be  in  part,  or  wholly,  coincident  with  a  stratifi- 
cation- or  fracture-plane. 

It  is  quite  a  common  practice  among  miners  to  designate  as 
"  contact-deposits "  ore-bodies  occurring  along  the  dividing- 
plane  between  two  bodies  or  beds  of  different  rocks,  even  when 
such  plane  is  simply  a  stratification-plane.  Such  practice 
should  in  my  opinion  be  avoided,  and  the  term  confined  to  the 
planes  defined  above,  which  are  distinctly  of  later  formation 
than  stratification-planes,  and  in  which  the  conditions  of  depo- 
sition would  have  certain  distinctive  characters. 

5  This  volume,  p.  14;  Trans.,  xv.,  137  (1886-87). 


38  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

Contact-planes  as  defined  above  will  more  frequently  be 
found  to  coincide  or  connect  with  planes  of  rock- fracture,  since 
one  can  hardly  conceive  of  sheets  of  eruptive  rock  being  forced 
through  existing  rock-masses  in  the  form  in  which  we  now 
find  them,  unless  they  had  followed  some  already-determined 
line  of  fracture,  or  at  least  of  readiness  to  be  forced  open,  and 
it  is  well  known  that  eruptions  of  lava  at  the  present  day  are 
generally  preceded  by  earthquake-shocks,  which  probably  in- 
volve a  very  considerable  shattering  and  fissuring  of  the  earth's 
crust  in  the  vicinity  of  the  eruption. 

Ore-deposits  along  contact-planes  are  very  common,  and 
mining  engineers  can  doubtless  recall  frequent  instances  which 
have  come  under  their  own  observation.  The  famous  Lead- 
ville  deposits  are  in  great  part  instances  of  the  less  common 
type  of  deposits,  in  contact  with  intrusive  bodies  which  have 
generally  followed  stratification-planes.  Among  them,  how- 
ever, are  deposits  along  the  contact  of  cross-cutting  eruptive 
sheets,  the  so-called  second  contacts,  and  in  some  instances  the 
ore-currents  have  followed  rock-fractures,  and  hence  belong  to 
the  third  class.  As  in  all  deposits  in  limestone,  owing  to  the 
readily  attackable  character  of  the  rock,  the  actual  form  of  the 
various  deposits  at  Leadville  is  extremely  irregular ;  more  so 
than  it  would  be  in  a  more  siliceous  rock ;  but  I  have  as  yet 
been  unable  to  conceive  of  any  classification,  founded  on  the 
form  alone,  that  would  essentially  aid  in  the  description  of 
such  bodies,  or  help  the  miner  in  exploiting  them. 

Of  deposits  along  the  contacts  of  dikes  or  cross-cutting 
bodies  of  eruptive  rock,  hence  generally  occupying  a  more 
nearly  vertical  position,  abundant  examples  are  found  through- 
out the  Archaean  areas  of  the  Rocky  Mountain  region,  most  of 
which  are  commonly  classed  by  the  miner  as  fissure-veins,  be- 
cause of  the  prevailing  prejudice  in  favor  of  the  supposed 
greater  value  of  that  type  of  deposit.  It  may  be  that  the  whole 
mass  of  a  narrow  dike  is  impregnated  with  mineral,  and  thus 
constitutes  the  ore-body;  but  in  the  structural  sense  it  is  none 
the  less  a  contact-deposit,  since  the  deposit  has  been  made  by 
waters  acting  from  the  contact-planes  outward.  Instances  of 
such  deposits  are  frequent  in  Boulder,  Gilpin,  and  Clear  Creek 
counties,  in  Colorado. 

On  the  other  hand,  when  the  deposit  occurs  along  a  plane  of 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  39 

contact  of  two  dissimilar  bodies  of  rock  brought  into  juxtaposi- 
tion by  faulting,  like  the  Comstock  lode,  it  would  more  prop- 
erly belong  to  the  third  class. 

Deposits  Along  Planes  of  Rock-Fracture  or  Fissures  Produced 
by  Dynamic  Movements. — Many  somewhat  divergent  views  have 
been  entertained  at  various  times  by  geologists  as  to  the  origin, 
manner  of  formation,  and  even  the  proper  designation  of  the 
many  kinds  of  fissures,  cracks,  and  joints  that  traverse  the  rock- 
masses  forming  the  earth's  crust.  Those  that  I  propose  to 
briefly  present  here  are  the  ones  which  a  long  field-experience 
has  shown  to  accord  best  with  the  facts  of  nature,  and  which, 
as  far  as  my  reading  has  extended,  are  in  essential  harmony 
with  those  entertained  at  the  present  time  by  the  best  structural 
geologists  both  of  this  country  and  of  Europe. 

The  most  prominent  and  readily  remarked  of  these  rock- 
fractures  are  the  great  faults  which  have  played  so  important 
a  part  in  determining  the  orographic  relief  of  our  globe,  a  part 
second  in  importance  only  to  that  of  the  flexures  or  plications 
of  the  strata,  to  which,  as  I  shall  show,  they  are  closely  allied 
both  in  origin  and  manner  of  formation.  The  greatest  of  these 
faults  often  extend  for  miles  in  length,  and  the  displacement 
of  the  opposed  rock-masses  on  either  side  of  the  fault  may 
amount  to  several  thousand  feet.  Minor  faults  or  displace- 
ments, which  are  found  in  infinite  variety,  especially  in  regions 
of  great  dynamic  disturbance,  may  not  produce  any  readily 
apparent  effect  upon  the  surface-features,  and  yet  may  be  rec- 
ognizable as  determining  the  flow  of  springs,  or  be  detected 
by  the  underground  workings  of  mines.  They  have  been  most 
thoroughly  studied  in  the  workings  of  coal-mines,  where  the 
importance  of  careful  underground  mapping  is  most  generally 
appreciated,  since  the  determination  of  the  direction  and  amount 
of  throw  of  such  faults  has  an  actual  money-value.  Much  has 
been  written  about  methods  of  making  such  determinations, 
but  more  attention  seems  to  have  been  given  to  reducing  them 
to  mathematical  formulae  than  to  tracing  their  origin  or  con- 
nection with  other  earth-movements.  In  all  these  rock-frac- 
tures the  evidence  of  a  movement  of  displacement,  as  disclosed 
by  the  discrepancy  or  want  of  correspondence  in  the  adjoining 
walls,  is  usually  very  prominent. 

There  are  other  and  much  more  numerous  rock-fractures,  in 


40  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

which  there  is  either  no  movement  of  displacement,  or  it  is  so 
slight  as  to  be  with  difficulty  detected.  Among  them  certain 
classes  are  characterized  by  their  frequency  and  their  general 
parallelism  in  two  or  more  co-ordinated  directions,  and  at 
angles  often  approaching  a  right  angle  with  each  other.  To 
these,  owing  to  their  apparent  uniformity  of  character,  the 
name  of  joints,  or  cross-joints  (inasmuch  as  they  are  apt  to  cut 
across  the  strata),  has  generally  been  given  by  English-speak- 
ing geologists. 

As  regards  the  designation  of  these  various  forms  of  fissure 
or  rock-fracture,  from  the  very  fact  that  there  has  been  so  little 
agreement  as  to  their  genetic  relations,  there  has  necessarily 
been  a  great  want  of  uniformity  in  nomenclature.  In  different 
countries,  and  even  in  different  districts  in  the  same  country, 
local  terms  have  been  used  to  describe  phenomena  supposed  to 
be  peculiar  to  the  locality,  which  have  been  perpetuated  by 
geologists  and  have  thus  introduced  into  geological  literature 
a  greater  diversity  and  variety  of  terms  than  is  justified  from  a 
strictly  genetic  point  of  view. 

Daubree,  in  his  comprehensive  view  of  the  phenomena  at- 
tending the  flow  of  underground  waters,  recognizing  the  hope- 
lessness of  assimilating  all  these  local  terms,  proposes  the  gen- 
eral name  of  Lithoclases  (rock-fractures)  for  all  rock-fractures 
of  whatever  nature,  and,  as  principal  subdivisions,  uses  Para- 
clases,  to  designate  those  in  which  the  movement  of  displace- 
ment is  readily  apparent  (in  other  words,  what  are  generally 
called  faults),  and  Diaclases  to  designate  those  that  are  gener- 
ally known  as  joints  and  in  which  there  is  no  perceptible 
movement  of  displacement,  but  which  are  characterized  by 
a  parallelism  and  uniformity  of  distribution,  and  traverse  dif- 
ferent rock-masses.  To  both  of  these  he  attributes  a  mechani- 
cal origin ;  in  other  words,  considers  that  they  are  the  result  of 
dynamic  movements  of  the  earth's  crust.  He  further  desig- 
nates all  the  rock-fractures  of  feeble  dimensions,  which  are 
confined  to  a  given  rock-mass  and  render  it  liable  to  break  up 
into  small  fragments  under  various  influences,  as  Leptodases 
(small  fractures),  subdividing  these  further  into  Syndases  (con- 
traction-fractures), or  those  which,  like  prismatic  joints,  are 
produced  by  the  contraction  of  the  rock-mass,  and  Piesodases 
(compression-fractures),  those  small  fractures,  without  any  ap- 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  41 

parent  regularity,  whose  frequent  striated  surfaces  show  them 
to  result  from  a  movement  of  compression  like  the  diadases. 

On  the  other  hand,  Heim,  who  is  the  best  representative  of 
the  German  ideas  on  structural  geology,  in  his  classic  work  on 
the  mechanism  of  mountain-building,6  simply  divides  the  larger 
rock-fractures  into  two  classes :  fold-faults  (Faltenverwerfunyeri) 
and  fissure-faults  (Spaltenverwerfunyeri),  both  of  which  are  pro- 
duced by  tangential  or  .lateral  compression  of  the  upper  por- 
tions of  the  earth's  crust.  In  the  former,  this  pressure  has 
resulted  in  a  general  plication  of  the  beds  involved,  which  has 
progressed  to  such  a  point  that  the  limit  of  their  plasticity 
or  capability  of  bending  has  been  passed,  and  the  tension  re- 
lieved by  actual  fracture  and  displacement.  In  the  latter,  the 
fracture  has  taken  place  without  any  perceptible  bending  of 
the  rock-masses  adjoining  the  fault,  the  tension  being  relieved 
by  sudden  shatterings  in  the  nature  of  earthquake-shocks,  or  be- 
cause the  lines  of  fracture  were  already  determined,  and  the 
cohesion  sufficient  to  admit  of  the  preliminary  plication  of  the 
beds  no  longer  existed.  He  afterwards  traces  the  effects  of 
the  same  forces  upon  the  internal  structure  of  individual  rock- 
masses,  and  shows  that  cleavage-  and  foliation-planes  are,  so 
to  speak,  diminutive  faults,  and  that  the  effects  of  these  move- 
ments are  appreciable  even  in  the  microscopic  structure  of  the 
rocks. 

While  DaubreVs  nomenclature,  as  such,  is  the  most  com- 
plete and  comprehensive  thus  far  presented,  the  attempt  to  in- 
troduce into  so  practical  a  science  as  mining  geology  so  many 
new  and  strange  terms  would  seem  to  be  of  very  doubtful  ad- 
visability. For  the  present  purposes,  therefore,  it  seems  suffi- 
cient to  use  the  terms  "  fold-faults,"  "  fissure-faults,"  and 
"  compression-joints  "  to  designate  the  most  marked  types  of 
the  various  rock-fractures,  bearing  in  mind  that,  as  they  are 
supposed  to  be  the  result  of  the  same  general  force  of  compres- 
sion, it  may  not  always  be  possible  to  draw  a  definite  line  of 
distinction  between  the  types. 

Causes  of  Fracture. — It  seems  hardly  necessary  to  state  at  the 
present  day  that  the  force  which  produces  the  folding,  fault- 
ings,  and  rock-fractures — in  short,  the  mountain-building  force, 

6   Untersuchungen  iiber  den  Mechanismus  der  Gebirgsbildung,  vol-.  ii.,  p.  44  (1878). 


42  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

is  to  be  considered  as  a  result  of  the  secular  contraction  of  the 
earth's  crust.  Of  late  years,  however,  some  theoretical  argu- 
ments have  been  presented  by  physicists  tending  to  throw 
doubt  upon  the  adequacy  of  the  force  which  might  be  produced 
by  secular  contraction  to  account  for  what  they  assume  to  be 
observed  facts.  Further,  certain  American  geologists  have 
thought  to  find  conditions  which,  according  to  their  reading  of 
the  facts,  contraction  could  not  account  for,  and  for  some  of 
which  it  has  even  been  thought  necessary  to  revive  the  old  and 
long  ago  abandoned  hypothesis  of  a  vertical  upthrust. 

As  regards  the  theoretical  objections,  it  may  be  said  that 
mathematical  demonstrations  are  of  questionable  value  in  a 
science  like  the  geology  of  the  present  day,  in  which  the  ex- 
actly determined  facts  are  as  yet  too  few  to  afford  premises  of 
mathematical  exactitude  upon  which  to  base  them,  and  that 
those  who  are  arguing  against  the  contraction  theory  have 
presented  no  adequate  hypothesis  to  take  its  place. 

On  the  other  hand,  among  practical  observers  in  geology 
the  personal  equation  forms  so  large  a  factor  that  it  may  be 
fairly  questioned  whether  the  readiness  of  the  gentlemen  re- 
ferred to  above  to  find  facts  that  could  not  be  accounted  for 
by  the  contraction  theory  was  not  enhanced  by  a  previously- 
formed  opinion  of  its  inadequacy  and  a  desire  to  see  it  dis- 
proved. In  my  own  pretty  large  experience  in  the  same 
general  field  in  which  they  have  worked,  I  have  found  that 
this  theory  not  only  accounts  for,  but  is  the  only  one  that  will 
account  for,  all  the  observed  facts ;  and  where  my  observations 
extended  over  regions  actually  mentioned  by  them,  I  have 
found  their  explanations  not  to  be  in  accordance  with  the  facts 
of  nature,  as  I  read  them. 

Under  the  contraction  hypothesis,  the  forces  exerted  may  be 
concisely  described  as  resulting  from  the  attempt  of  an  already 
consolidated  crust  to  fit  itself  more  closely  to  a  shrinking 
nucleus.  Their  effect  is  felt  probably  only  upon  a  compara- 
tively thin  outer  portion  of  the  earth's  crust :  at  any  rate,  it  is 
a  very  thin  portion  of  this  crust  which  comes  under  our  obser- 
vation. This  crust  may  be  conceived,  therefore,  as  having 
been  since  its  first  formation  in  a  condition  of  tension,  a  gradu- 
ally increasing  force  which  from  time  to  time  found  its  relief 
in  earth-movements  producing  corrugations  on  its  surface,  and 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  43 

hence  relative  elevations  along  certain  orographic  lines,  which 
from  some  reason  or  other  were  lines  of  least  resistance  or  of 
weakness.  Such  lines,  once  determined,  have  been  the  scene 
of  most  marked  expression  of  these  constantly-recurring  move- 
ments of  relief  from  tension.  Closely  connected  with  such 
movements  have  been  the  eruptions  of  igneous  material,  forced 
up  from  below,  either  frorn  a  region  of  permanent  fusion  of  the 
material  of  the  earth's  crust,  as  was  formerly  most  generally 
maintained,  or,  according  to  later  views,  from  local  reservoirs 
brought  into  a  fused  condition  as  a  more  or  less  direct  result 
of  these  movements,  by  the  disturbance  of  equilibrium  between 
the  various  forces  involved  in  the  general  condition  of  tension. 
Whatever  their  source,  the  eruptions  of  igneous  rocks  have 
unquestionably  had  a  very  close  connection  with  orographic 
disturbances,  and  further,  have  indirectly  played  an  important 
part  in  the  formation  of  most  ore-deposits. 

Observation  teaches  us  that  these  successive  periods  of 
dynamic  disturbance,  or  of  mountain-building,  must  have  been 
followed  by  periods  of  relative  quiescence,  during  which  the 
regions  elevated  into  land-masses  were  worn  down  by  atmos- 
pheric abrasion,  and  their  comminuted  debris  carried  into  the 
adjoining  oceans  to  form  a  new  series  of  sedimentary  beds. 
Each  successive  series  of  dynamic  movements  would  involve 
not  only  this  newer  series,  but  also  the  older  and  already 
plicated  and  fractured  series  of  rocks ;  and  thus  the  structural 
conditions  are  found  to  be  the  more  complicated  and  more 
difficult  to  decipher,  the  older  the  rocks  in  which  we  have 
occasion  to  study  them. 

The  rock-masses  of  which  the  earth's  crust  is  formed  possess 
to  a  certain  degree  both  rigidity  and  plasticity:  the  relative 
degrees  of  these  qualities  may  vary  not  only  with  the  composi- 
tion, association,  and  molecular  structure  of  the  different 
masses,  but,  in  the  same  mass,  with  differing  conditions  of  heat 
and  pressure  under  which  it  exists  at  a  given  moment.  Hence 
it  is  impossible  to  determine  a  priori  whether  a  given  amount 
of  compression  will  produce  plication  and  fracture  combined, 
or  fracture  alone. 

In  a  general  way  we  know  that  certain  rocks  are  more  plastic 
than  others :  for  instance,  argillaceous  rocks  more  than  sili- 
ceous rocks;  amorphous  rocks  more  than  crystalline  rocks. 


44  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

Further,  it  is  evident  that  under  moderate  temperatures  dis- 
tinctly stratified  rocks  will  be  more  readily  plicated  than 
massive  or  crystalline  rocks ;  in  other  words,  under  given  con- 
ditions the  latter  would  be  more  fractured  than  the  former. 

The  fracturing  of  rocks,  moreover,  takes  place  the  more 
readily  the  lighter  the  load  upon  them ;  in  other  words,  plas- 
ticity increases  with  pressure.  Thus,  at  sufficient  depths  below 
the  surface,  or  under  the  weight  of  a  sufficient  mass  of  super- 
incumbent rocks,  fracturing  of  the  rock-mass  would  no  longer 
be  possible,  and  compression  would  only  result  in  some  plastic 
deformation.  Heim  places  at  15,000  ft.  the  depth  at  which  all 
fissures  sufficiently  open  to  admit  the  passage  of  waters  must 
necessarily  cease. 

Heim  further  shows  that  the  plasticity  of  a  given  rock-mass 
will  be  greater  under  a  slow-working  pressure  than  under  a 
sudden  shock,  or  under  the  effects  of  a  force  of  rapidly-devel- 
oped energy.  Now  it  is  a  fact  of  observation  that  the  elevation 
of  mountains,  which  is  in  the  main  the  result  of  plication,  is  an 
immensely  slow  movement,  lasting  at  times  through  entire 
geological  periods.  We  can  readily  conceive,  therefore,  that 
while,  as  observation  shows  us,  under  this  slow-moving  force 
great  thicknesses  of  beds  have  been  folded  together  like  so  many 
sheets  of  paper,  when  the  limit  of  plasticity  was  reached  and 
fracture  took  place,  that  this  would  be  a  relatively  rapid  action 9 
more  in  the  nature  of  a  sudden  shock;  indeed,  that  under  such 
enormous  pressure  as  must  necessarily  exist,  the  movement 
past  each  other  of  the  lips  of  the  fracture,  involving  hundreds 
or  even  thousands  of  feet  of  rock-masses,  may  have  produced  a 
series  of  violent  shocks,  which  propagated  themselves  through 
the  adjoning  rock-masses,  and  produced  in  them  a  series  of 
fractures  such  as  we  see  in  so-called  cross-joints.  According 
to  the  theory  that  earthquakes  are  the  relief  of  tension  in  the 
earth's  crust,  this  propagation  of  movement  would  resemble 
the  vibratory  movement  observed  in  modern  earthquakes. 
Such  an  origin  for  cross-joints  has  already  been  suggested  by 
W.  0.  Crosby.7 

It  has  been  objected,  however,  that  while  the  propagation  of 
such  vibratory  movements  would  produce  the  main  parallel 

7  Proceedings  of  the  Boston  Society  of  Natural  History,  vol.  xxii.,  pp.  72  to  85 

(1882-83). 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  45 

joints  at  right  angles  to  the  direction  of  movement  of  the  wave, 
it  is  not  so  easy  to  account  for  the  correlated  joints  which  cross 
the  primary  joints,  generally  at  a  large  angle. 

If,  however,  we  assume  that  all  the  rocks  thus  fractured  were 
under  a  tension  which,  acting  more  slowly,  would  have  pro- 
duced folds,  and  if  this  tension  was  not  simple,  but  complex,  or 
acting  in  more  than  one  direction  at  the  same  time,  so  that 
not  one,  but  two  or  more  systems  of  folds  would  finally  be  pro- 
duced ;  then,  by  the  crossing  of  these  systems  of  folds,  there 
would  result  not  only  a  plication  along  parallel  axes,  but  at  the 
same  time  a  torsion  of  the  beds  or  rock-masses  involved.  The 
assumption  of  a  torsional  strain,  combined  with  that  tending 
to  produce  plication,  admits  of  an  almost  infinite  complexity  of 
rock-fractures  as  a  product  of  these  forces  under  the  various 
conceivable  conditions  attending  dynamic  movements. 

The  foregoing  theoretical  consideration  of  the  forces  which 
may  have  produced  .the  various  rock-fractures  under  consider- 
ation has  been  purposely  made  very  brief,  and  is  hence  possibly 
somewhat  incomplete,  for  the  reason  that  in  so  practical  a 
science  as  mining  geology,  the  outward  manifestations  of  geo- 
logical phenomena — the  effects — are,  in  my  opinion,  of  more 
importance  than  the  causes,  which  always  remain  to  a  certain 
extent  in  the  region  of  hypothetical  conjecture,  and  that  if  one 
becomes  too  much  wedded  to  a  certain  theory  he  is  in  danger 
of  adjusting  his  facts  to  that  theory. 

I  shall,  therefore,  insist  more  particularly  upon  the  physical 
phenomena  which  characterize  these  rock-fractures,  as  deter- 
mined by  actual  observation,  and  for  which,  while  the  above- 
mentioned  hypotheses  seem  at  present  to  account  for  them,  I 
shall  be  quite  ready  in  the  future  to  adopt  any  other  explana- 
tion'that,  by  my  own  studies  or  by  those  of  others,  may  be 
presented  as  more  reasonable  and  adequate. 

Common  Characteristics  of  Compression-Fractures — There  are 
three  phases  of  structural  evidence  of  rock-fractures  and  dis- 
placement resulting  from  compression,  one  or  more  of  which 
I  have  found  to  characterize  the  various  types  of  fissures  carry- 
ing ore-deposits,  which  have  come  under  my  observation. 
These  are : 

1.  Striations  and  "  slickenside  "-surfaces. 

2.  Breccia  or  fragmentary  material  in  the  fissure  itself,  or 


46  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

zones  of  crushed  or  broken  rock-material  included  between 
intersecting  systems  of  fissures. 

3.  A  sheeting  of  the  country-rock  parallel  with  the  main 
fracture ;  in  other  words,  the  occurrence  of  a  system  of  minor 
fractures  which  divide  the  country-rock  up  into  a  system  of 
approximately  parallel  plates  or  sheets.  The  distance  between 
these  parallel  fractures,  or  the  thickness  of  the  sheets,  may  be 
reckoned  by  inches,  by  feet,  or  by  hundreds  of  feet,  according 
to  the  varying  texture  of  the  rock-masses  involved,  or  the  dif- 
ferent dynamic  conditions  which  have  produced  the  fracture. 

It  will  at  once  suggest  itself  that  these  are  all  phenomena 
characteristic  of  faults.  But  they  are  also  found,  at  times, 
where  there  may  be  no  recognizable  evidence  of  actual  dis- 
placement of  the  rock-masses  on  either  side  of  the  fissure  or 
fracture.  On  the  other  hand,  it  will  be  equally  evident  that 
fissures  characterized  by  these  phenomena  can  hardly  be  the 
result  of  contraction,  or  shrinkage-cracks. 

Striations  are  not  confined  to  well-defined  fissures,  but  are 
found  on  smaller  planes  within  rock-masses ;  but  in  any  case 
they  necessarily  seem  to  give  evidence  of  movement  under 
pressure,  be  the  amount  of  that  movement  ever  so  small. 

Fragments  of  country-rock  are  often  rounded,  and  writers 
upon  ore-deposits  are  accustomed  to  speak  of  them  as  having 
fallen  into  the  fissures  from  the  walls,  and,  when  rounded,  as 
having  become  so  by  attrition  either  against  the  walls  or 
against  each  other.  As  regards  the  falling  in,  which  seems  to 
imply  a  fall  in  a  free  or  open  space  of  considerable  dimensions, 
my  observations  have  led  me  to  consider  it  of  rare  occurrence, 
and  to  infer  that  the  fragments  generally  found  have  been  pro- 
duced rather  by  the  rubbing  or  dragging  of  one  wall  against 
the  other.  The  greater  or  lesser  size  of  the  fragments  would, 
in  a  measure,  prove  a  greater  or  less  distance  between 'the 
walls,  but  it  seems  that  under  the  enormous  pressure  that  must 
have  accompanied  these  rock-fractures,  the  space  between  the 
walls  must  have  been  more  or  less  completely  filled  with  attri- 
tion-material, only  part  of  which  would  be  actual  rock-frag- 
ments, and  the  rest  finely-comminuted  material,  which,  under 
the  dissolving  agency  of  percolating  waters,  would  finally  result 
in  more  or  less  impure  clays.  The  rounding  of  the  fragments, 
on  the  other  hand,  is  readily  accounted  for  as  the  action  of 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  47 

these  same  percolating  waters,  it  being  a  well-recognized  fact 
that  the  decomposing  action  of  moisture  in  any  form  acts  more 
rapidly  on  the  corners  or  angles  of  a  rock-mass  than  on  its  flat 
surfaces,  and  the  sharper  the  corner  the  more  rapidly  is  it 
eaten  away. 

Crushed  zones  are  merely  larger  phases  of  the  same  actions 
as  produce  the  breccia-material,  and  are  subject  to  the  same 
general  laws,  only  differing  in  their  greater  dimensions  and 
the  more  irregular  shape  of  the  inclosing  walls. 

The  sheeting  of  the  country-rock  in  faulted  or  fractured  re- 
gions where  ore-deposits  abound,  is  a  phenomenon  to  which 
hitherto  too  little  attention  has  been  paid.  Its  importance  as 
a  feature  of  fissure-veins  is,  however,  great  both  from  a  geo- 
logical and  from  a  practical  point  of  view.  That  it  has  hith- 
erto escaped  due  recognition,  is  probably  due  to  the  prevalence 
of  the  old  idea  that  vein-deposits  are  necessarily  the  filling  of 
open  fissures,  and  to  the  failure  to  appreciate  to  how  great  an 
extent  they  are  .actually  the  replacement  of  rock-material  ren- 
dered more  readily  accessible  and  attackable  by  the  dynamic 
movements  which  produced  the  fissure.  This  feature  will  be 
more  fully  illustrated  in  the  practical  examples  given  later. 

Before  proceeding  to  the  consideration  of  how  far  these 
features  appear  in  actual  ore-deposits,  it  will  be  well  to  exam- 
ine the  typical  manifestations  of  the  above-enumerated  rock- 
fractures  where  their  relations  are  best  shown,  independently 
of  whether  they  may  have  been  mineralized  or  not. 

Typical  Rock-Fractures. — The  typical  form  of  the  fold-fault, 
as  observed  by  Heim  in  his  studies  in  the  Alps,  and  as  shown 
experimentally  by  Daubree  in  his  Geologic  JZxperimentale,  may 
be  produced  in  the  following  way :  If  a  given  series  of  strata 
are  compressed  into  a  sharp  anticlinal  fold  by  longitudinal 
pressure,  the  individual  strata  will  tend  to  expand  or  swell 
along  the  axis,  or  in  the  crest  of  the  anticline  and  in  the  bottom 
of  the  adjoining  syncline,  while  in  the  intermediate  portions — 
the  sides,  or  as  the  Germans  express  it,  the  shanks  (Schenkelri) 
of  the  fold — they  will  be  contracted  and  attenuated  or  drawn 
out,  as  it  were.  When,  therefore,  the  beds  in  folding  have 
reached  their  limits  of  plasticity,  the  fracturing  will  take  place 
by  preference  along  the  contracted  portion;  that  is,  on  the 
sides  of  the  fold  rather  than  along  its  axis.  Such  a  fault,  it  is 


48  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

evident,  will  be  necessarily  accompanied  by  marked  plication 
of  the  strata  on  either  side.  Faults  exist  in  nature,  however, 
in  which  there  is  no  marked  plication  of  the  strata  on  either 
side,  but  which  are  quite  evidently  the  result  of  folding,  since 
at  one  or  both  ends  they  pass  into  an  unfractured  fold.  It  is 
evident,  therefore,  that  the  latter  type  may  be  undistinguishable 
from  the  fissure-fault,  in  cases  where  the  structure  of  the  ad- 
joining region  is  so  obscured  that  it  is  not  possible  to  determine 
whether  the  fault  actually  passes  into  a  fold  or  not. 

Characteristic  examples  of  the  above  faults  occur  in  the 
Mosquito  range  near  Leadville,  Colo.,  and  will  be  found  illus- 
trated in  the  maps  and  sections  of  the  Atlas  accompanying 
Monograph  XII.  of  the  U.  S.  Geological  Survey.  There  the 
Mosquito  fault,  which  splits  into  two  at  its  southern  end,  each 
branch  terminating  in  a  fold,  and  to  the  north  has  been  traced 
for  a  distance  of  about  25  miles  and  may  extend  as  much 
farther,  is  a  typical  illustration  of  Heim's  definition  of  the 
fault-fold.  Where  the  adjoining  strata  are  exposed  and  have 
not  been  eroded  away,  they  are  seen  to  be  sharply  folded  and 
to  have  once  formed  part  of  an  S-fold,  which  has  been  fractured 
along  one  side  of  the  anticlinal  axis  or  on  the  shank  of  the 
fold.  The  Iron  and  Carbonate  faults,  on  the  other  hand, 
which,  though  of  less  extent,  it  has  been  possible  to  study  more 
thoroughly,  owing  to  the  many  mine-openings  along  their 
course,  show  no  evidence  of  folding  in  the  bending  of  the 
strata  immediately  adjoining  them  on  either  side,  which  are 
cut  across  by  the  fracture  nearly  at  right  angles  to  the  bed- 
ding-planes throughout  the  greater  part  of  their  extent.  They 
form,  however,  a  definite  part  of  a  system  of  gentle  anticlinal 
and  synclinal  folds,  and  pass  into  an  unfractured  fold  at  either 
end,  being,  therefore,  properly  speaking,  fold-faults. 

In  other  prominent  faults  in  the  district,  such  as  the  Ball 
Mountain,  Mike,  and  Pilot  faults,  it  is  not  possible  to  trace 
their  direct  connection  with  folds,  and  yet  it  is  evident  that  they 
were  produced  by  the  same  general  dynamic  movements  as  the 
others,  and  form  part  of  the  same  tendency  towards  plication, 
which,  in  their  case,  has  evidently  been  counteracted  by  the 
greater  rigidity  of  the  rock-rnasses  as  a  whole,  resulting  from 
the  large  proportion  of  igneous  masses  entering  into  their 
composition. 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  49 

The  phenomena  of  striation,  brecciation,  and  sheeting  of 
the  country-rock  are  well  seen  in  the  Iron  and  Carbonate 
faults,  which  are  the  only  ones  that  have  been  explored  un- 
derground. As  I  have  shown  elsewhere,8  these  fault-planes 
are  not  mineral-bearing,  since  the  principal  mineral  deposition 
in  the  region  was  accomplished  before  the  faulting  took  place. 
But  in  cases  where  the  faults  cut  through  ore-bodies,  consid- 
erable broken  and  ground-up  vein-material  has  been  dragged 
into  the  fault-fissure,  in  quantity  sufficient  to  give  rich  returns 
for  extraction.  The  brecciated  character  of  this  material  is, 
however,  less  readily  recognized  than  when  the  fragments 
have  been  cemented  together  by  metallic  minerals,  as  is  the 
case  in  many  fissure-veins.  The  sheeting  of  the  country-rock 
in  these  two  faults  has  apparently  been  confined  to  the  side 
of  the  fault  opposite  to  that  from  which  the  pressure  came, 
and  has  produced  what  are  sometimes  called  step-faults,  the 
movement  of  displacement  having  been  partly  distributed  on 
several  minor  planes,  a  hundred  feet  or  more  apart,  and  par- 
allel to  the  main  fault-plane. 

The  best  region  for  studying  the  typical  fissure-fault  that  has 
come  under  my  observation  is  the  southwestern  portion  of  the 
Elk  mountains,  in  Gunnison  county,  Colo.  This  has  been  a  re- 
gion of  intense  and  repeated  dynamic  disturbance,  accompanied 
by  enormous  eruptions  of  a  great  quantity  of  igneous  rocks  in  all 
the  varied  forms  in  which  they  occur.  Elevated  glacial  am- 
phitheaters or  basins,  at  altitudes  of  about  11,000  ft.,  whose 
walls  consist  of  thinly-stratified  and  nearly  horizontal  beds  of 
variegated  colors,  afford  unusually  favorable  opportunities  for 
tracing  the  many  faults,  which  form  a  complicated  network 
over  a  large  area,  and  for  determining  the  amount  of  displace- 
ment produced  by  them,  which  is  generally  slight  and  meas- 
ured by  tens  or  hundreds  of  feet.  Although,  as  seen  on  a 
cliff-face,  these  faults  seem  to  consist  of  a  single  plane  of  frac- 
ture, it  is  found,  when  they  are  examined  in  underground 
workings,  that  what  might  be  called  the  fissure-plane  consists  of 
a  series  of  thin  sheets  of  more  or  less  altered  and  intensely 
compressed  and  striated  country-rock,  generally  only  an  inch 

8  Notes  on  Some  Colorado  Ore-Deposits,  Proceedings  of  the  Colorado  Scientific 
Society,  vol.  ii.,  part  ii.,  p.  85  (Oct.,  1886). 


50  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

or  two  thick.  Where,  as  is  frequently  the  case,  these  fissures 
have  been  mineralized  and  constitute  important  ore-deposits, 
the  original  character  of  the  sheets  is  not  readily  apparent ; 
but  the  amount  of  breccia,  consisting  ordinarily  of  small  angu- 
lar fragments  of  country-rock,  cemented  by  vein-material,  suffi- 
ciently proves  that  the  fissure  is  a  fault-fissure;  and,  when  explo- 
rations on  the  strike  have  extended  beyond  the  zone  of  miner- 
alization, the  sheets  of  country-rock  are  found  to  retain  enough 
of  the  original  structure  to  prove  their  origin.  Further,  when 
cross-cut  drifts  have  been  run  into  the  country  on  either  side, 
a  series  of  more  or  less  parallel  cracks  or  fissures  are  found, 
gradually  disappearing  as  the  distance  from  the  central  fissure 
increases.  As  only  the  ore-bearing  portions  of  such  fissures 
are,  as  a  rule,  explored,  it  is  evident  that  the  fracturing  and 
the  directions  and  extent  of  the  fissures  can  be  determined  but 
incompletely.  Still,  owing  to  the  frequent  surface-exposures, 
a  certain  regularity  of  direction  is  easily  detected,  showing 
that  the  fractures  have  been  determined  by  definite  series  of 
dynamic  movements.  Although  in  this  particular  region  the 
faults  are  unaccompanied  by  any  considerable  plication,  yet  at 
no  great  distance,  and  nearer  a  center  of  disturbance,  there 
has  been  intense  plication,  accompanied  by  fold -faulting. 

Similar  fissure-faults,  with  the  same  phenomena  of  thin 
sheeting  of  the  country-rock,  and  with  breccia  cemented  by 
vein-material,  are  found  in  the  San  Juan  region.  Here,  also, 
the  directions  of  the  various  faults  follow  certain  systems,  which 
a  thorough  orographic  study  of  the  region  would,  doubtless, 
enable  one  to  connect  with  the  dynamic  movements  which 
produced  them. 

From  these  individual  fissure-faults  there  is  a  gradual  transi- 
tion into  the  co-ordinated  fractures,  as  a  rule  greater  in  number 
in  a  given  area  but  of  less  individual  extent,  which  form  a  sort 
of  fractured  zone  with  two  or  more  prominent  directions  of 
fracture,  apparently  of  nearly  contemporaneous  formation, 
which  I  have  called  compression-joints,  because  where  I  have 
studied  them  in  mining-districts,  either  by  personal  observa- 
tion or  from  the  description  of  others,  I  find  one  or  more  of 
the  evidences  of  compression  present,  viz.,  striation,  brecciation 
or  crushed  material,  and  sheeting  of  the  country-rock.  Such 
complicated  systems  of  fracture  would  appear  to  involve,  as  I 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  51 

have  already  suggested,  the  action  of  more  than  one  system  of 
dynamic  movement;  that  is,  of  forces  of  compression  acting  at 
the  same  time  in  several  directions,  and  hence  combining  with 
the  direct  plicational  strain  more  or  less  strain  of  torsion. 

The  effects  of  such  torsional  strain  can  be  best  understood 
by  considering  the  effect  of  torsion  alone.  This  is  well  shown 
in  Daubree's  experiment  upon  a  sheet  of  glass  held  firmly  at 
either  end,  and  subjected  to  a  torsional  strain  up  to  the  point 
of  rupture.  The  following  diagram,  Fig.  1,  showing  the  cracks 
thus  produced  in  the  glass,  is  copied  from  that  in  his  Geologie 
Experimentale. 

It  is  to  be  remarked  in  regard  to  the  cracks  or  fissures  thus 
produced : 

1.  That  they  follow  two  general   directions,  crossing  each 
other  at  a  nearly  uniform  angle. 

2.  That  certain  cracks  are  more  prominent  and  fully  devel- 
oped than  the  others,  and  often  consist  of  groups  of  nearly 
parallel  cracks. 


FIG.  1. — SHEET  OF  GLASS  CRACKED  BY  TORSIONAL  STRAIN  (FROM  DAUBREE). 

3.  That,  among  the  subordinate  cracks,  some  extend  only 
from  one  of  these  greater  cracks  to  the  other,  and  do  not  con- 
tinue on  in  the  same  line,  but  at  a  little  distance  dn  the  one 
side  or  the  other,  so  that  they  might  appear  to  have  been 
faulted  or  displaced  by  the  larger  crack,  if  one  did  not  know 
that  all  had  been  formed  contemporaneously  and  by  the  same 
strain. 

In  nature  no  such  regularity  or  uniformity  could  be  expected ; 
and  yet,  when  one  considers  the  cross-joints  of  sedimentary 
rocks,  it  is  surprising  to  observe  how  much  they  recall  the 
lines  in  this  diagram.  In  the  larger  joints  or  fractures  ob- 
served in  mining-districts,  the  effects  of  direct  compression 
have  been  more  marked,  and  the  effects  of  the  torsional  strain 
are  probably  more  seen  in  the  minor  fractures,  or  stringers 
and  leaders,  as  the  miners  call  them.  Still,  if  one  calls  to 


52  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

mind  the  map  of  a  mining-district  characterized  by  a  multitude 
of  small  veins,  it  will  be  found  that  the  more  detailed  the  map 
arid  the  more  thoroughly  the  veins  have  been  explored  and 
represented  thereon,  the  more  regularity  and  uniformity  in 
their  directions  are  shown.  It  must  be  borne  in  mind,  however, 
that  such  a  map  never  represents  the  totality  of  the  fissures  in 
the  district,  but  only  such  parts  of  them  as  have  been  found 
sufficiently  rich  to  exploit  for  ore. 

The  following  diagram,  Fig.  2,  represents  the  veins  of  a  por- 
tion of  the  region  around  Freiberg,  Saxony,  as  given  on  the 
official  maps.  Here  two  general  directions  are  prominent,  and 
combined  with  them  are  certain  directions  which  would  appear 
to  be  resultant  of  these  two.  Even  more  striking  is  the  uni- 
formity of  system  in  the  mining-districts  of  Cornwall,  which 
have  been  worked  for  so  many  years  that  the  various  fractures 
are  exceptionally  well  explored. 


FIG.  2. — VEINS  IN  THE  ERZGEBIRGE,  NEAR  FREIBERG,  SAXONY. 

The  predominance  of  certain  directions  in  the  lines  of  frac- 
ture in  these,  as  in  almost  all  well-studied  mining-districts,  has 
been  the  subject  of  remark,  and  has  given  rise  to  considerable 
speculation ;  but  generally  this  speculation  has  been  based  upon 
the  idea  that  the  veins  were  the  filling  of  considerable  open 
fissures  by  mineral  currents  coming  from  some  unknown  source 
below,  and  has  been  rather  mineralogical  than  structural;  that 
is,  more  attention  has  been  given  to  the  character  of  the  filling 
than  to  the  structural  origin  of  the  fissure.  If  all  those  who 
have  described  mines  and  ore-deposits  had  devoted  as  much 
and  as  intelligent  study  to  the  structural  features  of  the  regions 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  53 

where  they  occur  as  the  late  von  Groddeck  did  in  the  Harz, 
we  should  probably  be  much  nearer  a  satisfactory  theory  of  the 
origin  and  manner  of  formation  of  the  ore-deposits  than  we  are 
at  the  present  day. 

It  is  evident  that  by  a  succession  of  dynamic  movements, 
especially  when  accompanied  by  torsional  strains,  an  almost 
infinite  variety  of  fissures  and  passages  for  mineral-bearing 
waters  may  be  produced,  and  that  it  would  therefore  not  be 
possible  beforehand  to  describe  all  the  various  structural  con- 
ditions under  which  ore-deposits  may  occur.  It  is  only  by  an 
intelligent  description  of  such  fissure-deposits  as  are  observed 
in  nature  in  all  parts  of  the  world  that  we  can  get  a  compre- 
hensive view  of  the  various  possibilities.  Still  there  are  cer- 
tain conditions  that  suggest  themselves  as  a  result  of  the  struc- 
tural method  of  considering  them  that  would  seem  to  have  a 
general  application. 

Structural  Generalizations. — Extent,  of  Fissures. — Since  the 
dynamic  movements  are  confined  to  the  crust  of  the  earth,  it 
is  evident  that  the  fissures  produced  by  them  cannot  literally 
have  an  indefinite  extent  in  depth,  though  in  certain  cases  it  is 
very  possible  that  this  extent  may  be  practically  indefinite,  as 
it  may  go  beyond  the  limits  at  which  mining  is  practicable. 
It  is  fair  to  assume  that  those  fissures  which  have  the  greatest 
horizontal  extent  will  have  the  greatest  extent  in  depth ;  in 
other  words,  that  their  vertical  and  horizontal  dimensions  bear 
some  sort  of  proportion  to  each  other.  If,  therefore,  as  some 
have  maintained,  the  vein-filling  has  in  all  cases  been  brought 
from  some  source  at  great  depths  in  the  earth,  the  'greatest 
fault-fissures  would  be  expected  to  be  the  greatest  and  most 
frequent  ore-producers,  since  they  would  reach  nearer  to  this 
unknown  source. 

In  my  own  experience,  however,  I  have  found  rather  the  re- 
verse to  be  the  case,  which,  as  far  as  it  goes,  furnishes  an  argu- 
ment in  favor  of  the  view  that  the  vein-material  has  been 
derived  from  the  surrounding,  though  not  of  necessity  abso- 
lutely contiguous,  rocks.  On  the  great  fold-faults  I  have  found 
no  considerable  deposits  of  ore,  and  it  is  comparatively  rare 
that  continuous  deposits  are  found  along  a  single  well-defined 
fault-fissure.  The  majority  of  deposits  seem  to  occur  where 
there  are  a  series  of  fissures,  more  or  less  regularly  co-ordinated, 


54  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

in  which  several  of  the  series  are  prominently  accentuated.  In 
such  systems  there  seems  to  be  a  tendency  for  the  rich  ore- 
bodies  or  bonanzas  to  extend  in  a  direction  which  lies  at  an 
angle  with  that  of  the  main  fissure,  or  to  continue  for  a  certain 
distance  along  one  fissure  and  then  to  pass  into  another  fissure, 
set  off  at  a  little  distance  from  the  first.  It  would  seem  prob- 
able that  there  must  be  some  structural  reason  for  the  concen- 
tration of  ore  in  this  way,  and  that  sufficiently  wide  and  detailed 
studies  might  discover  this  reason  and  thus  throw  some  light 
on  this,  at  present,  so  obscure  subject. 

The  practical  lesson  to  be  learned  from  the  above  phenomena 
is  that  the  miner  should  not  confine  his  explorations  to  the 
single  fissure  in  which  his  ore  occurs ;  but  when  he  runs  out 
of  bonanza  in  that,  he  should  seek  a  continuance  of  it  in  some 
adjoining  fissure  or  plane,  in  a  direction  to  be  determined  by 
the  study  of  the  system  of  the  fracturing  of  the  region  and  of 
the  general  direction  of  the  bonanzas. 

Vein-  Walls. — The  second  generalization  is  in  regard  to  the 
walls,  which  have  generally  been  considered  an  important  and 
almost  indispensable  characteristic  of  a  true  fissure-vein.  The 
typical  wall  which  the  miner  considers  an  evidence  of  a  strong 
and  well-defined  fissure-vein  is  a  comparatively  smooth,  gener- 
ally striated,  rock-plane,  and  frequently  coated  with  a  clay 
selvage — a  band  of  decomposed  argillaceous  material  which 
itself  generally  shows  evidence  of  pressure  and  movement. 
From  the  above  structural  point  of  view  of  the  origin  of  vein- 
fissures  it  is  evident  that  the  character  of  the  wall  and  selvage 
is  dependent  on  the  composition  of  the  rock  and  the  amount 
of  displacement  and  pressure.  The  grinding  of  one  face  of 
rock  against  another  will  undoubtedly  tend  to  plane  oft  both 
and  to  produce  a  certain  amount  of  fine  attrition-material ;  but 
this  attrition-material  will  not  necessarily  be  reduced  to  clay 
unless  it  has  further  been  subjected  to  the  decomposing  action 
of  water,  which  has  carried  off  certain  portions  and  left  an 
argillaceous  residue.  The  extreme  instance  of  such  decompo- 
sition is  found  in  the  muddy  accumulations  at  the  bottom  of 
caves  in  limestone,  which  are  simply  the  less  soluble  residues, 
mostly  silica  and  alumina,  resulting  from  the  dissolution  of 
large  quantities  of  more  or  less  impure  limestone. 

These  walls  and  selvages  are  a  frequent  accompaniment,  but 


STRUCTURAL    RELATIONS    OF.  ORE-DEPOSITS.  55 

by  no  means  an  essential  characteristic,  of  an  ore-bearing  fis- 
sure. It  is  quite  conceivable  that  one  or  both  may  be  wanting ; 
and  such  occurrences  are  not  uncommon  in  nature.  Take,  for 
instance,  the  veins  of  Butte,  of  which  I  gave  a  brief  description 
at  a  former  meeting.9  These  are  a  series  of  co-ordinated  frac- 
tures or  compression-fissures  in  a  remarkably  homogeneous 
mass  of  granite.  Apparently  there  has  been  little  or  no  dis- 
placement in  the  walls  of  these  fissures  relatively  to  each  other ; 
hence,  but  little  attrition-material  has  been  produced;  and 
for  this  reason — and  probably,  also,  on  account  of  the  char- 
acter of  the  rock  and  because  it  was  not  much  decomposed 
along  the  fissure-planes  before  the  advent  of  the  ore-bearing 
solutions — no  clay  selvages  have  been  formed,  and  the  ore- 
bearing  solutions  have  eaten  into  the  wall-rock  to  varying 
distances,  replacing  it  more  or  less  completely  by  vein-material, 
and  leaving  no  definite  boundaries  or  walls  to  the  deposits. 
There  is  no  reason,  however,  for  considering  them  any  the  less 
true  fissure-veins  or  less  valuable  ore-deposits  on  this  account. 

On  the  other  hand,  under  certain  conditions,  instead  of  an 
absence  of  well-defined  walls,  there  may  be  so  many  as  to  mis- 
lead the  miner  who  depends  too  implicitly  upon  them  as  a 
boundary  of  his  ore-body.  In  the  Gunnison  region  above  men- 
tioned, for  instance,  where,  owing  to  the  plasticity  of  the 
country-rock,  it  has  been  divided  along  the  main  fracture- 
planes  into  a  series  of  very  thin  parallel  sheets,  the  space 
between  these  sheets  has  frequently  been  filled  by  quartz, 
which  thus  forms  a  thin  sheet,  often  so  completely  reproducing 
the  form  of  the  fissure  as  to  present  a  cast  of  the  striation-sur- 
faces.  Such  a  sheet  of  quartz,  when  the  adjoining  bands  of 
country-rock  have  been  replaced  by  vein-material,  forms  a  hard, 
well-defined  wall  to  the  ore-body,  which  delights  the  eye  of  the 
honest  miner  and  enhances  in  his  mind  the  value  of  his 
property. 

Ore  may  be  found  as  well  on  one  side  as  on  the  other  of  such 
a  wall,  and  not  infrequently  is  apparently  confined  to  one  side 
for  a  considerable  extent  along  the  length  of  the  vein,  and  then 
is  found  almost  as  exclusively  on  the  other  side.  Thus,  in  one 
prominent  mine  in  this  district  I  found  a  drift  run  for  several 

9  Notes  on  the  Geology  of  Butte,  Mont.,  Trans.,  xvi.,  49  (1887-88). 


56  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

hundred  feet  in  barren  country,  but  following  what  was  appa- 
rently the  direct  continuation  of  the  vein  which  had  been 
yielding  a  large  amount  of  rich  ore.  After  a  change  of  admin- 
istration in  the  mine,  it  was  found  by  cross-cutting  that  there 
was  a  continuous  ore-body  only  from  4  to  6  ft.  to  one  side  of 
this  drift  and  parallel  with  it.  In  another  mine  in  the  same 
district,  which  had  produced  a  great  deal  of  very  rich  ore,  I 
found  that  though  there  were  frequent  cross-cuts  into  the 
country  on  the  hanging-wall  side,  disclosing  the  usual  systems 
of  parallel  fissures,  none  had  been  made  on  the  foot-wall  side. 
The  reason  given  was  that  this  foot-wall  was  so  uniform  and 
well  defined  throughout  the  mine  that  it  was  considered  useless 
to  explore  beyond,  since  it  must  necessarily  be  the  limit  of  ore 
in  that  direction.  An  examination  showed  that  there  was  no 
geological  reason  for  this  assumption  in  the  character  of  the 
rock,  and  that  it  was  simply  one  of  a  number  of  quartz-fillings 
between  two  sheets  of  country-rock.  On  visiting  the  mine  a 
few  weeks  later,  I  was  told  that  in  the  southern  portion  of  the 
mine,  where  the  vein  had  seemed  to  be  running  out  at  the  time 
of  my  first  visit,  a  new  body  of  rich  ore  had  been  struck  by 
cross-cutting  into  the  foot-wall  country. 

The  moral  is  that  judicious  cross-cutting  forms  a  very  im- 
portant part  of  vein-mining,  but  should  be  conducted  with  due 
regard  to  the  fracture-system  of  the  adjoining  country,  and  to 
the  evidence  to  be  obtained  as  to  the  course  followed  by  the 
ore-bearing  currents,  or  it  may  involve  an  unnecessary  amount 
of  dead  work. 

Banded  Structure. — In  most  of  the  deposits  of  the  Gunnison 
region,  referred  to  above,  there  is  a  noteworthy  appearance  of 
banded  structure  parallel  with  the  walls  of  the  fissures.  The 
evidence  of  faulting  and  of  the  thin  sheeting  of  the  country-rock 
is  there  so  clear  that  the  explanation  at  once  presents  itself  that 
this  appearance  arises  from  the  fact  that  the  deposits  are  partly 
a  filling-in  of  interstitial  spaces,  and  partly  a  replacement  of 
thin  sheets  of  country-rock,  the  differing  composition  of  the 
bands  resulting  rather  from  the  necessary  variation  in  the  pro- 
cess of  deposition  than  from  essential  differences  in  the  ore- 
bearing  solutions.  Were  one  to  examine  there  only  a  large 
body  of  rich  ore,  and  neglect  to  examine  the  adjoining  poorer 
deposits  and  to  study  the  structural  conditions  of  the  region, 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  57 

one  might  be  led  to  adopt  some  of  the  complicated  explanations 
set  forth  in  books  on  ore-deposits,  such  as  successive  reopenings 
of  the  vein,  to  account  for  the  conditions  found,  instead  of  the 
simple  one  given  above.  Reasoning  inversely,  I  am  led  to 
think  that  much  of  the  banded  structure  described  in  books  on 
ore-deposits  might  be  accounted  for  in  this  way,  if  the  deposits 
could  be  re-examined  with  a  view  to  determining  the  structural 
evidence  in  favor  of  it.  For  instance,  in  the  excellent  work  of 
J.  Arthur  Phillips  10  there  is  given  a  diagrammatic  section  of  a 
vein  at  Cam  Marth,  in  Cornwall,  consisting  of  six  successive 
bands  composed  of  quartz,  with  metallic  minerals  in  some  of 
them,  separated  from  each  other  and  from  the  adjoining 
country-rock  by  clay  partings  or  selvages.  The  explanation 
there  given  to  account  for  this  condition  of  things  is,  that  it  is 
"  a  fissure  that  has  been  several  times  reopened ;  "  and  the 
author  says,  "  It  will  be  observed  that  each  reopening  has  been 
attended  by  an  amount  of  grinding  action  between  the  walls 
sufficient  to  produce  a  clay  parting  of  considerable  thickness." 
This  explanation  involves  so  much  that  is  geologically  improb- 
able that  I  feel  convinced  that  it  is  not  the  true  one,  and  that 
some  condition  of  things  analogous  to  that  described  above 
might  be  found  on  examination  of  the  mine  itself.  The  clay 
parting  might  prove  to  be  a  more  or  less  completely  decom- 
posed band  of  country-rock ;  for  it  is  difficult  to  conceive  that 
clay  could  be  produced  by  the  grinding  of  quartz  on  quartz. 
In  reading  such  descriptions  one  has  to  bear  in  mind  that  in 
making  a  diagrammatic  section  one  is  liable,  consciously  or 
unconsciously,  to  bring  out  strongly  points  that  are  in  favor  of 
the  explanation  one  has  in  mind,  and  to  neglect  those  that  are 
opposed  to  it.  That  there  may  be  repeated  or  continued  move- 
ments along  the  same  fracture-plane  cannot  be  denied,  but,  as 
will  be  argued  later,  one  should  not  resort  to  such  explanations 
for  phenomena  that  can  be  accounted  for  otherwise. 

Crushed  Zones. — Thus  far  we  have  been  considering  mainly 
the  sheet-like  bodies  deposited  along  fissures  having  a  generally 
parallel  direction.  But  cases  must  also  occur  where  the  sys- 
tems of  rock-fracture  intersect  each  other,  and  under  suitable 
conditions  considerable  portions  of  the  country-rock  included 

10  A  Treatise  on  Ore-Deposits,  p.  48  (1884). 


58  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

between  such  intersecting  fractures  may  be  broken  up  or 
crushed  to  such  an  extent  as  to  admit  a  relatively  free  passage 
of  percolating  waters.  Where  such  waters  are  mineral-bear- 
ing, the  interstices  between  the  fragments  will  offer  spaces  for 
the  precipitation  of  their  contents,  or  where  the  rock  is  readily 
soluble  the  fragments  themselves  may  be  replaced  by  vein- 
material.  The  forms  of  ore-bodies  thus  deposited  may  evi- 
dently present  much  greater  variety  and  irregularity  than  those 
deposited  along  single  or  parallel  fissure-planes.  J.  S.  Curtis, 
in  his  memoir  on  the  Eureka  district,11  gives  a  detailed  de- 
scription of  the  extremely  complicated  and  irregular  zones  of 
crushed  limestone  to  which  the  ore-deposits  there  are  practi- 
cally confined. 

Where  three  or  more  nearly  vertical  fracture-planes  inter- 
sect each  other  near  the  same  point,  the  prismatic  body  of  rock 
included  between  these  intersections  may  be  so  crushed  and 
broken  as,  in  a  district  rich  in  mineral-bearing  solutions,  to 
give  rise  to  what  are  generally  known  as  chimney-deposits. 
Where  the  fracture-planes  are  merely  joints  along  which  there 
has  been  but  little  movement,  and  consequently  no  clay  sel- 
vages have  been  formed,  the  ore-solutions  will  eat  out  into  the 
rock  in  such  a  way  that  the  ore-chimney  may  appear  to  have 
a  rounded  instead  of  an  angular  horizontal  section,  and  the 
fracture-planes  themselves  may  have  become,  by  the  decompo- 
sition of  the  adjoining  country-rock,  so  obscured  as  to  be  with 
difficulty  traced  in  the  immediate  vicinity  of  the  ore-body. 
Instances  of  deposits  to  which  this  origin  may  be  ascribed  are 
the  Bull-Domingo  and  Bassick  mines  in  the  Silver  Cliff  dis- 
trict, and  the  Yankee  Girl  mine  in  the  San  Juan  region  of 
Colorado. 

The  first-named  deposit  occurs  in  Archaean  rocks,  traversed 
by  a  dike  of  compact  syenite  which  in  places  forms  one  bound- 
ary of  the  ore-body.  The  ore  is  mainly  galena,  which  consti- 
tutes the  cementing-material  of  fragments  of  the  country-rock 
resulting  from  the  movement  of  displacement.  These  frag- 
ments are  mostly  of  gneiss,  and  as  this  rock  is  readily  decom- 
posed by  aqueous  solutions,  the  fragments  are  generally 
rounded ;  the  few  fragments  of  the  less  readily  attackable  sy- 

11  Monograph  VII.,  U.  S.  Geological  Survey  (1884). 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  59 

enite,  however,  retain  in  great  degree  their  original  angular 
form. 

The  deposit  of  the  Bassick  mine  is  a  nearly  vertical  chimney 
of  somewhat  square  or  lozenge-shaped  outline,  which  has  been 
explored  to  a  depth  of  about  1,100  ft.  from  the  surface.  It 
occurs  in  an  andesitic  breccia,  composed  of  angular  fragments 
of  various  sizes  and  forms  cemented  together  by  material  of 
essentially  the  same  composition  as  the  fragments.  This  ce- 
menting-material,  probably  by  reason  of  its  later  consolidation, 
has  been  more  readily  attackable  than  the  fragments,  for  the 
ore  has  replaced  it,  forming  concentric  layers  around  the  frag- 
ments, whose  angles  have  become  rounded  during  the  process 
of  deposition.  Here  the  fragments  were  original  and  not 
necessarily  produced  by  the  dynamic  movements,  which  prob- 
ably resulted  in  a  simple  fracturing  of  the  rock  without  much 
displacement. 

In  the  Yankee  Girl  there  are  several  chimneys  in  which  the 
ore  occurs.  They  are  of  elliptical  outline,  the  longer  axis  cor- 
responding in  direction  with  a  main  system  of  fractures  run- 
ning through  the  region.  Although  the  striated  surfaces  of 
these  planes  show  that  there  has  been  movement  along  them, 
there  is  but  little  evidence  left  of  actual  brecciation  of  the 
country-rock,  the  ore-solutions  having  completely  replaced  the 
andesitic  country-rock  between  the  fracture-planes  which  ad- 
mitted them.  In  places  a  siliceous  skeleton  is  left,  the  basic 
constituents  being  replaced  by  vein-materials;  in  other  places 
a  solid  body  of  metallic  minerals  is  found,  while  the  country- 
rock  adjoining  the  body  of  pay-ore  is  impregnated  to  a  consid- 
erable distance  with  low-grade  sulphurets. 

Repeated  Movements  along  Fissure-Planes. — It  is  a  well-recog- 
nized fact  of  structural  geology  that  in  successive  dynamic 
movements  in  the  same  region  there  will  be  a  tendency  for 
fractures  to  follow  alreadyTdetermined  planes  of  fracture.  Fur- 
thermore, it  appears  that  the  faulting  of  a  rock-mass  is  not 
necessarily  a  geologically  instantaneous  movement,  but  that 
the  displacement  may  continue  for  some  time  after  the  first 
fracture  has  been  determined,  probably  dying  out  very  gradu- 
ally. Some  such  continued  movement  seems  necessary  to  give 
time  for  the  reduction  by  the  action  of  water  of  the  attrition- 
material  to  the  clayey  condition  in  which  it  is  often  found. 


60  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

We  may  expect,  therefore,  to  find  evidence  in  large  fissures  of 
repeated  movements.  In  the  Comstock  lode,  for  instance, 
which  G.  F.  Becker 12  has  so  well  demonstrated  to  be  a  great 
fault-fissure,  accompanied  by  sheeting  of  the  country-rock  on  a 
grand  scale,  the  crushed  and  sugary  condition  of  the  quartz,, 
which  in  the  fissure  has  replaced  the  included  masses  of  coun- 
try-rock, can  hardly  be  explained,  except  by  movement  along 
the  fault-plane  subsequent  to  this  replacement,  though  per- 
haps prior  to  the  final  completion  of  the  ore-deposition. 

On  the  other  hand,  it  is  easy  to  conceive  that  the  healing  of 
a  fissure,  as  we  might  regard  the  filling-in  of  its  interstices  by 
vein-material,  might  make  it  better  able  to  resist  fracture  than 
it  was  before,  and  a  second  fracture  in  such  a  case  would  not 
necessarily  follow  the  already-determined  plane.  Moreover,  if 
we  recall  the  diagram  given  on  p.  51,  showing  the  fractures 
produced  by  torsion  in  a  sheet  of  glass,  it  will  be  seen  that 
cross-fractures,  and  even  apparent  displacement  of  one  fracture 
by  another,  may  be  produced  by  one  and  the  same  strain. 
Hence,  in  studying  a  system  of  fissures,  one  must  not  too 
hastily  conclude  that  each  direction  of  fracture  means  a  distinct 
movement,  or  even  that  displacement  of  one  fissure  by  another 
necessarily  proves  that  the  latter  was  produced  by  a  distinct 
and  later  movement;  to  be  sure  of  this,  some  of  the  other 
evidences  of  movement  must  be  found. 

The  famous  Ontario  mine  in  Utah  affords  an  excellent  in- 
stance of  a  strong  fault-fissure  deposit  in  a  region  which  has 
been  subjected  to  repeated  dynamic  movements,  associated 
with  successive  intrusions  of  eruptive  rock,  and  illustrates  the 
above-mentioned  points.  I  had  intended  to  submit  detailed 
plans  of  the  underground  workings  of  this  mine,  drawn  to 
scale,  with  the  geological  data  indicated  thereon,  but  find  that 
the  notes  gathered  somewhat  hastily  during  my  visit  of  last 
summer  are  not  sufficiently  complete  for  this  purpose.  I  shall 
therefore  describe,  as  clearly  as  I  can  in  words,  the  character- 
istic structural  features  of  the  deposit. 

It  occurs  in  distinctly-bedded  quartzites  of  middle  Carbon- 
iferous age,  which  dip  about  20°  to  the  northward  and  strike 
here  nearly  east  and  west.  These  rocks  are  traversed  by  nu- 


12  Geology  of  the  Comstock  Lode,  Monograph  TIL,  U.  S.  Geological  Survey  (1882). 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  61 

merous  bodies  of  eruptive  porphyry,  some  in  the  form  of  dikes, 
•others  of  irregular  shapes.  But  few  appear  at  the  surface  in 
the  immediate  neighborhood  of  the  mines;  they  are  mostly 
disclosed  by  the  underground  workings,  many  of  the  dikes 
having  a  direction  parallel  with  the  vein-fissure  and  sometimes 
forming  one  of  its  walls  for  considerable  distances.  An  older 
•dike  is  faulted  by  the  vein-fissure. 

The  vein-fissure  has  a  somewhat  curving  direction,  running 
about  east  and  west,  or  parallel  with  the  strike  of  the  forma- 
tion, in  the  eastern  part  of  its  course,  and  bending  towards  the 
southwest  in  the  west  half.  Its  dip,  however,  is  much  steeper 
than  that  of  the  quartzites,  being  from  45°  to  50°  north,  in- 
stead of  20°,  so  that  it  cuts  these  at  an  angle  of  from  25°  to 
30°.  In  the  western  part  of  the  mine  it  is  a  double  fissure,  or, 
as  the  miners  express  it,  there  are  two  veins,  a  north  and  a 
south  one.  These  are  connected  by  what  the  miners  call 
"  cross-courses,"  which  are  smaller,  co-ordinated,  and  nearly 
parallel  fractures,  forming  an  acute  angle — about  30° — with 
the  main  fissures.  These  are  regarded  there,  in  accordance 
with  generally-received  ideas,  as  a  distinct  system  of  fractures 
formed  at  a  different  time  from  the  main  fissure.  I  find  no 
geological  evidence  of  this,  however,  either  in  the  structural 
•conditions  or  in  the  composition  of  the  vein-material. 

The  fissures  show  plentiful  evidence  of  movement  in  stria- 
tions  and  crushed  country-rock,  the  ore  being  a  filling-in  of  the 
interstices  between  the  quartzite  fragments,  and  perhaps  a 
partial  replacement  of  the  same.  The  principal  fissure  con- 
sists in  places  of  a  zone  of  broken  quartzite,  sometimes  over 
100  ft.  wide,  the  ore  being  distributed  in  seams  along  the 
boundaries  of  this  zone  and  crossing  it  along  a  somewhat 
irregular  series  of  planes,  but  in  which  a  certain  co-ordination 
of  system  can  be  traced. 

Three  distinct  series  of  dynamic  movements  can  be  traced  in 
the  structural  condition  of  this  mine.  The  first  is  proved  by 
the  existence  of  a  narrow  dike  of  older  porphyry,  crossing  at 
right  angles  the  western  part  of  the  vein-fissures,  where  the 
two  members  are  about  600  ft.  apart.  This  is  locally  called 
the  trap  dike,  from  its  somewhat  darker  color  than  the  other 
porphyry  bodies.  By  the  second  series  of  movements  the 
vein-fissures  themselves  were  produced  and  this  trap  dike  was 


62  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

faulted  and  displaced.  On  the  600-ft.  or  drain-level  of  the 
mine  this  displacement  can  be  observed  in  each  of  the  principal 
fractures.  The  lateral  or  horizontal  movement  is  about  40  ft., 
and,  as  the  striation-surfaces  across  the  face  of  the  dike  are 
inclined  at  an  angle  of  about  45°  with  the  horizon,  it  may  be 
assumed  that  the  vertical  movement  was  of  the  same  amount. 
The  third  dynamic  movement  is  shown  by  what  is  locally  called 
the  "  dislocating  fissure,"  which  runs  in  the  same  general 
direction  with  the  western  part  of  the  vein,  and  on  the  drain- 
level  is  intermediate  between  the  two  veins,  cutting  and  dis- 
placing the  cross-fissures. 

There  are  also  large  faults  in  the  country-rock  at  both  ends 
of  the  workings,  which  now  have  a  linear  extent  along  the 
vein-fissure  of  about  6,000  ft.  I  had  not  time  to  determine  de- 
finitely to  which  period  of  movement  these  last  faults  belong. 

A  careful  and  accurate  study  of  the  structural  relations  of 
this  most  important  mine,  of  which  the  above  is  only  a  hasty 
glimpse,  gathered  during  a  couple  of  visits  to  a  part  only  of 
the  underground  workings,  would  form  a  most  valuable  con- 
tribution to  our  knowledge  of  vein-structure. 

Another  mine  recently  visited  by  me,  whose  structural  condi- 
tions seem  peculiarly  instructive,  is  the  Queen  of  the  West 
mine,  near  Kokomo,  in  the  Ten-Mile  district  of  Colorado.  '  It 
is  situated  on  the  steep  southeast  face  of  a  shoulder  of  Jacque 
mountain,  and  the  vein-fissure  runs  nearly  parallel  with  this 
slope,  or  in  a  northeasterly  direction,  and  has  been  explored  to 
a  length  of  about  2,000  ft.  It  stands  nearly  vertical,  thus 
crossing  about  at  right  angles  the  sedimentary  beds  in  which 
it  occurs,  and  which  have  a  slight  dip  eastward,  or  down  the 
slope  of  the  hill.  These  beds  consist  of  sandstone,  rather  rich 
in  feldspar,  some  shaly  beds,  and  intrusive  sheets  of  porphyry 
generally  conformable  with  the  stratification  of  the  sedimentary 
beds. 

The  faulting  of  these  rocks  has  taken  place  not  along  a 
single  plane,  but  along  a  series  of  parallel  and  closely  con- 
tiguous planes.  In  other  words,  by  the  dynamic  movement 
the  country-rocks  have  been  divided  into  thin  sheets,  each  of 
which  has  moved  past  the  other  a  certain  distance,  and  in  the 
central  part  of  the  fissured  zone  the  interstices  between  the 
sheets  have  been  filled  with  vein-material  and  the  sheets  them- 


STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS.  68 

selves  decomposed,  impregnated,  and  to  a  greater  or  less  extent 
replaced  by  it.  There  results  a  condition  of  things  which  is 
extremely  puzzling  for  the  miner  who  expects  to  find  his  ore 
between  well-defined  walls.  Walls  there  are  in  abundance, 
and  of  excellent  definition  at  times ;  but  no  one  wall  can  be 
followed  continuously  for  any  great  distance.  Experience  has, 
therefore,  taught  those  who  are  managing  the  mine,  while  they 
follow  in  their  main  drifts  or  levels  as  nearly  as  possible  the 
center  of  the  mineralized  zone  or  vein,  to  run  frequent  and  ex- 
tended cross-cuts  on  both  sides  of  this  central  drift,  which  have 
disclosed  ore-bodies  running  parallel  with  it,  now  on  one  side, 
now  on  the  other,  and  often  from  15  to  25  ft.  distant  from  it. 
The  longer  cross-cut  drifts,  which  have  been  run  30,  50,  or 
even  100  ft.  into  the  adjoining  country-rock,  disclose  a  series 
of  parallel  fissures,  in  general  farther  apart  as  the  distance 
from  the  central  drift  increases.  Although  mostly  barren  of 
pay-ore,  they  always  give  evidence  of  a  certain  amount  of 
mineralization  :  sometimes  they  are  filled  by  a  vein  of  massive 
crystalline  calc  spar  from  a  few  inches  to  a  foot  in  thickness. 
In  the  portion  above  the  water-level,  owing  to  the  secondary 
decomposition  of  both  ore  and  country-rock,  and  to  the  diffu- 
sion of  metallic  oxides  which  have  stained  the  whole,  it  is  often 
difficult  to  recognize  whether  partly-replaced  portions  of  the 
vein-material  were  originally  sandstone  or  porphyry.  The  out- 
crops of  no  less  than  four  sheets  of  the  latter  rock  have  been 
traced  on  the  surface ;  but,  owing  to  the  complicated  move- 
ments along  the  fissured  zone,  there  would  appear  at  first 
glance  to  be  many  more  there;  for  not  only  do  the  walls 
change  from  sandstone  to  porphyry  and  vice  versa,  in  alternate 
levels,  but  on  one  and  the  same  level  one  finds  these  rocks 
alternating  with  each  other  in  an  apparently  unaccountable 
manner  in  either  wall.  One  can  conceive  of  such  a  thing  as 
resulting  from  the  movements  described  above,  combined  with 
the  gentle  inclination  of  the  beds ;  but  to  represent  it  accu- 
rately on  paper  would  require  most  full  and  accurate  surveys 
and  detailed  studies  along  every  drift,  map  in  hand. 

A  second  and  apparently  quite  recent  dynamic  movement  is 
evidenced  by  a  faulting  of  the  vein-fissures  in  the  upper  part  of 
the  mine.  The  displacement  is  slight  in  amount,  and,  what  is 
rather  unusual,  it  is  along  a  nearly-horizontal  plane.  As  this 


64  STRUCTURAL    RELATIONS    OF    ORE-DEPOSITS. 

plane  dips  gently  east,  it  is  probable  that  it  is  a  movement 
along  a  bed  of  decomposed  shale,  rendered  slippery  by  the 
percolating  of  surface-waters. 

Similar  horizontal  faults  along  stratification-planes  were  ob- 
served by  me  in  some  of  the  gold-veins  of  the  north  slopes  of 
Mt.  Guyot,  east  of  Breckenridge,  Colo.  By  these  the  veins  are 
faulted  in  a  series  of  gently-inclined  steps,  only  a  few  feet  wide, 
the  movement  following  the.  stratification-planes.  The  veins 
themselves  are  narrow  cracks  in  a  dense  blue-black  argillaceous 
shale  of  Cretaceous  age.  Owing  to  the  insoluble  character  of 
the  country-rock,  there  has  been  comparatively  little  replace- 
ment of  it  by  the  mineral-bearing  solutions.  Sulphurets  of 
iron  and  gold  have  been  deposited  in  narrow  fissures,  seldom 
over  an  inch  thick,  and  by  secondary  decomposition  the  iron  is 
oxidized  and  the  gold  left  in  the  form  of  leaf-  or  wire-gold. 
Sometimes  a  mat  of  interwoven  wires  of  gold,  an  inch  thick  and 
larger  than  the  palm  of  the  hand,  is  found.  Small  quantities 
of  gold  have  been  deposited  along  the  minute  natural  joints  of 
the  shales  also,  so  that  extraordinarily  rich  placers  have  re- 
sulted from  their  disintegration  and  abrasion  by  atmospheric 
agents. 

Many  more  instances  of  different  structural  conditions  might 
be  presented  did  space  and  time  allow ;  but  I  think  the  above 
are  sufficient  to  illustrate  the  main  proposition  which  I  wish  to 
lay  down,  namely :  that  careful  structural  study  of  the  district 
in  which  a  mine  occurs  and  of  the  manner  in  which  the  water- 
passages  were  formed,  which  originally  gave  access  to  the 
mineral-bearing  solutions,  is  of  the  greatest  importance  to  the 
mining  engineer  in  his  determination  of  the  probable  extent 
and  value  of  a  deposit  and  of  the  best  method  of  exploiting  it. 
Hence,  that  he  must  be  something  of  a  structural  geologist,  as 
well  as  a  technical  mining  engineer. 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  65 


No.  3. 


Geological  Distribution  of  the  Useful  Metals  in  the 
United  States. 

BY  S.   F.    EMMONS,   WASHINGTON,   D.    C. 

{Chicago  Meeting,  being  part  of  the  International  Engineering  Congress,  August,  1893. 
Trans.,  xxii.,  53.    Here  reprinted  in  extract  only.) 

THE  first  paper  which  appears  in  the  published  Transactions 
of  our  Institute  is  that  read  by  our  respected  Secretary  at  its 
first  meeting  in  Wilkes-Barre,  in  May,  1871.  It  is  entitled 
The  Geological  Distribution  of  Mining  Districts  in  the  United 
States,  and  presents  a  brief  but  masterly  review  of  what  was 
known  of  the  distribution  of  our  deposits  of  useful  minerals, 
particularly  the  metals,  not  only  from  a  geographical  but  from 
a  geological  stand-point. 

At  the  request  of  Dr.  Raymond,  I  agreed,  somewhat  hastily, 
perhaps,  to  write  for  this  occasion  a  brief  sketch  of  the  geo- 
logical distribution  of  the  deposits  of  the  useful  metals  in  this 
country,  in  the  light  of  the  increased  knowledge  of  the  present 
day.  In  the  time  given  no  personal  investigation  was  possible, 
and  as  it  was  therefore  out  of  the  question  to  attempt  to  make 
anything  that  could  be  considered  an  original  contribution  to 
the  history  of  our  ore-deposits,  I  have  been  obliged  to  limit 
myself  to  an  examination  of  such  published  data  within  my 
reach  as  bore  upon  this  subject,  and  could  be  consulted  in  the 
brief  time  I  have  been  able  to  give  to  it.  Had  the  geological 
investigations  undertaken  by  the  Tenth  Census  been  continued 
systematically  by  the  United  States  Geological  Survey  or  by 
the  Eleventh  Census,  it  might  have  been  possible  to  make  a 
fairly-complete  review  of  the  subject.  As  it  is,  the  principal 
result  of  my  examination  *  has  been  to  show  how  very  unequal 

1  It  would  occupy  too  much  space  to  give  a  complete  list  of  the  various  papers 
and  authors  consulted  in  this  examination,  and  it  must  suffice  to  say  that  they 
have  been  found  for  the  most  part  in  the  publications  of  the  following  organiza- 
tions :  Tenth  and  Eleventh  Census,  Director  of  the  Mint,  various  United  States 
and  State  Geological  Surveys,  American  Institute  of  Mining  Engineers,  Colorado 
Scientific  Society  ;  and  in  the  American  Journal  of  Science,  American  Geologist, 
Engineering  and  Mining  Journal,  Zeitschrift  fur  praktische  Geologic,  etc. 

5 


66  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

and  in  many  directions  extremely  meager  are  the  data  of  any 
kind  that  are  available,  and  to  demonstrate  the  great  need 
that  exists  for  a  systematic  investigation  of  this  important  sub- 
ject by  some  scientific  organization,  for  its  field  is  too  vast  to 
be  covered  by  any  single  individual,  and  such  an  investigation 
will  be  of  little  permanent  value  unless  carried  out  on  some 
uniform  plan  by  which  the  relative  accuracy  of  its  results  may 
be  assured. 

The  utmost  that  I  can  hope,  therefore,  for  the  very  imper- 
fect, and  from  a  statistical  stand-point  possibly  somewhat  inac- 
curate, review  here  presented,  is  that  it  may  offer  to  other 
workers  in  the  field  a  suggestion  of  lines  of  investigation  that 
may  be  profitably  pursued  in  the  future. 

In  the  22  years  that  have  elapsed  since  Dr.  Raymond's  paper 
was  written,  many  important  contributions  have  been  made  to 
our  knowledge  of  the  geological  structure  of  the  continent,  but 
a  great  part  of  these  contributions,  especially  in  late  years, 
have  been. rather  in  the  line  of  modifications  and  reversals  of 
preconceived  theories,  than  in  the  firm  establishment  of  new 
ones.  We  seem  now  to  have  removed  most  of  the  unstable 
stones  from  the  foundation  of  our  geological  knowledge,  and 
to  be  nearly  ready  to  build  up  a  permanent  structure  in  the 
immensely  enlarged  field  that  progress  in  various  lines  has 
opened  to  us.  In  like  manner  the  special  study  of -ore-deposits 
and  of  their  relations  to  geological  structure,  which  had  hitherto 
been  rather  neglected  by  field-geologists,  has  in  the  last  decade 
received  more  attention,  though  perhaps  not  as  much  as  it  de- 
serves ;  many  false  conceptions  have  been  cleared  away,  and 
important  progress  has  been  made  towards  a  more  rational 
method  of  correlating  their  phenomena. 

In  the  realm  of  eruptive  or  igneous  rocks,  the  great  change 
that  has  come  about  has  been  the  gradual  abandonment  of  the 
theory  that  the  mineralogical  or  structural  character  of  the  rock 
is  a  criterion  of  its  age.  It  is  no  longer  a  necessary  conclu- 
sion, for  example,  that  because  a  rock  is  a  trachyte,  rhyolite, 
or  basalt,  it  is  of  Tertiary  or  later  age.  Well-defined  rocks  of 
types  formerly  classed  as  Tertiary  have  been  found  to  be  as  old 
as  Cambrian,  and  the  petrographical  character  of  a  rock  is  now 
admitted  to  be  dependent  on  other  causes  besides  geological 
age.  It  still  holds  good  that  most  of  the  so-called  volcanic 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  67 

rocks  are  of  Tertiary  or  recent  eruption,  but  many  crystalline 
rocks,  actually  granitoid  in  structure,  are  also  of  Tertiary  age, 
and  it  is  now  necessary  for  the  geologist  -to  determine  the  age 
of  the  various  eruptives  of  each  district  by  their  relations  to 
sedimentary  rocks  of  known  age. 

From  the  internal  structure  of  the  eruptive  rock,  whether 
more  or  less  completely  crystalline,  one  can  judge  whether  it 
has  consolidated  at  considerable  depths  and  under  the  pressure 
of  great  weight  of  superincumbent  rock-masses,  hence  very 
slowly,  or  at  or  near  the  surface  and  with  comparative  rapidity. 
In  many  cases  this  furnishes  a  further  aid  in  the  determination 
of  the  relative  age  of  different  varieties  of  eruptive  rock  occur- 
ring in  a  given  region. 

As  regards  the  origin  of  eruptive  rocks  and  the  determina- 
tion of  the  natural  order  of  succession  of  the  many  types  dis- 
tinguished by  their  different  chemical  and  mineralogical  com- 
position, most  of  the  theories  hitherto  held  are  gradually  being 
discarded  or  merged  into  what  may  be  called  the  theory  of 
differentiation  of  igneous  magmas,  which  is  now  being  worked 
out  by  the  more  advanced  petrologists  in  this  country  and  in 
Europe,  and  which  promises  to  throw  important  light  upon 
the  origin  of  ore-deposits  also.  It  proceeds  from  what  is 
known  as  Soret's  principle,  that  in  a  cooling  solution  of  a  salt, 
the  salt  will  concentrate  in  the  parts  of  the  solution  which  cool 
first,  and  reasons  that  in  a  molten  rock-magma  a  similar  sepa- 
ration or  differentiation  of  substances  may  take  place.  For  in- 
stance, it  has  long  been  observed  that  in  eruptive  dikes  of 
moderate  dimensions,  those  portions  of  the  dike  adjoining  the 
walls,  which,  when  the  matter  forming  the  dike  was  injected, 
may  be  supposed  to  have  been  relatively  cold,  have  a  finer- 
grained  texture  than  the  interior  of  the  dike,  and  in  certain 
cases  there  is  a'concentration  of  the  more  basic  minerals  com- 
posing the  general  mass  in  the  outer  zone  or  in  different  parts 
of  the  rock-mass.  It  is  assumed  that  on  a  larger  scale  the 
different  varieties  of  eruptive  rock  which  belong  to  one  general 
period  of  eruption  in  a  given  district  and  are,  so  to  speak,  con- 
sanguineous, proceed  from  one  general  molten  magma  in  the 
depths  of  the  earth ;  and  that  in  this  magma  a  chemical  and 
mineralogical  differentiation  takes  place  by  virtue  of  which 
each  successive  eruption  of  igneous  rocks  differs  in  character 


68  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

from  the  one  which  has  preceded  it,  according  to  laws  not  yet 
fully  made  out,  but  which,  according  to  the  preponderance  of 
chemically  acid  or  basic  material,  under  varying  conditions, 
produce  in  the  erupted  rock  a  corresponding  preponderance  of 
acid  or  basic  minerals. 

On  the  other  hand,  considerable  advance  has  been  made  in 
the  classification  of  the  crystalline  rocks,  which  were  formerly 
all  grouped  indefinitely  as  Archsean.  More  detailed  and 
systematic  field-studies  in  the  areas  occupied  by  typical  series 
of  crystalline  rocks  have  shown  that  there  are  several  series 
that  can  be  distinguished  as  originally  sediments  made  up  of 
debris  of  older  series,  with  a  greater  or  less  proportion  of  erup- 
tive material,  in  which  there  is  evidence  of  the  former  existence 
of  organic  life,  and  which  are  older  than  the  oldest  known 
Cambrian  beds,  and  younger  than  Archaean,  the  latter  term 
being  limited  to  non-clastic  rocks,  in  which  there  is  no  evidence 
of  life.  Petrological  investigation,  in  the  light  of  the  most  ad- 
vanced studies  in  this  branch  of  geology,  has  shown  the  enor- 
mous capabilities  of  metamorphism,  in  that  a  crystalline  and 
more  or  less  schistose  product  may  result  from  the  alteration 
of  either  sedimentary  or  eruptive  rocks,  the  original  form  of 
which  may  be  entirely  undeterminable  if  such  rock  cannot  be 
traced  continuously  in  the  field  to  some  less  altered  condition 
in  which  sufficient  traces  of  its  original  character  can  be  found 
to  admit  of  its  satisfactory  determination.  As  a  result  of  these 
investigations,  so  much  discredit  has  been  thrown  upon  the 
classification  and  subdivisions  of  Eastern  crystalline  rocks  by 
Hunt  and  his  school,  which  were  based  on  petrological  distinc- 
tions now  shown  to  be  unessential  and  local  in  their  character, 
that,  until  the  areas  covered  by  them  have  been  systematically 
and  carefully  studied,  the  relative  age  of  different  parts  of  the 
series  must  remain  a  matter  of  doubt.  In  a  few  cases,  fossil 
evidence  has  been  found  in  the  Appalachian  areas  to  show  that 
certain  crystalline  beds  are  altered  sediments  of  Cambrian  or 
later  age.  In  others,  remains  of  organic  life  have  been  found 
which  are  older  than  any  known  Cambrian  forms.  In  most 
cases,  however,  it  can  only  be  determined  on  stratigraphical 
grounds  or  lithological  evidence  that  the  rocks  in  question  are 
older  than  any  known  Cambrian,  and  younger  than  the  funda- 
mental complex  of  non-clastic  crystallines  for  which  the  term 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  69 

"  Archaean"  is  still  retained.     To  these  rock-series  the  general 
designation  "Algonkian"  has  been  given. 

The  Algonkian,  as  thus  defined,  necessarily  includes  a  great 
many  rock-series  in  different  parts  of  the  continent,  which,  in 
the  absence  of  palseontological  evidence,  cannot  be  correlated 
in  age,  and  whose  relative  succession  must  be  determined  in 
each  geological  province  separately  and  by  itself.  They  have 
been  thus  far  systematically  studied  only  in  the  Lake  Superior 
region,  where  the  new  classification  was  first  proposed  by  Irving 
and  Van  Hise.  Here  they  consist  of  an  aggregate  thickness  of 
over  60,000  ft.  of  rocks,  in  which  three  general  subdivisions, 
separated  by  great  unconformities  or  time-breaks,  have  thus 
far  been  recognized,  the  Keweenawan  or  copper-bearing  series, 
which  consists  of  sandstones,  conglomerates,  lavas,  and  tuffs, 
being  the  upper,  and  resting  unconformably  upon  the  two  great 
iron-bearing  series,  the  Upper  and  Lower  Huronian,  which  in- 
clude all  the  at  present  economically  important  iron-deposits  of 
the  region.  Two,  and  possibly  three,  series  of  Algonkian  rocks, 
each  of  great  thickness,  and  some  showing  a  large  development 
of  eruptive  rocks,  have  been  recognized  in  the  Eocky  moun- 
tains, but  for  the  Appalachians,  where  geological  study  is 
rendered  more  difficult  by  the  intense  complications  of  struc- 
ture, great  metamorphism,  and  deep  covering  of  weathered 
material  and  soil,  it  can  only  be  said  as  yet  that  certain  rocks 
hitherto  called  Archaean  are  certainly  either  altered^Palseozoic 
or  Algonkian,  while  of  the  greater  part  it  remains  for  further 
study  to  determine  whether  they  belong  to  either  of  these 
systems  or  may  properly  be  classed  as  Archaean. 


Genesis  of  Iron-Deposits. 

It  has  always  been  a  matter  of  wonder  to  the  geologist,  as 
well  as  to  the  layman,  how  such  enormous  concentrations  of 
metallic  minerals  as  occur  in  the  great  iron-mines  could  be 
brought  about,  and  whence  their  materials  could  have  been 
derived.  In  the  light  of  the  more  exact  studies  of  modern 
times,  the  easy  reference  of  such  knotty  questions  to  the  "  un- 
known source  in  depth  "  is  no  longer  available,  especially  since, 
in  the  case  of  the  Lake  Superior  deposits,  the  last  stronghold 
of  the  little  band  of  geologists  who  still  maintained  the  erup- 


70  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

tive  origin  of  iron-ores,  the  careful  and  systematic  researches 
of  Irving  and  Van  Hise  have  demonstrated  that  the  supposed 
eruptive  bodies  of  iron  oxide  have  been  deposited  from  aque- 
ous solutions  as  replacements  of  carbonates,  and  that  the 
eruptive  contact-phenomena  result  from  the  fact  that  the  in- 
closing rocks,  instead  of  the  iron-ores  themselves,  are  of 
igneous  origin. 

That  iron-minerals,  such  as  pyrite,  magnetite,  and  ilmenite, 
are  frequent  and  almost  universal  constituents  of  eruptive 
rocks,  is  well  known,  but  they  occur  as  original  constituents 
of  the  rock,  that  have  formed  within  its  mass  more  or  less  con- 
temporaneously with  the  other  mineral  constituents,  and  not  as 
later  injections  into  an  already  consolidated  rock-mass ;  whereas, 
critical  studies  of  existing  ore-deposits  have  so  universally 
proved  them  to  be  of  distinctly  later  origin  than  the  inclosing 
rocks,  that  the  burden  of  proof  lies  upon  those  who  would  main- 
tain a  contemporaneous  origin  for  any  particular  deposit.  The 
truly  scientific  method  in  the  study  of  such  questions,  at  the 
present  day,  is  the  reverse  of  that  which  was  followed  in  the 
early  days  of  geology,  when,  after  the  observation  of  a  few 
isolated  facts,  some  great  geological  mind  was  led  to  a  general 
theory,  and  humbler  followers  were  only  too  apt  to  do  mild 
violence  to  nature  in  order  to  make  her  facts  conform  to  it.  It 
accumulates,  year  after  year,  a  multitude  of  facts  of  patient  ob- 
servation, gupported  by  studies  with  the  microscope  and  in  the 
laboratory,  avoiding  general  theories,  an^.  only  making  such 
deductions  in  regard  to  local  conditions  as  are  supported  by  the 
overwhelming  evidence  of  facts. 

Although  we  are  yet  far  from  having  a  sufficient  accumula- 
tion of  facts  bearing  upon  the  origin  of  iron-ores  to  justify  the 
putting  forth  of  any  general  theory,  it  may  be  allowable  in  the 
present  case  to  indicate  the  lines  of  research  to  which  the  facts 
that  have  lately  been  accumulated  seem  to  point  as  promising 
the  most  remunerative  results. 

A  great  deal  of  light  has  been  thrown  upon  the  manner  of 
formation  of  iron-ore  deposits  by  the  researches  of  Irving  and 
Van  Hise  in  the  Lake  Superior  region,  and  by  the  discussion 
of  replacement  of  limestones  by  iron-ores  in  general  by  J.  P. 
Kimball.  By  both,  the  process  of  formation  of  workable  iron- 
ore  deposits  is  regarded  as  a  concentration  by  the  agency  of 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  71 

percolating  waters,  such  concentration  being  influenced  by 
physical  or  structural  conditions,  and  localized,  it  may  be,  by  a 
pre-existing  nucleus  of  iron-bearing  minerals  as  original  con- 
stituents of  the  rock.  The  deposition  is  considered  to  be  in 
very  large  degree  a  metasomatic  replacement  of  the  rock-mate- 
rial, and  only  to  a  very  limited  extent  a  deposition  in  pre-exist- 
ing open  cavities. 

For  the  Marquette  region,  it  is  found  that  though  the  Lower 
Huronian  carried  iron  originally,  the  concentration  into  work- 
able deposits,  of  both  this  and  the  Upper  Huronian  series,  was 
brought  about  subsequent  to  folding  and  erosion,  and  that 
hence  the  age  of  the  deposits  as  such  is  Upper  Huronian  or 
later.  Evidence  is  also  found  that  the  deposition  was  a  second- 
ary concentration  from  waters  percolating  downward  along 
the  paths  of  great  water-channels  until  stopped  by  some  im- 
pervious base.  The  original  condition  of  the  ore  is  regarded 
as  probably  iron  carbonate,  though  it  is  admitted  that  this  may 
have  been  a  replacement  of  calcium  carbonate. 

In  the  Palaeozoic  limestones  and  shales  of  the  Appalachians, 
•the  iron-bearing  solutions  appear  in  most  cases  to  have  been 
also  downward-going  currents,  or  water  sinking  from  the  sur- 
face under  the  influence  of  gravity,  rather  than  hot  ascending 
solutions.  The  original  mineral  was  the  carbonate  or  the  sul- 
phide of  iron  (pyrrhotite  or  pyrite),  and  instances  are  adduced 
where  the  limestones  carry  in  their  mass  over  2  per  cent,  of 
iron  carbonate,  and  in  other  cases  pyrite  is  known  to  occur  in 
about  the  same  proportion.  Whether  these  minerals  were 
chemically  or  mechanically  deposited  with  the  limestones  or 
were  introduced  subsequently  remains  to  be  determined,  but  it 
appears  improbable  that  deposits  (of  sufficient  size  to  consti- 
tute workable  deposits)  were  formed  simultaneously  with  the 
inclosing  rocks  by  chemical  precipitation  from  sea- waters. 

If  it  be  admitted,  then,  that  our  workable  deposits  of  iron- 
ore  are  mainly  concentrations  of  iron-minerals  already  dissemi- 
nated in  sedimentary  beds,  and  that  these  concentrations  have 
occurred  in  different  forms  and  places  according  to  varying 
local  structural  Or  chemical  conditions,  it  still  remains  to  be 
determined  what  was  the  original  source  of  the  iron  in  different 
regions,  and  why  the  concentrations  are  so  much  greater  in  one 
place  than  in  another. 


72  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

A  line  of  investigation  that  seems  to  promise  interesting 
results  is  suggested  by  recent  researches  by  Swedish  geologists 
on  the  formation  of  concentrations  of  titaniferous  ore  by  the 
so-called  differentiation  process  in  basic  eruptive  magmas.  In 
Sweden  and  Norway,  according  to  them,  actually  workable 
deposits  of  titaniferous  iron  have  been  formed  by  differentia- 
tion within  the  eruptive  magmas  of  labradorite,  hypersthene,  or 
olivine  rocks.  Van  Hise  had  already  suggested  for  the  titanif- 
erous magnetites  of  the  eruptive  gabbro  of  Lake  Superior  that 
in  the  crystallization  of  these  rocks,  before  the  magma  had 
solidified,  magnetite,  which  is  one  of  the  early  minerals  to 
separate,  had  slowly  settled  to  the  base  of  the  mass  by  virtue 
of  its  superior  specific  gravity.  But  it  is  still  questionable 
whether  in  this  differentiation  process  gravity  is  a  controlling 
influence,  since  in  most  observed  cases  it  is  evident  that  some 
other  force  must  have  influenced  the  concentration.  Metallic 
concentrations  in  eruptive  rocks  have  been  observed  before, 
the  most  remarkable  of  which  is  the  body  of  metallic  iron  at 
Ovifak  in  Greenland.  Although  in  these  cases  the  ores  may 
properly  be  said  to  be  of  eruptive  origin,  it  may  still  be  doubted 
whether  their  concentration  as  workable  deposits  is  not  due, 
in  a  measure  at  least,  to  secondary  action,  as  has  been  observed 
in  the  case  of  the  Lake  Superior  gabbros. 

While,  therefore,  one  may  not  necessarily  expect  to  find 
economically-valuable  deposits  in  such  rocks,  the  question 
naturally  suggests  itself  whether  the  occurrence  of  large  areas 
of  older  basic  eruptives,  which  in  some  parts  contain  a  rela- 
tively large  proportion  of  iron-bearing  minerals,  may  not  fairly 
be  considered  to  be  an  indication  that  neighboring  sedimentary 
beds  may  contain  large  concentrations  of  iron-ores,  which  have 
been  derived  from  them.  Where  such  basic  eruptives  are  older 
than  the  beds,  this  derivation  would  be  mainly  mechanical,  the 
ores  being  sediments  resulting  from  the  abrasion  of  the  erup- 
tives, more  or  less  concentrated  according  to  varying  condi- 
tions of  sedimentation.  Where  the  eruptives  are  younger  and 
have  broken  through  or  overflowed  the  sedimentary  beds,  the 
derivation  would  be  mainly  chemical,  through  leaching-out 
and  redeposition  by  the  agency  of  percolating  waters. 

While  there  seems  to  be  some  genetic  connection  between 
the  greatest  concentrations  of  iron-ore  and  considerable  devel- 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  73 

opments  of  ancient  basic  eruptives,  important  deposits  also 
occur  where  no  such  relation  can  be  traced.  The  frequent 
association  of  iron-deposits  in  the  West  with  large  bodies  of 
eruptive  diorite,  suggests  that  though  the  very  basic  rocks 
would  naturally  afford  the  greatest  amount  of  iron,  even  a  rela- 
tively acid  rock,  like  diorite,  may  contain  concentrations  by 
differentiation,  which  have  yielded  to  the  action  of  percolating 
waters  and  thus  allowed  their  basic  constituents  to  be  trans- 
ferred to  easily-soluble  rocks  like  limestone. 

Since  water  is  the  principal  agent  in  the  final  concentration 
of  ore-deposits,  it  is  important  in  searching  for  them  to  study 
the  physical  conditions  which  will  favor  its  ready  action  both 
in  taking  up  and  in  throwing  down.  In  the  Northwest,  Van 
Hise  has  found  an  impervious  basement  a  general  favoring 
condition.  This  assumes  downward  percolation,  but  within 
the  crust  of  the  earth  the  circulation  of  waters  may  be  in  any 
direction,  according  to  local  conditions.  It  may  possibly  be 
safe  to  assume  that  iron-ores  which  occur  mainly  as  oxides- 
would  have  been  deposited  from  oxidizing  waters  or  those 
which  come  recently  from  the  surface,  and  that  pyritous  ores 
would  be  more  likely  to  bespeak  a  derivation  from  subterra- 
nean waters.  Types  of  the  former  are  furnished  by  the  Lower 
Silurian  ores  which  pass  in  depth  into  ferriferous  limestone, 
and  are  apparently  a  concentration  due  to  leaching  by  surface- 
waters,  in  which  other  minerals  have  been  removed  in  greater 
proportion  than  the  iron  oxide.  The  so-called  gossan-ores  oc- 
curring in  the  eastern  or  metamorphic  belt  of  the  Appalachians, 
and  which  pass  into  pyritous  ores  in  depth,  would  appear  to  be 
good  types  of  the  latter  class. 

Much  remains  yet  to  be  done  in  the  study  of  the  structural 
relations  of  iron-ore  deposits.  One  of  the  interesting  problems 
is  furnished  by  the  line  of  magnetic  deposits  occurring,  in 
Pennsylvania  and  southward,  in  limestones  at  the  contact 
of  Mesozoic  sandstones,  and  frequently  associated  with  trap 
dikes.  If  this  prove  to  be  a  line  of  displacement,  as  there 
seems  to  be  reason  to  assume,  it  would  afford  a  natural  water- 
channel  for  the  collection  of  iron-bearing  waters  from  various 
series  of  iron-bearing  rocks,  which  would  preferably  collect  in 
limestones,  and  more  readily  from  their  broken  edges.  "Whether 
the  function  of  the  trap  has  been  to  furnish  heat  for  magneti- 


74  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

zation  of  the  iron  oxides,  as  has  been  frequently  assumed,  or 
to  interrupt  the  ore-bearing  currents  and  thereby  induce  pre- 
cipitation, may  well  be  the  subject  of  further  investigation. 

There  is  reason  to  assume  that  the  concentration  of  iron- 
ores  in  the  more  southern  parts  of  the  Appalachians,  especially 
in  the  extremely  complicated  regions  of  the  Carolinas,  Ten- 
nessee, Alabama,  and  Georgia,  will  be  found  to  have  more  or 
less  intimate  structural  relations  with  the  many  fault-zones 
that  abound  there. 

A  careful  study  of  the  magnetite-deposits  in  Colorado  is 
likely  to  throw  some  light  upon  the  true  genetic  connection, 
if  any  exists,  between  the  occurrence  of  this  oxide  and  the  vi- 
cinity of  eruptive  bodies.  In  the  light  of  present  knowledge 
it  would  appear  that  the  iron-ores  occur  as  magnetite  in  the 
vicinity  of  large  bodies  of  eruptive  diorite  and  as  limonite 
elsewhere  at  the  same  horizon.  It  has  been  asserted,  more- 
over, that  there  is  no  evidence  of  an  intermediate  hematite  or 
limonite  stage  in  the  alteration  from  pyrite  to  magnetite.  As 
against  the  theory  that  in  these  cases  the  formation  of  the 
magnetic  oxide  is  due  to  the  heat  of  the  eruptive  body,  it  is 
probable,  in  the  opinion  of  the  writer,  that  these  ores  have 

been  concentrated  since  the  eruption  of  the  diorite. 

********** 

Genesis  of  Manganese-Deposits. 

The  same  lines  of  genesis  suggest  themselves  for  manganese 
as  for  iron,  but  owing  to  its  much  smaller  percentage  as  a  con- 
stituent of  original  rocks,  it  will  be  less  easy  to  detect  the 
probable  localities  favorable  for  secondary  concentration  in 
workable  bodies. 

In  this  secondary  concentration  the  study  of  structural  con- 
ditions which  would  produce  natural  water-channels  is  equally 
important.  It  has  already  been  observed  that  the  manganese- 
ores  of  the  southern  Appalachians  occur  along  a  great  faulted 
zone,  and  the  frequent  mention  of  breccia  conditions  in  other 
deposits  suggests  that  further  study  may  show  that  the  concen- 
trations of  this  mineral,  as  well  as  of  iron,Jiave  been  along  such 
lines  of  displacement  more  frequently  than  has  been  hitherto 
realized. 

In  the  relative  chemical  behavior  of  the  salts  of  manganese 


GEOLOGICAL  DISTRIBUTION  OF  THE  USEFUL  METALS.     75 

and  iron  in  terrestrial  economy  there  are  certain  unexplained 
contrasts  which  would  appear  to  offer  remunerative  results  to 
those  who  would  occupy  themselves  with  its  study. 


Genesis  of  Nickel-Deposits. 

The  frequent  connection  in  nature  of  nickel  and  magnetic 
pyrites,  and  of  nickel  with  native  iron  and  magnesia,  in  meteor- 
ites and  at  Ovifak  in  Greenland,  is  suggestive  of  an  intimate 
connection  between  the  two  metals  in  fused  magmas.  The 
frequent  occurrence  of  its  silicate  ores  in  connection  with  ser- 
pentine and  associated  with  chrome  and  magnetic  iron  has 
often  been  remarked  by  geologists  and  chemists  as  pointing  to 
a  genetic  connection  between  these  minerals  and  magnesian 
silicate  rocks.  It  is  to  be  noted,  however,  that  both  the  silicate 
of  nickel  and  serpentine  are  secondary  products.  Serpentine 
is  known  to  result  from  the  metamorphism  of  many  rocks,  both 
eruptive  and  sedimentary,  most  commonly  from  basic  magne- 
sian silicate  rocks  in  the  first  case,  and  from  calcareous  sedi- 
mentary rocks.  The  silicates  of  nickel  may  well  be  assumed  to 
have  resulted  from  the  secondary  alteration  of  sulphides,  if  the 
assumption  is  correct,  that  in  those  cases  where  it  so  occurs  in 
association  with  magnetic  pyrites  the  neighboring  basic  erup- 
tives  have  not  yet  reached  the  extreme  of  serpentinous  alteration. 
As  with  iron,  therefore,  certain  portions  of  basic  eruptive 
magmas  may  be  supposed  to  have  been  relatively  rich  in  nickel- 
bearing  minerals,  and  by  secondary  concentration  these  may 
have  been  transferred  to  the  water-channels  of  adjoining  rocks. 
The  greater  this  alteration  of  the  rock  the  greater  concentration 

of  nickel-ore,  as  a  general  rule,  would  one  expect  to  find. 

********** 

Genesis  of  Copper-Deposits. 

The  observed  facts  with  regard  to  copper-deposits  seem  to 
point  to  eruptive  rocks  as  the  original  source  of  the  metal,  and 
to  indicate  that  its  original  form  in  deep-seated  concentrations 
or  deposits  was  that  of  sulphide.  There  seems  to  be  less 
ground  for  supposing  it  to  have  been  generally  disseminated  in 
marine  sediments  than  in  the  case  of  some  of  the  other  metals, 
though  very  strong  arguments  have  been  advanced  by  geolo- 


76  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

gists  of  great  ability  in  favor  of  the  theory  of  its  chemical  pre- 
cipitation from  the  waters  of  the  Triassic  ocean  by  the  agency 
of  decaying  organic  remains.  Its  concentration,  either  in  sedi- 
ments generally  or  in  ore-deposits,  seems  to  have  been  by 
chemical  rather  than  by  mechanical  processes.  The  assump- 
tion that  certain  portions  of  eruptive  magmas  are  exceptionally 
rich  in  this  and  associated  metals  furnishes  a  good  working 
basis  for  explaining  its  concentration  in  most  well-known  ore- 
deposits.  Its  chemical  behavior,  especially  in  deposition,  pre- 
sents some  peculiarities  not  always  easy  to  explain.  In  its 
ready  assumption  of  the  metallic  state,  as  in  certain  other 
actions,  it  resembles  gold  and  silver.  Pumpelly  explains  the 
absence  of  the  baser  metals  in  the  Lake  Superior  deposits  on 
the  assumption  that  the  copper  has  been  reduced  from  its  salts 
by  protoxide  of  iron,  which  would  not  have  acted  on  the  salts 
of  the  baser  metals,  which  would  have  been  carried  farther  on ; 
and  that  once  reduced  to  a  metallic  state,  the  copper  was  in  a 
condition  of  greatest  permanence  in  presence  of  the  usual  rea- 
gents. To  account  for  the  unusual  amount  of  metal  in  this 
region,  there  is  an  extraordinary  amount  of  eruptive  material 
to  draw  from,  and  unusually  intense  and  long-continued  action 
of  metamorphic  or  alterative  processes  to  produce  the  concen- 
tration. On  Keweenaw  Point,  traces  of  sulphur  are  found  in 
the  melaphyre ;  and  in  two  mines,  copper  occurs  as  sulphide 
associated  with  other  metals.  Other .  exposures  of  this  same 
series  of  rocks,  in  Wisconsin  and  Minnesota,  where  no  ore- 
deposits  have  yet  been  found,  are  said  to  carry  small  quantities 
of  metallic  copper,  associated  with  sulphides  of  iron  and 
copper. 

It  is  worthy  of  remark  that  the  native  silver  which  occurs 
with  the  copper  in  this  region  is  never  alloyed,  but  separates 
from  it  by  polling. 

The  unusual  richness  in  copper  of  the  ores  along  the  limits 
of  the  zone  of  oxidation  in  veins  at  Butte  and  in  the  Appa- 
lachians is  readily  explainable  by  the  leaching- clown  of  this 
metal  and  the  removal  of  the  less  permanent  salts  of  the  baser 
metals.  It  is  more  difficult  to  account  for  the  frequent  sudden 
appearance  and  disappearance  of  copper  at  different  parts  of  an 
unaltered  deposit  of  mixed  ores,  as  at  Leadville  and  other 
places.  There  does  seem  to  be  a  more  frequent  association  of 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  77 

•deposits  of  gold  and  copper  with  relatively  acid  rocks,  as  of 
iron,  chrome,  and  nickel  with  basic  magnesian  rocks,  but  ex- 
ceptions are  so  frequent  and  data  so  incomplete,  that  it  is 
questionable  whether  this  association  can  properly  be  assumed 
to  have  a  genetic  cause.  The  pebbles  in  the  copper-bearing 
conglomerate  of  Lake  Superior,  for  instance,  are  said  to  be 
mostly  of  acid  eruptives ;  but  this  may  result  from  the  supe- 
rior hardness  of  these  rocks  over  the  altered  basic  rocks.  In 
Leadville,  the  ores  carrying  copper  in  the  most  important  de- 
posits are  in  a  more  siliceous  limestone  than  are  those  which 
contain  no  copper,  but  other  copper-deposits  in  the  same  region 
are  in  the  more  pure  magnesian  limestone,  and  both  here  and 
in  Arizona  more  copper  is  found  in  the  relatively  basic  lime- 
stones than  in  the  adjoining  acid  eruptives. 

The  presence  of  copper  in  nature  is  so  easily  detected  on 
account  of  the  bright  colors  of  its  surface  alteration-products, 
that  it  may  be  assumed  to  have  been  so  thoroughly  prospected 
that  no  important  sources  of  the  ore  remain  undiscovered.  It 
seems  probable,  however,  that  the  belt  of  pyritous  ores  with 
limonite  caps  which  stretches  through  the  crystalline  zone  of 
the  Appalachians,  and  contains  generally  small  percentages  of 
copper,  may  yet  prove  a  source  of  this  metal  of  commercial 
importance  in  connection  with  other  products  of  these  great 
deposits. 


Genesis  of  Lead-  and  Zinc-Deposits. 

For  the  original  source  of  lead  and  zinc  there  seems  no  valid 
reason  why  we  should  not  look  to  the  massive  eruptive  rocks, 
as  in  the  case  of  other  metals.  It  is  true,  that  their  mineral 
combinations  do  not  form  prominently-visible  constituents  of 
these  rocks,  as  do  the  iron-bearing  minerals,  nor  have  concen- 
trations of  them  yet  been  discovered  which  could  be  considered 
to  be  the  result  of  differentiation  in  an  eruptive  magma.  As 
their  deposits  are  found  in  nature,  they  are  essentially  precipi- 
tations from  aqueous  solutions,  and  their  favorite  habitat  ap- 
pears to  be  sedimentary  limestones.  Moreover,  for  the  very 
extensive  and  important  deposits  of  the  Mississippi  valley  there 
.are  no  known  eruptive  rocks  within  reach  from  which  their 
metals  could  have  been  derived,  and  the  opinion  of  most  of  the 


78  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

geologists  who  have  made  careful  study  of  these  deposits  is 
that  the  metals  in  them  were  originally  deposited  with  the 
limestones  in  a  disseminated  form,  and  that  the  present  de- 
posits are  merely  concentrations  of  these  finely-disseminated 
minerals  by  downward-percolating  waters.  On  the  other  hand, 
chemical  analysis  has  detected  their  presence  in  appreciable 
amounts  in  some  eruptive  rocks  not  directly  connected  with 
ore-deposits,  which  is  sufficient  proof  that  portions  of  eruptive 
magmas  may  contain  them  as  original  constituents.  If  it  is  ad- 
mitted that  they  were  deposited  with  the  Mississippi  Valley 
limestones,  whether  chemically  or  mechanically,  they  must 
have  been  derived  from  some  earlier  rock-masses,  and  may 
well  have  resulted,  either  in  first  or  second  instance  or  even 
further  back,  from  the  disintegration  or  decomposition  of  older 
eruptive  masses.  The  latest  student  of  the  Mississippi  Valley 
deposits  (W.  P.  Jenney),  whose  most  detailed  studies  were 
made  in  the  southeastern  Missouri  region,  finds  the  fissures  in 
the  limestones  to  be  fault-fissures,  and  argues  that  they  are 
probably  deep-seated,  and  that  the  minerals  have  probably 
been  brought  up  through  these  fissures  from  some  deep-seated 
source  in  crystalline  or  eruptive  rocks  below.  The  fact  that, 
in  the  upper  Mississippi  region,  blende,  which  is  at  the  lowest 
horizon,  is  generally  of  earlier  deposition  than  galena,  might 
be  considered  an  argument  in  favor  of  this  hypothesis,  though 
it  is  explainable  otherwise.  On  the  other  hand,  their  general 
association  with  barite  in  Silurian  limestones,  and  the  fact  that 
fluorspar  is  found  with  lead  only  in  Sub-Carboniferous  lime- 
stone, is  in  so  far  an  argument  of  derivation  from  the  lime- 
stones themselves. 

In  the  West,  the  frequent  association  of  the  deposits  with 
eruptive  rocks  is  most  striking,  and  it  seems  likely  that  more 
systematic  studies  in  the  Appalachians  may  discover  a  probable 
association  of  areas  of  concentration  of  their  minerals  with 
eruptives,  from  which  they  might  indirectly  have  been  derived. 
A  most  fruitful  field  of  investigation  lies  open  here,  and  one 
that  is  comparatively  untouched,  for  no  general  truths  can  be 
derived  from  the  study  of  a  single  deposit  or  group  of  deposits, 
and,  as  yet,  the  work  either  of  individuals  or  organizations,  in 
this  country,  has  scarcely  gone  beyond  this  stage.  It  would 
also  be  interesting  to  determine  how  far  the  segregation  of  the 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  79 

minerals  of  the  two  metals  was  due  to  differentiation  in  the 
original  magma,  and  how  far  to  a  process  of  gradual  selection  in 
successive  concentrations.  In  composite  sulphide  deposits  of 
great  extent,  like  those  of  Leadville,  which  may  be  assumed  to 
be  the  first  concentration  after  that  in  the  original  magma, 
there  appears  to  have  been  a  certain  amount  of  selective  segre- 
gation by  which  certain  portions  contain  a  larger  proportion 
of  one  or  of  the  other  metal,  comparable  to  the  imperfect  sepa- 
ration of  the  first  part  of  an  ore-dressing  process.  In  the  min- 
eral economy  of  nature  there  is  a  generally-observed  tendency 
for  like  to  seek  like,  as  far  as  freedom  of  movement  admits. 
It  suggests  itself,  therefore,  that  those  deposits  which  contain 
one  metal,  to  the  practical  exclusion  of  the  other,  may  be  the 
result  of  a  succession  of  such  selective  concentrations,  and 
hence  more  removed  from  the  original  source  than  the  more 
mixed  deposits. 

********** 

Genesis  of  Quicksilver-Deposits. 

The  original  source  of  the  quicksilver  and  the  associated 
metals  is  believed  to  have  been  in  or  below  the  deep-seated 
granites.  The  deposits  are  regarded  as  having  been  precipi- 
tated from  heated  solutions  containing  sodium  sulphide,  rising 
through  fissure-systems,  by  relief  of  pressure  and  contact  with 
surface-waters.  The  quicksilver-minerals  have  been  deposited 
in  interstices  between  rock  fragments  and  in  masses  of  porous 
texture,  particularly  sandstones,  but  nothing  like  actual  mo- 
lecular substitutions  or  pseudomorphosis  has  been  observed 
either  in  California  or  in  Spain.2  In  the  Bavarian  palatinate, 
however,  cinnabar  has  been  found  to  play  the  part  of  a  fossil- 
izing mineral  and  has  therefore  replaced  organic  matter. 

The  only  recent  important  development  of  quicksilver-ores 
in  California  is  at  the  Mirabel  mine,  formerly  known  as  the 
Bradford,  in  the  Mayacmas  belt,  Lake  county.  This  mine 
yielded  in  1892,  3,245  flasks.  The  production  at  the  older 
mines,  and  particularly  at  the  New  Almaden,  has  fallen  to  a 
very  low  point. 


2  Data  with  regard  to  this  metal  are  from  G.  F.  Becker's  monograph  on  the 
subject,  1888,  and  from  private  information  communicated  by  him.  He  draws 
a  distinction  between  molecular  substitution  and  the  deposition  of  ores  in  porosities 
which  are  due  to  precedent  chemical  action. 


80  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

Genesis  of  Gold-  and  Silver-Deposits. 

The  frequent  association  of  deposits  of  gold  and  silver  with 
•eruptive  .rocks,  the  world  over,  has  long  been  remarked. 
Chemical  investigation  of  many  eruptive  rocks  has  detected 
their  presence  under  such  conditions  as  leave  little  doubt  that 
they  were  original  constituents  of  these  rocks.  Kecently  a 
German  geologist  has  reported  the  discovery  of  gold  in  a  late 
eruptive  rock  in  Chile,  which  could  be  actually  seen,  by  the 
aid  of  the  microscope,  to  be  an  original  constituent  of  the  rock. 
There  seems  very  good  reason  to  assume,  therefore,  at  any  rate 
as  a  working  hypothesis,  that  the  original  or  ultimate  source  of 
these  metals  has  been  the  eruptive  rocks. 

With  regard  to  their  subsequent  dissemination  in  sedimen- 
tary beds,  whether  by  mechanical  or  chemical  agencies,  there 
appears  to  be  less  satisfactory  evidence,  as  there  are  few  known 
concentrations  which  can  with  much  probability  be  assumed  to 
have  derived  their  material  exclusively  from  sedimentary  rocks. 
The  concentration  of  the  metals  in  workable  ore-deposits  has 
evidently  been  by  the  agency  of  aqueous  solutions;  detrital 
deposits  are  only  the  mechanical  rearrangement  of  such  con- 
centrations, though  some  maintain  that  these  have  been  en- 
riched by  precipitation  from  solutions. 

Aside,  then,  from  the  study  of  the  structural  relations  which 
would  afford  favorable  conditions  for  the  concentration  of  metal- 
bearing  solutions  and  the  precipitation  of  their  contained  salts 
in  workable  ore-bodies,  which  is  of  common  interest  and  im- 
portance with  regard  to  deposits  of  all  the  metals,  a  most 
fruitful  field  of  research,  and  one  which  promises  results  of 
economic  as  well  as  scientific  importance,  is  afforded  by  the 
study  of  the  chemical  and  mineralogical  affinities  of  these  two 
metals,  and  their  probable  behavior  under  the  conditions  which 
may  have  existed  where  deep-seated  deposits  were  formed. 
Much  obscurity  still  exists  as  to  the  actual  chemical  condition 
of  silver  in  galena  and  of  gold  in  pyrite.  The  suggestion  has 
recently  been  made  that  combinations  of  these  metals,  as  alloys 
or  otherwise,  with  small  amounts  of  tellurium,  bismuth,  etc., 
are  much  more  common  in  nature  than  has  hitherto,  been  sus- 
pected, and  may  be  the  reason  of  the  unexplainable  difficulties 
found  in  amalgamating  certain  ores,  and  further  investigation 
on  this  line  may  produce  important  results.  There  are  some 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  81 

features,  also,  with  regard  to  the  behavior  of  these  metals 
under  the  action  of  atmospheric  waters,  and  their  consequent 
concentration  along  the  zone  of  alteration  of  sulphide  deposits, 
which  are  not  entirely  clear,  and  demand  more  systematic  and 
»careful  investigation. 

Conclusion. 

What  is  at  present  known  about  the  distribution  of  ore- 
deposits  west  of  the  100th  meridian  does  not  seem  to  call  for 
any  serious  modification  of  the  statement  as  to  their  general 
distribution  made  by  Clarence  King  in  1870.  It  is  probable 
that  if  the  subject  were  carefully  worked  up  in  detail  it  would 
be  found  that  the  meridional  zones  laid  out  by  Mr.  King  con- 
tain, as  Kaymond  has  suggested,  a  greater  variety  of  minerals 
than  he  was  at  that  time  aware  of. 

In  the  eastern  half  of  the  continent  it  is  evident,  from  the 
facts  given  above,  that  certain  geographical  areas  are  peculiar 
in  containing  great  concentrations  of  certain  varieties  of 
minerals,  but  it  seems  hardly  necessary  to  recapitulate  the 
peculiarities  of  these  areas,  since  it  is  the  geological  rather  than 
the  geographical  distribution  that  is  of  practical  importance. 
The  former  must  have  a  genetic  bearing ;  the  latter  can  only 
have  such  bearing  through  geological  causes.  Unfortunately, 
our  knowledge  of  the  geological  relations  of  the  ore-deposits  of 
our  country  is  as  yet  too  incomplete  to  afford  material  for  any 
exhaustive  generalizations  on  the  geological  relations  of  the 
useful  metals  as  a  whole,  or  the  underlying  genetic  causes  of 
such  relations.  The  fissure-systems,  or  the  natural  water- 
channels  which  have  admitted  of  the  concentration  of  the 
metals  into  workable  deposits,  have,  as  pointed  out  by  King, 
Becker,  and  others,  certain  definite  relations  with  the  great 
orographic  movements,  and  these  relations  admit  of  our  form- 
ing an  idea  of  the  relative  age  of  the  deposits.  They  do  not, 
however,  afford  any  reason  why  certain  minerals  are  more 
prevalent  in  one  district  and  certain  others  in  another ;  nor  do 
they  necessarily  afford  any  clue  to  the  original  source  of  the 
metals.  A  certain  amount  of  systematic  geological  work  has 
already  been  done  by  our  Geological  Surveys  towards  the  solu- 
tion of  these  important  problems,  which  are  of  practical,  as 
well  as  scientific,  importance,  but  a  vast  amount  remains  yet 


82  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

to  be  done,  and   many,  large    fields    are    still   practically  un- 
touched. 

The  suggestion  afforded  above  as  a  working  hypothesis  seems 
to  be  one  worthy  of  consideration  by  the  workers  in  this  field. 
'If  the  metallic  minerals  do  concentrate  in  eruptive  magmas* 
within  the  crust  of  the  earth  in  accordance  with  some  law  not 
yet  clearly  known,  but  which  results  in  what  is  called  differen- 
tiation, by  virtue  of  which  certain  areas  of  igneous  rocks, 
formed  by  successive  extrusions  of  material  of  differing  chemi- 
cal composition  which  have  cooled  at  or  near  the  surface,  are 
found  to  be  unusually  rich  in  minerals  containing  a  given  metal 
or  class  of  metals,  a  basis  is  afforded  to  account  for  the  un- 
usual abundance  of  deposits  of  these  metals  in  a  given  area. 
In  the  case  of  the  older  eruptive  rocks,  the  accumulation  of 
mineral  combinations  of  the  metals  into  workable  deposits 
may  be  the  result  of  many  processes  of  concentration,  both 
mechanical  and  chemical.  The  concentration  of  material  de- 
rived from  younger  eruptive  rocks,  on  the  other  hand,  would 
be  more  direct,  and  mainly  chemical,  by  the  sole  action  of  per- 
colating waters.  In  either  case,  did  investigation  prove  that 
certain  areas  of  eruptive  rock  were  unusually  rich  in  mineral 
combinations  containing  a  given  metal,  it  would  afford  reason- 
able ground  for  looking  for  valuable  deposits  of  that  metal  in 
the  vicinity,  especially  if  the  geological  conditions  of  rock- 
alteration  or  metamorphism  and  dynamic  movements  are  such 
as  to  favor  concentration. 

If  sedimentary  beds  carry  disseminated  minerals,  or  concen- 
trations of  such  disseminated  minerals  into  ore-deposits,  they 
might  have  been  derived  ultimately  from  the  abrasion  of  bodies 
of  igneous  rocks  rich  in  their  minerals  by  differentiation.  How 
close  a  proximity  would  constitute  a  vicinity  would  vary  widely 
under  varying  geological  conditions.  It  is  quite  uncertain 
how  far  percolating  waters  carrying  minute  amounts  of  metallic 
minerals  in  solution  might  travel  through  underground  water- 
passages  without  depositing  their  load,  but  the  possible  dis- 
tance is  evidently  very  considerable ;  and  the  argument  some- 
times advanced  against  the  lateral-secretion  theory,  that  proof 
can  be  found  in  certain  cases  that  the  mineral  of  a  vein  could 
not  have  been  derived  from  the  immediate  wall-rock,  is  no 
valid  argument  against  this  theory  in  its  broader  acceptation,. 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  83 

which  admits  the  secretion  from  neighboring  bodies  of  rock 
not  necessarily  in  immediate  proximity,  but  possibly  at  con- 
siderable distance  and  not  visible  at  the  surface. 

For  the  derivation  of  sediments,  the  possible  distance  of  the 
source  of  materials  has  still  wider  limits ;  but  analogy  from  the 
conditions  under  which  sediments  are  deposited  in  present 
oceans  would  bring  it  within  100  miles  as  a  probable  limit. 
Here,  also,  it  may  readily  happen  that  the  eruptive  body  from 
which  the  metallic  minerals  were  derived  is  not  visible  on  the 
surface. 

DISCUSSION. 

(Trans.,  xxii.,  732.) 

JOHN  A.  CHURCH,  New  York,  K  Y. :  It  requires  some  cour- 
age to  appear  as  a  critic  of  a  theory  which  is  not  only  the 
fashion  among  American  geologists,  but  is  usually  presented 
by  them  in  terms  which  imply  that  any  other  views  are  an 
exhibition  of  ignorance.  Still,  I  am  obliged  to  say  that  the 
theory  of  lateral  secretion  as  it  is  stated  in  this  and  other 
writings  of  Mr.  Emmons  and  other  geologists  has  not  added 
much  to  our  real  knowledge  or  clearness  of  view.  In  the  ear- 
lier and  less  developed  stages  of  the  theory,  when  it  was  used 
as  Sandberger  used  it,  to  show  that  certain  veins  were  proba- 
bly'derived  from  the  rocks  in  which  they  lie,  or  which  are 
adjacent,  it  was  valuable  in  pointing  us  to  an  immediate  source 
of  ore-deposition.  When  we  are  driven  to  assume  the  exist- 
ence of  undiscoverable  rocks  at  an  unknown  but  certainly  a 
considerable  distance,  and  in  an  unknown  direction  from  the 
vein,  I  do  not  see  that  we  have  improved  upon  the  despised 
"  unknown  source  in .  depth  "  jvith  which  our  ignorance  has 
been  covered  so  long.  The  new  theory  may  suffer  from  ado- 
lescence, and  these  points  may  be  cleared  up  by  further  study, 
but  I  speak  of  it  as  it  is. 

Differentiation  in  a  magma,  by  which  a  metal  is  concen- 
trated in  one  member  of  a  series  of  outflows,  may  explain  why 
certain  ores  have  favored  a  given  locality  with  their  presence ; 
but  it  is  not  a  necessary  precedent  to  ore-formation.  Concen- 
tration in  the  source  of  supply  cannot  be  a  requirement,  for 
the  forces  that  have  been  able  to  take  up  four  or  five  tons  of 
gold  from  an  extensive  body  of  rock  must  be  able  to  collect 


84  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

four  or  five  thousand  tons  of  lead,  copper,  or  nickel  from  a 
proportionately  more  extended  body  of  rock.  That  is  to  say, 
concentration  is  no  more  essential  for  these  metals  than  it  is 
for  gold. 

In  fact,  differ entiatron,  as  it  is  now  explained,  is  not  an  ad- 
vance upon  old  ideas,  but  a  retreat  from  them.  It  was  noticed 
long  ago  that  violent  eruptive  phenomena,  however  long  con- 
tinued, died  away  in  solfataras ;  and  when  a  vein  came  to  be 
looked  upon  as  an  extinct  solfatara  the  inference  was  ready 
that  veins  are  eruptive  in  the  sense  that  the  solfataric  waters 
collected  the  metals  from  the  unerupted  residue  of  the  magma 
and  carried  them  to  the  veins.  The  early  views  carried  differ- 
entiation further  than  the  modern  school. 

It  is  the  fashion  of  the  new  school,  to  which  I  believe  all 
professional  geologists  in  this  country  adhere,  while  all  profes- 
sional mining  engineers  keep  themselves  aloof  from  it,  to  speak 
of  these  old  ideas  as  if  they  were  very  ignorant,  and  were 
necessarily  brushed  aside  by  the  advance  of  experimental 
knowledge.  It  seems  singular  to  me  that  the  new  school 
should  recognize  no  other  origin  for  ores  than  the  leaching  of 
rocks  by  comparatively  shallow  water-currents  and  yet  recog- 
nize no  other  origin  for  the  fissures  that  carry  the  ores  than 
cataclysmic  action  !  If  it  had  been  found  that  bed-planes  were 
commonly  the  channels  by  which  the  ore-solutions  entered, 
we  might  accept  the  fact  as  evidence  of  lateral  secretion ;  but 
when  I  find  the  adherents  of  this  theory  declaring,  as  does 
Mr.  Emmons  (and  as  do  all  the  others),  that  every  ore-deposit 
lies  in  a  plane  of  faulting,  or  has  been  filled  from  a  fault,  it 
seems  to  me  hardly  logical  to  carry  one  branch  of  the  volcanic 
theory  to  such  an  extreme,  and  totally  reject  the  other  branch, 
with  which  this  view  is  undoubtedly  in  sympathy. 

The  older  geologists  looked  upon  a  vein  as  a  channel  estab- 
lished between  the  surface  and  the  interior  of  the  earth.  Into 
its  lower  termination  poured  solutions,  the  character  of  which 
was  determined  by  the  pressure  and  heat  normal  to  the  depth 
at  which  they  may  have  been  formed.  The  almost  uniformly 
siliceous  filling  of  veins  shows  that  this  depth  was  uniform  in 
its  conditions  of  solution.  It  may  have  been  the  whole  bary- 
sphere  or  only  that  upper  portion  within  which  we  may  imag- 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  85 

ine  a  comparatively  lively  circulation.  At  least  it  was  lower 
than  the  vein. 

The  crevice  was  supposed  to  be  an  open  chamber,  or  series 
of  chambers,  with  occasional  points  of  support.  Through  this 
chamber  the  waters  rose  to  the  surface,  where  they  were  dis- 
charged. As  they  rose,  they  necessarily  passed  through  zones 
of  continually-decreasing  pressure  and  temperature,  and  "  relief 
of  pressure  "  and  "  lowering  of  temperature  "  were  the  potent 
agents  which  were  supposed  to  effect  precipitation  of  the  dis- 
solved solids,  discharge  of  gas  being  another.  The  idea  that 
the  rocks  inclosing  the  crevice  could  act  as  precipitants  re- 
ceived early  attention,  and  has  led  directly  to  some  of  our  most 
widely  accepted  modern  ideas. 

Undoubtedly,  these  are  plausible  views;  and  the  agencies 
invoked  are  real  agencies  of  precipitation,  as  we  know  from 
the  action  of  hot  telluric  waters  discharging  upon  the  surface. 
One  of  our  most  noted  veins — the  Comstock — was  studied  and 
explained  in  the  light  of  this  older  theory  by  Eichthofen,  in 
1865  ;  and  these  ideas  have  not  been  entirely  abandoned  there. 

Mr.  Becker,  within  the  last  ten  years,  has  gone  into  an  elabo- 
rate argument  to  prove  that  there  has  been  almost  no  erosion 
of  the  Comstock  rocks.  If  this  argument  is  sound,  the  outcrop 
now  is  within  25  or  50  ft.  of  where  the  original  outcrop  was 
formed.  It  is  true,  his  views  contradict  each  other;  and,  if 
the  dynamical  conduct  of  the  rocks  had  been  what  he  describes, 
there  would  never  have  been  an  outcrop  where  the  Comstock 
was  found.  Still,  I  believe  all  writers  upon  that  noted  vein, 
except  myself,  have  represented  it  as  a  solfatara,  in  the  sense 
that  it  was  formed  by  hot  waters  from  a  deep  unknown  source 
discharging  into  the  atmosphere.  The  attempts  to  connect 
lateral  secretion  with  the  lode  have  been  failures;  and  the 
Comstock  still  represents  the  old  theories  in  their  advanced 
form.  It  seems  to  me,  that  the  solfataric  origin  of  ores  is  a 
more  reasonable  explanation  of  the  observable  facts,  in  some 
cases,  than  the  theory  of  lateral  secretion.  That  minute  quan- 
tities of  the  metals  are  found  in  all  or  many  rocks,  is  true ;  but 
the  crucial  question  of  their  origin  has  never  been  determined. 
Do  they  form  an  original  source,  or  a  secondary  deposition  like 
the  vein?  is  a  question  that  has  not  been  conclusively  an- 


86  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

swered ;  but  I  agree,  and  I  think  most  mining  engineers  agree, 
with  Posepny,  in  believing  them  to  be  the  latter. 

We  owe  to  the  distinguished  author  of  this  paper  one  of  the 
most  striking  and  valuable  contributions  to  the  discussion  of 
the  lateral-secretion  theory.  From  his  description  we  may  say 
that,  in  his  view,  the  ores  at  Leadville  were  not  exotic,  since 
the  rocks  in  which  they  lie,  the  rocks  from  which  they  were 
leached,  and  the  water-currents  that  formed  them,  were  all  at 
substantially  the  same  depth.  These  features  are  essential  to 
lateral  secretion ;  for,  if  we  allow  that  the  circulating  waters 
sink  deep  enough  to  reach  the  unerupted  residue  of  the  magma 
before  they  take  up  their  metallic  contents,  we  have  the  old 
solfataric  theory  of  origin. 

Sandberger's  original  idea,  that  veins  are  filled  by  leaching 
from  the  rocks  that  contain  them,  has  been  so  expanded  by  the 
discussion  of  ore-bodies  formed  under  a  cover  of  three  or  four 
miles  of  rock,  that  it  is  brought,  riot  into  conflict,  but  into  close 
sympathy  with  the  solfataric  theory.  The  question  whether 
the  origin  was  in  erupted  or  in  non-erupted  magma  is  interest- 
ing ;  but  it  is  not  controlling  when  the  action  is  acknowledged 
to  have  taken  place  at  very  great  depth,  far  within  the  "  bary- 
sphere  "  in  either  case. 

Having  reached  that  amount  of  agreement,  it  seems  to  me 
that  the  next  task  of  the  structural  geologists  is  to  determine 
critically  whether  any  vein  has  really  been  formed  in  a  crevice 
discharging  directly  into  the  atmosphere.  The  conditions 
found  at  Steamboat  Springs  and  elsewhere  seem  to  me  to  point 
to  vein-action  (if  vein-action  there  is)  at  some  other  point.  The 
discharging  waters  may  be  regarded  as  the  nitrate  derived  from 
metasomatic  precipitation  lower  down,  or  as  a  mixture  of 
waters  from  the  upper  and  lower  regions.  As  yet,  I  doubt  if 
we  have  any  proof  that  ore  carried  by  the  deep  circulation  has 
been  retained  long  enough  to  be  deposited  at  the  surface.  Mr. 
Becker  entertained  that  view,  but  I  believe  his  conclusions 
upon  the  geology  of  the  Comstock  to  be  radically  wrong. 

ARTHUR  WINSLOW,  Jefferson  City,  Mo. :  I  think  that  others 
will  join  me  in  expressing  thanks  to  Mr,  Emmons  for  his  ad- 
mirable resume  of  our  ore-deposits,  and  for  the  many  valuable 
suggestions  embodied  in  it.  The  ground  is  so  well  covered 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  87 

that  there  remains  little  -room  for  additions,  jet  I  should  like 
to  make  a  few  remarks  concerning  some  subjects  touched  on 
of  which  I  have  personal  knowledge. 

Mr.  Emmons  refers  to  the  specular  ores  of  southeastern  Mis- 
souri collectively,  as  probably  of  Algonkian  age.  There  is,  how- 
ever, a  distinction  to  be  made.  Those  of  Iron  Mountain  occur  in 
Archaean  porphyry,  in  tongue-like  masses  or  veins  which  taper 
out  with  depth.  The  ore  of  Pilot  Knob,  on  the  contrary, 
occurs  as  a  bed  interstratified  with  Algonkian  elastics  com- 
posed of  debris  of  the  pre-existing  Archaean  porphyries.  These 
ores  have  recently  been  made  the  subject  of  renewed  study  by 
the  Geological  Survey  of  the  State,  through  Mr.  Nason.  He 
thinks  that  the  facts  at  Iron  Mountain  are  such  as  to  favor 
the  theory  that  the  ores  there  are  derived  from  the  decay  of 
great  thicknesses  of  porphyry,  accompanied  by  a  leaching-out 
of  the  abundant  iron-content  and  its  deposition  elsewhere  in 
crevices  and  openings  of  the  same  rock,  at  times  possibly  re- 
placing the  decomposed  porphyry  adjacent  to  these  crevices. 
These  deposits  would  thus  be  examples  of  chemical  concentra- 
tion from  older  basic  eruptives.  In  the  case  of  Pilot  Knob, 
Mr.  Nason  concludes  that  the  iron-ore  body  is  probably  the 
result  of  replacement  of  certain  members  of  the  Algonkian 
series  of  strata.  This  would  again  be  an  example  of  chemical 
concentration  from  an  older  basic  eruptive,  though  if  we  allow 
that  the  Archaean  specular  ores  were  formed  prior  to  the  deposi- 
tion of  the  Algonkian  series  here,  it  is  possible  that  this  Pilot 
Knob  bed  is  of  direct  mechanical  origin  from  the  abrasion  of 
these  earlier  ore-masses. 

In  the  iron-deposits  of  central  Missouri,  which  consist  of  a 
mixture  of  blue  specular  and  red  hematite  ores,  Mr.  Nason 
concludes  that  we  have  instances  of  accumulation  in  cavities 
and  depressions  produced  by  subterranean  erosion  of  lime- 
stone. The  disturbed  condition  of  the  adjacent  strata,  their 
converging  dips  and  other  facts  corroborate  this.  That  there 
was  some  replacement  of  limestone  by  the  iron-solutions  is  also 
undoubted.  This  is  well  illustrated  by  the  recent  discovery  of 
crinoid  remains  in  the  body  of  the  ores,  replaced  entirely  by 
blue  ore.  An  interesting  fact  about  these  fossil  remains,  and 
one  which  adds  support  to  the  theory  that  the  ore  accumulated 
in  depressions  or  cavities,  is  that  they  are  not  fossils  found  in 


88  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

the  Cambrian  country-rocks,  but  belong  probably  to  a  Lower 
Carboniferous  fauna.  All  over  the  Cambrian  area  of  the 
Ozark  uplift  patches  and  fragments  of  such  later  rocks  are 
found,  indicating  that  a  thin  covering  once  existed  there,  of 
which  portions  are  preserved  in  depressions  and  pockets  in  the 
older  dolomites. 

Remote  as  these  ore-bodies  are  from  eruptive  rocks,  we  are 
obliged  to  seek  for  their  source  in  the  surrounding  sedimenta. 
ries.  Mr.  Nason  has  fixed  upon  the  sandstones  of  this  area  as 
the  probable  contributors.  These  are  often  highly  ferruginous, 
and  are  readily  leached  by  percolating  waters.  It  is  probable 
that  the  decaying  dolomites  also  contributed  a  share. 

In  referring  to  the  zinc-  and  lead-ores  of  Missouri,  Mr. 
Emmons  has  brought  forward  for  discussion  a  series  of  most 
interesting  and  at  the  same  time  most  perplexing  deposits,  so 
far  as  a  satisfactory  theory  of  their  origin  is  concerned.  Those 
of  the  southwestern  portion  of  the  State  occur  essentially  in 
the  Mississippian  or  Lower  Carboniferous  limestones.  The 
statement  that  they  extend  into  the  Coal  Measures  should  be 
made  with  limitations.  They  are  found  in  shales  of  that  age 
in  Jasper  county,  but  those  shales  are  in  isolated  patches, 
which  occupy  depressions  in  the  older  ore-bearing  Mississip- 
pian rocks.  Hence,  the  metallic  contents  of  the  shales  may  be 
derived,  by  some  secondary  process  of  transfer,  from  adjacent 
ore-bodies.  In  any  case,  the  Coal  Measures  in  the  State,  as  a 
whole,  are  practically  destitute  of  these  ores,  which,  therefore? 
can  hardly  be  declared  to  belong  to  that  formation,  whether 
their  general  absence  from  it  be  due  to  their  prior  formation, 
or  to  limitations  in  their  distribution  determined  by  physical 
causes. 

Cross-fissures  or  fault-fissures  in  these  Mississippian  rocks, 
to  which  Mr.  Emmons  alludes,  if  they  exist,  are  not  very  appa- 
rent. The  strata  are,  undoubtedly,  very  much  shattered  in 
certain  limited  areas,  have  been  subjected  to  extensive  subter- 
ranean erosion  and  corrasion  and  great  silicification.  Of  a 
system  of  extensive  or  considerable  faults,  recent  stratigraphic 
work  in  this  region  has,  however,  revealed  nothing. 

In  the  Cambrian  limestones  of  the  eastern  part  of  the  State, 
the  conditions  are  somewhat  different.  Crevices  and  fissures 
are  there  plainly  developed,  and  evidence  of  considerable  fault- 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  89 

ing  is  indubitable.  In  Franklin  county,  such  vertical  crevices 
have  supplied  large  quantities  of  ore.  In  that  portion  of  the 
Southeast  to  which  Mr.  Emmons  especially  refers,  however, 
and  which  has  produced  by  far  the  greater  part  of  the  lead, 
the  crevices  are  of  insignificant  dimensions,  and  the  experience 
has  been  that  they  contain,  themselves,  little  or  no  ore.  On 
the  contrary,  the  great  ore-masses  consist  of  galena  dissemi- 
nated through  a  thickness  of  the  country-rock  often  of  50  ft. 
and  more.  At  Bonne  Terre,  a  tract  1,300  ft.  long  by  800  ft 
wide  has  been  mined  out  of  such  diffused  ore. 

The  crevices  which  traverse  this  ore-body  are  frequently 
almost  blind,  and  can  only  be  detected  by  the  drip  of  roof- 
water.  These  are  such  as  traverse  almost  any  massive  rock. 
They  have  possibly  had  their  influence  upon  the  ore-deposi- 
tion ;  but  to  picture  them  as  veins  and  channels  of  direct  ore- 
supply  seems  hardly  justifiable,  even  under  the  existing  differ- 
ences of  opinion  among  geologists  as  to  just  what  a  vein  is. 
The  questions  of  the  source  and  mode  of  accumulation  of  these 
ores  are  very  broad,  and  involve  considerations  of  the  ore- 
deposits,  and  of  the  geological  history  of  the  whole  Mississippi 
valley.  Only  through  studious,  detailed  analytic  methods  can* 
a  satisfactory  solution  be  reached.  I  hope,  at  a  later  date,  to 
have  something  further  to  contribute  to  the  Institute  on  this 
subject. 

Concerning  the  distribution  of  barite,  to  which  Mr.  Emmons 
refers  on  page  78,  I  would  add,  that  it  is  not  confined  to  the 
older  Cambrian  rocks  of  Missouri,  but  is  found  in  Cooper  and 
adjacent  counties,  at  a  number  of  localities,  in  Lower  Carbon- 
iferous limestones,  sometimes  associated  with  lead-ores.  In  a 
previous  paper,  presented  to  the  Institute,3  Mr.  Emmons  has 
suggested  the  use  of  the  apparent  fact  of  the  limited  distribu- 
tion of  barite  in  determining  the  origin  of  the  ores.  This  oc- 
currence in  the  Lower  Carboniferous  lessens  the  value  of  the 
suggestion,  though  it  remains  still  locally  serviceable. 

MR.  EMMONS  :  I  am  very  glad  to  have  the  details  which  Mr. 
Winslow  has  given  us  with  regard  to  the  ore-deposits  of  Mis- 
souri ;  and  as  my  knowledge  of  the  greater  part  of  them  is 

3  Trans.,  xxi.,  41  (1892-93). 


90  GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS. 

derived,  not  from  personal  observation,  but  from  the  descrip- 
tions of  others,  I  am  quite  willing  to  accept  his  corrections  of 
my  facts,  since  his  information  is  of  later  date  than  that  to 
which  I  had  access.  I  was  aware  that  barite  occurs  at  times 
in  the  Lower  Carboniferous  limestones  of  the  Mississippi  val- 
ley; indeed,  small  amounts  have  been  found  in  the  fluorspar- 
deposits  of  Rosiclare,  HI.,  since  I  wrote  my  previous  paper  to 
which  he  refers ;  but  I  think  it  still  remains  true  that  fluorspar 
is  characteristic  of  the  one  horizon  and  barite  of  the  other. 

(Trans.,  xxiv.,  755.) 

WILLIAM  HAMILTON  MERRITT,.  Toronto,  Ont. :  With  refer- 
ence to  Mr.  Emmons's  remarks  on  the  nickel-deposits  of  Sud- 
bury  in  the  district  of  Algoma,  Province  of  Ontario,  Canada, 
and  his  general  argument  in  connection  with  igneous  rocks  as 
the  source  of  supply  of  ores,  I  would  draw  attention  to  two 
series  of  facts  personally  observed  in  connection  with  the  Sud- 
bury  deposits. 

1.  The  Diorite  as  a  Source  of  Supply. — The  diorite,  as  a  rule, 
is  speckled  with  pyrrhotite,  and  to  a  less  extent  with  chalcocite. 
In  the  diorite  I  have  seen  a  speck  of  free  gold  quite  visible  to 
the  naked  eye.     The  same  diorite,  decomposed,  has  been  run 
through   a  prospector's  stamp-mill  in  an  earthy  and  gossany 
state,  and  free  gold  and  the  new  platinum  mineral,  sperrylite 
(PtAs2),    perfectly    crystalline,  have   been    collected   from    it, 
Near  by,  a  quartz  vein,  cutting  the  same  diorite  formation,  has 
yielded  rich  samples  of  free  gold,  which  occurs  also  in  the 
diorite  walls  beside  the  vein,  the  wall-rock  being,  in  some  places, 
thickly  interlaced  with  threads  of  gold. 

2.  Secondary  Action  in  Concentration  Has  Produced  Some  of  the 
Ore-Bodies. — As  has  been  noted  by  Mr.  Emmons,  the  theory  of 
differentiation,  or  the   concentration  of  the  ore-bodies  in  the 
fused  magma,  is  offered  to  explain  the  source  of  the  Sudbury 
nickeliferous  pyrrhotite  masses  in  the  intrusive  diorite.     This 
would  not  appear  unreasonable.    Yet  I  am  satisfied  that  a  sec- 
ondary concentration  must  have  taken  place  to   explain  the 
presence  of  some  of  the  ore-bodies ;  at  all  events,  where  the 
contents  of  copper  run  comparatively  high.     The  presence  of 
the  horses  of  country-rock  cemented  by  the  ore  (alluded  to  by 


GEOLOGICAL    DISTRIBUTION    OF    THE    USEFUL    METALS.  91 

Mr.  Emmons),  and  which  I  have  observed  sharply  brecciated, 
seems  to  strengthen  this  belief;  for  if  they  had  been  floating 
in  a  fused  magma,  surely  all  abrupt  demarcation  would  be 
obliterated. 

Moreover,  I  have  seen  such  signs  of  secondary  action  as  thin 
films  of  native  copper  in  connection  with  the  ore-body;  also  a 
band  of  "  fluccan  "  cutting  across  it,  which  may  indicate  a  por- 
tion of  the  chief  channel  which  may  have  filled  the  cavities 
caused  by  movement.  Native  copper  grains  are  also  seen  in 
the  crystalline  hornblende  rock  associated  with  the  deposit.  I 
have  not  observed  serpentine,  which  might  be  expected  to 
occur.  In  another  portion  of  the  same  ore- body  there  is  free 
gold  visible  in  chalcopyrite ;  and  where  a  very  small  crack  or 
vug  had  occurred  in  the  ore,  wire-gold  has  been  developed. 
The  ore-body  is  distinctly  more  quartzose  than  the  diorite  in 
which  it  occurs. 


92  THE    TORSIONAL    THEORY    OF    JOINTS. 


No.  4. 
The  Torsional  Theory  of  Joints. 

BY   GEORGE  F.    BECKER,    WASHINGTON,    D.    C. 

(Virginia  Beach  Meeting,  February,  1894.  Trans,  xxiv.,  130.) 

Complexity  of  Rock-Fractures. — The  strains  to  which  rocks 
have  been  subjected  are  manifestly  very  complex,  and  it  is  en- 
tirely safe  to  presume  that  every  possible  mode  of  deformation 
and  rupture  is  exemplified.  The  most  superficial  inspection  of 
any  ordinary  mountain  region  is  sufficient  to  assure  the  ob- 
server that  the  rocks  have  been  pressed,  stretched,  bent, 
buckled,  twisted,  and  shorn.  The  study  of  torsional  rupture 
cannot  fail,  therefore,  to  throw  light  on  geological  phenomena. 
The  question  is,  how  areas  which  have  been  broken  in  this 
manner  are  to  be  distinguished  from  those  which  have  yielded 
to  other  systems  of  forces. 

Phenomena  of  Joints. — It  is  well  known  that  a  large  part  of 
the  more  homogeneous  rocks  and  some  very  heterogeneous 
rocks  are  intersected  by  partings,  often  called  joints.  These 
partings  are  frequently  flat  surfaces,  even  when  seen  in  very 
large  exposures,  but  are  sometimes  surfaces  of  moderate  single 
or  double  curvature.  Joints  usually  occur  in  groups,  in  each 
of  which  the  several  partings  are  parallel  to  one  another,  and 
several  such  groups  often  intersect  the  same  rock-mass.  In  such 
cases  the  different  systems  make  large  angles  with  one  another. 
Nearly  all  students  of  the  subject  of  jointing  have  reached  the 
conclusion  that  joints  are  faulted  surfaces,  the  dislocations 
usually  being  of  small  amplitude ;  and  this  conclusion  receives 
abundant  support  from  the  study  of  thin  sections  under  the 
microscope.  It  has  thus  been  shown  that  much  even  of  what 
would  be  regarded  in  hand-specimens  as  mere  slaty  cleavage 
consists,  in  reality,  of  innumerable  microscopic  faults.  For 
this  reason,  Mr.  Daubree  rejects  the  term  "joint,"  as  failing  to 
imply  the  existence  of  relative  motion,  and  has  introduced  the 
terms  "diaclase"  and  "paraclase"  as  substitutes.1 

1  Bulletin  de  la  Societe  Oeologique  de  France,  Third  Series,  vol.  vii.,  p.  108  (1879). 


THE    TORSIONAL    THEORY    OF    JOINTS.  93 

Although  the  word  "joint"  does  not  imply  relative  motion, 
it  does  not  necessarily  preclude  such  movement,  and,  as  it  is 
universally  intelligible,  I  prefer  it.  In  nearly  all  cases  where 
joints  are  suitably  exposed  they  show  slicken siding.  In  many 
hundreds  of  joints  I  have  found  polished  surfaces,  although  the 
throw  of  the  faults  was  so  small  as  scarcely  to  be  determinable. 
Slickensiding  is  a  very  important  genetic  characteristic  of 
joints,  for  wherever  it  prevails  over  any  considerable  portion 
of  the  parting,  it  is  good  evidence  that  the  joint-walls  have  not 
only  undergone  relative  motion,  but  have  remained  in  contact 
during  the  dislocation. 

It  does  not  follow  that  gaping  joints  should  be  infrequent, 
for  a  rock-mass  once  affected  by  joints  will  present  but  small 
resistance  to  any  disturbing  force,  and  such  a  force  may  readily 
spread  the  joint  walls.2  Indeed,  it  is  somewhat  surprising  that 
joints  are  so  often  found  closed.  When  a  bar  of  metal  is  cut 
by  shears,  the  two  parts  are  in  contact  immediately  after  the 
continuity  is  destroyed  and  they  slickenside  one  another,  but 
under  ordinary  conditions  they  then  fall  apart.  The  compara- 
tive rarity  of  gaping  joints  is  explicable  in  part  by  the  presence 
of  water.  The  surface-tension  of  thin  films  of  water  leads  to 
adhesions  which  seem  to  me  of  much  importance.  Thus,  if 
two  surfaces  of  rock  are  distant  0.01  in.  from  one  another,  and 
if  the  space  is  filled  with  water,  the  rock-surfaces  are  drawn 
together,  in  consequence  of  the  surface-tension  of  the  liquid, 
with  a  force  equal  to  18.5  Ib.  per  sq.  ft. ;  and  if  the  opening  is 
only  0.001  in.  wide,  the  pressure  will  be  135  Ib.  per  sq.  ft.3 
There  can  be  no  doubt  that  many  jointed  rock-masses,  which 
project  above  the  local  water-level,  are  prevented  from  dis- 
organization by  this  means. 

Explanatory  Hypotheses. — Jointing  is  now  regarded  by  all  in- 
vestigators as  of  mechanical  origin.  It  has  been  referred  by 

2  Prof.  William  King,  Transactions  of  the  Royal  Irish  Academy,  vol.  xxv.  (1875), 
has  collected  much   evidence  to  show  that  joints  were  originally  close.     Mr. 
Daubr^e  also  draws  from  observations  by  himself  and  others  the  conclusion  (I.e.) : 
"A  cutting  or  shearing  force,  then,  was  operative  during  the  formation  of  joints." 
This  is  equivalent  to  asserting  that  contact  existed  during  and  immediately  after 
rupture. 

3  The  pressure  is  equivalent  to  that  of  a  column  of  water,  the  height  of  which  is 
c  centimeters  when  the  distance  of  the  surfaces  from  each  other  is  d  centimeters, 
and  c  d  —  162/981.4.     Compare  Tait's  Properties  of  Matter,  p.  258  (1890). 


94  THE    TORSIONAL    THEORY    OF    JOINTS. 

eminent  authorities  to  simple  tensile  stresses,  but  observers 
have  long  protested  against  this  explanation,  because  such 
joints  would  gape  from  the  start  and  would  not  be  slickensided. 
Even  if  a  tensile  stress  leading  to  rupture  were  associated  with 
slipping,  slickensides  would  be  produced  only  on  a  few  small 
portions  of  the  surfaces  involved.  These  surfaces  can  never  be 
true  mathematical  planes,  and  a  rupture  like  that  just  sug- 
gested might  bring  into  contact  protuberances,  however  small, 
but  in  such  cases  slickensides  would  be  confined  to  small  por- 
tions of  the  surface.  In  heterogeneous  masses,  particularly  in 
conglomerates,  tensile  stresses  leading  to  rupture  would  pro- 
duce rough  and  irregular  partings.  Even  in  masses  so  homo- 
geneous as  steel,  tensile  rupture  takes  place  on  very  uneven 
surfaces. 

For  these  reasons,  jointing  has  been  explained  most  satisfac- 
torily by  reference  to  pressure,  though  it  does  not  follow  that 
all  jointing  is  thus  brought  about.  Mr.  Daubree  has  shown  by 
direct  experiments  with  simple  pressure  that  all  the  more  usual 
phenomena  of  joints  can  be  artificially  produced,  the  line  of 
pressure  making  an  angle  of  about  45°  with  the  joint-planes.  In 
this  case  the  immediate  cause  of  the  jointing  is  shearing  stress, 
and  the  walls  of  the  joints  are  not  only  in  juxtaposition,  but 
are  pressed  together  during  the  rupture  and  dislocation.  The 
dynamic  theory  of  this  case  is  not  difficult  even  when  the 
strains  are  finite  and  the  angle  between  the  joint- surfaces  is 
greater  than  45 °.4 

Some  geologists  hesitate  to  accept  the  explanation  of  joint- 
ing by  pressure  in  a  given  direction,  on  the  ground  that  an 
accompanying  lateral  pressure  of  sufficient  intensity  would  pre- 
clude rupture.  It  is  a  very  important  truth  that,  under  proper 
conditions,  rupture  cannot,  and  flow  must,  take  place.  A  mass 
may  be  subjected  to  such  confining  forces  that  rupture  is  im- 
possible by  any  deformation  or  change  of  volume ;  but  this  is 
true  of  tension,  torsion,  or  shearing  as  well  as  of  simple  pres- 
sure. Since  rock-fractures  are  abundant,  it  is  certain  that  con- 
ditions permitting  of  rupture,  as  well  as  those  compelling  flow, 
have  frequently  prevailed. 

While  Mr.  Daubree  and  others  refer  many  joint-systems  to 

4  Bulletin  of  the  Geological  Society  of  America,  vol.  iv.,  p.  57  (1892). 


THE    TORSIOXAL    THEORY    OF    JOINTS.  95 

the  action  of  pressure,  the  famous  author  of  the  Etudes  Synthe- 
tique  has  also  made  beautiful  experiments  on  the  torsion  of 
glass  plates,  which  produces  systems  of  fractures  highly  resem- 
bling joints  in  their  distribution.  He  has  consequently  ex- 
pressed the  opinion  that  torsion,  as  well  as  pressure,  has  led  to 
joint-systems.5 

Character  of  Torsion- Fractures. — Mr.  Daubree  has  minutely 
described  the  phenomena  of  the  rupture  by  torsion  of  glass 
plates,  these  being  mounted  on  paper  to  avoid  the  scattering  of 
the  fragments.  Torsion,  as  he  describes  it,  produces  two  main 
sets  of  fractures,  approximately  at  right  angles  to  one  another, 
and  usually  at  nearly  45°  to  the  axis  of  torsion.  The  fissures 
cut  the  broad  surfaces  in  lines  which  are  nearly  straight,  and 
the  surfaces  of  fracture  are  approximately  warped  surfaces,  the 
inclination  to  the  vertical  in  some  cases  reaching  50°  on  each 
side.  Some  few  fissures  reach  from  edge  to  edge  of  the  plate,, 
while  many  do  not  entirely  cross  it,  and  sometimes  single  fis- 
sures neither  reach  the  edge  nor  any  other  crack,  and  are  thus 
isolated  in  the  mass.  The  fissures  which  reach  the  edge  of  the 
plate  cut  the  narrow  face  at  angles  with  the  line  measuring  the 
thickness,  which  varies  greatly — from  20°  or  less  up  to  50°  or 
thereabout.  Besides  the  more  regular  systems  of  parallel 
fissures,  fan-shaped  groups  are  not  uncommon.  In  the  neigh- 
borhood of  the  finer  groups  of  fissures  the  glass  loses  its  optical 
and  thermal  isotropy. 

By  the  kindness  of  Prof.  T.  C.  Mendenhall  I  have  been  ena- 
bled to  make  experiments  similar  to  those  of  Mr.  Daubree  in 
an  apparatus  which  permits  of  gradually  straining  the  plates 
and  of  measuring  the  angle  of  torsion.  Besides  common 
window-glass,  I  employed  glass  ground  on  one  side,  for  the 
purpose  of  making  sure  that  surface-tension  played  no  part  in 
the  result.  Well-polished  plate-glass  was  also  used,  sometimes 
in  simple  strips  and  sometimes  cut  in  the  shape  of  a  cross-sec- 
tion of  an  I-beam,  in  order  to  confine  the  initial  rupture  to 
points  remote  from  the  jaws.  In  a  large  number  of  the  experi- 
ments the  cut  edges  were  ground  with  emery,  so  that  imper- 
fections of  the  edges  might  not  influence  the  result.  Many 

5  W.  O.  Crosby  also  adopts  the  torsional  hypothesis,  with  the  modification  that 
he  supposes  the  final  rupture  to  be  determined  by  shock. — American  Geologist,  vol. 
xii.,  No.  6,  p.  368  (Dec.,  1893). 


96  THE    TORSIONAL    THEORY    OF    JOINTS. 

different  dimensions  were  selected,  and  the  plates  varied  from 
nearly  square  rods  to  sheets  wider  than  they  were  long.  It 
was  found  best  to  substitute  a  thin  fabric,  known  as  "  cheese- 
cloth," for  the  paper  on  which  Mr.  Daubree  mounted  his  plates. 
The  paper,  in  drying,  exerts  a  considerable  tension,  and  the 
specimens  mounted  on  cloth,  besides  being  more  easily  handled 
after  fracture,  show  smaller  tendency  to  fan-fracture. 

All  of  Mr.  Daubree's  descriptions  are  illustrated  by  my  speci- 
mens,6 and  I  have  but  few  observations  to  add.  It  scarcely 
requires  mention  that  the  curvature  of  the  surfaces  of  rupture 
is  ordinarily  such  as  to  permit  of  the  free  torsion  of  the  broken 
plate.  Sometimes,  however,  short  cracks  extending  from  the 
main  fissure  to  the  edges  of  the  plate  are  so  warped  as  to  ob- 
struct torsion.  Hence,  when  the  axis  of  torsion  is  not  in  the 
vertical,  all  the  principal  faults  produced  in  the  experiments 
are  reversed,  the  hanging-wall  rising  relatively  to  the  foot. 

When  the  breadth  of  a  glass  plate  is  large  relatively  to  its 
thickness,  the  surfaces  of  rupture  are,  as  Mr.  Daubree  remarks, 
nearly  coincident  with  warped  surfaces ;  but  when  the  breadth 
is  only  a  few  times  the  thickness,  the  departure  of  the  surface 
from  a  warped  surface  is  well  marked.  In  such  eases  it  is  in- 
teresting to  note  that  one  cropping  of  the  fissure  is  usually 
wonderfully  straight,  while  that  on  the  opposite  side  is  an 
inflected  curve.  From  the  point  of  view  of  pure  dynamics  the 
exact  shape  of  these  surfaces  would  be  interesting,  but  I  have 
reason  to  believe  that  the  geometrical  character  depends  essen- 
tially upon  that  of  the  cross-section  of  the  twisted  bar;  and 
since  it  will  seldom  or  never  be'  practicable  to  determine  the 
shape  of  a  twisted  rock-mass,  there  seems  no  geological  interest 
in  ascertaining  the  precise  form  of  the  surface  of  rupture.  It 
is  probable  that  the  forms  are  all  closely  related  to  the  warped 
surface. 

Among  the  excessively  fine  cracks  in  the  glass  which  are 
mentioned  by  Mr.  Daubree,  there  are  some  which  are  super- 
ficial. These  are  usually  near  the  middle  of  the  plate;  they 
are  very  straight,  and  invariably  parallel  to  the  straighter  edges 
of  the  ruptures  on  the  same  surface,  and  do  not  seem  to  pene- 

6  I  have  not  tested  the  anisotropy  in  the  neighborhood  of  the  terminations  of 
cracks  not  crossing  the  plates.  As  the  mass  at  such  points  is  in  a  permanent  state 
of  strain,  anisotropy  is  to  be  expected. 


THE    TORSIONAL    THEORY    OF    JOINTS. 


97 


trate  quite  to  the  center  of  the  plate.  They  are  clearly  in- 
cipient fractures,  and  the  observations  indicate  that  rupture 
begins  on  one  of  the  broad  faces  in  a  very  straight  line,  the 
surface  twisting  as  it  spreads  through  the  plate  in  such  a  man- 
ner as  best  to  relieve  the  torsional  stress.  Even  on  rather  thin 
plates  it  is  visible  that  one  cropping  of  each  well-formed  crack 
is  straighter  than  the  cropping  on  the  opposite  face,  and  that 
the  straight  cropping  has  a  definite  relation  to  the  direction  of 
twist.  When  torsion  is  so  applied  as  to  tend  to  twist  the  bar 
into  a  righ1>handed  screw,  the  straight  lines  are  inclined  like 
the  thread  of  a  left-handed  screw,  and  vice  versa.  Thus  the 
straight  croppings  on  one  surface  of  a  plate  are  at  right  angles 
to  the  straight  lines  on  the  other  side  of  the  plate. 

The  angles  at  which  the  cracks  cross  the  narrow  edge-sur- 
faces of  the  plate  vary  considerably,  as  Mr.  Daubree  has 
observed.  I  cannot  find  that  the  inclination  of  these  lines 
varies  in  any  regular  manner  with  the  width  of  the  plate.  The 
average  angle  which  the  cracks  on  these  narrow  surfaces  make 
with  the  long  edges  seems  to  be  about  63 J°,  or  the  angle 
whose  tangent  is  2.  These  croppings  are  in  fact  curved  lines 
in  almost  all  cases,  and  the  curvature  is  such  that  the  acute- 
angled  fragments  bounded  by  the  edge  of  the  plate  and  the 
ruptures  are  somewhat  grooved. 

The  following  diagram  shows  two  warped  surfaces  intersect- 
ing a  bar  supposed  four  times  as  wide  as  it  is  thick,  and  a 
sketch  of  two  of  the  more  complex  surfaces,  referred  to  above, 
generalized  from  a  considerable  number  of  cases.7 


FIG.  1. — DIAGRAM    ILLUSTRATING    INTERSECTION  OF  SURFACES  OF  RUPTURE 

WITH  A  BAR. 

7  If  the  axis  of  the  bar  is  the  x  axis,  y  the  distance  from  this  axis  parallel  to  the 
broad  surface,  z  the  distance  parallel  to  the  narrow  surface,  b  the  breadth,  c  the 
thickness,  then  the  following  equation  represents  both  the  warped  surfaces. 


98  THE    TORSIONAL    THEORY    OF    JOINTS. 

Rupture  by  Shear. — In  a  pure  (or  irrotational)  shear  the  re- 
sultant load  on  any  section  passing  through  the  center  of  the 
strain  ellipsoid  is  the  same.  On  the  sections  perpendicular 
respectively  to  the  greatest  and  least  axes  the  load  is  wholly 
normal.  On  the  sections  of  unchanged  area  (which  stand  at 
45°  to  the  greatest  and  least  axes  when  the  strain  is  very 
small)  the  load  is  purely  tangential.8  In  a  homogeneous  mas& 
thus  strained,  rupture  may  conceivably  occur  by  the  tension 
along  the  greatest  axis,  or  by  pressure  along  the  smallest  axisr 
or  by  tangential  motion  at  45°  to  the  axes.  A  mass  ruptured 
by  tension  sometimes  breaks  perpendicularly  to  the  direction 
of  tension  with  a  smooth  surface,  and  sometimes,  as  in  the  case 
of  mild  steel,  with  a  rough  or  " cupped"  surface,  the  facets  of 
which  are  in  the  direction  of  the  planes  of  unchanged  area.  A 
mass  broken  by  uniformly-distributed  pressure  breaks  in  the 
direction  of  the  planes  of  unchanged  area.  A  mass  ruptured 
by  tangential  stress  also  breaks  on  these  planes.  Thus  a  homo- 
geneous mass  subjected  to  a  shear  can  break  in  only  two  waysr 
viz. :  perpendicular  to  the  greatest  axis  or  at  45°  to  this  axis. 
In  the  present  state  of  knowledge  concerning  the  constitution 
of  matter,  experiment  only  can  determine  which  rupture  will 
occur.  The  experiments  on  glass  plates  in  connection  with  the 
theory  of  torsion,  due  to  the  genius  of  Barre  de  Saint- Venanty 
render  a  decision  very  easy  for  this  substance. 

Points  From  the  Theory  of  Torsion. — When  a  rectangular  bar 
of  an  elastic,  homogeneous  solid  is  twisted  through  a  small 
angle  the  following  conditions  are  fulfilled :  The  lateral  sur- 
faces of  the  bar  become  warped;  the  length  of  every  edge 
remaining  substantially  unchanged,  while  diagonal  lines  are 
elongated  or  contracted,  but  the  volume  of  the  mass  is  neither 
increased  nor  diminished  by  a  sensible  amount.  At  the  sur- 
faces of  the  bar  the  resultant  strains  lie  in  these  surfaces.  The 
directions  of  maximum  extension  and  compression  are  at  45° 
to  the  axis  of  torsion,  and  at  right  angles  to  each  other.  If  the 
rotation  of  the  torsion-couple  is  positive  (opposite  to  that  of  the 
hands  of  a  watch)  the  directions  of  greatest  extension  on  all  the 
sides  are  inclined  in  the  same  sense  as  the  thread  of  a  right- 
handed  screw.  The  strain  at  any  point  in  the  mass  is  a  pure  or 

8  American  Journal  of  Science,  Third  Series,  vol.  xlvi.,  No.  275,  p.  339  (Nov.,, 
1893). 


THE    TORSIONAL    THEORY    OF    JOINTS.  99 

irrotational  shear.  The  points  of  maximum  strain  are  on  the 
surface  and  nearest  the  axis;  in  other  words,  the  danger-line  is 
the  median  line  of  the  broad  surface ;  and  on  the  narrow  surface 
of  the  prism  the  strain  is  also  greater  half  way  between  its  long 
edges  than  elsewhere. 

Most  of  these  conclusions  can  be  exemplified  in  a  very  easy 
and  striking  manner  with  a  rectangular  bar  of  rubber,  such  as 
is  in  common  use  for  erasing  pencil-marks.  The  surface  of 
such  a  mass,  cross-hatched  with  lines  parallel  to  the  edges, 
shows,  when  the  bar  is  twisted,  that  deformation  is  greatest 
nearest  the  axis  and  insignificant  near  the  edges  of  the  prism. 
Lines  at  45°  to  the  edges  are  greatly  extended  or  shortened  by 
twist,  and  a  very  small  circle  is  converted  into  an  ellipse  with 
axes  at  45°  to  the  edges. 

It  evidently  follows  that  rupture  should  begin  at  the  middle 
of  the  broad  surface.  If  rupture  takes  place  by  slipping  on  the 
planes  of  no  distortion  of  the  shear  ellipsoid,  the  cracks  of 
the  broken  mass  will  be  parallel  to  or  perpendicular  to  the  axis 
of  torsion.  If  the  mass  yields  to  the  tensile  component  of  the 
shearing  stress  the  cracks  will  coincide  in  direction  with  the 
lines  of  greatest  linear  compression  and  stand  at  45°  to  the 
axis  of  torsion.  This  is  precisely  what  occurs  in  the  experi- 
ment on  glass.  On  the  other  hand,  the  theory  shows  that  the 
resultant  stresses  within  the  body  of  the  plate  are  not  in  general 
parallel  to  the  surfaces,  and  it  is  therefore  to  be  expected  that 
curved  surfaces  of  rupture  should  ensue. 

Character  of  Torsional  Rupture. — It  now  appears  certain  that 
the  experiments  on  the  torsion  of  glass  are  equivalent  to  the 
application  of  a  system  of  tensions  peculiarly  distributed,  and 
that  the  fissures  produced  by  torsion  in  any  mass  physically 
resembling  glass,  will  exhibit  the  peculiarities  of  tensional 
fractures,  together  with  some  marked  characteristics  of  their 
own.  The  fissures  will  gape  from  the  start,  excepting  at  cer- 
tain points,  which  alone  will  be  slickensided.  The  surfaces 
will  be  rough,  excepting  when  the  mass  is  uncommonly  homo- 
geneous. The  surfaces  will  also  show  double  curvature,  which 
will  be  very  strongly  marked  unless  the  mass  of  rock  affected 
by  torsion  is  immense.  If  the  axis  of  torsion  is  vertical  the 
particles  originally  in  contact  will  separate  along  horizontal 
lines,  and  there  will  be  no  faults  as  these  are  usually  estimated. 


100  THE    TORSIONAL    THEORY    OF    JOINTS. 

In  all  other  cases  every  surface  will  be  faulted,  and  every  master 
fault  will  be  reversed.  The  network  of  fissures  will  show 
marked  regularity,  provided  that  the  exposure  is  an  approxi- 
mately flat  surface  nearly  parallel  to  the  axis  of  torsion,  but  any 
section  forming  an  angle  with  the  axis  of  torsion,  will  expose  a 
very  complex  arrangement  of  curved  partings.  If  rocks  break 
under  torsion  at  all  as  glass  does,  a  pronounced  characteristic 
will  be  the  frequency  of  fissures  completely  "  cut  oif"  by 
others,  these  being  much  more  numerous  than  "  master  "joints. 
Conclusion  as  to  Jointing. — It  appears  from  the  foregoing  that 
though  torsional  rupture  may  be  of  frequent  occurrence  in 
disturbed  regions,  the  systems  of  dislocations  familiar  under 
the  designation  of  joints  cannot  aptly  be  ascribed  to  pure  tor- 
sion, while  direct  pressure  will  produce  the  phenomena  called 
jointing.  But  the  forces  acting  upon  a  rock-mass  are  in  general 
very  far  from  simple ;  indeed,  it  may  be  assumed  that  every 
variety  of  stress  exists  in  a  strained  rock-mass.  Nevertheless  a 
general  idea  of  the  nature  of  rupture  even  under  such  condi- 
tions may  readily  be  reached.  The  strain  ellipsoid  at  any 
point  must  either  be  torn  apart  by  tension  or  cut  across  by 
shearing,  and  in  all  ordinary  cases  it  is  easy  to  distinguish 
these  modes  of  rupture.  In  a  mass  subjected  to  a  complex 
stress  the  orientation  of  the  strain  ellipsoid  will  vary  from 
point  to  point,  and  so  will  the  direction  of  the  rupture;  but 
smooth,  slickensided  surfaces,  though  curved,  will  still  be  due 
to  pressures  acting  at  approximately  45°  to  the  local  direction 
of  the  surfaces  when  the  material  is  a  hard  and  homogeneous 
one ;  and  tension-cracks  will  form  at  right  angles  to  the  local 
direction  of  the  effective  tension.  Thus  in  typically  jointed 
areas,  curvature  of  the  joint-planes  indicates  that  the  direction 
of  the  effective  pressure  has  varied  from  point  to  point,  as  it 
does,  for  example,  in  the  compressed  portion  of  a  flexed  bar. 
The  existence  of  curved  joint-planes  is  consequently  by  no 
means  inconsistent  with  the  ascription  of  jointing  to  pressure, 
while  it  does  indicate  that  the  entire  system  of  forces,  operative 
and  inoperative,  which  has  been  brought  to  bear  on  the  mass 
is  complex.  The  action  of  pressure  on  heterogeneous  materials 
is  much  more  regular  than  the  action  of  tension ;  and  it  might 
be  possible  in  some  cases  from  the  study  of  curved  joint-sur- 
faces to  infer  the  nature  of  the  complete  stress- system. 


THE  TORSIONAL  THEORY  OF  'JOINTS.'  ' 
DISCUSSION. 

(Trans.,  xxiv.,  863.) 

H.  M.  HOWE,  New  York,  N.  Y. :  It  is,  of  course,  not  easy  to 
discuss  offhand  the  paper  which  Mr.  Becker  has  presented 
with  so  much  lucidity.  I  will  make  only  one  remark,  which 
is  outside  of  the  line  of  his  argument,  and  concerns  merely  a 
passing  allusion  in  his  paper.  Mr.  Becker  speaks  of  the  fact 
that  glass  breaks  with  a  flat  or  conchoidal  fracture,  and  that 
steel  shows  a  rough  or  "  cupped "  surface  of  fracture.  This 
difference  we  would  naturally  ascribe  to  the  great  difference 
in  the  other  physical  properties  of  the  two  substances.  Yet  I 
have  seen  copper-steel  which  did  break  in  a  perfectly  flat  frac- 
ture, or  apparently  so.  It  seemed  to  be  accurately  perpen- 
dicular; a  smooth,  mirror-like  fracture,  such  as  mineralogists 
called  "  splendent."  Yet  the  physical  properties  of  this  steel 
did  not  differ  from  those  of  common  steel,  or  resemble  those 
of  glass  in  the  way  which  this  fracture  suggests. 

R.  W.  RAYMOND,  New  York,  N.  Y. :  The  general  conclusions 
reached  by  Mr.  Becker  seem  to  me  to  be  fairly  demonstrated. 
His  paper  does  not  contain  any  precise  definition  of  what  we 
call  joints;  and  possibly  such  a  definition  ought  to  be  offered 
as  the  basis  of  any  complete  theory  of  the  subject.  Without 
venturing  to  supply  such  a  definition  here,  I  infer  from  Mr. 
Becker's  paper,  and  in  accordance  with  our  general  usage  of 
the  term,  that  joints  are  to  be  distinguished,  on  the  one  hand, 
from  cleavage- planes,  which  we  may,  perhaps,  consider  as 
potential  rather  than  actual  partings,  and,  on  the  other  hand, 
from  fissures  on  a  larger  scale,  such  as  become  the  receptacles 
of  mineral  veins.  And  I  understand  his  view  to  be,  that  joint- 
ing is  neither  produced  by  tensile  stress  nor  by  pure  torsion, 
while  direct,  more  or  less  oblique,  pressure  will  account  for 
the  observed  phenomena.  At  the  same  time,  he  recognizes 
the  inevitable  complexity  of  the  stresses  involved. 

This  conclusion  may  have  an  important  bearing  on  the  sub- 
ject of  larger  rock-faults.  At  the  "Washington  meeting  of 
February,  1882,  I  presented  a  paper  on  Hoefer's  Method  of 
Determining  Faults  in  Mineral  Veins,9  based  upon  the  author's 

9  Trans.,  x.,  456  (1881-82). 


102  THE    TORSIONAL    THEORY    OF    JOINTS. 

essay,  which  appeared  in  volume  xxix.  of  the  Austrian  Zeit- 
schrift.  The  peculiarity  of  Professor  Hoefer's  method  is,  that 
it  provides  for  the  case  of  a  relative  movement  of  the  two  walls 
of  a  fault  which  is  not  rectilinear,  but  to  some  extent  rotatory ; 
that  is,  in  which  a  partial  revolution  of  the  mass  on  one  side  of 
the  fault  has  taken  place  around  an  axis  normal  to  the  plane 
of  the  fault-fissure.  The  evidence  of  such  a  motion  is  found 
in  changes  of  dip  and  strike,  produced  by  the  fault,  in  the 
fissure  faulted.  I  wrote  to  Professor  Hoefer  at  that  time, 
telling  him  that  this  phenomenon  had  not  been  recognized  in 
our  mining-districts  to  any  great  extent,  and  asking  whether 
such  movements,  distinct  from  rectilinear  ones,  had  been  fre- 
quently observed  by  him.  His  reply  was  : 

''Circular  movements,  combined  with  movements  in  straight  lines,  are  very  fre- 
quent in  our  faults  ;  in  fact,  I  do  not  doubt  at  all  that  a  continued  careful  study 
will  show  them  to  be  the  rule.  Whether  simple  revolutions  often  occur,  is  very 
difficult  to  decide  from  the  observations  thus  far  available."  w 

It  is  my  present  belief  that  the  circular  movements  have 
been,  as  a  rule,  not  only  accompanied  by  straight-line  move- 
ments, but  that  the  latter  have  been  predominant;  and  it  seems 
to  me  most  reasonable  to  suppose  that  rotation  has  been  caused, 
not  by  the  direction  of  the  forces  which  caused  rupture,  but  by 
the  resistance  encountered  in  the  course  of  a  rectilinear  slide. 
It  is,  indeed,  almost  inevitable  that  such  a  movement  would 
not  be  wholly  rectilinear,  but  that  the  mass  would  be  turned 
more  or  less  around  points  of  greater  friction.  In  other  words, 
the  seeming  effects  of  torsion  might  be  produced  after  the 
occurrence  of  a  rupture  in  which  torsion  had  taken  no  part. 

In  this  view  the  causes  of  rupture  on  the  large  scale  would 
be  entirely  analogous  to  those  observed  on  the  small  scale  in 
joints.  This  is  a  familiar  principle  to  those  who  have  worked 
upon  rocks  with  the  microscope,  or  have  studied  in  hand- 
specimens  the  features  exhibited  in  rock-masses.  We  find  in 
all  sizes  the  phenomena  of  faults,  contortions,  cavities,  segrega- 
tions, etc. ;  and  we  are  almost  irresistibly  led  to  the  conclusion 
that  the  microscopic  is  but  the  image  of  the  macroscopic,  and 
vice  versa.  But,  in  accordance  with  this  principle,  it  may  be 
(indeed,  it  ought  to  be)  true  that  the  small  ruptures  are  some- 

10  For  a  single  and  uncertain  instance  of  possibly  simple  circular  movement, 
adduced  by  Professor  Hoefer,  see  my  paper  above  cited,  p.  463. 


THE    TORSIONAL    THEORY    OF    JOINTS.  103 

times  produced,  as  are  larger  faults,  by  tensile  stress.  In  fact, 
I  think  such  minute  tension- ruptures  are  frequently  to  be 
observed,  but  they  do  not  generally,  if,  indeed,  they  ever  do, 
exhibit  the  smoothness  and  regularity  of  joints. 

MR.  BECKER  :  I  may  remark  that  faults  supposed  to  be  pro- 
duced by  torsion  are  said  to  be  so  common  in  certain  French 
mining-districts  that  the  miners  have  a  special  name  for  them. 
They  call  them  hinge-faults,  which  is,  I  think,  a  very  good 
name. 

The  term  "joint"  I  regard  as  used  simply  for  convenience 
to  designate  those  partings  in  rocks  on  which  the  throw  is  not 
apparent  without  close  observation.  Excepting  in  the  amount 
of  throw,  they  are  not  distinguishable  from  the  paraclastic  rup- 
tures on  which  mineral  veins  form.  Even  on  joints  ores  some- 
times occur,  e.g.,  the  "  paints  "  of  the  quicksilver-mines.  Joints 
also  pass  over  into  cleavage.  This  structure  sometimes  con- 
sists of  closely-grouped  joints  of  microscopic  throw,  and  some- 
times of  mere  deformation  not  carried  quite  far  enough  to 
induce  rupture.  Cleavage  and  faulting  are  equally  orogenic 
disturbances. 

C.  R.  BOYD,  Wytheville,  Va. :  In  examining  a  silver-mining 
property  at  Conrad  Hill,  6  miles  southeast  of  Lexington, 
Davidson  county,  K  C.,  several  years  ago,  I  found  two  series 
of  fissures  crossing  each  other,  one  set  being  mainly  filled  with 
carbonate  of  iron  and  magnesia,  the  other  with  iron  and  copper 
pyrites,  carrying  gold  and  silver.  The  individual  fissures  of 
each  series  were  not  more  than  15  or  20  ft.  apart.  The  car- 
bonate veins  had  a  north-and-south  strike,  and  a  dip  of  30° 
west.  The  pyrites  veins  ran  east  of  north  and  west  of  south, 
dipping  40°  west  of  north.  The  angle  between  the  two  series 
was  about  the  same  as  that  which  the  mountain  ranges  of  that 
section  make  with  the  true  meridian.  That  both  series-  could 
have  resulted  from  simple  tangential  strains  or  thrusts  would 
be  difficult  to  prove,  and  that  they  could  both  be  fissures  of 
contraction  I  hardly  believe.  Possibly  torsion  may  have  caused 
them ;  but  it  is  more  probable,  in  my  judgment,  that  they  re- 
sulted from  disturbances  proceeding  from  separate  foci,  and 
not  necessarily  simultaneous. 


104  THE    TORSIONAL    THEORY    OF    JOINTS. 

MR.  BECKER  :  The  angle  depends  on  the  amount  of  distor- 
tion which  has  preceded  rupture.  If  a  substance  is  brittle,  like 
glass  or  cast-iron,  and  yields  to  rupture  before  it  has  been 
deformed  to  any  considerable  extent,  the  fissures  will  cross  at 
right  angles.  If,  on  the  other  hand,  the  character  of  the  mass 
or  its  confined  position  (as  is  often  the  case  with  rocks)  pre- 
vents rupture  from  occurring  until  deformation  has  reached  an 
extreme  limit,  the  angle  between  the  direction  of  the  force  and 
that  of  fracture  may  be  even  50°  or  60°,  and  large  angles  seem 
always  to  mean  great  preliminary  deformation. 

The  most  usual  conditions  of  rock-fracture  involve  the  simul- 
taneous formation  of  two  sets  of  fissures ;  but  when  the  resist- 
ances in  all  directions  perpendicular  to  the  line  of  force  are 
substantially  uniform,  four  sets  of  ruptures  may  form,  each 
being  at  45°  or  more  to  the  line  of  force,  and  all  four  sets  will 
be  slickensided.  A  single  system  of  parallel  faults  involves  the 
action  of  a  "  rotational "  stress  (which  is,  of  course,  utterly  dif- 
ferent from  a  torsional  stress) ;  and  a  solitary  fault  arises  as  an 
extreme,  and  in  my  experience  rare,  case  of  a  rotational  stress. 
I  am  inclined  to  believe  that  when  two  or  three  or  four  sys- 
tems of  joints  or  fissures  intersect  a  rock-mass  they  were,  as  a 
rule,  formed  simultaneously.  When  a  rock  is  once  shattered 
a  fresh  force  meets,  in  general,  with  very  unequal  resistance  in 
different  directions,  and  will  cause  disturbance  on  the  old  fis- 
sures or  brecciate  the  whole  mass  rather  than  induce  a  new, 
regular  system  of  intersecting  partings. 


THE    ALLOTROPISM    OF    GOLD.  105 


No.  5. 
The  Allotropism  of  Gold. 

BY   HENRY  LOUIS,    LONDON,    ENGLAND. 

(Virginia  Beach  Meeting,  February,  1894.    Trans.,  xxiv.,  182.) 

IT  can  scarcely  be  considered  a  matter  of  doubt,  in  the 
present  state  of  our  knowledge,  that  the  existence  of,  at  any 
rate,  two  well-marked  allotropic  modifications  of  gold  can  be 
recognized,  namely  (a),  the  ordinary,  yellow  variety,  and  (6) 
the  red,  brown  or  purple,  non-lustrous,  amorphous  variety. 

There  are,  indeed,  not  wanting  indications  that  still  other 
allotropic  forms  may  be  capable  of  existing.  It  is,  for  instance, 
possible  that  the  green  colors  of  gold  obtained  under  cer- 
tain conditions,  or  the  black  powder  produced  when  the  alloy 
of  gold  with  potassium  is  decomposed  by  water,  may  represent 
further  allotropic  modifications,  although  this  proposition  is 
open  to  doubt.  .  It  can  scarcely  be  pretended  that  the  two  first- 
named  varieties  have  been  absolutely  isolated,  yet  it  is,  perhaps, 
quite  permissible  to  speak  of  the  ordinary  and  the  amorphous 
modifications  as  having  a  proved  existence. 

Ordinary  gold  is  sometimes  found  crystallized  in  nature, 
although  never  in  a  state  of  purity.  When  gold  is  melted  and 
cooled  slowly,  its  surface  shows  crystalline  markings,  and  the 
fact  that  it  is  capable  of  crystallizing  in  the  cubic  system  may 
be  looked  upon  as  established.  When  gold  is  produced  by 
precipitation,  the  form  which  it  assumes  is  dependent  on  the 
conditions  of  precipitation.  G.  Rose l  says  that  gold  precipitated 
by  ferrous  sulphate  from  very  dilute  solutions  is  so  finely 
divided  that  no  regular  form  can  be  recognized,  but  in  more 
concentrated  solutions  the  precipitate  consists  of  minute  cubes. 
When  oxalic  acid  is  used  as  a  precipitant,  the  gold  is  coarser 
and  forms  octahedral  crystals.  J.  Thomsen2  has  obtained 
similar  results.  Working  with  dilute  and  with  highly-dilute 

1  Poggendorff's  Annalender  Physik  und  Chemie,  vol.  Ixxiii.,  p.  8  (1848). 
a  Journal  fur  praktische  Chemie,  vol.  xiii.,  p.  348. 


106  THE    ALLOTROPISM    OF    GOLD. 

solutions,  I  have  myself  been  quite  unable  to  recognize  any 
crystalline  structure,  even  under  the  highest  powers  of  the 
microscope ;  nor  did  there  seem  to  be  even  any  tendency  of 
the  particles  to  group  themselves  into  arborescent  forms,  such 
as  might  indicate  incipient  crystallization.  Precipitates  from 
solutions  containing  between  0.0001  and  10  per  cent,  of  gold 
gave  no  indications  of  crystallization,  even  when  magnified  800 
diameters. 

Thomsen  (loc.  cit.)  has  also  pointed  out  that  the  physical 
characters  of  precipitated  gold  differ  according  as  it  has  been 
precipitated  from  solutions  of  its  chloride  or  its  bromide.  He 
also  found  that  these  different  forms  possessed  different  degrees 
of  thermic  energy,  and  hence  deduced  a  strong  argument  in 
favor  of  their  being  allotropic  varieties. 

The  specific  gravities  of  various  forms  of  gold  differ  con- 
siderably. G.  Rose  (loc.  cit.)  found  that  fused  gold  had  a 
density  of  19.3336  after  it  had  been  compressed  in  a  coining- 
press,  it  being  a  little  lower  before  this  mechanical  treatment. 
The  density  of  precipitated  gold  thrown  down  by  ferrous  sul- 
phate he  found  to  vary  from  19.5419  to  20.6882,  the  highest 
figures  being  obtained  from  extremely-dilute  solutions,  the 
precipitate  from  which  showed  no  trace  of  crystalline  form ; 
when  precipitated  by  oxalic  acid  its  specific  gravity  was 
19.4791.  When  such  amorphous  gold  was  struck  in  the  coin- 
ing-press, its  density  became  reduced  to  18.0194.  I  have  found 
that  the  density  of  gold  left  on  dissolving  out  various  metals 
alloyed  with  it,  when  the  gold  remains  behind  in  a  brown, 
amorphous,  lusterless  condition,  varies  between  20.3  and  19. 5.3 

It  is  only  fair  to  notice  that  Rose  did  not  ascribe  the  differ- 
ences in  the  densities  of  the  different  forms  of  gold  to  allot- 
ropism,  but  has  suggested  another  explanation,  which  is 
hardly,  to  my  mind,  a  sufficient  one.  It  is  probably  safe  to 
assume  that  there  are  two  modifications  of  gold — one  a  light 
one,  of  density  19.3  or  thereabouts,  and  the  other  a  heavy  one, 
the  density  of  which  approaches  20.7 — while  various  combina- 
tions of  these  extreme  forms  are  capable  of  occurring. 

In  this  connection  the  curious  divergencies  in  the  densities 
of  specimens  of  native  gold,  from  different  localities  but  of 

3  See  note  by  the  writer,  Trans.,  xxii.,  117  (1893). 


THE    ALLOTROPISM    OF    GOLD.  107 

about  the  same  composition,  may  also  be  referred  to ;  allotro- 
pism  may,  at  any  rate,  be  suggested  as  a  possible  explanation 
of  them.  There  are  thus  sufficiently  well  marked  differences 
in  physical  characteristics  to  support  the  hypothesis  of  allot- 
ropism. 

As  regards  chemical  properties,  Thomsen  has  also  pointed 
out  that  when  amorphous,  pulverulent  gold  is  acted  on  by 
chlorine  or  bromine,  aurylic  compounds  (Au2Cl4  or  Au2Br4)  are 
produced ;  whereas,  these  same  substances  produce  auric  com- 
pounds (AuCl3  or  AuBr3)  with  ordinary  gold. 

I  have  found  another  point  of  difference,  of  far  greater 
practical  importance,  in  the  behavior  of  these  modifications 
towards  mercury.  Ordinary  gold,  of  course,  amalgamates 
readily,  as  is  well  known.  I  have  found  that  gold  precipitated 
from  highly-dilute  solutions  by  ferrous  sulphate  is  not  attacked 
at  all  by  mercury  when  freshly  precipitated,  and  only  slightly 
after  drying  on  an  air-bath.  Near  the  boiling-point  of  mer- 
cury, partial  amalgamation  took  place,  but  it  was  by  no  means 
complete.  Mercury  containing  a  large  amount  of  sodium 
amalgam  was  equally  without  effect  on  the  dry  gold,  although 
it  readily  and  completely  amalgamated  it  when  moist.  In 
these  observations  I  seem  to  have  been  partly  anticipated  by 
Ludwig  Knaffl,4  who,  however,  appeared  to  attach  little  im- 
portance to  his  observations.  In  a  brief  note  on  the  prepara- 
tion of  certain  amalgams  of  gold,  he  says  : 

"Gold  precipitated  by  green  vitriol  or  mercurous  nitrate  is  not  suitable  for 
amalgamation,  as  it  is  too  finely  divided  and  always  floats  on  the  surface  of  the 
mercury6  as  a  black  powder,  whether  heated  mercury  be  poured  upon  heated  gold 
or  vice  versa.  I  examined  this  floating  black  powder,  and  found  it  to  contain  gold 
and  mercury.  .  .  .  Gold  precipitated  either  by  means  of  arsenious  acid  or  by 
boiling  a  solution  of  the  chloride  in  amylic  alcohol,  when  it  separates  out  in  small, 
lustrous  octahedra,  is  best  suited  for  amalgamation." 

It  may  also  be  added  that  the  purple  of  Cassius,  which  prob- 
ably contains  an  allotropic  modification  of  gold,  is  not  attacked 
by  mercury.  The  black  pulverulent  form  of  gold  resulting 
from  the  decomposition  of  the  potassium-gold  alloy  likewise 
resists  amalgamation.  On  the  other  hand,  the  coherent  gold 

*  Dingkr's  Polytechnisches  Journal,  vol.  clxviii.,  p.  282  (1863). 
5  The  italics  are  mine. — H.  L. 


108  THE    ALLOTROPISM    OF    GOLD. 

sponge  left  on  dissolving  out  the  alloying  metal  from  a  gold- 
alloy  amalgamates  fairly  readily,  as  does  also  the  coherent  pale- 
brown  powder  produced  by  precipitating  with  sulphurous  acid 
a  strong  solution  of  auric  chloride. 

All  forms  of  gold  are  converted  into  the  ordinary  yellow, 
lustrous  variety  by  the  action  of  heat.  A  very  high  tempera- 
ture is  not  required,  but  the  exact  point  has  not  yet  been 
determined;  it  is  certainly  well  above  200°  C.,  but  probably 
under  600°  C.6  Powerful  mechanical  action,  such  as  percus- 
sion, friction,  or  compression,  has  the  same  effect. 

I  do  not  pretend  that  the  above  data  form  anything  like  a 
complete  chain  of  evidence  proving  irrefragibly  the  allotropism 
of  gold,  or  that  our  knowledge  of  this  subject  is  precise  or 
definite ;  yet  I  venture  to  think  that  the  facts  do  warrant  us  in 
looking  upon  the  following  deductions  as  probably  correct: 

1.  Gold  is  capable  of  existing  in  allotropic  modifications. 

2.  One  of  these  modifications  is   capable  of  amalgamation 
only  with  great  difficulty,  if  at  all. 

3.  This  modification  is  capable  of  being  produced  and  of 
subsisting  under  conditions  that  may  reasonably  be  supposed 
to  exist  in  nature  when  gold  is  deposited  in  reefs. 

Whatever  may  have  been  the  nature  of  the  solution  by 
means  of  which  gold  has  been  introduced  into  the  deposits  in 
which  we  find  it,  whether  as  a  soluble  haloid  salt,  as  is  generally 
supposed,  or  as  an  alkaline  aurate,  as  I  venture  to  suggest,7  it 
must  have  been  precipitated  from  such  solution  in  various 
ways  and  under  varying  conditions.  We  have  but  few  indica- 
tions of  the  cause  of  this  precipitation,  but  it  is  reasonable  to 
conjecture  that  such  reagents  as  ferrous  sulphate  or  sulphurous 
acid,  both  resulting,  perhaps,  from  the  slow  oxidation  of  iron 
pyrites,  may  have  found  their  way,  in  solution,  into  the  fissures 
within  which  the  gold-solution  was  circulating,  and  may  thus 
have  caused  the  deposition  of  gold  within  the  reefs.  Now,  if 
the  gold,  thus  deposited  from  highly-dilute  solutions,  happened 
never  to  be  exposed  to  a  particularly  high  temperature,  or  to 
violent  mechanical  action,  the  conditions  would  be  favorable 

6  I  am   at  present  engaged  in   investigating  this   point,  and   hope  to  publish 
shortly  the  result  of  my  research. — H.  L. 

7  On  the  Mode  of  Occurrence  of  Gold,  Mineralogical  Magazine,  vol.  x.,  No.  47, 
p.  241. 


THE    ALLOTROPISM    OF    GOLD.  109 

to  the  production  of  that  allotropic  modification  of  gold  which 
is  indifferent  to  the  action  of  mercury.  In  other  words,  under 
the  above  conditions,  an  auriferous  deposit  will  have  been  pro- 
duced in  which  a  greater  or  smaller  part,  or  perhaps  even  the 
whole,  of  the  gold  is  what  gold-miners  term  "  rusty."  I  have 
little  doubt  that  the  "  rustiness  "  of  gold  is  in  different  cases 
due  to  widely-different  causes — that,  in  fact,  there  is  more  than 
one  kind  of  "  rustiness ; "  but  I  venture  to  think,  also,  that 
there  is  sufficient  evidence  to  warrant  us  in  classing  allotropism 
among  such  causes  of  "  rustiness."  If  this  is  correct,  I  need 
hardly  point  out  either  the  great  practical  value  or  the  applica- 
tion of  this  deduction.  The  gold  which  is  thus  allotropically 
indifferent  to  mercury  is  in  a  condition  in  which  it  is  readily 
attacked  by  such  reagents  as  chlorine  and  potassic  cyanide.  I 
have  pointed  out  long  ago  that  the  gold  of  the  Witwatersrand 
deposits  of  the  Transvaal  was  probably  deposited  in  situ  under 
some  such  conditions  as  I  have  sketched  above,  and  it  is  now 
notorious  that  a  large  proportion  of  the  gold  in  them  is  not 
attacked  by  mercury,  but  readily  by  potassic  cyanide  solution. 
Again,  in  some  cases  it  may  be  economically  feasible  to  con- 
vert the  non-amalgamable  modification  of  gold  into  the  common 
amalgamable  variety  by  heating  the  ore  to  a  moderate  tem- 
perature, or  the  same  end  may  be  attained  by  mechanical 
means.  In  any  case,  the  only  really  sound  method  of  prevent- 
ing losses  of  gold  in  the  process  of  gold-extraction  is  that  of 
ascertaining,  in  the  first  place,  the  ultimate  causes  of  such  loss; 
and  I  venture  to  hope  that  it  will  be  found  that  among  such 
causes,  the  one  here  treated  of — namely,  allotropism  of  gold — 
will  be  found  worthy  of  more  consideration  than  it  has  hitherto 
received  from  scientific  gold-miners. 


110  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 


No.  6. 
The  Superficial  Alteration  of  Ore-Deposits. 

BY  R.  A.  F.  PENROSE,  JR.,  U.  S.  GEOLOGICAL  SURVEY. 

(Reprinted  from  The  Journal  of  Geology,  vol.  ii.,  No.  3,  Apr.-May,  1894.) 

I.  INTRODUCTION. 

THE  superficial  alteration  of  ore-deposits  is  a  recognized 
principle  of  geology,  in  the  same  way  as  is  the  superficial  altera- 
tion of  any  of  the  common  rocks.  Its  importance  in  some 
classes  of  ore-deposits  is  also  well  understood,  as  in  many 
precious-metal  deposits;  while  in  other  classes,  its  importance 
has  been  proved  in  individual  cases,  as  in  the  Lake  Superior 
iron-deposits.  The  causes  and  effects  of  superficial  alteration 
in  many  classes  of  deposits,  however,  are  not  so  generally  under- 
stood; and  it  is  the  object  of  the  present  paper  to  show  that 
such  changes  almost  invariably  give  rise  to  exceedingly  im- 
portant chemical  and  physical  phenomena,  while  in  many 
deposits,  the  question  as  to  whether  they  can  or  cannot  be 
profitably  worked  depends  largely  on  the  extent  and  character 
of  this  alteration. 

The  various  treatises  on  ore-deposits  published  in  the  United 
States  and  Europe  make  frequent  mention  of  superficial  altera- 
tion, but  have  not  treated  the  subject  fully.  As  early  as  1854, 
however,  before  which  time  but  little  accurate  information  was 
had  on  the  geologic  nature  of  ore-deposits,  Prof.  J.  D.  Whit- 
ney in  his  classic  volume,  The  Metallic  Wealth  of  the  United 
States,  describes  the  alteration-products,  or  gossans,  in  certain 
deposits  and  mentions  others.  On  the  more  purely  chemical 
side  of  the  question,  the  work  of  Bischof,  Daubree,  Roth,  Rose,. 
Hunt,  Breithaupt,  Blum,  Julien,  Deville,  Debray,  Volger,  Mois- 
san,  Fremy,  Levy,  Fouque,  and  others  has  afforded  much  valu- 
able information  and  many  useful  suggestions.  The  chemical 
principles  brought  out  by  these  various  authors  have  been  ap- 
plied, to  a  certain  extent,  to  the  solution  of  the  phenomena  of 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  Ill 

the  origin  of  ore-deposits,  but  have  not  as  yet  been  applied 
to  anything  like  their  possible  extent  to  the  solution  of  the 
phenomena  of  the  alteration  of  ore-deposits. 

II.  GENERAL  FEATURES. 

Scope  of  the  Subject. 

The  modern  idea  of  ore-deposits  teaches  that  formations  of 
this  kind  represent  a  process  of  concentration  of  mineral  matter, 
either  by  chemical  or  physical  means;  in  other  words,  that 
they  are  unusual  localizations  of  certain  minerals  which  are 
often  found  disseminated  in  smaller  quantities  in  many  common 
rocks,  and  that  they  differ  from  the  same  minerals  situated  in 
other  conditions,  only  in  their  degree  of  concentration.  These 
concentrations  may  take  place  at  different  times  in  the  history 
of  the  rocks  in  which  the  deposits  occur.  If  they  occur  in 
sedimentary  rocks,  they  may  sometimes  be  formed  during  the 
deposition  of  the  rocks  with  which  they  are  associated,  as  in 
the  cases  of  placer-gold,  stream-tin,  and  sometimes  of  other 
ores;  while  if  they  occur  in  igneous  rocks,  they  may  some- 
times be  the  result  of  concentration  by  differentiation  from 
fused  magmas.1  More  usually,  however,  ore-deposits  are  a 
result  of  a  concentration  after  the  formation  of  the  inclosing 
rock,  whether  the  latter  be  of  sedimentary  or  of  igneous  origin. 
The  mineral  matter  represented  in  this  concentration  may  be 
derived  from  the  inclosing  rocks  or  closely-adjacent  rocks,  as 
in  the  case  of  many,  if  not  most,  iron-ore  deposits ;  or  it  may 
be  derived  from  more  distant  sources,  often  from  greater  or  less 
depths,  as  in  some  of  the  precious-metal  deposits.  Occasion- 
ally, both  these  sources  may  be  drawn  on  for  mineral  matter 
in  one  deposit.  In  this  subject  of  the  original  source  of  an  ore, 
we  enter  a  field  concerning  which  there  has  been  much  dispute 
of  late  years  between  the  advocates  of  the  lateral-secretion 
theory  and  those  who  favor  the  idea  of  a  deep-seated  source  for 
many  ore-deposits.  It  is  not,  however,  the  purpose  of  the 
present  paper  to  enter  into  this  discussion,  and  the  following 

1  This  has  been  shown  by  J.  H.  L.  Vogt  (Zeitschrift  filr  praktische  Geologic,  Jan., 
1893)  to  be  true  of  certain  titaniferous  iron-ores  and  other  deposits  in  the  eruptive 
rocks  of  Norway.  It  may  also  be  true  of  certain  titaniferous  iron-ores  in  the 
United  States. 


112  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

remarks  are  confined  to  what  happens  in  the  superficial  parts 
of  ore-deposits,  and  to  a  less  extent  of  allied  formations,  after 
the  materials  forming  them  have  been  brought  into  their 
present,  or  approximately  their  present,  positions. 

Relation  of  Alteration  in  Ore-Deposits  and  in  Country -Hocks. 

Ore-deposits  are  generally  more  or  less  changed  in  their 
upper  parts  by  atmospheric  influences,  so  that  very  rarely  do 
the  same  mineralogical  and  physical  features  that  are  found  in 
these  parts  continue  to  very  great  depths.  In  considering  this 
superficial  alteration,  we  discuss  a  subject  analogous  to  the 
secular  decay  of  rocks.  The  latter,  however,  involves  usually 
but  a  limited  number  of  common  rock-forming  minerals,  while 
the  secular  decay  of  ore-deposits  involves  a  great  variety  of 
minerals,  not  only  the  oxides,  carbonates,  and  silicates  common 
in  most  rocks,  but  also  sulphides,  arsenides,  tellurides,  sele- 
nides,  antimonides,  chlorides,  bromides,  iodides,  fluorides,  sul- 
phates, phosphates,  tungstates,  molybdates,  and  numerous  other 
classes  of  minerals,  many  of  which,  under  surface-influences, 
give  rise  to  intricate  chemical  changes.  In  discussing  the  sub- 
ject of  the  superficial  alteration  of  ore-deposits,  therefore,  we 
treat  a  similar,  but  much  less  understood,  subject  than  the 
superficial  alteration  of  rocks. 

Technical  Names  of  Alteration- Products. 

The  altered  surface-outcrop  of  ore-deposits  is  known  by 
various  names  in  different  regions.  Among  the  Cornish 
miners  of  England  it  is  known  as  gossan,  a  name  which  has 
also  been  adopted  into  American  mining  nomenclature,  though 
other  special  names  are  given  in  special  classes  of  deposits.  In 
France  it  is  known  &a-chapeau  de  fer;  in  Germany  as  eisener 
Hut ;  among  the  Spanish  Americans  as  pacos  or  colorados.  As 
almost  all  deposits  contain  more  or  less  iron-minerals,  the  out- 
crops are  usually  stained  brown  from  their  oxidation,  and 
hence  the  reference  to  iron  in  the  French  and  German  names. 
Sometimes,  however,  the  outcrops  are  stained  black  by  the 
oxidation  of  manganese  carbonate  or  silicate,  or  green  by  cop- 
per-minerals, or  other  colors  by  the  formation  of  other  com- 
pounds. 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  113 

Agents  of  Alteration. 

The  superficial  alteration  of  ore-deposits,  as  of  any  rock, 
results  from  a  combination  of  mechanical  and  chemical  disinte- 
gration, brought  about  by  the  combined  action  of  the  atmos- 
phere, surface-waters,  changes  in  temperature,  and  the  various 
organic  and  inorganic  materials  contained  in  the  air  and  water. 
In  nature,  we  never  deal  with  perfectly  pure  water,  but  dif- 
ferent waters  contain  different  ingredients  derived  from  the  air 
and  from  the  different  materials  with  which  they  come  in  con- 
tact. Among  the  most  important  of  these  ingredients  are 
oxygen,  numerous  organic  acids  like  carbonic,  oxalic,  malic, 
citric,  formic,  propionic,  butyric,  acetic  acids,  etc.,  certain  inor- 
ganic acids,  such  as  sulphuric,  nitric,  hydrochloric,  hydrobro- 
mic,  etc.  Some  of  the  acids  mentioned  occasionally  occur 
in  the  free  state,  but  most  of  them  are  generally  combined 
with  some  of  the  bases  present,  such  as  the  alkalies,  lime,  mag- 
nesia, iron,  alumina,  etc.  These  various  ingredients,  of  course, 
are  not  all  contained  in  the  same  waters,  but  are  found  in 
various  associations  in  different  waters.  The  organic  acids 
mentioned  represent  various  stages  of  oxidation  of  materials 
from  organic  matter,  but  they  all  eventually,  if  allowed  to  be- 
come completely  oxidized,  pass  into  carbonic  acid;  while  if 
they  are  in  combination  with  different  bases,  these  salts  are 
eventually  converted  to  carbonates. 

Method  and  Chemical  Effects  of  Alteration. 
Surface-waters  thus  charged  with  various  chemical  ingre- 
dients percolate  down  into  ore-deposits,  and  there  meet  various 
materials  which  are  even  less  stable  under  their  influence  than 
most  of  the  common  rocks.  The  alteration,  therefore,  is  com- 
paratively rapid,  and,  though  only  superficial,  generally  extends 
to  much  greater  depths  than  in  the  surrounding  country-rock. 
From  a  chemical  stand-point,  the  first  effect  of  this  superficial 
influence  is  usually  the  oxidation,  or  hydration,  or  both,  of  cer- 
tain ingredients,  followed  generally  by  the  formation  of  other 
chemical  combinations  and  by  the  leaching  of  certain  materials. 
In  the  formation  of  these  other  chemical  combinations,  how- 
ever, the  base  usually  remains  the  same,  and  the  alteration 
consists  generally  in  a  change  of  the  materials  associated  with 
the  base,  that  is,  in  the  acidic  portion  of  the  mineral  or  the 


114  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

part  that  represents  the  acidic  portion.  Thus,  iron  sulphides 
are  oxidized  to  iron  sulphate,  and  then  this  is.  converted  by 
further  oxidation  and  by  hydration  to  the  hydrous  sesquioxide. 
Copper  sulphides  may  be  oxidized  to  copper  sulphate;  and 
from  the  sulphate,  by  the  agency  of  materials  in  surface-waters, 
may  be  formed  copper  carbonates,  haloid  compounds,  silicates, 
oxides,  and  even  metallic  copper;  while  from  some  of  these, 
still  other  compounds  may  be  produced.  Similar  reactions 
occur  in  many  lead-,  zinc-,  silver-,  gold-,  and  other  deposits. 

Occasionally,  chemical  changes  may  occur  without  previous 
oxidation,  and  sometimes,  though  rarely,  surface-influences 
under  peculiar  conditions  may  have  a  reducing  effect,  as  in  the 
formation  of  iron  pyrites  and  copper  pyrites  from  the  sulphates 
of  iron  and  copper,  or  in  the  formation  of  native  copper  by  the 
action  of  a  ferrous  salt  on  certain  copper  salts,  or  in  the  forma- 
tion of  native  silver  in  surface-outcrops.  In  many  of  such 
cases,  however,  the  chemical  action  is  primarily  one  of  partial 
oxidation,  and  the  reducing  action  follows  as  the  effect  of  one 
of  the  partly-oxidized  compounds  on  the  other,  as  in  the  case 
of  copper  just  mentioned.  In  deposits  such  as  gypsum,  a 
reduction,  due  sometimes  to  superficial  influences,  is  seen  in 
the  occasional  formation  of  sulphur  from  gypsum. 

An  important  chemical  effect  of  surface-influences  is  the  re- 
moval in  solution  of  certain  ingredients  of  the  ore-deposit 
which  are  soluble  in  surface-waters ;  as  the  removal  of  the  cal- 
cite  gangue  of  many  silver-  and  other  deposits;  the  oxidation 
and  removal  of  the  sulphur  in  various  silver-,  lead-,  zinc-,  cop- 
per-, and  other  deposits;  the  oxidation  and  removal  of  both 
the  iron  and  sulphur  of  iron  pyrites  in  auriferous  quartz  veins; 
the  removal  of  silica  from  certain  iron-deposits,  such  as  those 
in  the  Lake  Superior  region,  etc.  Probably  many  phosphate- 
deposits  are  formed  by  the  superficial  leaching  of  carbonate  of 
lime  from  calcareous  beds,  and  the  corresponding  concentra- 
tion of  phosphate  of  lime  once  finely  disseminated  in  the  same 
beds. 

Another  chemical  effect  of  superficial  alteration  is  seen  in 
the  occasional  formation  of  mineral  deposits  of  importance  by 
certain  materials  carried  from  outside  sources  and  deposited 
in  a  rock  of  otherwise  no  commercial  value.  Thus  certain 
phosphate-deposits  of  the  South  Pacific  ocean,  the  West  Indies,. 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  115 

and  possibly  of  Florida,  are  formed  by  the  leaching  of  soluble 
phosphates  from  guano,  their  transportation  down  into  under- 
lying limestone  or  coral  reefs,  and  the  precipitation  of  the 
phosphoric  acid  as  tribasic  phosphate  of  lime,  which,  being 
almost  insoluble,  arrests  further  escape  of  the  phosphatic 
materials. 

Again,  another  chemical  effect  is  seen  in  the  incrustations, 
and  even  extensive  beds,  of  saline  materials,  like  borax,  niter, 
and  the  various  alkaline  salts  of  the  Western  arid  regions, 
formed  by  precipitation  from  water  rising  by  capillary  action 
through  the  soil,  becoming  evaporated  on  the  surface  and  de- 
positing the  saline  materials  which  it  has  dissolved  from  below. 
Many  saline  deposits  are  formed  by  the  simple  evaporation  of 
surface-waters,  such  as  lakes,  seas,  etc.,  but  certain  deposits 
undergo  only  an  initial  concentration  in  this  way,  and  are  laid 
down  with  clay,  sand,  and  gravel,  while  further  concentration 
is  due  to  this  capillary  action.  In  the  case  of  niter,  indeed,, 
the  saline  material  is  very  often,  if  not  generally,  formed  in 
soils  or  guano-beds  and  undergoes  its  first  concentration  by 
this  capillary  action. 

In  the  various  chemical  changes  mentioned  above,  the  class 
of  salts  that  remains,  whether  oxides,  carbonates,  haloid  com- 
pounds, etc.,  varies  with  the  nature  of  the  bases  affected. 
Thus,  iron  sulphides  and  copper  sulphides  are  both  oxidized 
and  form  sulphates.  But  here  the  similarity  of  their  behavior 
ends,  for  the  iron  sulphate  probably  passes  then  into  a  basic 
sulphate  and  then  into  a  hydrous  sesquioxide,  while  the  copper 
sulphate  takes  up  carbonic  dioxide  and  water  and  forms  basic 
carbonates.  The  iron  sulphate  might,  under  certain  condi- 
tions, form  a  carbonate  in  a  similar  manner,  but  this  compound 
would  be  very  unstable  under  the  conditions  existing  in  the 
alteration  of  sulphide  deposits  and  would  quickly  go  into  the 
form  of  the  hydrous  sesquioxide,  while  the  carbonate  of  copper 
is  stable  under  existing  conditions  and  remains. 

In  the  same  way,  if  silver  sulphide  and  iron  sulphide  are 
both  oxidized  and  then  affected  by  waters  carrying  common 
salt  or  other  chlorides  in  solution,  the  silver  is  converted  to 
chloride,  which  is  insoluble  and  remains ;  while  the  chlorides 
of  iron  are  much  less  liable  to  be  formed,  as  they  are  soluble, 
and  some  of  them  unstable,  compounds,  and  even  if  they  were 


116  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

formed,  they  would  be  leached  out  or  oxidized.  Hence,  though 
chloride  of  silver  is  a  common  product  of  alteration,  in  silver- 
deposits,  chloride  of  iron  is  never  found,  at  least  to  any  extent, 
as  a  product  of  alteration  of  iron-deposits. 

Again,  it  is  frequently  found  that  unaltered  auriferous  iron 
pyrites  contains  a  certain  amount  of  silver,  while  the  altered 
part  often  carries  almost  none.  In  such  cases,  the  gold  has 
remained  stable  during  the  alteration,  while  the  silver,  in  the 
absence  of  a  chloride  or  other  reagents  to  convert  it  to  an  in- 
soluble compound,  has  been  dissolved  and  carried  away  in 
solution  by  the  acid  materials  generated  during  alteration. 

Hence,  the  materials  in  surface-waters  affect  different  bases 
differently,  and,  therefore,  there  is  a  great  difference  in  the 
classes  of  salts  formed  by  the  same  surface-waters  on  the  ores 
of  different  metals.  In  the  same  deposit  there  may  be  formed 
an  oxide  of  one  metal,  a  carbonate  of  another,  a  chloride  of 
another,  etc.  In  fact,  in  some  of  the  silver-deposits  of  southern 
New  Mexico,  there  can  be  found  hydrous  sesquioxide  of  iron 
formed  from  iron  sulphide,  carbonates  of  copper  formed  from 
copper  sulphides,  and  chloride  of  silver  formed  probably  from 
silver  sulphides,  and  yet  in  all  probability  the  same  surface- 
waters  produced  all  these  changes  practically  simultaneously. 

As  a  result  of  these  various  changes,  certain  materials  are 
sometimes  leached  from  the  upper  parts  of  ore-deposits,  which 
have  become  porous  by  alteration,  and  carried  down  to  the  less 
pervious  unaltered  parts.  Here  they  are  precipitated  by  meet- 
ing other  solutions  or  in  other  ways,  and  hence  the  richest 
bodies  of  ore  in  a  deposit  often  occur  between  the  overlying 
altered  part  and  the  underlying  unaltered  part.  This  is  not 
always  the  case,  but  it  is  true  of  some  copper-,  silver-,  iron-, 
.and  other  deposits. 

Physical  Effects  of  Alteration. 

From  a  physical  stand-point,  the  effect  of  superficial  altera- 
tion is  generally  to  make  the  deposit  more  open  and  porous,  to 
cause  it  to  shrink,  and,  in  some  cases,  to  convert  it  to  a  loose 
material  of  the  consistency  of  sand  and  clay.  In  some  cases, 
however,  especially  where  considerable  hydration  goes  on,  an 
expansion  may  be  caused.  This  is  well  seen  in  the  formation 
of  gypsum  by  the  hydration  of  anhydrite,  often  causing  an  ex- 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  117 

pansion  sufficient  to  brecciate  and  fold  the  associated  rocks,2 
and  amounting  to  about  33  per  cent,  of  the  original  material.3 
In  the  conversion  of  carbonate  of  iron  to  the  hydrous  sesqui- 
oxide  of  iron,  or  limonite,  it  has  been  found*  that  there  is 
a  contraction  of  19.5  per  cent.,  giving  the  deposit  the  loose 
porous  structure  characteristic  of  limonite  and  forming  the 
familiar  limonite  geodes.5  In  this  case  carbon  dioxide  has  been 
removed  from  the  iron,  but  oxygen  and  water  have  been 
added.  A  porosity  is  also  produced  by  the  removal  of  certain 
ingredients  in  an  ore-deposit  without  the  addition  of  others,  as 
in  the  oxidation  and  leaching  of  iron  pyrites  in  veins  of  aurif- 
erous quartz,  leaving  a  loose,  porous,  spongy  quartz  mass. 

Surface-decomposition  has  also,  in  many  places,  not  only 
affected  the  ore-deposit  itself,  but  also  the  country-rock  in  the 
immediate  vicinity,  and  has  converted  it  into  a  loose  material 
of  a  sandy  or  clayey  consistency,  as  at  Iron  Mountain,  Mo.,  in 
the  Batesville  manganese-region  of  Arkansas  and  in  other 
localities  described  beyond.  In  the  iron-  and  manganese- 
deposits  of  the  Cambrian  and  Lower  Silurian  rocks  in  the 
Appalachian  region,  the  limestones  and  shales,  which  once  in- 
closed the  ore-bodies,  have  often  been  converted  to  clay  in  the 
same  way  as  in  the  Batesville  region ;  and,  in  fact,  the  com- 
mon mode  of  occurrence  of  these  deposits  is  as  residual  clays 
carrying  irregular  bodies  and  nodules  of  ore. 

This  decay  of  the  country-rock  in  immediate  association  with 
ore-deposits,  is  generally  more  extensive  than  in  similar  rocks 
not  associated  with  such  deposits,  and,  therefore,  requires  fur- 
ther explanation  than  the  simple  action  of  ordinary  surface- 
waters.  The  explanation  is,  doubtless,  in  many  cases,  that  the 
rock  has  decayed  under  the  influence  of  the  same  waters  that 
originally  concentrated  the  ore ;  and  as  these  waters  differed 
from  most  waters  in  character  and  in  the  materials  they  held 
in  solution,  they  often  had  an  abnormal  effect.  Moreover, 
when  subsequently  the  ore-body  is  affected  by  surface-influ- 

2  Elie  de  Beaumont,  Explic.  Carte  geologique  de  France,  vol.  ii.,  p.  89.     E.  A.  F. 
Penrose,  Jr.,  Arkansas  Geological  Survey,  vol.  i.,  pp.  535  to  538  (1890). 

3  A.  Geikie,  Text  Book  of  Geology,  3d  ed.,  p.  345  (1893). 

4  T.  Sterry  Hunt,  Mineral  Physiology  and  Physiography,  p.  262  (1889). 

5  K.  A.  F.  Penrose,  Jr.,  The  Tertiary  Iron  Ores  of  Arkansas  and  Texas,  Bulletin 
of  the  Geological  Society  of  America,  vol.  iii.,  pp.  44  to  50  (1891). 


118  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

ences,  sulphuric  acid  is  liberated  from  sulphides  and  carbonic 
acid  from  carbonates,  as  well  as  other  acids  from  other  min- 
erals, and  all  these  materials  have  an  active  effect  on  most 
rocks.  Moreover,  the  porous  nature  of  many  ore-deposits, 
after  they  have  been  altered  on  the  surface,  allows  a  freer  per- 
colation of  surface-waters  than  elsewhere  in  the  same  country- 
rock,  and,  hence,  a  correspondingly  greater  decay. 

Another  physical  effect  of  surface-influences  on  ore-deposits 
is  seen  in  certain  forms  of  brecciation  due  to  physical  or  chemi- 
cal causes,  such  as  expansion  by  hydration,  etc.  Such  breccia- 
tion, however,  has  usually  occurred  in  the  country-rock  before 
the  concentration  of  the  ore-deposit;  in  fact,  its  existence,  by 
offering  favorable  conditions  for  deposition,  has  often  been  the 
cause  of  the  formation  of  the  ore-deposit  in  a  given  place. 
Though  brecciation,  therefore,  is  very  important  as  a  factor  in 
the  concentration  of  ore-deposits,  it  does  not  belong,  to  any 
large  extent,  in  a  discussion  of  the.  surface-alteration  of  ore- 
deposits  after  their  formation,  and,  therefore,  it  will  not  be 
treated  further  in  this  paper. 

Depth  of  Alteration. 

Having  thus  discussed  briefly  the  means  by  which  superficial 
alteration  in  ore-deposits  is  produced,  and  the  results  of  this 
alteration,  the  next  feature  to  be  taken  up  is  the  depth  to  which 
it  extends.  As  already  shown,  the  alteration  is  primarily  one 
of  oxidation  and  generally  of  hydration;  and,  though  either 
may  occur  without  the  other,  they  both  very  often  occ^r 
together.  When  surface-waters  percolate  into  the  rock,  thefi* 
influence  is  more  active  near  the  surface,  because  they  carry 
large  quantities  of  oxygen,  and  because  the  oxygen  of  the  air 
itself  also  has  some  influence.  As  they  sink  deeper,  the  effect 
of  the  oxygen  of  the  air  becomes  less  active,  and  the  oxygen 
dissolved  in  the  water  is  consumed  in  oxidizing  various  ma- 
terials which  it  meets  on  the  way,  until  finally  most  of  the 
oxygen  is  lost  and  active  oxidation  ceases.  Theoretically,  this 
oxidizing  action  may  extend  down  as  far  as,  and  sometimes  be- 
low, the  level  of  the  drainage  of  the  surrounding  country,  which 
is  called  also  the  zone  of  permanent  saturation.  Above  that 
level,  there  is  a  constant  circulation  of  water  from  the  surface 
downward,  thus  affording  means  of  active  oxidation ;  but  when 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  119 

the  water  reaches  that  level,  not  only  has  most  of  the  oxygen 
contained  in  solution  generally  been  used  up,  but  also  the  cir- 
culation of  the  water  is  much  more  sluggish,  so  that  oxidation 
is  less  active.6 

The  process  of  hydration,  when  the  materials  affected  do  not 
require  oxidation  before  they  can  become  hydrated,  may  ex- 
tend down  indefinitely  below  the  limit  of  oxidation ;  but  when 
oxidation  is  necessary  before  hydration  is  possible,  the  latter 
process  of  course  can  extend  no  deeper  than  oxidation.  Thus 
the  silicate  of  aluminum  in  feldspar  may  become  hydrated  and 
form  kaolin  without  the  intervention  of  oxygen.  This  is 
brought  about  by  the  action  of  carbonic  acid  and  water,  which 
react  on  the  feldspar  and  form  alkaline  carbonates,  kaolin,  and 
free  or  hydrous  silica.  Theoretically,  therefore,  kaolinization 
ought  to  go  on  to  any  depth  that  can  be  reached  by  water  and  its 
almost  universal  accompaniment,  carbonic  acid.  In  this  case, 
however,  the  base  in  question  is  already  in  its  peroxide  condi- 
tion (A12  03) ;  but  when  a  base  is  not  in  this  condition,  it 
frequently  requires  oxidation  previous  to  hydration.  Thus 
sulphide  of  iron  does  not  become  hydrated  until  it  is  peroxi- 
dized,  and  this  mineral,  therefore,  requires  oxidation  previous 
to  hydration.7 

The  various  materials  other  than  oxygen  in  surface-waters 
have  a  very  important  effect  on  the  mineral  matter  with  which 
they  come  in  contact,  and  their  action  sometimes  takes  place 
before  that  of  oxidation,  though  it  often  requires  at  least  a  par- 
tial previous  oxidation.  The  effect  is  both  to  form  new  chemical 
compounds  with  the  materials  involved,  and  to  dissolve  and 
bodily  remove  certain  materials.  As  with  oxygen,  however,  so 
with  these  other  agents  of  alteration,  they  are  more  active 
above  the  drainage-level  of  the  country  than  below  it,  and  an 
additional  reason  for  this  is  that  many  of  the  materials  affected 
require  a  primary  oxidation  before  they  enter  into  other 
chemical  combinations.  Thus  sulphide  of  lead  is  oxidized  to 

6  It  is  possible  that  the  oxidation  near  the  surface  is  due  largely  to  free  oxygen 
in  the  waters,  while,  when  this  becomes  exhausted  at  a  depth,  the  oxidation  may 
be  due  to  the  abstraction  by  mineral  matter  of  the  oxygen  in  combination  with 
materials  in  solution. 

7  For  a  full  discussion  of  this  subject  see  H.  Kose,  Ueber  den  Einfluss  des 
Wassers  bei  chemischen  Zersetzungen,  Poggendor/'s  Annaltn  der  Physik  und  Chemie, 
vol.  Ixxxii.  (1851)  et  seq. 


120  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

sulphate  of  lead  before  it  can  take  up  carbonic  acid  and  form 
carbonate  of  lead ;  while  on  the  other  hand,  carbonate  of  lime 
can  be  converted  to  sulphate  of  lime  (gypsum)  by  the  action 
of  sulphuric  acid  or  certain  sulphates  without  any  change  in 
the  degree  of  oxidation  of  the  lime, 

It  will  thus  be  seen  that  in  going  from  the  surface  downward, 
we  pass  from  a  zone  of  active  oxidation  into  a  zone  in  which 
oxidation  practically  ceases.  Below  the  level  of  permanent 
saturation,  the  waters  may  sometimes  gradually  sink  to  very 
great  depths,  even  deep  enough  to  become  intensely  heated 
and  possibly  dissociated.  Such  waters  may  have  a  very  im- 
portant effect  in  the  formation  of  ore-bodies,  though  in  a  man- 
ner quite  different  from  their  action  on  the  surface.  The 
present  discussion,  however,  relates  not  to  this,  but  to  only 
superficial  influences. 

Though  theoretically,  therefore,  alteration  of  one  kind  or 
another  may  extend  down  to,  and  in  some  cases  much  below, 
the  level  of  permanent  saturation,  and  if  given  sufficient  time 
would  actually  go  to  such  depths ;  yet  in  many,  if  not  most, 
cases  it  has  not  yet  reached  that  level.  The  actual  depth  to 
which  alteration  does  extend  varies  with  the  topographic  con- 
ditions of  the  region,  the  chemical  nature  and  the  porosity  of 
the  deposits  affected,  the  character  of  the  climate,  and  other 
minor  conditions. 

The  topography  of  a  region  affects  the  depth  of  alteration 
because  it  is  one  of  the  principal  features  in  determining  the 
depth  of  permanent  saturation.  The  chemical  nature  of  the 
deposit  affects  the  depth  of  alteration  because  on  this  depends 
the  degree  of  resistance  it  will  offer  to  the  chemical  effects  of 
percolating  waters.  The  porosity  of  the  deposit  affects  the  depth 
of  alteration  because,  in  deposits  of  similar  kind  but  of  different 
porosity,  the  more  porous  will  be  more  accessible  to  surface- 
influences,  and  will,  therefore,  be  more  affected,  in  a  given 
time,  than  the  less  porous  deposit. 

The  climatic  conditions,  such  as  the  amount  and  manner  of 
occurrence  of  rain-fall  and  other  forms  of  atmospheric  moisture, 
and  the  rate  and  degree  of  variation  in  temperature,  have  a  large 
influence  on  superficial  alteration.  On  the  amount  of  rain-fall 
and  other  forms  of  atmospheric  moisture  depends  the  amount 
of  moisture  available  as  an  agent  of  alteration ;  while  on  their 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  121 

mode  of  precipitation  depends,  other  things  being  equal,  the 
amount  of  water  which  would  sink  into  the  deposit,  thus  effect- 
ing alteration,  and  the  amount  that  would  immediately  run  off 
the  surface  or  be  evaporated  and  thus  have  but  little  altering 
effect.  The  rate  and  degree  of  variation  in  temperature  affect 
the  amount  of  breaking  in  the  rock  by  expansion  and  contrac- 
tion, and,  therefore,  the  accessibility  of  the  rock  to  surface- 
influences.  The  character  of  the  climate  also  influences,  to  a 
certain  extent,  the  nature  and  amount  of  vegetation,  and  from 
the  vegetation  are  obtained  many  organic  acids  which  assist 
the  action  of  surface-waters.  In  other  ways,  also,  such  as  in 
the  generation  of  nitric  acid  in  the  atmosphere,  the  character 
of  the  climate  influences  the  agents  of  alteration. 

As  a  result  of  all  these  influences,  surface-alteration  is  found 
to  extend  in  different  ore-deposits  to  depths  varying  from  only 
a  few  inches,  or  in  fact  only  a  fraction  of  an  inch,  to  several 
hundred  and  even  a  thousand  or  more  feet.  In  glaciated  re- 
gions the  products  of  decay  have  often  been  swept  away  by 
glacial  action,  and  the  time  which  has  elapsed  since  then  has 
not  been  sufficient  for  alteration  to  have  extended  to  any  great 
depths ;  while  in  regions  of  moist  climates,  the  erosion  some- 
times, though  not  always,  keeps  pace  with  the  alteration,  so 
that  the  depth  of  the  change  is  shallow.  In  those  regions, 
however,  which  have  not  been  recently  glaciated  and  which 
have  dry  or  only  moderately  moist  climates,  so  that  erosion  is 
slight;  or  in  places  which  have  moist  climates,  but  which,  on 
account  of  their  topography,  are  not  subjected  to  very  active 
erosion,  the  products  of  alteration  collect,  and  the  changes  are 
traceable  downward  often  to  great  depths. 

In  the  copper-regions  of  Michigan,  the  deposits  have  been 
exposed  to  glaciation,  and  are  still  exposed  to  the  active  effects 
of  erosion  in  a  moist  climate,  so  that  here,  though  the  native 
copper  of  the  region  is  a  material  very  easily  affected  by  surface- 
alteration,  yet  the  only  change  observable  is  a  slight  stain  of 
copper  carbonate  or  oxide  on  the  surface  of  some  of  the  native 
copper,  and  even  this  is  not  always  present.  On  the  other 
hand,  in  the  arid  region  of  the  West,  most  of  which  has  not 
been  recently  glaciated  and  which  has  an  exceedingly  dry 
climate,  the  residual  products  of  alteration  have  accumulated 
to  great  thicknesses.  This  region,  however,  had  once  a  much 


122  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

more  moist  climate  than  now,  and  some  of  the  alteration  may 
have  occurred  then.  Many  of  the  Arizona  copper-deposits  in 
this  region  originally  contained  their  copper  in  the  form  of 
copper  pyrites,  which,  under  similar  conditions,  is  probably 
more  resistant  to  surface-alteration  than  the  native  copper  of 
Michigan,  and  yet  it  has  been  changed  to  various  other  copper- 
minerals  for  depths  often  reaching  from  100  to  over  700  ft. 
In  Chile  some  of  the  copper  sulphide  deposits  are  said  to  have 
been  altered  to  a  depth  of  1,500  ft.,  but  it  is  very  rare  that 
much  alteration  extends  in  any  ore-deposits  to  greater  depths 
than  this.  In  the  more  moist  climate  of  Tasmania,  the  results 
of  alteration  are  also  very  marked. 

The  depth  of  alteration  of  ore-deposits  in  unglaciated  regions 
in  the  United  States  varies  from  a  few  feet  to  over  1,000  ft.  In 
the  Appalachian  region,  many  of  the  deposits  of  auriferous 
quartz,  iron  pyrites,  copper  pyrites,  etc.,. are  altered  to  depths 
varying  from  less  than  1  to  100  ft.  or  more.  Many  of  the 
Clinton  iron-ore  deposits  are  altered  to  still  greater  depths. 
The  depth  of  alteration  in  these  Appalachian  deposits  is  usu- 
ally much  greater,  other  things  being  equal,  south  of  the  limit 
of  glaciation  than  north  of  it.  •  In  the  silver-,  lead-,  gold-,  and 
copper-deposits  of  the  Rocky  mountains  and  the  Western  arid 
region,  such  as  at  Butte  City,  Leadville,  Central  City,  Cripple 
Creek,  Silver  City,  Lake  Valley,  Eureka,  Virginia  City,  Park 
City,  the  Coeur  d'Alene  district,  and  elsewhere,  the  alteration 
has  reached  depths  ranging  from  50  to  600  or  700  ft.,  and  in 
some  rare  cases  still  more.  At  Granite  Mountain,  in  Montana, 
signs  of  alteration  are  seen  in  the  argentiferous  quartz-deposits 
of  that  region,  even  at  depths  of  900  ft.,  though  of  course  at 
such  depths  the  alteration  is  slight  as  compared  with  that 
nearer  the  surface. 

Complete  alteration  rarely  extends  to  these  greater  depths, 
and  usually  parts  of  a  deposit  which  have  as  yet  escaped  altera- 
tion appear  comparatively  near  the  surface.  These  are  at  first 
very  few  and  may  be  entirely  inclosed  by  altered  products,  but 
with  increased  depth  they  become  more  numerous  and  continu- 
ous, until  they  predominate  over  the  altered  products,  and 
finally,  when  the  limit  of  alteration  is  reached,  they,  entirely 
replace  them.  The  planes  of  contact  between  an  ore-deposit 
and  the  country- rock,  that  is,  the  walls,  afford,  when  well 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  123 

defined,  easy  passages  for  the  downward  percolation  of  surface- 
waters,  and  therefore  alteration  frequently  continues  down 
along  these  lines  for  considerable  distances  after  the  limit  of 
alteration  in  the  main  part  of  a  deposit  has  been  reached.  Any 
other  possible  channels,  such  as  the  planes  of  contact  of  dif- 
ferent minerals  in  banded  deposits  or  the  series  of  drusy  cavi- 
ties often  found  in  the  central  parts  of  ore-deposits,  may  act  in 
the  same  way  as  passages  for  water.  Hence  the  not  infrequent 
abundance  of  alteration-products,  such  as  hydrous  sesquioxide 
of  iron,  and  native  copper  and  silver,  along  the  walls  and  else- 
where in  certain  deposits. 

Classification  of  the  Products  of  Alteration. 

The  products  of  superficial  alteration  may  be  divided  into 
two  general  classes  :  (1)  Those  which  occupy  the  same  position 
as  the  materials  from  which  they  were  derived,  or  are  only 
slightly  removed,  and  possess  the  same  general  environment. 
Thus  the  altered  outcrops  of  auriferous  quartz  and  iron  pyrites, 
of  argentiferous  galena,  of  sulphides  of  copper  and  many  other 
similar  deposits,  represent  alteration-products  occupying  the 
same  general  position  as  the  original  sulphide  ores ;  while  the 
iron-ore  bodies  of  the  Lake  Superior  region  represent  alteration- 
products  changed  somewhat  in  position  from  that  occupied 
originally,  but  yet  in  the  same  series  of  rocks  and  sometimes 
with  somewhat  similar  environment.  (2)  In  the  second  class 
are  included  those  deposits  which  have  been  entirely  removed 
from  their  original  position  and  redeposited  under  totally  dif- 
ferent environments.  Thus,  placer  gold-deposits,  stream-tin, 
most  of  the  deposits  carrying  platinum  and  the  allied  metals, 
magnetic  and  chromite  sand,  the  gravels  and  sands  carrying 
precious  stones,  and  many  other  similar  deposits,  represent  this 
class.  They  have  been  derived  by  the  decay  and  erosion  of 
veins,  dikes,  or  country-rocks  carrying  the  materials  now  con- 
centrated in  these  fragmental  deposits.  The  materials  in  their 
original  environment  may  or  may  not  have  been  sufficiently 
concentrated  to  serve  as  commercial  sources  of  supply,  but  the 
fragmental  deposits  mentioned  almost  always  represent  a  fur- 
ther concentration.  This  class  of  deposits  is  of  great  importance, 
but  the  present  discussion  relates  more  especially  to  the  super- 
ficial alteration  of  deposits  that  remain  in  situ,  and  therefore 


124  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

these  will  be  treated  more  in  detail  than  the  other  class  (No. 
2),  though  the  latter  will  be  mentioned  as  occasion  requires. 

III.  SUPERFICIAL  ALTERATION  IN  DIFFERENT  DEPOSITS. 

Alteration  in  Iron-Deposits. 

It  was  once  generally  believed  that  most  iron-deposits  were 
the  result  of  direct  precipitation  from  aqueous  solution,  or  in 
rarer  cases,  were  igneous  masses.  It  has  long  since  been 
shown,  however,  that  most  workable  iron-deposits  are  the 
result  of  a  concentration  subsequent  to  their  deposition,  while 
very  few  are  due  to  a  direct  precipitation  during  the  formation 
of  sedimentary  rocks,  though  some  may  be  due  to  a  process 
of  differentiation  in  the  cooling  of  eruptive  magmas.8  The 
original  presence  of  the  iron  in  sedimentary  rocks  was  doubt, 
less  due  to  a  direct  precipitation  during  the  formation  of  the 
inclosing  rock,  but  it  was  then  in  a  finely-disseminated  condi- 
tion, and  it  was  only  by  being  subsequently  taken  into  solution 
again  by  percolating  waters  and  concentrated,  that  it  was  con- 
'verted  into  bodies  of  greater  or  less  purity.  Generally,  though 
possibly  not  always,  this  process  is  superficial,  and  though  it 
may  extend  to  a  depth  of  several  hundred  or  even  a  thousand 
feet  or  more,  it  can  be  traced  directly  to  surface-influences,  and 
its  effects  are  seen  to  decrease  gradually  with  depth.  Shaler,9 
in  1877,  showed  that  some  of  the  limonites  of  Kentucky,  Ohio 
and  elsewhere  were  concentrations  of  iron  derived  in  solution 
from  shales  and  other  rocks  and  reprecipitated  in  underlying 
limestone. 

Van  Hise,10  in  1889,  showed  that  the  iron-deposits  of  the 
Lake  Superior  region  are  concentrations  of  iron  formerly  dis- 
seminated in  a  siliceous  rock  containing  carbonate  of  iron  and 
other  carbonates,  and  called  by  him  cherty  iron  carbonate. 
This  disseminated  iron  was  taken  into  solution  by  surface- 

8  See  foot-note  *,  p.  111. 

9  N.  S.  Shaler,  Kentucky  Geological  Survey,  Report  of  Progress,  vol.  iii.,  New- 
Series,  p.  164  (1877). 

10  C.  K.  Van  Hise,  The  Iron  Ores  of  the  Penokee-Gogebic  Series  of  Michigan 
and  Wisconsin,  American  Journal  of  Science,  Third  Series,  vol.  xxxvii.,  No.  217, 
pp.  32  to  47  (Jan.,  1889)  ;   The  Iron  Ores  of  the  Lake  Superior  Region,  Transac- 
tions of  the  Wisconsin  Academy  of  Science,  vol.  viii.  (1891).     For  a  fuller  discussion 
by  Van  Hise  on  this  subject  see  Tenth  Annual  Report,  U.  S.  Geological  Survey,  Pt. 
I.,  pp.  409  to  422  (1888-89) ;  Monograph  XIX,  U.  S.  Geological  Survey  (1892). 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  125 

waters,  carried  down  until  its  passage  was  obstructed  or  im- 
peded by  less  pervious  rocks,  often  dikes,  and  there  precipitated 
by  meeting  with  other  solutions  of  a  different  nature.  These 
other  solutions  contained  oxygen,  while  the  iron-bearing  solu- 
tions had  been  largely  robbed  of  their  oxygen  and  had  been 
freed  from  silica  by  the  large  amount  of  carbonic  acid  they 
contained.  When,  therefore,  the  two  solutions  met,  the  iron 
in  solution  was  oxidized  and  precipitated;  while  the  silica,  in 
the  spot  where  this  precipitation  occurred,  was,  on  account  of 
the  dilution  of  the  carbonated  waters  with  the  other  waters, 
and  through  the  agency  of  alkaline  carbonates,  dissolved  and 
carried  off,  thus  gradually  increasing  the  amount  of  iron  and 
removing  the  silica.  By  this  theory,  the  iron  is  largely  a  re- 
placement of  the  silica  of  the  cherty  iron  carbonates,  and  has 
been  derived  from  the  parts  of  the  strata  exposed  to  superficial 
influences.  The  deposits  are,  therefore,  of  only  superficial  ex- 
tent, though  they  may  reach  over  1,000  ft.  below  the  surface, 
yet  when  they  pass  below  the  action  of  surface-influences  the 
iron  has  not  been  concentrated,  and  they  are  of  too  low  grade 
to  be  mined  for  iron-ore.  The  methods  of  local  concentration 
proposed  by  Professor  Van  Hise  for  these  Lake  Superior  iron- 
deposits  are  equally  applicable  to  certain  other  iron- deposits, 
and  are  a  most  valuable  addition  to  our  knowledge  of  chemical 
geology.  They  also  bring  out  in  a  most  prominent  manner, 
the  fact  that  even  rocks  composed  of  materials  like  silica, 
which  are  very  resistant  to  surface-influences,  may,  under 
proper  conditions,  be  replaced  on  a  large  scale. 

The  iron-deposits  of  the  Mesabi  range,  in  Minnesota,  which 
have  lately  been  described  by  H.  Y.  Winchell,11  are  supposed  to 
have  had  a  somewhat  similar  origin  to  that  given  for  the 
Michigan  and  Wisconsin  ores  by  Van  Hise.  Winchell  believes 
that  they  are  due  to  the  concentration  by  surface-agencies  of 
iron  disseminated  as  oxides  in  a  highly-siliceous  rock,  and  that 
in  this  concentration  the  silica  has  been  replaced  by  iron. 

The  red  hematites  of  the  Clinton  horizon  of  the  Upper  Silu- 
rian in  the  Appalachian  region  have  been  at  least  partly  formed 
by  superficial  concentration  which  extends  to  only  limited 
depths. 

11  Twentieth  Annual  Report,  Minnesota  Geological  Survey,  pp.  136  to  148  (1891). 


126  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

The  iron-deposits  in  other  geologic  horizons  of  the  Appala- 
chian valley,  especially  in  the  Cambrian,  Lower  Silurian,  and 
Carboniferous  rocks,  are  also  often  much  changed  by  the 
action  of  surface-influences.  Many  of  the  deposits  in  the 
Cambrian  and  Lower  Silurian  can  be  clearly  shown  to  be  due 
to  a  superficial  replacement  of  limestone,  or  even  of  more  sili- 
ceous rocks  like  shales,  by  iron  dissolved  from  ferruginous 
rocks  in  the  neighborhood.  In  such  cases,  the  iron  in  the 
original  rock  has  been  dissolved  and  carried  off  in  carbonated 
surface-water,  and  re-precipitated  in  the  other  rocks,  all  these 
stages  being  directly  due  to  surface-influences.  Many  of  the 
carbonate  iron-ores  of  the  Carboniferous  rocks  are  rendered 
not  only  of  higher  grade,  but  also  more  easy  to  treat,  by  the 
oxidation  of  the  carbonate  to  the  sesquioxide  and  the  removal 
of  the  carbonic  acid.  Moreover,  these  carbonate  ores  often 
occur  as  nodules,  "  kidney  ores,"  in  shale,  and,  on  the  surface, 
this  shale  has  been  softened  by  atmospheric  conditions,  thus 
facilitating  mining;  while  away  from  the  surface,  the  shale 
becomes  harder  and  makes  mining  more  expensive. 

Surface-influences  on  carbonate  of  iron  have  been  made  use 
of  artificially  in  Styria,  where  a  very  hard  spathic  iron-ore  has 
been  mined  and  spread  out  on  a  hill-side  for  from  20  to  25 
years.  By  this  process  the  ore  was  oxidized  and  made  more 
porous,  and  thus  became  very  much  more  cheaply  treated.12 

At  the  celebrated  Iron  Mountain,  in  Missouri,  a  large  part 
of  the  ore  came  from  conglomerates  composed  largely  of  frag- 
ments of  iron-ore,  which  had  been  weathered  out  of  the  pre- 
Cambrian  rocks  that  had  originally  contained  them.  These 
conglomerates  lie  at  the  base  of  the  Cambrian  strata  which 
overlie  the  pre-Cambrian  rocks,  and  even  in  the  latter  rocks, 
where  exposed,  the  original  ore  has  been  made  much  more 
easy  to  work  by  the  decay  of  the  inclosing  material  and  its 
conversion  to  clay. 

In  the  iron-region  of  eastern  Texas,  the  limonite  ores  are 
often  a  result  of  the  solution  of  iron  from  the  superficial  oxi- 
dation of  iron  pyrites,  iron  carbonate,  and  glauconite.  Some- 
times the  sequel  of  this  process  is  the  downward  passage  of  the 
solution  to  an  underlying  laminated  clay,  and  the  gradual  re- 

12  Letter  from  Charles  E.  Smith,  Philadelphia,  Pa. 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  127 

placement  of  this  bed,  forming  a  hard  limonite,13  which  still 
preserves  the  laminated  structure  of  the  clay. 

In  Mexico  certain  hematite-deposits  described  by  E.  T. 
Hill 14  as  occurring  in  Lower  Cretaceous  limestone  at  or  near 
the  contact  with  intrusive  masses  of  diorite,  and  sometimes 
even  in  the  diorite  itself,  may,  as  Hill  suggests,  be  the  result 
of  superficial  concentration  from  the  limestone. 

Very  large  deposits  of  hematite  also  occur  in  Grant  county, 
N".  M.,  at  the  contact  of  limestone  and  an  eruptive.  The 
origin  of  this  ore  is  as  yet  somewhat  obscure,  but  is  probably 
due  to  a  concentration  after  the  original  deposition  of  the 
iron. 

The  iron-deposits  in  the  lakes  of  Sweden  and  Norway  are 
most  striking  instances  of  a  concentration  of  iron-ore  due  to 
surface-influences  and  going  on  at  the  present  time.  The  iron 
is  derived  from  the  oxidation  of  the  neighboring  rocks,  car- 
ried by  carbonated  surface-waters  to  the  lakes,  and  there,  by 
further  oxidation  and  hydration,  precipitated  as  hydrous  ses- 
quioxide  (limonite).  The  iron-ore  is  dredged  up  and  used,  but 
the  processes  of  nature  gradually  replace  it,  and,  in  the  course 
of  years,  the  lakes  again  accumulate  a  considerable  thickness 
of  ore. 

Many  other  similar  cases  of  superficial  enrichment  in  iron- 
deposits  might  be  mentioned,  but  the  above  are  enough  to  illus- 
trate the  point  in  question,  and  it  will  be  seen  that,  of  the 
regions  which  are  the  active  producers  of  iron-ore  in  this 
country,  almost  all,  if  not  all,  owe  the  existence,  or  at  least  the 
availability,  of  their  large  bodies  of  ore,  to  superficial  concen- 
tration. 

Alteration  in  Manganese-Deposits. 

Manganese-deposits  are  affected  by  superficial  influences  in 
much  the  same  way  as  iron-deposits.  Many  of  the  manganese- 
deposits  in  the  Cambrian  -and  Lower  Silurian  rocks  of  the 
Appalachian  valley  were  concentrated  in  a  manner  somewhat 

18  R.  A.  F.  Penrose,  Jr.,  First  Annual  Report,  Geological  Survey  of  Texas,  pp. 
72  to  76,  79  to  81  (1890) ;  also  Bulletin  of  the  Geological  Society  of  America,  vol.  iii., 
pp.  47  to  50  (1891). 

14  American  Journal  of  Science,  Third  Series,  vol.  xlv.,  No.  266,  pp.  Ill  to  120 
(Feb.,  1893). 


128  THE    SUPERFICIAL    ALTERATION    OP    ORE-DEPOSITS. 

similar,  though  not  always  so,  to  the  iron-deposits  in  the  same 
regions.15 

In  the  Bates ville  manganese-region  of  Arkansas,  the  ore 
originally  occurred  in  irregular  masses  in  Silurian  limestone, 
but  surface-decay  has  leached  the  carbonate  of  lime  out  of  the 
limestone,  leaving  a  red  siliceous  clay,  which  represents  the 
less  soluble  part  of  the  original  rock.  This  clay  now  lies  in 
hollows  on  the  surface  of  the  limestone  and  contains  the  masses 
of  ore  once  disseminated  through  that  rock.  The  removal  of 
the  carbonate  of  lime  has  concentrated  the  ore-masses  in  the 
clay,  and  has  also  rendered  them  more  easily  mined ;  in  fact, 
the  only  manganese-ore  that  can  now  be  profitably  mined  in 
this  region  is  that  in  the  residual  clay.16 

The  frequent  occurrence  of  deposits  of  bog  manganese-ore 
in  the  areas  of  crystalline  rocks,  generally  represents  a  concen- 
tration of  manganese  resulting  from  the  oxidation  of  dissemi- 
nated carbonate  and  silicate  of  manganese  in  the  country-rock. 
This  oxidation-product  is  taken  into  solution  in  surface-waters, 
and  transported  until  subjected  to  such  conditions  that  it  is 
oxidized  and  precipitated  as  a  hydrous  oxide. 

Alteration  in  Copper-Deposits. 

In  many  copper-deposits  superficial  alteration  has  produced 
very  remarkable  chemical  and  economic  results,  and  this  is 
especially  well  seen  in  the  copper  sulphide  deposits  of  Arizona, 
Chile  and  elsewhere.  In  Arizona  the  upper  parts  of  the 
deposits  are  composed  of  brown  or  black  ferruginous  masses, 
with  brilliantly  colored  oxidized  copper-minerals,  as  cuprite, 
malachite,  azurite,  chrysocolla,  etc. ;  while  below,  at  depths 
varying  from  a  few  feet  to  several  hundred  feet,  the  deposits 
usually  pass  into  a  mixture  of  copper  pyrites  and  iron  pyrites, 
the  latter  usually  being  far  in  excess.  Sometimes  other  copper 
sulphides  occur,  either  mixed  with  copper  pyrites  or  free  from 
it,  and  they  may  or  may  not  have  been  derived  from  it.  Here 
the  carbonates  and  some  of  the  other  alteration-minerals  con- 
tain not  only  more  copper  than  the  unaltered  copper  pyrites, 
but  they  are  also  in  a  much  more  concentrated  condition  than 

15  K.  A.  F.  Penrose,  Jr.,  Journal  of  Geology,  vol.  i.,  No.  4,  pp.  356  to  370  (1893). 

16  R.  A.  F.  Penrose,  Jr.,  Manganese:    Its  Uses,  Ores,  and  Deposits,  Arkansas 
Geological  Survey,  vol.  i.,  pp.  166  to  209  (1890). 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  129 

the  sulphide  which  is  disseminated  through  iron  pyrites.  The 
total  amount  of  copper  has  not  been  increased,  in  fact  it  may 
be  decreased  by  leaching,  but  it  is  in  a  more  concentrated 
form,  and  therefore  the  ore  obtained  from  these  concentrations 
averages  from  8  to  30  per  cent,  or  more  in  copper,  while  the 
mixture  of  unoxidized  copper  pyrites  and  iron  pyrites  below 
averages  only  about  5  per  cent,  in  copper.  Moreover,  the 
altered  ores  are  much  more  cheaply  treated  than  the  unaltered 
ones,  and  are  therefore  still  more  desirable.  It  will  thus  be 
seen  that  the  economic  value  of  the  deposits  as  a  whole  has 
been  greatly  increased. 

In  the  surface-alteration  of  these  deposits,  the  copper  sul- 
phides have  first  been  converted  to  copper  sulphate  and  then, 
by  the  action  of  surface-waters  and  the  materials  contained  in 
solution  in  them,  they  pass  into  the  forms  of  copper  carbonates, 
oxides,  silicates,  and  occasionally  to  the  chlorides  and  bromides, 
and  sometimes  to  native  copper.  The  iron  sulphide  is  first 
converted  to  sulphate  and  then  this,  through  other  stages,  is 
converted  into  the  hydrous  sesquioxide  (limonite),  though  the 
iron  sometimes  now  occurs  in  the  form  of  the  anhydrous 
sesquioxide  (hematite).  This  may  have  been  derived  from 
the  limonite  by  dehydration,  or,  under  certain  conditions,  may 
have  been  formed  directly  by  the  oxidation  of  iron  pyrites. 
The  oxidized  copper-minerals  in  the  upper  part  of  the  ore- 
deposit  have  been  concentrated  partly  by  segregation  during 
alteration,  and  partly  by  the  leaching  of  the  associated  materials. 
As  a  result  of  this,  these  minerals  occur  as  seams,  pockets,  or 
irregular  bodies,  often  a  hundred  feet  or  more  in  diameter, 
generally  inclosed  by,  and  often  intimately  associated  with, 
the  oxidized  iron-materials  which  represent  the  gangue. 

In  the  case  of  the  Arizona  deposits,  alteration  has  progressed 
just  far  enough  to  increase  greatly  the  value  of  the  deposits 
without  to  any  extent  injuring  it.  Such  products  of  alteration, 
however,  are  more  or  less  soluble  in  surface-waters  containing 
various  organic  and  inorganic  compounds,  so  that  in  a  moist 
climate  there  is  a  constant  tendency  to  leach  them  out  and 
leave  only  the  less  soluble  parts  of  the  gangue.  In  Arizona, 
this  stage  has  not  yet  progressed  to  a  noticeable  degree,  and 
one  reason  for  this  may  be  the  extreme  dryness  of  the  climate, 

9 


130  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

which  affords  opportunity  for  only  comparatively  slight  per- 
colation of  surface-waters. 

In  the  copper-deposits  of  Montana  and  the  Appalachian 
region,  however,  a  further  stage  of  alteration  is  often  observ- 
able. The  copper-deposits  of  Butte  City,  Mont,  are  composed 
.largely  of  chalcocite,  with  copper  pyrites,  bornite,  enargite, 
iron  pyrites,  and  other  minerals,  in  a  siliceous  gangue.  On 
the  surface  the  copper  in  these  deposits  has  been  almost  en- 
tirely oxidized  and  leached  out,  and  the  ore  consists  of  a 
porous,  rusty,  siliceous  mass,  which  was  once  mined  for  the 
small  percentage  of  silver  it  contained.  As  depths  were 
reached,  the  oxidized  copper-minerals  began  to  appear,  and 
eventually  the  sulphides  formed  the  mass  of  the  veins.  *In 
this  case,  a  further  stage  of  alteration  is  seen  than  that  in 
Arizona. 

At  Ducktown,  in  eastern  Tennessee,17  deposits  of  mixed  iron 
and  copper  pyrites  occur  and  have  been  altered  in  a  somewhat 
similar  manner  on  the  surface.  The  copper-minerals  have 
been  leached  out  of  the  ferruginous  gangue  in  the  upper  parts 
of  the  deposits,  and  for  a  depth  of  from  20  to  80  ft.  or  more, 
the  deposits  are  composed  simply  of  a  porous  mass  of  more  or 
less  hydrous  sesquioxide  of  iron.  Below  this  a  part  of  the 
copper,  which  has  been  leached  from  above,  has  been  carried 
down  and  deposited  as  a  dark  material,  probably  composed 
largely  of  oxides  and  sulphides  of  copper,  and  averaging  some- 
times from  20  to  25  per  cent,  or  more  in  metallic  copper.  This 
material  immediately  overlies  the  unoxidized  mixture  of  cop- 
per and  iron  pyrites,  which  averages  only  from  2  per  cent,  to 
4  or  5  per  cent,  in  copper.  The  commercial  copper  mined  in 
this  region  came  from  the  part  of  the  deposit  below  the  iron 
capping  and  above  the  unoxidized  sulphides.  When  this  was 
exhausted  the  mines  had  to  be  closed,  for  the  unaltered  sul- 
phides were  too  poor  to  be  utilized. 

In  Chile,  Peru,  and  elsewhere  in  South  America,  changes 
in  copper-deposits,  somewhat  similar  to  those  described  in  the 
United  States,  frequently  occur.  In  fact,  the  great  reputation 
which  Chile  once  had  as  a  copper-producer  was  largely  due  to 
this  surface-alteration,  for  the  oxidized  ore  once  supplied  a  rich 

17  J.  D.  Whitney,  The  Metallic  Wealth  of  the  United  States,  pp.  322  to  324. 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  131 

and  easily-treated  source  of  copper;  but  when  the  mines  reached 
the  unoxidized  sulphides,  the  ores  became  poor  in  copper  and 
more  difficult  to  treat,  so  that  the  copper  industry  of  Chile 
began  to  decline.     In  that  region,  however,  the  oxidation  has  • 
in  some  places  extended  down  as  far  as  1,500  feet. 

^  Alteration  in  Lead-Deposits. 

In  the  case  of  lead-deposits,  the  mineral  galena,  which  is  the 
commonest  ore,  is  frequently  more  or  less  altered  on  its  sur- 
face-outcrops and  converted  to  the  sulphate  (anglesite)  and  the 
carbonate  (cerussite).  The  first  product  of  oxidation  is  angle- 
site,  but  this  is  a  soluble  compound  and  readily  unites  with  car- 
bonic acid  or  soluble  carbonates  in  surface-waters,  forming  the 
carbonate  of  lead,  or  cerussite.  In  rarer  cases,  other  lead-min- 
erals, like  phosphates,  may  also  be  formed. 

Alteration  in  Silver-Deposits. 

Galena-deposits  often  contain  silver,  possibly  sometimes  in 
the  same  condition  of  sulphide  as  the  galena,  and  this  material 
is  altered  at  the  same  time  as  the  lead,  with  the  formation  of 
native  silver,  chloride  of  silver  (cerargyrite),  bromide  of  silver 
(bromyrite),  iodide  of  silver  (iodyrite),  and  various  other  min- 
erals. The  native  silver  is  formed,  probably,  only  after  a  pre- 
ceding oxidation  of  the  sulphide.  Deposits  carrying  other 
unaltered  silver-bearing  minerals,  such  as  the  various  silver 
sulphides,  arsenides,  antimonides,  tellurides,  etc.,  are,  when 
exposed  to  surface-influences,  affected  in  much  the  same  way 
as  the  silver  in  argentiferous  galena. 

Alteration  in  Zinc- Deposits. 

In  the  case  of  zinc,  the  most  common  ore  is  the  sulphide 
known  as  blende.  This  mineral,  like  galena,  is  generally  oxi- 
dized on  the  surface,  and  forms  by  other  chemical  changes  the 
carbonate  (smithsonite),  the  basic  carbonate  (hydrozincite),  and 
the  basic  silicate  (calamine),  in  a  manner  similar  to  that 
described  in  copper-  and  lead-ores. 

In  the  cases  of  both  lead  and  zinc,  oxidized  ores  are  very 
desirable  for  metallurgical  purposes,  and  are  much  sought 
after.  To  be  sure,  the  carbonates,  sulphates,  etc.,  of  lead  and 
zinc  contain  less  of  these  metals  than  the  pure  sulphides,  but 


132  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

they  occur  in  a  more  concentrated  form  than  the  sulphides, 
and,  therefore,  the  ores  containing  them  frequently  carry  as 
much  or  more  of  the  metals  than  the  ores  containing  the  sul- 
phides. Moreover,  the  oxidized  ores  are  much  more  easy  to 
treat  and,  therefore,  have  an  additional  value  over  the  sulphide 
ores. 

Alteration  in  Gold-Deposits. 

In  the  case  of  gold-deposits,  surface-alteration  has  a  most 
marked  effect,  and  probably  in  no  class  of  deposits  is  the 
change  of  more  geologic  and  economic  importance.  The  typi- 
cal unaltered  condition  of  gold  in  nature  is  in  association  with 
iron  pyrites  in  quartz,  the  gold  being  sometimes  in  such  asso- 
ciation with  the  pyrites  that  it  cannot  be  separated  by  mechani- 
cal means,  while  in  rarer  cases  it  can  be  so  separated.  The 
effect  of  surface-oxidation  on  such  a  deposit,  is  first  to  convert 
the  iron  pyrites  into  a  hydrated  sesquioxide  of  iron,  which  per- 
meates the  white  quartz,  with  which  the  pyrites  is  usually  as- 
sociated, and  turns  it  into  a  rusty  brown  mass.  The  next  stage 
is  the  gradual  leaching-out  of  the  hydrous  sesquioxide  by  the 
action  of  surface-waters.  The  iron  is,  in  this  way,  finally  re- 
moved altogether,  and  the  remaining  product  is  a  pure-white 
quartz,  containing  the  gold  which  was  originally  in  the  iron 
pyrites,  and  which  has  remained  stable  during  the  oxidation 
and  leaching  of  that  mineral.  Such  quartz  is  usually  porous 
and  spongy,  and  is  filled  with  cavities  which  represent  the 
shapes  of  the  original  crystals  of  iron  pyrites,  and  which, 
during  an  intermediate  stage,  have  been  partly  filled  with  hy- 
drous sesquioxide.  This  leaching,  however,  is  rarely  complete, 
and  the  quartz  is  usually  stained  brown  on  the  surface. 

In  gold-deposits  of  this  kind,  other  minerals,  such  as  copper 
pyrites,  galena,  blende,  etc.,  frequently  occur,  and  when  the 
•deposit  is  affected  by  surface-influences,  these  minerals  act  in 
the  manner  already  described  under  copper,  lead,  and  zinc.  It 
is  not  uncommon  to  see  gold-bearing  quartz  stained  green  by 
-oxidized  copper-minerals,  or  black  by  manganese-minerals. 
Sometimes,  especially  in  the  Rocky  Mountain  region,  gold 
occurs  in  the  form  of  a  telluride  instead  of  in  iron  sulphide, 
and  in  such  cases,  the  telluride  is  oxidized  and  the  gold  set  free 
from  its  combined  state.  The  gold,  in  being  freed  from  pyrites 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  133 

or  other  minerals,  is  not  only  concentrated  by  the  removal  of 
certain  ingredients  of  the  deposits,  but  it  is  brought  into  a  con- 
dition in  which  it  is  much  easier  to  treat  than  the  unaltered 
part  of  the  deposit,  and,  therefore,  the  upper  parts  of  most 
gold-bearing  veins  are  greatly  enhanced  in  value.  The  ore 
from  these  parts  is  known  as  "  free-milling "  ore,  because  it 
can  generally  be  ground  and  the  gold  extracted  by  direct 
amalgamation  with  mercury ;  while  the  ore  in  the  unaltered 
parts  of  the  deposit  cannot  usually  be  thus  easily  extracted, 
but  must  be  smelted  or  treated  by  chlorination  or  some  other 
more  or  less  expensive  process. 

When  such  deposits  as  those  described  are  eroded,  the  parti- 
cles of  gold  separate  from  the  quartz  and  are  concentrated  in 
the  streams  as  placer-gold.  These  detrital  deposits  are  the 
source  of  a  large  part  of  the  gold  of  commerce,  and,  in  fact, 
were  once  the  source  of  most  of  it.  Now,  however,  many  of 
the  richest  placer-deposits  known  have  been  exhausted;  and 
besides,  the  methods  of  treating  the  ores  in  the  original  de- 
posits are  better  understood,  so  that  the  latter  are  supplying 
yearly  a  larger  and  larger  percentage  of  the  gold-production 
of  the  world.  Hence,  it  will  be  seen  that,  in  gold-deposits, 
surface-alteration  not  only  plays  an  important  part  in  freeing 
the  gold  from  the  iron  pyrites,  but  also  in  forming  placer-de- 
posits. Detrital  deposits  similar  to  gold-placers  and  carrying 
various  other  materials  are  not  at  all  uncommon,  as  in  the 
cases  of  the  platinum  group  of  metals,  cassiterite,  diamonds 
and  many  other  gems,  chromite  and  magnetite  sands,  and,  in 
fact,  even  with  some  of  the  more  common  ores,  as  with  the 
iron-conglomerate  at  Iron  Mountain,  Mo. 

Alteration  in  Tin-Deposits. 

In  tin-deposits,  the  typical  mode  of  occurrence  of  the  metal 
is  in  veins,  dikes,  or  country-rocks,  in  the  form  of  the  oxide 
known  as  cassiterite.  Cassiterite  is  not  easily  affected  chemi- 
cally by  surface-influences,  so  that  it  is  not  much  changed  by 
superficial  alteration,  but,  for  this  very  reason,  its  concentration 
is  most  markedly  affected  by  surface-alteration,  for  in  the  ero- 
sion of  tin-bearing  deposits  the  masses  of  cassiterite  are  broken 
up  and  carried  off  mechanically  by  surface-waters,  to  be  de- 
posited somewhere  else  in  the  form  of  gravel-beds,  instead  of 


134  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

being  dissolved  and  possibly  disseminated.  In  this  transition, 
the  fragments  of  cassiterite  are  largely  separated  from  the 
accompanying  materials  by  reason  of  their  greater  specific 
gravity,  and  hence,  gravel-deposits  rich  in  cassiterite  frequently 
occur.  These  represent  the  stream-tin  of  the  miner,  and  have 
been  formed  in  much  the  same  manner  as  have  the  placer  gold- 
deposits.  Some  chemical  action,  however,  has  gone  on  in  the 
tin-ore  itself,  but  this  seems  to  have  been  simply  a  process  of 
solution  and  redeposition,  as  is  seen  in  the  pseudomorphs  of 
cassiterite  after  other  minerals  and  in  the  impregnations  of 
animal  remains  in  Cornwall,  such  as  antlers,  with  oxide  of  tin.18 

Alteration  in  Antimony-Deposits. 

In  many  antimony-deposits,  alteration  similar  to  that  de- 
scribed in  some  of  the  deposits  already  mentioned  frequently 
occurs.  The  metal  occurs  most  commonly  as  the  sulphide 
known  as  stibnite.  By  alteration,  however,  this  passes  into 
the  oxides  valentinite,  senarmontite,  cervantite,  stibiconite,  etc., 
or  into  the  combined  sulphide  and  oxide  known  as  kermesite. 
Yalentinite  and  senarmontite  have  the  same  chemical  composi- 
tion but  differ  in  their  crystalline  forms.  Native  antimony 
sometimes  occurs,  and  this  also,  by  alteration,  gives  rise  to  the 
oxides. 

Alteration  in  Bismuth-Deposits. 

The  allied  metal  bismuth  occurs  most  commonly  as  native 
bismuth,  though  the  sulphide  (bismuthinite),  the  selenide 
(guanajuatite),  the  telluride  (tetradymite),  etc.,  also  occur. 
Native  bismuth,  by  alteration,  forms  the  carbonate  (bismutite) 
and  probably  also  the  oxide  (bismite)  and  the  silicate  (eulytite). 

Alteration  in  Mercury- Deposits. 

In  the  case  of  mercury  the  metal  commonly  occurs  as  the 
sulphide  (cinnabar),  though  other  mercury-minerals  also  occur. 
By  the  alteration  of  cinnabar  and  some  of  the  other  mercury- 
minerals,  metallic  mercury  is  set  free  and  occurs  as  globules 
or  filling  cavities  in  the  ore. 

18  J.  H.  Collins,  Mineralogical  Magazine,  vol.  iy.,  p.  115  (1882). 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  135 

Alteration  in  Molybdenum-Deposits. 

Another  case  of  surface-alteration  in  metalliferous  deposits  is 
that  seen  in  molybdenite.  This  mineral  is  the  sulphide  of  the 
metal  molybdenum,  and  often  occurs  in  quartz  or  calcite  veins 
in  the  crystalline  rocks  of  parts  of  Canada,  and  in  many  ore- 
deposits  of  the  Rocky  mountains  and  elsewhere.  By  surface- 
oxidation,  molybdenite  passes  into  a  brilliant  yellow  oxide  of 
molybdenum,  commonly  known  as  molybdite  or  molybdic  ocher, 
which,  in  the  Canadian  region,  occurs  as  a  powdery  coating  on 
the  cleavage-planes  of  the  molybdenite. 

Alteration  in  Other  Deposits. 

Superficial  alteration  like  that  already  described  in  various 
deposits  occurs  also  in  many  others  not  yet  mentioned,  as  in 
aluminum-,  nickel-,  cobalt-,  chromium-,  tungsten-,  and  many 
rarer  deposits,  but  the  changes  already  described  show  the 
general  features  of  the  subject.  It  may  be  said,  however,  that 
one  of  the  important  ores  of  aluminum,  known  as  bauxite,  is 
probably  derived  from  the  alteration  of  feldspar  under  certain 
conditions;  and  its  source,  therefore,  is  not  altogether  unlike 
that  of  the  hydrous  sesquioxide  of  iron  derived  from  the  altera- 
tion of  certain  silicates.  The  conditions  during  formation,  how- 
ever, were  probably  quite  different. 

IV.  THE  FORMATION  OF  HALOID  COMPOUNDS  IN  ORE-DEPOSITS 
IN  ARID  EEGIONS. 

The  formation  of  chlorides  and  other  haloid  compounds  has 
already  been  mentioned  as  one  of  the  phenomena  of  superficial 
alteration  in  ore-deposits.  As  soluble  chlorides  and  some- 
times other  haloid  compounds  are  common  in  surface-waters, 
chlorides  and  the  allied  compounds  are  not  at  all  uncommon 
as  alteration-products,  especially  in  such  cases  as  that  of  silver, 
where  the  chloride,  bromide,  and  iodide  are  insoluble  com- 
pounds, and  are  not  leached  out.  For  this  reason,  chloride 
ores  of  silver  are  found  to  a  greater  or  less  extent  in  almost  all 
silver-districts  in  America,  Europe,  and  elsewhere,  but  the 
occurrence  of  such  compounds  in  very  large  quantities  in 
certain  parts  of  North  and  South  America  deserves  special 
explanation. 

Over  a  large  part  of  the  arid  region  of  the  "West,  lying  be- 


136  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

tween  the  Rocky  mountains  and  the  Sierra  Nevada,  ores  con- 
taining chloride  of  silver  (cerargyrite)  are  abundant,  and  some- 
times the  bromides  and  iodides  also  occur;  in  fact,  parts  of 
this  region  are  characterized  by  chloride  ores.  They  are 
especially  well  developed  in  parts  of  New  Mexico,  Arizona, 
Utah,  Nevada  and  other  States  and  Territories,  and  it  seems 
probable  that  their  abundance  can  be  traced  to  the  effect  of 
the  peculiar  climatic  conditions  which  have  prevailed  in  that 
region  in  late  geologic  times.  Most  of  this  arid  country  was 
once  covered  with  numerous  bodies  of  water,  some  of  them  of 
great  size.  In  late  geologic  times,  however,  these  began  to 
dry  up,  until  their  waters  no  longer  rose  high  enough  to  have 
outlets,  and  then,  as  a  natural  result,  they  became  highly  im- 
pregnated with  salt  and  other  saline  matter.  Finally,  they 
became  desiccated,  leaving  deposits  of  various  earthy  and  saline 
materials  in  their  old  basins,  and  among  the  most  common  of 
these  was  common  salt.  It  seems  probable  that  the  abundance 
of  chloride  ores  is  due  to  the  action  of  this  salt  on  the  pre- 
existing ore-deposits  of  the  region,  in  the  basins  of  the  lakes, 
and  that  the  smaller  quantities  of  bromides  and  iodides  were 
formed  by  a  similar  action  of  the  soluble  bromides  and  iodides 
in  association  with  the  salt.  Such  ores,  in  some  of  the  mines 
that  have  gone  to  sufficient  depths,  have  passed  into  various 
other  silver-compounds,  such  as  the  sulphide  (argentite),  argen- 
tiferous galena,  etc.,  which  represent  the  original  condition  of 
the  ores.  This  transition  proves  the  chlorides  and  other  haloid 
compounds  to  be  of  only  superficial  extent. 

This  transition  to  haloid  compounds  is  not  confined  to  silver- 
ores,  for  the  basic  chloride  of  copper  (atacamite)  occurs  at 
Jerome,  in  Arizona,  and  both  chlorides  and  bromides  of  copper 
occur  in  the  Bloody  Tanks  district  west  of  Globe,  in  Arizona, 
though  here,  as  elsewhere  in  Arizona,  the  other  copper-minerals 
already  mentioned,  such  as  carbonates,  sulphides,  etc.,  form 
the  bulk  of  the  copper-deposits. 

In  parts  of  Mexico,  Chile,  and  Peru,  where  saline  materials 
have  collected  in  a  manner  somewhat  similar  to  that  in  the 
arid  regions  of  the  United  States,  the  chloride  of  silver  is  one 
of  the  important  ores  mined,  and  it  sometimes  occurs  intimately 
mixed  with  chloride  of  sodium,  or  common  salt,  forming  the 
mineral  huantajayite,  or  the  lechedor  of  the  miners.  The 


THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS.  137 

bromides  of  silver  are  also  abundant  in  Chile,  and,  in  fact,  at 
the  mines  of  Chanarcillo,  a  common  ore  is  the  double  chloride 
and  bromide  known  as  embolite.  Again,  the  atacamite,  or 
basic  chloride  of  copper,  from  the  Desert  of  Atacama  is  well 
known. 

It  seems  probable  that  this  transformation  of  the  silver-  and 
copper-minerals  did  not  necessarily  occur  exclusively  while  the 
deposits  were  covered  by  saline  lakes,  but  may  have  occurred 
even  more  actively  afterwards,  when  the  surface-waters  were 
highly  impregnated  with  chlorides  from  the  residue  left  by  the 
lakes,  and  when  oxidation  in  the  ore-deposits  was  much  more 
active  than  when  they  were  covered  by  water.  This  seems  all 
the  more  likely  w?hen  we  consider  that  the  original  silver-  and 
copper-minerals  probably  had  to  be  oxidized  before  they  were 
converted  to  chlorides,  etc.  Of  course  the  oxidation  may  have 
partly  occurred  before,  or  during,  the  existence  of  the  lakes, 
but  in  many  cases  it  probably  also  occurred  after  they  were 
desiccated.19 

V.  SUMMARY. 

It  will  be  seen  from  the  above  discussion  that : 

(1)  After  the  deposition  of  ore-deposits  and  their  subsequent 
exposure'to  surface-influences,  such  as  air,  water  and  the  mate- 
rials contained  in  it,  changes  of  temperature,  etc.,  chemical 
and  physical  alterations  occur  which   cause  a  total  change  in 
the  mineralogical  condition,  and  generally  in  the   economic 
value,  of  the  ore-deposit. 

(2)  The  process  of  this  alteration  is  primarily  one  of  oxida- 
tion and  generally  of  hydration,  and  both  of  these  actions  may 
go  on  alone,  but  generally  both  have  their  effect  on  the  same 
material.     The  other  materials  in   solution  in   surface-waters 
also  react  on  the  substances  in  the  ore-deposit,  either  before  or 
after  the  oxidation  of  the  latter,  though  generally  after  at  least 
partial  oxidation,  and  form  various  compounds  different  from 
those  originally  in  the  deposit.     The  difference,  however,  with 
few  exceptions,  is  not  in  the  metal  or  other  base  which  forms 
the  important  feature  of  the  deposit,  but  in  the  acidic  portion 

19  Chlorides  of  other  materials  than  silver  and  copper  may  also  have  been 
formed  by  a  similar  process,  but  the  solubility  of  many  metallic  chlorides  would 
prevent  their  being  accumulated  in  any  but  very  dry  regions. 


138  THE    SUPERFICIAL    ALTERATION    OF    ORE-DEPOSITS. 

or  material  representing  this  portion  of  the  mineral.  Thus, 
sulphide  of  copper  may  be  altered  to  carbonate  of  copper,  but 
the  base  remains  the  same.  The  action  of  surface-influences  is 
in  rare  cases  one  of  reduction,  which,  however,  often  follows  a 
previous  oxidation.  The  process  of  alteration  also  frequently 
causes  a  leaching  of  certain  ingredients  of  the  ore-deposit, 
either  with  or  without  previous  oxidation,  as  in  the  removal  of 
iron  pyrites,  calcite,  etc.  It  also  sometimes  renders  a  hitherto- 
worthless  material  valuable  by  the  introduction  of  a  valuable 
constituent,  as  in  the  replacement  of  carbonate  of  lime  by 
phosphate  of  lime.  -It  also  causes  the  concentration,  by  capil- 
lary action  in  soils,  of  certain  deposits  like  niter,  etc.  The 
compounds  formed  with  different  ore-deposits  vary  with  the 
ores  affected  and  the  stability  of  the  compounds  formed  by  the 
action  of  the  materials  in  the  surface-waters  on  the  constituents 
of  the  ores. 

(3)  The  physical  effect  of  superficial  alteration  is  generally 
to  make  the  deposit   more  open   and  porous,  to  cause  it  to 
shrink,  and,  in  some  cases,  to  convert  it  into  a  loose  material 
of  the  consistency  of  sand  and  clay.     In  some  cases,  however, 
especially  where  hydration  is  active,  expansion  may  be  caused. 

(4)  Superficial  alteration  extends  downward  as  far  as  sur- 
face-influences are  able  to  act,  though  generally  alteration  is 
not  complete  down  to  the  possible  limit.     The  depth  of  altera- 
tion depends  on  the  topography  of  the  region,  the  nature  of 
the  rocks,  and  on  the  climate.  '  In  glaciated  regions,  the  glacial 
action  has  swept  away  the  products  of  alteration,  and  sufficient 
time  has  not  elapsed  since  then  for  alteration  to  have  gone  on 
to  any  great  extent,  but  in  many  other  regions  the  products  of 
alteration    have   accumulated   to    considerable    depths.      The 
depth  of  alteration,  under  different  conditions,  varies  from  a 
fraction  of  a  foot  to  1,500  ft.  or  possibly  more. 

(5)  Superficial  alteration  is  well  illustrated  in  iron-,  man- 
ganese-, copper-,  lead-,   zinc-,   silver-,  gold-,  tin-,   and   many 
other  deposits.     For  special  descriptions  see  text. 

(6)  The  accumulation  of  soluble  saline  materials,  like  salt, 
on  the  surface  has  a  very  important  effect  in  converting  certain 
materials  in  underlying  ore- deposits  to  chlorides,  etc. 


SOME    MINES    OF    ROSITA    AND    SILVEK    CLIFF,  COLORADO.       139 


No.  7. 


Some  Mines  of  Rosita  and  Silver  Cliff,  Colorado. 

BY   S.    F.    EMMONS,    WASHINGTON,    D.    C. 

(Colorado  Meeting,  September,  1896.    Trans.,  xxvi.,  773.    Published  by  permission  of  the 
Director  of  the  U.  S.  Geological  Survey,  and  here  reprinted  in  part  only). 


MINES  IN  RHYOLITE  NEAR  SILVER  CLIFF. 

Geological  Sketch. — The  rhyolite  area  near  Silver  Cliff  includes 
what  may  be  called  the  Silver  Cliff  plateau,  with  Round  moun- 
tain and  the  intervening  valley.  The  plateau  is  about  2  miles 
long  and  1  mile  wide.  From  its  northern  part  rise  the 
White  hills,  which  have  no  special  topographic  importance,  as 
their  highest  point  is  only  400  ft.  above  the  northern  edge  of 
the  rhyolite  mass.  Round  mountain,  on  the  other  hand,  is  a 
quite  sharply  pointed  conical  hill,  so  steep-sided  as  to  consti- 
tute an  important  topographic  feature,  although  its  elevation 
above  the  plains  around  it  is  barely  700  ft.  The  summit  of 
Round  mountain  is  dense  banded  rhyolite,  with  steep,  irregular 
dip;  the  southern  end  is  breccia  containing  fragments  of  the 
banded  rock.  There  are  slight  exposures  of  glassy  forms  of 
rhyolite  on  the  lower  slopes.  On  the  east,  the  Archaean  rocks 
extend  half-way  up  the  side  of  the  mountain,  and  the  contact 
between  them  and  the  rhyolite  is  vertical,  or  dips  steeply  to 
the  west.  This  mountain  is  supposed  to  be  at  the  vent  from 
which  the  rhyolite  of  the  plateau  was  poured  out. 

The  Silver  Cliff  plateau  occupies  the  site  of  a  former  basin, 
in  which  at  one  time  there  was  probably  a  lake.  At  the  time 
of  the  rhyolitic  outburst  of  the  Rosita  hills  there  was  a  local 
eruption  of  the  same  character  in  this  region,  commencing  with 
showers  of  volcanic  ash  and  of  rock-fragments,  which  filled  the 
lake  and  built  up  about  it  hills  which'  have  since  been  removed 
in  great  measure  by  erosion.  At  present  the  southern  half  of 
the  plateau  is  capped  by  solid  lava  to 'a  depth  in  places  of  150 
ft.  The  cliff  of  blackened  rhyolite  on  the  southern  edge,  where 
the  main  discovery  of  ore  was  made,  is  from  30  to  50  ft. 


140       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

high.  In  many  places,  as  in  the  Yanderbilt  mine,  the  rock  is 
plainly  fragmental  and  stratified,  and  has  a  well-defined  dip. 
The  contact  of  Archsean  and  rhyolite  along  the  western  border 
is  a  gently-undulating  surface,  and  in  most  of  the  prospect-holes 
the  Archaean  is  much  broken  and  resembles  a  breccia.  The 
northern  half  of  the  area  is  breccia  and  tuff,  except  a  few  dikes 
of  massive  rock.  At  the  Songbird  and  Mountain  View  mines, 
and  along  the  western  border  generally,  the  gneiss  under  the 
rhyolite  has  been  much  altered  and  is  locally  ore-bearing,  car- 
rying magnetite,  pyrite,  and  some  galena,  as  in  the  Immortal 
and  Keystone  mines.  Near  the  Sunrise,  and  along  the  eastern 
border  as  far  south  as  the  Vanderbilt,  the  rock  is  a  finely- 
bedded  tuff',  dipping  south  and  west.  The  thickness  of  frag- 
mental material  below  the  highest  point  of  the  hills  is  more 
than  550  ft.  These  beds  terminate  abruptly  to  the  south  along 
an  east-and-west  line  running  near  the  Yanderbilt,  which  Mr. 
Cross  thinks  may  be  a  fault-line. 

The  massive  rock  is  everywhere  characterized  by  a  banded 
or  fluidal  structure,  and  in  it  topaz  and  garnet  have  been  found. 
Under  the  massive  lava  on  the  southern  portion  of  the  plateau 
is  pitchstone  or  glassy  rhyolite,  about  50  ft.  thick,  with  about 
as  much  more  below,  containing  spherulites,  which,  when  de- 
composed, form  a  boulder-zone.  These  glassy  rocks  outcrop 
around  the  cliff  to  the  south  and  east,  and  are  found  in  cellars 
in  the  town  of  Silver  Cliff. 

Surface-Deposits. — The  original  outcrop  of  the  ore-bearing 
rhyolite  on  the  Silver  Cliff  and  Racine  Boy  claims  was  appar- 
ently nothing  more  than  the  ordinary  banded  rhyolite,  stained 
and  blackened  by  oxides  of  manganese,  extensively  cracked 
and  fissured,  and  carrying  little  flakes  of  chloride  of  silver  in 
the  cracks.  As  far  as  known,  no  other  metallic  minerals  were 
detected,  nor  was  there  any  definite  boundary  or  regularity  of 
form  to  the  part  that  constituted  the  ore.  An  area  several 
hundred  feet  in  diameter  and  from  30  to  50  ft.  thick  was  thus 
found  to  be  ore-bearing.  When  examined  by  us  in  the  quarry, 
the  principal  set  of  joints  or  rock-fractures  were  observed  to 
r,un  nearly  northwest  and  southeast,  and  it  was  on  these  that 
the  most  silver  was  found.  On  some  of  these  cracks  was  a 
considerable  coating  of  clear  black  manganese  oxide ;  in  others, 
where  there  was  more  iron  oxide,  the  coating  had  a  metallic 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       141 

luster;  and  it  was  on  the  latter,  according  to  the  observations 
of  the  miners  who  were  sorting  the  ore,  that  the  principal 
values  were  found.  A  set  of  secondary  joints  or  fractures, 
crossing  the  main  joints  nearly  at  right  angles  and  reaching  to 
the  surface,  could  be  observed  along  the  benches  of  the  quarry. 
These  also  were  heavily  coated  with  manganese  oxide,  and 
carried  ore.  It  was  but  rarely,  at  that  time,  that  the  flakes  of 
horn-silver  could  be  detected  by  the  naked  eye.  Our  observa- 
tions indicated  that  the  horn-silver  was  more  frequently  de- 
posited on  small  cracks,  adjoining  those  filled  by  iron  and 
.manganese  oxides,  and  apparently  of  later  formation.  The 
light-colored  mass  of  the  rock  had  a  faint  pink  tinge,  and  a 
specimen  analyzed  contained  0.06  per  cent,  of  manganese  oxide. 
It  was  the  experience  of  the  miners  that  the  silver-values  did 
not  occur  outside  of  the  stained  zone. 

When  the  ore-body  was  first  worked,  it  is  said  to  have  con- 
tained from  35  to  50  oz.  of  silver  per  ton,  but  it  gradually 
decreased  in  value  as  it  was  taken  at  a  greater  distance  from 
the  surface.  It  is  said  that,  while  the  mills  were  running,  the 
rock  was  not  sorted,  but  sent  in  bulk  to  the  crusher.  The  last 
mill-runs  are  said  to  have  assayed  only  about  7  oz.  to  the  ton, 
and  the  greater  part  of  this  went  off'  in  the  tailings. 

The  ore  taken  from  the  quarry  was  sorted,  so  as  to  average 
from  50  to  60  oz.  per  ton,  at  one  time ;  but  this  fell  off  later,  and 
it  was  apparently  so  low  finally  as  not  to  pay  for  working. 

It  has  been  a  cause  of  much  fruitless  speculation  that  the 
amalgamating-mills  were  so  unsuccessful  in  treating  this  ore. 
It  is  generally  conceded  that  much  the  larger  portion  of  the 
silver  was  carried  away  in  the  tailings,  which  were  afterwards 
profitably  concentrated  by  hand-jigs.  A  sample  of  these  tail- 
ings, carefully  quartered  down,  yielded  in  the  laboratory  of  the 
Survey  0.13  per  cent,  of  sulphur,  which  is  sufficient  to  combine 
with  the  silver  contained  and  form  sulphides.  It  is  also  said 
that  a  small  amount  of  antimony  has  been  found  in  the  ore  by 
those  who  smelted  it. 

If  the  silver  is  generally  in  the  form  of  sulphide,  it  would 
naturally  be  difficult  of  amalgamation,  and  the  presence  of 
antimony  would  heighten  that  difficulty. 

.  Small  amounts  of  ore  were  also  found  near  the  surface  at 
many  other  points  on  the  plateau,  which,  though  not  compara- 


142       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

ble  in  amount  to  the  Silver  Cliff  body,  were  sufficient  to  en- 
courage prospecting  to  such  an  extent  that  over  400  prospect- 
holes  were  counted  there  at  the  time  of  our  examination.  For 
the  most  part  they  had  been  already  abandoned,  and  there  was 
nothing  to  show  how  the  ore,  if  any  there  was,  occurred. 
Among  the  more  prominent  ones,  which  actually  produced 
considerable  values,  may  be  named  the  Boulder,  Vanderbiltr 
King  of  the  Valley  and  Silver  Bar  (formerly  the  Kate). 

DEEP  DEPOSITS  OF  THE  GEYSER  MINE. 

The  only  mine-workings  that  have  extended  to  any  consid- 
erable depth  on  the  plateau,  say  over  100  ft.,  are  those  of  the 
Security-Geyser  mine.  As  far  as  is  known,  the  ore  of  all  the 
plateau-deposits  had  given  out,  really  or  apparently,  within 
considerably  less  than  100  ft.  of  the  surface.  The  ore  was 
always  chloride  of  silver  where  its  character  could  be  distin- 
guished. That  from  the  Kate  (Silver  Bar)  claim,  worked  in 
early  days,  is  said  to  have  contained  some  gold  also ;  but  this 
is  the  only  case  reported  and  the  statement  has  not  been  veri- 
fied. It  does  not  seem  likely  that  silver  would  be  accompanied 
by  gold  in  one  place  and  free  from  it  in  all  the  others.  A& 
will  be  seen  later,  of  the  two  shipments  to  smelters  of  ore 
from  the  bottom  of  the  Geyser  shaft,  one  contained  only  0.1 
oz.  of  gold  per  ton,  the  other  but  a  trace. 

It  is  only  through  the  underground  workings  of  the  Geyser 
shaft,  therefore,  that  it  has  been  possible  to  obtain  any  informa- 
tion with  regard  to  the  conditions  of  ore-deposition  in  depth. 
The  data  which  it  has  been  possible  to  obtain  with  regard  to 
them  in  occasional  visits  during  past  years  will  therefore  be 
given  in  considerable  detail. 

The  Geyser  shaft,  as  it  is  now  called,  is  located  350  ft.  north, 
a  little  west,  of  the  mouth  of  the  adit  leading  from  the  floor  of 
the  Silver  Cliff  quarry,  and  its  collar  is  104  ft.  above  that  level. 
It  was  originally  intended  to  sink  the  shaft  only  500  ft.,  it  being 
supposed,  from  the  position  of  the  various  observable  contacts 
of  the  rhyolite  with  the  underlying  Archaean,  that  the  former 
was  a  rather  shallow  body,  and  that  the  underlying  granite  and 
gneiss  would  be  reached  within  the  depth-  named.  It  was, 
later,  decided  to  prepare  for  greater  depths,  and  the  hoisting- 
machinery  was  given  greater  capacity.  The  limit  of  this  ca- 


u.  OF  c. 

SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF, 


pacity  was  reached  in  the  summer  of  1894,  when  a  depth  of 
2,100  ft.  was  attained.  Entirely  new  and  heavier  machinery, 
with  a  capacity  of  4,500  ft.,  was  then  ordered,  which  is  now 
(May,  1896)  in  working-order,  and  sinking  has  been  resumed. 

Mine-Levels.  —  The  first  exploring-levels  or  drifts  were  started 
at  a  depth  of  500  ft.  These  were  run  500  ft.  west  and  700  ft. 
east  ;  likewise  some  distance  in  a  southerly  direction.  At  750  ft.r 
levels  were  run  to  the  east  and  south,  and  one  branch  passed 
directly  under  the  quarry.  Below  this,  levels  were  run  at 
1,450,  1,850,  2,000,  and  2,100  ft.  from  the  surface,  respectively. 
The  general  direction  of  exploration  in  these  levels  appears  to- 
have  been  to  the  west  and  northwest,  but  the  1,450-ft.  level 
had  a  drift  running  southward.  Accurate  maps  of  the  respec- 
tive levels  could  not  be  obtained,  but,  in  a  general  way,  it  is 
estimated  that  the  main  exploring-drifts  have  a  linear  extent  of 
about  1.5  miles  at  the  different  levels,  and  that  about  600,000 
sq.  ft.  of  area  was  more  or  less  thoroughly  explored.  Fig.  1 
(Fig.  7  of  original  paper)  gives  a  somewhat  diagrammatic  repre- 
sentation of  the  ground  explored. 

Country-Rocks.  —  For  the  first  150  ft.  the  shaft  passed  through 
banded  rhyolite.  In  the  tunnel  leading  to  the  shaft,  a  narrow 
zone  or  band  of  this  rock  was  found  to  be  changed  into  a 
plastic  white  clay,  which  was  almost  pure  kaolin. 

Below  the  solid  rhyolite  was  about  50  ft.  of  pitchstone,  then 
about  'the  same  thickness  of  the  boulder  or  spherulitic  zone. 
Veins  and  crystals  of  calcite  were  found  in  the  rhyolite  under 
the  pitchstone.  From  250  ft.  down  to  about  1,900  ft.  the  shaft 
passed  through  white  rhyolitic  tuff"  and  breccia,  the  former  often 
distinctly  stratified  and  generally  looking  like  white  sandstone,. 
much  kaolinized.  The  breccia  varies  from  fine  to  coarse,  and 
contains  fragments  of  all  the  varieties  of  Archaean  rocks  found 
in  the  region  ;  but  no  eruptive,  other  than  rhyolite,  was  observed 
among  the  fragments.  Some  of  the  Archaean  fragments  are 
kaolinized  and  disintegrated  ;  others  are  quite  fresh.  The  green 
decomposition-product  of  hornblende  and  mica  was  in  one  place 
thought  to  be  a  copper-stain. 

Here  and  there  through  the  tuff",  as  far  as  the  2,000-ft.  level, 
fragments  of  charcoal  or  carbonized  wood  were  observed  (the 
special  localities  are  marked  by  a  cross  on  the  section  in  Fig. 
1).  At  335  ft,  pieces  2  ft.  long  are  said  to  have  been  found  in 
the  shaft. 


144       SOME    MINES    OP    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

The  bedding  of  the  tuff  was  found  to  be,  for  the  most  part, 
nearly  horizontal.  In  the  shaft  a  slight  dip  to  the  west  was  noted 
at  times  for  considerable  vertical  distances.  In  the  drifts, 


PITCH 


Surface  Water 


STRATIFIED  TUFF  AND  BRECCIA 
500  ft. Level 


750  ft.Level 


RHYOLITIC  TUFF 


1450  ft.Level 


._..,_''    GRANITE 
-^2000  ft.Level 

2100  ft.Level 


Scale. 
100         0  100 


FIG.  1. — SECTION  THROUGH  GEYSER  SHAFT. 

the  dip  to  the  west  or  northwest  is  more  marked,  in  a  general 
way,  to  the  southeast  of  the  shaft,  and  in  one  place,  for  a  short 
distance,  this  dip  was  75°.  In  the  shaft  there  appears  to  have 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       145 

been  a  somewhat  irregular  alternation  of  white  tuff  and  breccia. 
For  instance,  the  former  was  found  continuously  from  775  to  905 
ft.,  and  from  there  to  1,000  ft.  the  rock  was  mostly  breccia,  at 
times  with  so  many  large  fragments  of  Archaean,  up  to  2.5  ft. 
in  diameter,  that  it  was  thought  the  solid  formation  would  soon 
be  reached. 

The  shaft  actually  entered  the  granite  and  gneiss  of  the 
Archaean  near  the  1,850-ft.  level.  Where  cut  in  the  drifts 
below,  the  contact  of  rhyolitic  tuff  or  breccia  and  Archaean  ap- 
pears to  be  on  fault-planes.  The  Archaean  consists  of  mica-  and 
hornblende-schists  cut  by  red  granite.  These  rocks  are  frac- 
tured and  sheeted  in  a  direction  parallel  to  the  ore-bearing  veins 
in  the  rhyolite ;  but  the  actual  contact  apparently  does  not,  as 
might  be  assumed  from  the  section  in  Fig.  1,  conform  in  every 
respect  to  these  planes.  The  intersections  of  the  contact  by 
drifts  are  too  few  to  permit  the  tracing  of  the  shape  of  the 
Archaean  wall  that  incloses  the  rhyolite.  It  was  noted,  however, 
that  the  drifts  pass  out  of  the  Archaean  into  rhyolitic  breccia  as 
they  go  north-northwest  or  west  from  the  shaft. 

In  the  2,100-ft.  level,  drifts  run  only  north  and  west,  and 
the  contact,  as  contrasted  with  that  in  the  level  above,  has  an 
inclination  to  the  northeast.  The  contact  on  this  level  is.  not 
sharp  and  well  defined,  but  rather  a  broken  zone,  first  of  very 
coarse  fragments  of  granite  and  gneiss,  then  of  normal  rhyo- 
litic breccia  with  small  fragments  of  granite  and  gneiss.  The 
three  lower  levels  have  been  run  from  300  to  500  ft.  north  and 
west  in  this  material,  which  is  sometimes  hard  and  jaspery  and 
of  dark-red  color,  but  bleaches  on  exposure  to  the  air.  It  is 
traversed  by  planes  of  movement,  sometimes  irregular  and  curv- 
ing, but  all  having  a  general  northwest  strike.  Beyond  one  of 
these  planes  is  a  dark  bluish  rock,  supposed  by  the  miners  to 
be  limestone  because  it  effervesces  freely  with  acid,  but,  on  mi- 
croscopic examination,  found  to  be  a  decomposed  basic  eruptive, 
containing  considerable  calcite. 

Ore-Bodies. — No  defined  ore-body  was  found  until  the  1,850- 
ft.  level  was  reached.  Thin  films  or  stains  of  metallic  sul- 
phides, said  to  assay  high  in  silver,  occurred  occasionally  in  the 
shaft  and  in  some  of  the  drifts;  lining  delicate  cracks  in  the 
tuff,  and  sometimes  also  in  the  Archaean  fragments.  On  the 
1,450-ft.  level,  about  450  ft.  south  of  the  shaft,  it  is  said  that 

10 


146       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

there  was  found  in  the  white  tuff  a  0.25-in.  seam  of  ruby-silver 
and  argentite,  with  crystalline  calcite,  which  had  a  general 
course  north-northwest,  and  was  traced  about  50  ft,  when  it 
disappeared. 

The  main  ore-vein  was  first  found  in  the  1,850-ft.  level,  about 
200  ft.  northwest  of  the  shaft,  as  a  narrow  seam,  a  fraction  of 
an  inch  wide,  with  barite  and  calcite  gangue,  which  widened, 
as  it  was  followed,  to  4  or  5  in.,  mostly  of  galena,  and  narrowed 
again  to  a  mere  knife-edge  seam  in  about  150  ft.  A  few 
nearly-parallel  seams,  containing  only  calcite  and  barite,  were 
observed  near  it.  This  vein  was  traced  by  a  winze  downward, 
and  was  cut  afterwards  in  the  2,000-ft.  and  2,100-ft.  levels, 
gaining  width  and  richness  as  it  went  down.  In  the  2,000-ft. 
level,  it  is  quite  thin  in  the  middle,  and  splits  into  several  thin 
seams  at  the  northwest,  which  gradually  wedge  out.  On  the 
2,100-ft.  level  a  smaller  vein  is  found  about  40  ft.  northeast  of 
and  parallel  to  the  main  vein ;  this  also  splits  at  the  northwest 
end.  The  general  strike  of  the  vein  is  K  37°  to  40°  W.,  and 
it  stands  nearly  vertical,  its  average  dip  from  the  1,850-ft.  to 
the  2,100-ft.  level  being  70°  to  the  northeast, 

Vein- Materials. — Although  very  thin,  in  no  case  attaining  as 
much  as  a  foot  in  width,  this  vein  has  been  remarkably  produc- 
tive, owing  to  the  richness  of  the  ore  and  the  relatively  small 
proportion  of  gangue.  The  principal  metallic  minerals  are 
galena,  zinc-blende,  chalcopyrite,  cupriferous  argentite,  tetra- 
hedrite,  ruby-silver,  and  possibly  stromeyerite  or  polybasite. 
Hessite  and  leaf-gold  are  said  to  occur,  but  their  presence  could 
not  be  verified.  The  galena  occurs  in  fine  scaly  form,  rather 
than  in  the  usual  massive  crystals.  The  zinc-blende  is  generally 
of  the  ferriferous  variety  known  as  "  black  jack  "  by  the  miners, 
and  is  rather  porous.  It  occurs  at  times  in  cup-shaped  forms, 
which  are  lined  with  fine  crystals.  It  sometimes  forms  cross- 
courses,  or  distinct  shoots  in*  the  vein,  which  carry  from  300 
to  400  oz.  of  silver  to  the  ton,  and  always  a  good  deal  of 
galena.  The  chalcopyrite  occurs  mostly  amorphous  and  easily 
disintegrate,  in  rounded  patches,  distinct  from  the  other  min- 
erals, and  prominent  by  its  dull  brass-yellow  color.  Where  the 
ore  occurs  in  botryoidal  form,  one  can  distinguish  the  following 
succession  from  the  center  outward :  (1)  barite  in  tabular  crys- 
tals ;  (2)  galena  (and  argentite) ;  (3)  copper  sulpKide ;  (4)  gray 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       147 

copper  in  crystals ;  (5)  small  crystals  of  chalcopyrite.  In  cer- 
tain parts  of  the  vein  which  consist  exclusively  of  metallic  min- 
erals, they  have  a  peculiarly  fresh  look,  as  if  quite  recently 
deposited  and  not  yet  completely  consolidated.  The  average 
composition  of  the  ore  from  the  Geyser  mine  is  best  shown  by 
the  following  analyses  of  two  car-load  lots  kindly  furnished  by 
the  Arkansas  Valley  Smelting  Co.,  of  Leadville,  to  whom  they 
had  been  sold : 


Lot  No.  1. 

Lot  No.  2. 

.     Per  Cent. 
Gold                                                                                                    Trace 

Per  Cent. 
n 

Silver                                                                    .                              b  1  05 

c  1  27 

Lead                                                                                                     23  80 

17  60 

Zinc                 .                                                                                         14  00 

11.10 

Copper  (wet  assay  )                                                                               1.50 

2  30 

Iron                                                                                                            2  30 

2  00 

Manganese              ...                                         .                             1  20 

0.80 

Lime                             .    .                   .                                                   1  70 

Sulphur  12  60 

9.50 

Silica    3360 

46.90 

Total  .  91.75 

91.47 

a  0.10  oz.  per  ton.  6  2 ',0.42  oz.  c  300.28  oz. 

In  addition  to  the  above  metals,  there  was  probably  anti- 
mony, wThich  had  been  proved  qualitatively,  in  the  mineral  that 
was  supposed  at  the  mine  to  be  hessite,  but  is  probably  either 
tetrahedrite  or  polybasite.  Barium  and  alumina  probably  make 
up  a  part  of  the  balance. 

Of  earthy  minerals,  the  most  common  are  barite,  calcite, 
and  quartz,  the  latter  generally  in  the  chalcedonic  form.  Frag- 
ments of  country-rock  are  found  in  the  vein,  more  or  less 
rounded,  and  changed  on  the  outer  part  into  hornstone-like 
material,  which,  in  turn,  is  coated  with  galena,  barite,  etc. 
Rounded  cavities  in  the  vein-material  are  often  filled  with  a 
white  powder,  apparently  an  infiltrated  decomposition-product 
of  the  rhyolitic  tuff. 

Water-  Courses. — This  mine  has  proved  unusually  dry  for  the 
region.  In  the  upper  part  of  the  shaft  the  first  considerable 
flows  of  water  came  in  at  340,  390,  and  especially  at  420  ft. 
This  water,  collected  at  the  500-ft.  level,  amounted  to  250  gal. 
per  minute,  and  was  undoubtedly  vadose  or  surface-water,  and 
probably  seeped  in  from  the  surrounding  country.  At  945  ft. 


148       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

it  had  decreased  to  65  gal.  per  minute,  and  below  1,000  ft.  had 
practically  ceased,  the  little  water  that  was  found  being  prob- 
ably due  to  leakage  along  the  shaft. 

In  the  1,450-ft.  level  what  may  be  considered  subterranean 
or  deep  waters  were  first  struck.  They  were  not  very  abund- 
ant, and  were  only  slightly  charged  with  gas.  At  one  point 
on  the  south  drift  there  was  a  slight  deposit  of  tufa.  A  con- 
siderable flow  was  obtained  from  a  vertical  drill-hole  sunk  300 
ft.  downward  from  this  level. 

In  the  1,850-,  2,000-,  and  2,100-ft.  levels  there  are  many 
small  water-courses,  from  which  proceeds  a  constant  flow  of 
water,  not  very  great  in  aggregate  amount,  but  highly  charged 
with  carbonic  acid  gas,  so  that  there  is  a  constant  hissing,  sput- 
tering, and  rumbling,  and  the  water  is  ejected  with  such  force  as 
to  go  entirely  across  the  drift  at  some  points.  These  waters 
apparently  ascend  along  fissures  having  a  general  parallelism 
with  the  ore-bearing  fissure ;  but  no  water  proceeds  from  the 
vein  itself.  They  often  come  into  the  drifts  through  small 
cracks  or  cross-fissures  at  an  angle  with  the  direction  of  the 
main  system.  As  they  emerge  into  the  air  of  the  drift  they 
deposit  freely  a  calcareous  tufa  or  sinter  on  the  wall  around 
the  crack  or  orifice  out  of  which  they  flow.  This  sinter  is 
sometimes  white,  sometimes  highly  iron-stained ;  it  has  the 
texture  and  the  peculiar  wavy  or  ripple-marked  surface  char- 
acteristic of  the  sinters  of  the  Yellowstone  Park.  In  some 
places  it  takes  a  pisolitic  form.  Again  its  surface  has  a  shiny 
glaze.  It  deposits  very  rapidly  in  some  places.  At  one  point 
on  the  2,000-ft.  level,  which  had  been  opened  only  four  months, 
the  water  issuing  from  a  minute  vertical  crack  on  the  side  of 
the  drift  had  built  out  a  little  ridge  of  sinter  over  the  crack, 
1.5  in.  from  its  base  and  less  than  0.5  in.  thick. 

The  water-courses  are  most  active  and  abundant  near  the 
vein  or  on  the  line  of  its  extension.  On  the  2,000-ft.  level, 
where  the  vein  splits  to  the  northwest,  the  water  comes  in  on 
all  sides ;  and  when  the  shaft  was  first  opened,  the  escape  of 
carbonic  acid  gas  was  so  abundant  at  this  point  that  it  filled  the 
lower  5  ft.  of  all  the  drifts  on  this  level  and  the  shaft  below  the 
level  so  that  no  light  would  burn,  and  the  miners  were  obliged 
to  abandon  work  until  a  blower  could  be  put  in  operation  to 
drive  the  gas  out.  Even  now,  a  light  is  soon  extinguished 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       149 

if  put  at  the  bottom  of  the  drift.  The  water-bearing  fissures 
are  mostly  in  the  rhyolitic  tuff,  but  a  few  are  found  in  the 
Archaean,  which  shows  evidence  of  faulting  within  itself,  in 
slickensided  clay  seams  and  zones  of  brecciation.  The  water- 
bearing fissures  decrease  in  number  and  in  strength  of  flow  as 
the  distance  from  the  line  of  the  ore-bearing  fissure  increases. 
The  abundant  escape  of  gas  is  the  most  striking  feature  of 
these  water-courses.  Even  where  no  water  comes  into  the 
drift,  one  can  often  hear  the  bubbling  and  sputtering  of  the 
escaping  gas  in  an  adjoining  fissure. 

The  temperature  could  not  be  accurately  determined,  but  is 
about  the  same  as  that  of  the  air  in  the  drift  at  the  2,000-ft. 
level,  viz.,  80°  F. 

Analyses  of  Sinters. — Three  typical  specimens  of  sinter  from 
the  2,000-ft.  level  were  selected  for  analysis:  one  of  the  per- 
fectly white,  with  very  slight  iron-stain ;  one  white  and  brown 
(both  showing  the  ripple-marked  structure  well);  a  third  of 
the  pisolitic  sinter,  strongly  iron-stained.  They  were  analyzed 
by  W.  F.  Hillebrand,  with  the  following  results : 

Analyses  of  Sinters  from  the  2,000-JFV.  Level,  Geyser  Mine. 


White. 

White  and 
Brown. 

Pisolitic 
Brown. 

Silica  and  insoluble  

Per  Cent. 
0.08 

Per  Cent. 
0  10 

Per  Cent. 
0.17 

CaO  

53.11 

52.60 

52.59 

CO.  

42  98 

42  57 

42.03 

FeA  

0.20 

1.08 

1.82 

Mn2O3  (Mn3O4?).....  

a  0.026 

a  0.03 

Undet. 

SrO  

0.17 

0.26 

0.22 

MgO  

1.50 

1.39 

1.01 

K2O  

0.03 

0.03 

0.04 

Na2O  

0.17 

0.16 

0.09 

Li2O  

Trace. 

Trace. 

Trace. 

H2O  below  110°  C  

0.33 

0.51 

0.53 

H2O  above  110°  C  

0.88 

0.72 

0.87 

SO3  

0.29 

0.50 

0.58 

P2OS  

Trace. 

Trace. 

Trace. 

cL?  ::::.:: 

Faint  trace. 

Faint  trace. 

Faint  trace. 

Total  

99.766 

99.95 

99.95 

a  Manganese  was  estimated  on  34  g.     The  same  samples  showed  also  minute 
traces  of  lead,  copper,  nickel,  cobalt,  zinc,  alumina,  and  a  double  trace  of  antimony. 

On  comparing  these  analyses  with  those  of  the  waters  which 
follow,  it  appears  that,  under  the  influence  of  free  access  of  air, 


150  SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

with  presumably  reduced  pressure  and  temperature,  the  pre- 
cipitation has  been  mainly  of  carbonates  of  lime,  iron,  and  man- 
ganese ;  of  the  alkalies,  magnesia,  and  of  other  metals  a  rela- 
tively small  proportion  seemed  to  have  been  precipitated. 

Analyses  of  Waters. — Carboys  of  water  from  the  500-ft.  level, 
i.e.,  surface  or  vadose  waters,  and  of  waters  from  the  2,000-ft. 
level  were  collected  with  great  care  by  the  foreman  of  the  mine 
under  the  direction  of  C.  H.  Johnson  and  sent  to  Washington 
for  analysis.  Upon  their  arrival,  there  was  found  to  be  con- 
siderable sediment  in  each  of  the  carboys,  which  had  presum- 
ably been  precipitated  during  the  journey,  since  they  had  been 
filtered  through  cotton  cloth  when  gathered.  Mr.  Hillebrand 
found  evidence,  however,  that  the  filtering  had  not  been  com- 
plete, as  some  splinters  of  wood  were  found  in  the  sediment, 
which  casts  some  doubt  on  the  analysis  of  the  sediment. 

In  the  42.6  1.  of  vadose  water  of  which  the  analysis  is  given 
below,  there  was  a  deep  blackish-brown  sediment,  containing, 
however,  no  organic  matter,  which,  after  drying  at  110°  C., 
weighed  0.5592  g.,  and  gave : 

Gram. 

Ignition,  .  .  ...  4 .  ,••...  0.0642 
HC1  extract,  .  /  .  .,  .  ...  .  0.1588 
Insoluble  silica  and  silicates,  .  .  .  .  .  .  0.3362 

Total,     .       ,.'       .         .         .        .         .        .         .    "(X5592 

It  was  assumed  that  the  silica  and  silicates  must  have  been 
mechanically  introduced,  through  want  of  sufficient  precautions 
in  filtering  at  the  mine;  and  this  portion  of  the  sediment  was 
not  analyzed.  Of  the  sediment  in  the  carboy  of  deep  water, 
however,  the  insoluble  portion  was  analyzed,  with  the  result 
given  in  the  following  tables.  The  total  sediment  in  the  carboy 
of  deep  water  was  10.6602  g.,  of  which  5.0134  g.  was  insoluble 
in  dilute  HC1  (at  110°  C.).  The  filtered  vadose  water  had  a 
slightly  alkaline  reaction  and  contained  no  organic  matter. 
The  results  of  analysis  are  given  in  the  following  tables  [pp. 

151  and  152]  : 

These  tables  present  a  remarkably  complete  series  of  actual 
analyses,  representing : 

1.  The  average  contents  of  a  vein-deposit  of  metallic  miner- 
als, rich  in  silver,  lead,  copper,  and  zinc,  which  was  first  found 
at  over  1,800  ft.  below  the  present  surface. 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       151 


Vadose  Water  from  the  Geyser  Mine,  500-Ft.  Level. 

(W.  F.  Hillebrand,  Analyst.) 


In  Sediment.    Soluble  in  HC1.                             In  Filtered  Water. 

Assumed 
Composi- 
tion Before 
Sediment 
was  i  e- 
posited. 

Amounts 
Found. 

Referred 
to  Parts 
in  1,000,000 
of  Water. 

Parts  in 
1,000,000. 

SiO9... 

Gram. 
0.0012 
0.0010 
0.0008 
0.0456 

0.0365 

0.0498 
0.0104 
0.0096 
0.0039 

(c) 

SiO2 

Trace. 
Trace. 
Trace. 
0.7 

0.8 

0.8 
0.2 
0.1 
0.05 
2.2 

Cl 

7.9 
43.2 
108.3 
10.6 
36.4 
Trace. 
37.3 
12.2 

7.9 
43.2 
110.5 
10.6 
36.4 
Trace. 
37.4 
12.25 
Trace. 
Trace. 
0.8 
0.2 
0.7 

0.8 
25.9 

PbO  

Cu 

SO 

CuO  

CO  a 

FeA-. 

Fe 

Al  A  1 

PA  f  
znd.  .!..'.".'! 

CaO  

A1A  \ 

Na... 

Li 

Ca 

Zn 

Me- 

Ca 

Pb 

MgO 

Mg  

CO3d 

Cu  
Mn 



CO,... 

0.1588 

4.85 

Fe 

A1A  \ 

PA   /  

Si"()2 

Free  and 
semi  -com- 
bined CO2, 

Total  C02, 

281.8 
38.8 

286.65 
37.2 

320.6 
118.2 

323.85 

a  Calculated.  6  Assumed  condition. 

c  Any  traces  of  CO2  present  have  been  neglected. 

d  Calculated  for  the  metals,  as  carbonates  before  deposition. 

NOTE. — No  tests  for  other  possible  constituents  were  made. 

2.  The  contents  of  subterranean  mine-waters  taken  at  2,000 
ft.  below  the  surface,  and  evidently  coming  from  still  greater 
depths,  very  highly  charged  with  carbonic  acid,  and  carrying 
small  amounts  of  most  of  the  metals  that  occur  in  the  deposit; 
also  the  sinter  deposited  by  these  waters  as  they  issue  from  the 
rock  into  the  mine-drifts — that  is,  under  ordinary  atmospheric 
pressure. 

3.  The  contents  of  atmospheric  waters  coming  from  the  sur- 
face, which,  in  their  downward   course,  had  traversed  rocks 
similar  to  those  in  which  the  first-named  deposit  is  inclosed, 
and  through  which  it  may  be  assumed  that  metallic  minerals 
similar  to  those  in  the  deposit  may  be  sparingly  disseminated. 


152       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 


Deep   Water  from  the  Geyser  Mine,  2,000-^.  Level. 

Specific  Gravity  27°  C.  =1.0036.  (W.  F.  Hillebrand,  Analyst.) 


Composition  of  Sediment. 
(From  43.76  kg.  of  Water.) 

Composition  of 
Filtered  Water. 

Assumed 
Composi- 
tion Be- 
fore Sedi- 
ment 
was  De- 
posited. 

Insoluble  in  Dilute  HC1. 

HC1  Extract. 

Parts  in 
1,000,000. 

Chiefly  Clayey  and 
Feldspathic  Matter., 
Weight  Dried  at  110°  C. 
5.0134  g. 

Amounts 
Found. 

Referred  to  Parts  in 
1,000,000. 

Cl 

186.40 
Traces. 
161.70 
Trace. 
/1.  60 
Trace. 
1,437.26 
None. 
19MIO 
719.45 
2.85 
108.84 
1.10 
176.60 
0.05 
Trace. 
0.19 
0.17 
0.14 
None. 
22.90 
Not  est. 

186.40 
Trace. 
161.70 
Trace. 
1.60 
Trace. 
1,513.44 
h  Trace. 
198.00 
719.45 
2.85 
146.41 
1.95 
177.67 
1.35 
0.02 
0.57 
0.34 
3.50 
i  1.06 
24.42 
Not  est. 

Br  and  I 

SO4 

P04  
NO,  

BA  

S?"  

SiO2  . 

Per  Cent. 
54.07 

29.70 

A  little 
(as 
CaFl2?) 
None. 
4.40) 
0.37  [• 

Grams. 
0.0667 

a  0.0461 
0.2100 

2.7921 

0.0778. 
Not 
tested 
for. 
2.3153 
0.0440 
None. 

SiO2  

ALA  
Fe  

1.52 

1.06 
3.36 

45.57 
1.07 

A1A   ) 

afi  

CaO  

Ca  

K   

Na  

MgO.... 

Mg.... 

Si 

Ca  

K2O 

Sr 

Na26 

MET 

SO3 

Pb       . 

CO26 

CO3 

c  76.18 
0.85 
None. 

Cu 

SrO 

Sr 

Mn 

BaO 

Ba 

Zn 

Fl 

A  little. 

Fe 

PbO 

0.0610 
0.0011 
0.0232 
0.0095 

(e) 

Pb 

1.30 

AIA  
SiO2  
Org.  mat. 

Total  CO2 

CuO 

Cu 

0.02 
0.38 
0.17 

(e) 

Mn  A  d 

Mn 

7nO 

Zn  

Ignition  

9.47 

3,009.25 
2,472.60 

3,140.73 
2,528.43 

98.01 

5.6468 

131.48 

a  Perhaps  derived  from  the  mechanically-included  minerals  of  the  sediment. 
Contains  a  little  P2O5. 

6  The  sediment  was  largely  incrusted  on  the  glass  of  the  carboy  and  could  only 
be  removed  by  acid  ;  hence  the  CO2  was  caculated  for  PbO,  ZnO,  SrO,  CaO,  MgO, 
as  normal  carbonates. 

c  This  value  includes  the  CO3  needed  by  Fe,  Mn  and  Cu,  as  well  as  the  metals 
named  in  the  preceding  notes. 

d  Assumed  condition  ;  perhaps  partly  as  MnCO3. 

e  Organic  matter  not  estimated. 

/  Approximation,  not  a  maximum. 

g  Calculated  for  normal  carbonates. 

h  The  fluorine  of  the  insoluble  part  of  the  sediment  is  probably  to  be  credited 
to  the  water. 

i  Possibly  from  the  insoluble  sediment. 

From  th'ese  analyses  it  is  possible  to  apply  a  practical  test  to 
some  of  the  assumed  theories  of  ore-deposition. 

Source  of  Solid  Constituents  in  the  Waters. — In  the  first  place, 
in  comparing  the  contents  of  the  vadose  and  deep  waters,  it  is 
seen  that  though  the  latter  contain  about  20  times  as  much 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       153 

dissolved  matter  as  the  former,  the  relative  proportions  of  the 
principal  constituents  are  sufficiently  alike  to  permit  the  assump- 
tion that  they  have  been  derived  from  a  similar  source;  and 
this  source,  in  the  case  of  the  surface-waters,  which  should  have 
been  practically  pure  when  they  entered  the  rocks,  must  have 
been  the  material  of  the  various  rocks  through  which  they 
have  passed  in  reaching  a  depth  of  500  ft.  below  the  surface. 
In  making  this  comparison,  one  must  bear  in  mind  that  the 
deep  waters  had  already  deposited  the  greater  part  of  their  lime 
as  sinter  before  they  were  analyzed ;  hence,  while  the  vadose 
waters  contain  three  times  as  much  lime  as  magnesia,  in  the 
analysis  of  the  deep  waters  lime  is  to  magnesia  in  the  propor- 
tion of  only  4  to  5. 

The  alkalies  appear  in  the  same  relative  proportions  in  each 
case,  though  the  aggregate  amount  of  the  two  constituents  is 
proportionately  less  in  the  vadose  than  in  deep  waters. 

Iron  and  manganese  are  in  nearly  equal  amounts  in  the  vadose 
waters,  the  latter  slightly  predominating,  whereas  in  the  deep 
waters  iron  is  in  a  hundred-fold  greater  relative  amount.  This 
might  be  explained  by  the  relatively  larger  amount  of  man- 
ganese oxides  present  in  the  surface-rocks.  It  has  often  been 
noted  by  the  writer  that  manganese  oxides  are  generally  pres- 
ent in  much  larger  proportion  in  the  oxidized  portions  of  ore- 
bodies  than  below  the  zone  of  oxidation,  which  may  be  due  to 
their  forming,  in  contact  with  atmospheric  agents,  less  soluble 
salts  than  do  the  iron  oxides. 

The  other  metals  are  in  such  small  proportions  in  either  case 
that  one  cannot  reason  from  their  relative  amounts ;  and  it  is 
not  surprising  that  most  of  them  could  not  be  detected  in  the 
vadose  waters. 

Such  constituents  as  fluorine,  boric  and  nitric  acids,  stron- 
tium, and  barium  are  characteristic  of  deep  sources,  but  they 
also  might  have  been  present  in  the  vadose  waters  without 
being  detected  in  the  small  amount  of  solid  constituents  avail- 
able for  analysis. 

The  greatest  apparent  discrepancy  is  the  ten-fold  greater 
proportion  of  silica  in  vadose  than  in  deep  waters ;  but  this  is 
likely  to  have  arisen  from  excess  of  C02  in  deep  waters  which 
would  throw  down  silica  in  solution,  or  from  the  uncertainty  in 
determining  what  part  of  the  solid  material  in  the  waters  was 
due  to  mechanical  admixture,  and  hence  might  be  neglected. 


154       SOME  'MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

In  the  deep  waters  chlorine  and  sulphuric  acid  are  present 
in  about  equal  proportions,  and  carbonic  acid  is  greatly  in  ex- 
cess of  both  combined.  In  the  vadose  waters,  while  carbonic 
acid  is  still  in  excess,  sulphuric  acid  appears  in  relatively 
greater,  and  chlorine  in  relatively  smaller,  proportion  than  in 
the  deep  waters.  In  what  manner  they  would  combine  with 
the  several  bases  in  either  case  it  is  of  course  impossible  to  say 
definitely. 

The  deductions  which  the  writer  draws  from  these  considera- 
tions are : 

1.  That  inasmuch  as  the  surface-waters  must  evidently  have 
derived  the  substances  they  contain  in  solution  from  the  rocks 
through  which  they  have  passed  in  seeping  downward,  it  is  fair 
to  assume  that,  in  like  manner,  the  deep  waters  have  obtained 
their  constituents  (in  great  part,  at  any  rate)  from  surrounding 
rocks,  and  not  necessarily  at  very  great  distances  from  where 
they  now  issue,  since  through  higher  temperature  and  greater 
acid  contents  they  would  probably  have  been  more  active  solv- 
ents than  the  surface-waters. 

2.  On  the  other  hand,  the  great  excess  of  carbonic  acid  in 
the  deep  waters,  combined  with  the  presence  of  fluorine,  boric 
acid,  and  chlorine  in  considerable  amount,  points  to  a  source 
where   chemical    decomposition  is  actively   going   on,  which 
might  readily  be  supposed  to  be  a  body  of  still  uncooled  igne- 
ous rocks,  which  surface-waters  had  reached,  and  from  which 
they  were  sent  back  towards  the  surface  again  along  the  present 
lines  of  fissuring.     Although  the  deep  waters  contain  most  of 
the  metals  found  in  the  vein-deposit  of  the  Geyser  mine,  it  is 
not  easy  to  conceive  how  the  metallic  sulphides  of  that  deposit 
could  have  been  derived  from  waters  of  such  chemical  composi- 
tion as  these ;  and  it  seems  more  reasonable  to  assume  that  the 
vein-minerals  were  deposited  by  earlier  waters  of  somewhat  dif- 
ferent composition,  carrying  more  barium  and  silica,  and  char- 
acterized by  sulphuretted  hydrogen  rather  than  by  carbonic  acid. 

3.  The  conditions  here  indicated  seem  to  negative  the  preva- 
lent belief  that  a  decrease  of  temperature  and  pressure  is  the 
principal  determining  cause  of  the  precipitation  of  vein-minerals 
from  ascending  solutions.     In    the  earlier  deposits  abundant 
precipitation  ceased  before  the  marked  decrease  of  temperature 
and  pressure  that  accompanies  an  approach  to  the  actual  rock- 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       155 

surface  was  reached ;  and  in  the  modern  mine-openings,  where 
present  ascending  waters  have  been  artificially  cooled  and  re- 
lieved from  pressure,  the  abundant  deposit  has  been,  like  that 
of  thermal  springs  at  the  surface,  mainly  of  carbonate  of  lime 
and  oxide  of  iron,  and  contains  only  faint  traces  of  the  other 
vein-materials  that  make  up  the  bulk  of  the  neighboring  vein- 
deposits. 

4.  It  might  be  assumed  that  the  surface-deposits  of  chloride 
of  silver  and  oxides  of  manganese  and  iron  which  are  thinly 
and  irregularly  disseminated  through  the  rhyolite  near  the 
actual  surface,  were  precipitated  from  the  carbonated  waters 
at  a  time  when  they  reached  the  present  surface,  the  oxides  hav- 
ing been  originally  carbonates,  and  the  silver  chloride  having 
been  deposited  as  such,  and  that  these  deposits  are  therefore 
a  later  phase  of  ore-deposition  than  the  vein-minerals.  A  cer- 
tain color  of  probability  is  lent  to  this  hypothesis  by  the  fact 
noted  by  Mr.  Johnson,  superintendent  of  the  Geyser  mine,  tha't 
there  is  evidence  of  an  escape  of  warm  air  or  gas  through  holes 
at  the  surface,  which  in  cold  weather  is  visible  as  steam,  along 
a  zone  about  100  ft.  wide,  running  east  and  west  through  the 
Geyser  shaft-house.  Moreover,  fluorite  and  barite  are  said  to 
have  occurred,  associated  as  gangue-minerals  with  chloride  of 
silver,  in  the  Silver  Bar  (formerly  Kate)  mine. 

On  the  other  hand,  all  our  evidence  goes  to  show  that  the 
chlorides  and  oxides  pass  into  sulphides  at  short  distances  be- 
low the  surface,  and  that  here,  as  in  other  deposits,  the  chloride 
of  silver  is  a  secondary  alteration  by  atmospheric  agents  of  an 
original  sulphide.  It  appears  more  probable,  therefore,  that 
all  the  metallic  minerals  of  the  plateau  were  formed  under  the 
same  conditions  and  during  the  same  general  phase  of  ore-de- 
position. That  they  are  so  irregularly  disseminated  is  prob- 
ably due  to  physical  rather  than  to  chemical  causes.  The 
rhyolitic  tuff  which  forms  the  main  country-rock  is  so  poorly 
consolidated,  and  of  so  plastic  a  nature,  that  fracture-planes 
are  less  continuous  and  less  open  in  it  than  in  harder  and  more 
rigid  rocks.  Moreover,  the  natural  planes  of  division,  the  bed- 
ding-planes, are  horizontal  rather  than  vertical.  Hence  there 
have  been  no  well-defined  and  continuous  water-channels  trav- 
ersing the  whole  thickness  of  the  mass,  but  the  ascending  solu- 
tions, after  leaving  the  vicinity  of  the  bounding-walls  of  the 


156       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

harder  Archaean  rocks,  have  been  obliged  to  follow  devious 
courses  along  minute  cracks  and  fissures  that  were  not  continu- 
ous. Thus,  comparatively  small  amounts  of  these  solutions 
have  reached  the  upper  lavas,  and  their  load  has  been  deposited 
as  thin  films  in  the  joints  or  minute  cracks  of  the  rocks.  The 
fact  that,  at  the  present  time,  the  descending  surface-waters 
penetrate  the  mass  to  so  moderate  a  depth  is  an  argument  in 
favor  of  this  view. 

It  is  probable  that  the  present  vein-fissure  will  soon  reach 
and  pass  into  the  Archaean  wall-rock,  in  which  it  may  widen 
out.  It  is  very  uncertain  whether,  in  this  case,  the  ore  will 
continue  to  be  as  rich  as  it  has  been ;  for  a  change  in  wall-rock 
is  generally  accompanied  by  a  change  in  the  character  of  the 
ore.  These  points  will  soon  be  settled,  however,  by  actual - 
development,  as  the  workings  of  the  Geyser  mine  follow  the 
present  vein  in  depth. 

GENERAL  CONCLUSIONS. 

Forms  of  the  Ore-Bodies. — The  preceding  pages  have  been 
mainly  devoted  to  the  description  of  the  Geyser  mine  in  the 
immediate  vicinity  of  Silver  Cliff.  Other  important  deposits 
within  this  area,  and  in  the  surrounding  region,  have  not  been 
mentioned,  because,  owing  to  the  irregular  and  disconnected 
manner  in  which  they  have  been  worked,  it  has  been  impossi- 
ble to  obtain  any  detailed  information  with  regard  to  them. 
With  but  few  exceptions,  these  deposits  belong  to  the  type  of 
the  Humboldt-Pocahontas  vein  ;  that  is,  they  are  vein-deposits 
on  fault-planes  in  some  of  the  many  varieties  of  igneous  rocks 
that  outcrop  in  the  region.  They  are,  in  general,  rather  nar- 
row fissures,  which  do  not  bear  evidence  of  having  at  any  time 
constituted  large  open  spaces,  but  in  which  the  ore-bearing  so- 
lutions have  deposited  their  contents  by  first  filling  the  inter- 
stices between  the  sheets  of  sheared  and  banded  country-rock 
and  afterwards  partly  replacing  these  sheets  or  bands  by  vein- 
materials.  The  ore  in  these  Ceases  is  generally  confined  to  the 
fault-fissure,  and  the  deposits  may  be  characterized  as  well- 
defined  vein-deposits  or  true  fissure-veins. 

The  mines  of  the  Silver  Cliff  plateau  show  a  different  type 
of  deposit,  but,  in  the  opinion  of  the  writer,  the  essential  dif- 
ferences lie  rather  in  the  form  of  the  ore-channels  than  in  the 


SOME    MINES    OP    ROSITA    AND    SILVER    CLIFF,  COLORADO.       157 

character  of  the  ore-bearing  solutions.  From  Mr.  Cross's  de- 
scription of  the  Democrat  and  Ben  Eaton  mines,  in  the  cen- 
tral rhyolitic  area,  these  deposits  seem  to  constitute  an  inter- 
mediate stage  between  the  two  types.  These  mines  occur  on 
the  south  point  of  Democratic  ridge,  known  as  Indian  Castle. 
This  is  a  rounded  eruptive  channel  of  rhyolite,  in  which  the 
rock  is  massive,  brecciated,  or  spherulitic,  as  the  case  may  be. 
There  are  indications  that  there  have  been  several  eruptions. 
It  has  since  been  much  altered,  and  the  alteration-products 
vary  from  hard  quartzite-like  material  to  softer  material,  re- 
sulting from  the  kaolinization  of  inter-spherulitic  glass.  Tra- 
chyte dikes  run  both  north  and  south  and  east  and  west 
through  the  mountain,  and  their  decomposition-product  is 
usually  soft.  The  ore-bearing  fissures  run  north  and  south, 
with  a  steep  eastern  dip,  through  both  rhyolite  and  trachyte. 
The  ore- solutions  followed  these  fissures  primarily,  but  found 
the  softened  spherulitic  glass  and  certain  brecciated  zones  also 
very  good  channels.  The  ore  is  now  found  in  these  seams  or 
fissures,  but  all  soft  kaolinized  parts  are  likely  to  be  impreg- 
nated. The  main  ore-body  was  an  oval  chimney,  of  varying 
size,  in  soft  matter,  which  is  connected  with  a  fissure  at  tunnel- 
level.  From  one  part,  on  stoping  upward,  a  soft  yellow  mud 
flowed  out,  which  was  found  to  carry  40  oz.  of  silver  and  $14 
in  gold  to  the  ton.  For  the  most  part,  the  solid  masses  of  ore 
are  less  than  1  in.  thick. 

It  has  already  been  suggested,  in  the  case  of  the  deposits  on 
the  Silver  Cliff  plateau,  that  the  fact  that  the  surface-deposits 
are  not  in  the  form  of  fissure- veins,  as  they  are  found  at  the 
bottom  of  the  Geyser  shaft,  is  due  to  physical  causes  which  have 
not  permitted  the  formation  of  long  continuous  water-channels 
along  fissures.  In  this  case  similar  irregularities  have  been 
produced  by  chemical  causes;  but  it  has  been  the  physical 
effect — the  production  of  channels  of  freer  flow,  through  the 
decomposition  of  the  rock — that  has  led  the  ore-depositing  cur- 
rents to  leave  the  regular  fissures. 

The  deposits  in  the  Archaean  rocks  on  the  borders  of  the  erup- 
tive region  are  likewise  unusually  irregular  in  form ;  and,  in 
most  of  the  observed  cases,  this  irregularity  may  be  ascribed 
to  a  combination  of  chemical  decomposition  with  dynamic  frac- 
turing of  the  rocks;  that  is,  while  the  ore-channels  have  been 


158       SOME    MINES    OF    RQSITA    AND    SILVER    CLIFF,  COLORADO. 

primarily  determined  by  the  dynamic  movements  that  produce 
the  ordinary  rock-fractures,  vein-fissures,  and  brecciated  zones, 
on  which  ore-bodies  are  generally  deposited,  their  course  has 
been  varied,  or  they  have  received  unusual  forms  as  the  result 
of  the  energetic  dissolving  or  decomposing  action  of  heated 
solutions  that  traversed  them  during  the  closing  phases  of  vol- 
canic action  in  the  region.  This  supposes  a  prolonged  altera- 
tion and  decomposition  of  the  rocks  along  the  water-channels 
before  the  actual  deposition  of  metallic  minerals.  In  some  of 
the  observed  cases,  there  are  fairly  well  defined  fissure-veins  in 
the  Archaean  rocks ;  but  more  commonly,  in  this  region,  the 
ore-deposition  appears  to  have  taken  place  along  a  zone  of  de- 
composed rock,  which  zone  was  undoubtedly  determined  in 
the  beginning  by  dynamic  action.  The  ore-deposition  along 
such  zones,  as  might  be  expected,  has  been  more  irregularly 
spaced  and  less  concentrated  than  would  have  been  the  case  in 
a  fissure  which  had  not  been  thus  enlarged  by  chemical  decom- 
position. The  Bull-Domingo  ore-body  is  apparently  an  extreme 
type  of  such  a  form. 

Whether  it  be  or  be  not  admitted  that  the  boulder-filled 
channel  of  the  Bull-Domingo  represents  the  neck  of  an  ancient 
crater  of  explosion,  the  Bassick  ore-body  is  unique  in  the  evi- 
dence it  affords  of  a  direct  connection  with  volcanic  agencies ; 
and  in  the  determination  of  its  form  dynamic  agencies  have 
apparently  played  a  very  subordinate  part. 

Cripple  Creek  Deposits  Compared. — It  is  interesting  to  contrast 
the  deposits  of  this  region  with  those  of  the  now  famous  Crip- 
ple Creek  district,  which  lies  in  a  closely  analogous  geological 
position,  40  miles  to  the  northward,  and  which  presents  in  its 
geological  structure  so  many  points  of  resemblance.  There,  as 
here,  the  main  ore-deposition  has  taken  place  in  and  around  a 
central  volcanic  focus,  where  a  series  of  comparatively  recent 
igneous  rocks  have  broken  through  an  older  series  of  pre-Cam- 
brian  crystalline  rocks.  There*  as  here,  the  principal  depo- 
sition has  taken  place  along  a  system  of  fracture-planes,  trav- 
ersing both  the  eruptives  and  the  underlying  crystalline 
complex,  and,  while  not  strictly  confined  to  the  eruptives,  it  has 
been,  so  far  as  present  developments  show,  more  abundant  in 
the  former  than  in  the  latter. 

In  the  Cripple  Creek  region  there  is  one  principal  and  pre- 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       159 

dominant  system  of  mineralized  fractures,  running  about  north 
and  south.  In  this  district  a  system  running  north  and  south 
or  a  little  west  of  north  is  apparently  the  more  frequent,  but 
there  are  also  abundant  fractures  running  east  and  west,  and 
others  quartering  between  the  two.  The  geological  history  of 
this  region  has  been  more  complicated ;  there  have  been  a 
greater  number  of  successive  eruptions ;  and  it  is  probably  in 
consequence  of  this  fact  that  the  fracture-systems  are  more  varied 
and  complicated. 

Mineralogically  the  contrast  is  greater.  In  Cripple  Creek  the 
important  metal  is  gold,  deposited  mainly  in  the  form  of  tellu- 
ride,  and  the  characteristic  earthy  mineral  associated  with  it  is 
fluorite.  Here,  gold  as  telluride  occurs  in  certain  parts  of  the 
district,  and  fluorite  is  sparingly  found ;  but  the  greater  part  of 
the  valuable  minerals  are  silver-minerals,  in  their  usual  asso- 
ciation with  sulphides  of  lead,  zinc,  and  iron,  and  with  barite 
as  the  leading  gangue-mineral.  They  differ  from  the  ordinary 
deposits  of  this  class  mainly  in  their  greater  average  richness. 

Source  of  the  Metallic  Minerals. — While  it  is  possible,  by  care- 
ful study  of  the  geological  and  mineralogical  conditions  of  a 
series  of  ore-deposits,  to  find  valid  reasons  why  the  ore-bearing 
solutions  deposited  their  load  in  certain  forms  and  certain  locali- 
ties, and  while  reasonable  deductions  may  be  made  as  to  the 
probable  direction  from  which  these  solutions  came,  the  ques- 
tion as  to  the  source  from  which  the  solvents  derived  the  mate- 
rials which  they  have  thus  deposited  in  the  form  of  ore-bodies  is 
one  that  trenches  somewhat  upon  the  domain  of  pure  specula- 
tion. Yet,  even  here,  there  are  many  facts  of  geological  observa- 
tion that  have  a  distinct  bearing,  one  way  or  the  other,  upon  the 
various  speculative  views  that  have  been  put  forth  by  geologists. 

The  general  views  of  the  writer  upon  this  question,  as  already 
expressed  in  earlier  publications,  are  :  that  the  heavy  metals 
have  probably  been  brought  up  from  the  interior  of  the  earth 
within  the  magmas  of  igneous  rocks,  and  that  by  some  process 
of  differentiation  not  yet  completely  understood,  either  previous 
to  or  during  the  process  of  cooling  and  consolidation,  they  have 
been  concentrated  within  certain  bodies  or  parts  of  bodies  of 
eruptive  rocks;  and,  further,  that  ore-bodies,  as  found  at  the 
present  day,  are  the  result  of  a  concentration  (perhaps  many 
times  repeated)  of  the  materials  thus  brought  up,  which  are  in 


160       SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO. 

all  probability  very  finely  disseminated  through  the  present 
rock-masses  or  combined  in  minute  amounts  in  the  more  com- 
mon basic  minerals.  This  seems  a  more  rational  hypothesis, 
and  one  more  in  accordance  with  modern  scientific  practice, 
than  to  content  oneself  with  assuming  simply  that  the  ascending 
waters  came  charged  with  metallic  minerals  from  the  bathy- 
sphere, meaning  thereby  a  region  in  the  interior  of  the  earth 
which  is  richer  in  heavy  metals  than  any  part  of  the  earth's 
crust  that  comes  under  our  observation;  for  this  simple  assump- 
tion affords  no  explanation  why  metallic  minerals  are  concen- 
trated in  one  part  of  the  earth's  crust  and  not  in  another,  and  it 
supposes  a  free  flow  of  waters  at  greater  depths  than  in  our 
present  state  of  knowledge  of  terrestrial  physics  it  is  considered 
possible  that  channels  which  would  admit  of  a  flow  of  water 
through  them  could  remain  open. 

Furthermore,  the  writer's  hypothesis  admits  of  a  practical 
test,  which  is  impossible  in  the  other  case.  If  the  vein-materials 
are  found  to  form  a  constituent  part,  even  in  minute  traces,  of 
comparatively  fresh  and  unaltered  country-rocks  in  a  given  ore- 
bearing  region,  and  at  such  distances  from  any  water-channels 
as  to  render  it  improbable  that  these  materials  could  have  been 
brought  in  through  these  channels,  it  is  reasonable  to  assume 
that  these  or  similar  rocks  have  been  permeated  by  the  waters 
from  which  the  known  ore-deposits  were  precipitated,  and  that 
from  them  they  derived  their  contained  vein-materials.  For 
this  reason  ,a  series  of  careful  tests  of  selected  country-rock  for 
possible  contents  in  the  precious  metals  was  carried  on  under 
the  direction  of  the  writer  at  the  laboratory  of  the  TJ.  S.  Geo- 
logical Survey  in  Denver.  Since  the  office  at  Denver  was 
broken  up,  it  has  not  been  possible  to  continue  these  tests, 
owing  to  want  of  proper  facilities  in  the  Washington  laboratory. 

Such  tests  of  the  rocks  from  this  district  as  were  completed 
(unfortunately  very  few  in  number)  are  given  below. 

The  five  assays  for  silver  were  made  upon  4  assay-tons  of 
each  sample,  and  blank  assays  of  a  like  amount  of  the  lead-flux 
were  simultaneously  made,  the  silver-content  of  the  flux  being 
deducted  from  that  found  by  the  rock-assay. 

In  the  case  of  the  black  granite  from  the  Blue  mountains, 
another  portion  of  the  rock  was  pulverized  and  the  constituent 
minerals  were  separated  by  the  Sonstadt  solution.  The  bi- 


SOME    MINES    OF    ROSITA    AND    SILVER    CLIFF,  COLORADO.       161 

silicates  in  this  case  were  found,  as  shown  below,  to  contain 
both  silver  and  lead ;  but  no  silver  was  found  in  either  quartz 
or  feldspar.  The  assays  of  Ouster  county  country-rock  for 
silver,  by  L.  G.  Eakins,  analyst,  were : 


Rock. 

Locality. 

Silver 
per  Ton. 

Trachyte 

('00  ft  southwest  of  Humboldt  shaft 

Ounce. 
0  007 

Trachvte 

Summit  of  Game  ridge 

None 

Rosita  breccia 

South  of  Game  ridge 

None 

Rosita  breccia 

South  of  Game  ridge 

None 

Fairview  diorite 

Mount  Fairview 

0  01 

Tvndall  andesite 

Northeast  spur  of  Mount  Tjndall. 

None. 

Rhyolite 

Top  of  Round  mountain      

0.402 

Red  granite     .    . 

Near  Haskell's  ranch           

0.005 

Black  granite      .  . 

Blue  mountains  

0.025 

Bisilicates  of  black  granite  (0.045 

0.04 

It  thus  appears  that  five  out  of  nine  of  the  rocks  tested  con- 
tain appreciable  amounts  of  silver;  and  that  in  one  of  these 
rocks  both  silver  and  lead  were  found  to  be  present  in  combi- 
nation with  other  bases  in  the  bisilicates.  It  seems,  therefore, 
probable  that  not  only  the  recent  eruptives,  but  the  older  gran- 
ites through  which  the  ascending  solutions  must  have  passed, 
contain  enough  of  the  precious  metals,  and,  it  may  be  assumed 
also,  of  the  other  vein-materials,  to  furnish,  in  the  long  time 
that  is  accorded  to  the  accomplishment  of  most  geological  phe- 
nomena, sufficient  material  for  the  formation  of  existing  ore- 
bodies.  The  analysis  of  the  vadose  waters  in  the  Geyser  mine 
has  demonstrated  the  capability  possessed  by  even  cold  surface- 
waters  of  taking  up  such  materials  in  their  passage  through  the 
rocks.  The  subterranean  waters  that  were  circulating  here  at 
the  time  of  the  formation  of  the  ore-deposits  must  have  been 
much  more  energetic  solvents,  being  heated  by  contact  with  the 
cooling  masses  of  igneous  rocks,  and  probably  deriving  a  cer- 
tain amount  of  active  and  energetic  mineralizing-agents,  such 
as  fluorine-,  chlorine,  etc.,  from  these  igneous  masses  at  the  time 
of  contact.  Hence  it  is  fair  to  assume  that  the  vein-materials 
in  this  region  were  originally  derived  from  both  recent  and 
ancient  eruptive  rocks — a  conclusion  similar  to  that  arrived  at 
by  Mr.  Penrose,  from  his  more  exhaustive  study,  for  the  ore- 
deposits  of  Cripple  Creek. 

11 


162  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


No.  8. 
The  Genesis  of  Certain  Auriferous  Lodes. 

BY  JOHN  R.   DON,    OTAGO,    NEW  ZEALAND. 

(Chicago  Meeting,  February,  1897.     Trans.,  xxvii.,  564.    Here  reprinted  in  part  only.) 


CHAPTER  V.  —  THE  EXAMINATION  OF  VARIOUS  CONSTITUENTS  OF 
CRYSTALLINE  AND  ERUPTIVE  ROCKS  FOR  GOLD  AND  SILVER. 
In  the  South  Island  of  New  Zealand  an  unusually  favorable 
opportunity  is  offered  for  the  analysis  of  the  older  crystalline 
rocks,  underlying  the  sedimentary  rocks  which  form  the 
"  country"  of  the  gold-deposits.  The  Manipori  formation  of 
this  island,  comprising  the  greater  part  of  the  mountainous 
district  west  of  lakes  Manipori  and  Te  Anau,  in  Otago,  con- 
sists of  an  enormous  thickness  (estimated  by  Professor  Hutton  l 
at  160,000  ft.)  of  crystalline  schists,  gneiss,  syenite,  and  syenitic 
gneiss,  with  associated  masses  of  granite  ;  the  whole  forming 
the  most  picturesque  part  of  New  Zealand.  The  famous 
West  Coast  sounds  occur  in  this  formation.  No  paying 
auriferous  lodes  have  been  discovered  in  it  ;  and  for  this  reason 
an  examination  of  the  rocks  is  specially  interesting  here.  Stelz- 
ner,  Posepny,  and  others,  who  have  criticised  the  conclusions 
of  Sandberger,  have  laid  great  stress  on  the  fact  that  all  the 
silicates  analyzed  by  him  were  taken  from  the  vicinity  of  ore- 
bodies  containing  those  heavy  metals  which  he  notes  as  oc- 
curring in  the  silicates  of  the  country-rock;  their  contention 
being  that  these  metals,  supposed  to  occur  as  silicates  in  gneiss 
and  other  crystalline  rocks,  were  really  contained  as  sulphides, 
and  were  therefore  impregnations  from  the  neighboring  ore- 
bodies.  The  same  objection,  whatever  be  its  weight,  might  be 
urged  with  equal  justice  against  Mr.  Becker's  derivation  of  the 
mercury  and  gold  of  the  lodes  of  the  Pacific  Coast  from  the 
granite  underlying  their  country-rock.  In  the  case  of  the 

1  Geology  of  Otago,  by  Hutton  and  Ulrich,  p.  28. 


THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES.       163 

Manipori  formation,  just  mentioned,  such  criticism  could  hardly 
be  made,  as  no  auriferous  lodes  have  been  found  within  many 
miles  of  the  district  from  which  samples  were  taken  for  the 
present  investigation. 

In  the  South  Island  also,  samples  were  taken  from  the  gran- 
ite abutting  on  the  Carboniferous  strata  near  Reefton,  which 
latter  are  the  chief  carriers  of  auriferous  lodes  in  the  western 
part  of  the  island. 

Other  samples  of  granite  were  collected  from  various  parts 
of  Westland  and  Nelson,  as  far  north  as  the  granite-quarries  of 
Cape  Foulwind. 

Selwyn  has  pointed  out 2  that  the  auriferous  Silurian  rocks  of 
Victoria  probably  rest  everywhere  on  granite ;  and  this  conclu- 
sion has  been  supported  by  the  later  observations  of  Murray 3 
and  others.  This  underlying  granite  has  not  been  reached  in 
any  of  the  mines  working  in  the  stratified  rocks  about  it;  but 
it  is  exposed  at  the  surface  in  many  parts  of  the  colony,  both 
near  to  gold-bearing  areas  and  distant  from  them.  Numerous 
samples  of  it  were  taken  for  this  investigation.4 

The  study  of  the  country-rock  from  Gympie  and  Charters 
Towers,  Queensland,  gave  a  good  opportunity  for  the  analysis 
of  silicates  from  crystalline  igneous  rocks.  In  the  case  of 
Charters  Towers,  the  whole  country-rock  (locally  termed  gran- 
ite) is  quartz-diorite,  with  a  little  accessory  mica;  while  at 
Gympie  a  thick  sheet  of  diorite-aphanite  (locally  termed  green- 
stone), containing  a  large  percentage  of  carbonate  of  lime,  is 
interbedded  with  the  shales  which  bound  the  auriferous  reefs, 
these  kindly  shales  occurring  both  above  and  below  it.  Messrs. 
Alfred  Lord  and  R.  Steele,  of  Gympie,  have  furnished  samples 
of  the  "  greenstone." 

Sandberger's  results  having  been  criticised  on  the  ground 
that  all  the  rocks  he  analyzed  contained  sulphides,  and  Po- 
sepny 5  having  urged  the  same  objection  to  Becker's  conclusions 

2  Geology  and  Physical  Geography  of  Victoria,  by  A.  K.  C.  Selwyn  and  G.  F.  H. 
Ulrich. 

3  Geology  and  Physical  Geography  of  Victoria,  by  A.  K.  F.  Murray  (1887). 

4  In  New  South  Wales,  granite  forms  the  country-rock  of  a  number  cf  aurifer- 
ous lodes;  and  it  is  much  to  be  desired  that  some  investigator  on  the  spot  would 
take  up  this  inquiry.     The  present  paper  contains  no  analyses  of  New  South 
Wales  granite. 

5  The  Genesis  of  Ore-Deposits,  Trans.,  xxiii.,  282  (1893). 


164  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

in  the  case  of  the  Comstock  lode,  this  point  was  carefully 
guarded.  In  every  instance  (even  though  an  examination  of  a 
hand-specimen  showed  no  sulphides),  an  analysis  of  the  rock 
was  first  made,  to  determine  whether  sulphides  were  present; 
and  whenever  such  was  the  case,  the  sulphides  were  isolated 
by  panning,  and  separately  assayed  for  gold  and  silver;  but 
when  sulphides  were  thus  found,  no  separation  of  the  other  crystalline 
constituents  of  the  rock  was  made. 

It  was  deemed  necessary  to  isolate  and  examine  the  follow- 
ing minerals  :  (1)  mica  and  (2)  hornblende,  because  to  these 
Sandberger  traces  the  silver  and  gold  of  many  European  lodes ; 
(3)  the  pyroxenes  of  the  later  eruptives,  because  Becker  traces 
the  gold  and  silver  of  the  Comstock  to  the  augite  of  the  dia- 
base, and  both  Hutton  and  Park  (already  cited)  are  inclined  to 
refer  the  gold  and  silver  of  the  Thames  district,  IN".  Z.,  to  the 
pyroxenes  of  the  andesite ; 6  and  (4)  magnetite,  because  of  Pro- 
fessor Huttou's  remark : 7 

"  I  would  suggest  that,  as  part,  at  least,  of  the  pyrites  has  been  formed  from 
magnetite,  the  gold  may  have  been  originally  in  the  magnetite,  and  have  been 
released  during  the  formation  of  the  pyrites.  I  do  not  think  that  this  has  been 
the  case,  but  it  is  a  point  worthy  of  investigation  by  the  chemist.  The  pyrites  is,  no 
doubt,  a  secondary  mineral,  formed  in  the  rock  after  consolidation  ;  and  if  it 
should  turn  out  to  be  generally  auriferous,  we  must  suppose  either  that  the  gold 
came  from  below  with  the  sulphur,  or  that  its  source  is  the  titaniferous  magnetite 
which  is  one  of  the  original  constituents  of  the  rocks." 

Isolation  of  Minerals. 

The  crystalline  rocks  examined  comprised :  (1)  those  in 
which  certain  minerals  were  distributed  in  large  crystals  or  ar- 
ranged in  folia,  so  that  clean  samples  could  be  picked  out  by 
hand ;  and  (2)  those  from  which  the  various  minerals  had  to 
be  separated  by  means  of  a  liquid  of  high  specific  gravity. 

The  first  class  included  many  samples  from  the  gneiss,  syen- 
ite, and  granite  of  the  Manipori  formation,  N.  Z.,  from  which 
the  separation  of  mica  and  hornblende  was  specially  easy.  In 
various  parts  of  this  formation  mica  veins  are  abundant.  It 

6  Professor  Hutton  says  on  this  point  (op.  tit.,  p.  272) :  "  If,  therefore,  we  assume 
that  the  pyroxenes  of  our  volcanic  rocks  contain  gold  and  silver,  that  the  condi- 
tions necessary  for  dissolving  them  rarely  obtain,  but  that  one  of  the  exceptions 
has  been  in  the  Hauraki  [Thames]  gold-fields,  we  have  a  hypothesis  which  will,  I 
think,  explain  most  of  the  facts." 

7  Op.  tit.,  p.  271. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  165 

was  sometimes  possible  to  pick  in  a  few  minutes  2  or  3  Ib.  of 
clean  mica  in  plates  up  to  2  or  3  in.  square.  The  syenite  and 
syenitic  gneiss  often  contain  bands  of  almost  pure  hornblende, 
quite  an  inch  thick,  permitting  a  similarly  easy  isolation. 
Finally,  magnetite  can,  of  course,  be  easily  separated  from  any 
rock  in  which  it  occurs. 

The  treatment  of  the  second  class,  comprising  many  of  the 
rocks  examined,  may  require  some  explanation. 

The  separation  of  minerals  from  rocks  by  means  of  heavy 
solutions  is  extremely  tedious,  and  it  is  therefore  desirable  to 
reduce  the  quantity  of  the  rock  to  be  operated  upon  if  this  can 
be  done  without  material  loss  of  the  mineral  to  be  isolated. 
As  all  crystalline  rocks  contain  a  large  percentage  of  material 
below  3  in  specific  gravity,  which  can  be  effectively  removed 
by  panning,  each  sample  was  concentrated  first  by  panning  to 
get  rid  of  quartz,  feldspar,  and  other  specifically  light  ma- 
terials. This  procedure  would,  of  course,  be  inadmissible  if  the 
object  had  been  to  determine  accurately  the  gold  and  silver  per 
ton  of  the  rock  examined ;  but  the  purpose  in  each  case  being 
simply  to  get  as  large  a  quantity  as  possible  of  a  given  mineral, 
and  to  get  that  sample  approximately  pure,  this  preliminary 
crude  concentration  seemed  to  be  unobjectionable. 

As  an  illustration,  the  following  record  of  the  process,  as  ap- 
plied in  one  instance  (Sample  7,  Table  I.  [Table  XVIII.  of 
original  paper] ),  is  here  given.  With  suitable  modifications, 
this  method  was  followed  in  all  similar  cases : 

Sample  of  Syenite. 

1.  The  sample  was  roughly  broken  and  examined  with  a  good  lens,  but  no  sul- 
phides were  discovered.     A  chemical  analysis  of  10  g.  of  the  sample  also  showed 
that  sulphides  were  absent. 

2.  A  portion  of  500  g.,  pulverized  so  as  to  pass  a  No.  30  sieve,  was  reduced  by 
careful  panning  to  217  g.,  of  which  58  g.  was  removed  by  a  weak  magnet.     The 
portion  thus  removed  proved,  under  the  microscope,  not  to  be  pure  magnetite,  but 
to  contain  a  good  proportion  of  hornblende  and  feldspar  (chiefly  orthoclase)  grains, 
probably  drawn  to  the  magnet  by  small  adhering  particles  of  magnetite. 

3.  The  159  g.  not  attracted  by  the  magnet  consisted  chiefly  of  hornblende  and 
feldspar,  with  a  little  mica  (biotite)  and  quartz.     This  powder  was  introduced  into 
an  apparatus  modeled  on  Thoulet's,  but  made  much  larger,  to  save  time.     The 
heavy  liquid  used  was  Sonstadt's  :  mercuric  iodide,  dissolved  in  excess  of  potassic 
iodide,  and  having  3.175  sp.  gr. 

On  exhausting  the  air  from  the  apparatus,  77.5  g.  of  practically-pure  horn- 
blende fell  to  the  bottom  of  the  liquid.  A  dilution  of  this  liquid  to  2.95  sp.  gr. 
was  followed  by  the  precipitation  of  35.5  g.  more — also  nearly-pure  hornblende. 


166  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

The  total  of  113  g.,  reckoned  as  hornblende,  was  finely  powdered  and  assayed  with 
pure  litharge.     No  trace  of  gold  or  silver  was  obtained. 

4.  The  58  g.  removed  by  the  magnet  was  similarly  powdered  and  assayed,  with 
the  same  result. 

Sonstadt's  solution  is  cheap  and  easily  prepared,  but  has  the 
great  disadvantage  of  being  extremely  corrosive.  Even  with 
the  greatest  care,  it  was  found  almost  impossible  for  the  op- 
erator to  avoid  burning  his  fingers.  Hence,  in  a  number  of 
instances  Klein's  solution  of  boro-tungstate  of  cadmium  was 
employed.  This  has  another  advantage  over  Sonstadt's  solu- 
tion, namely,  that  when  a  partial  separation  of  hornblende  from 
augite  is  desired,  the  greater  part  of  the  hornblende  can  be 
kept  from  sinking  in  the  liquid  by  using  the  latter  in  the  con- 
centrated state.8 

The  results  of  the  analysis  of  minerals  separated  from  47 
samples  of  rock  are  given  in  Table  I.  On  this  table  the  fol- 
lowing additional  notes  are  presented : 

1.  Sample  17  represents  a  rock  of  peculiar  occurrence,  occu- 
pying a  narrow  strip  in  an  area  of  Tertiary  trachyte  at  Porto- 
bello,  on  the  east  coast  of  the  Otago  peninsula.  Samples  taken 
short  distances  apart  vary  much  in  character ;  but,  on  the 
whole,  the  rock  may  be  classed  as  a  diorite.  Gold  was  said  to 
have  been  found  in  the  rock,  up  to  0.5  oz.  to  the  ton.  If  this 
were  the  case,  such  an  occurrence  of  gold  would  have  been,  so 
far  as  the  writer  knows,  unique. 

Of  the  three  samples  chosen,  one  (No.  17)  contained  pyrite, 
and  this  pyrite  was — but  the  rock  itself  was  not — auriferous. 
The  occurrence  of  auriferous  pyrite  in  such  an  area  (of  recent 
volcanic  rocks)  is  most  unusual,  and  Professor  Ulrich,  Director 
of  the  Otago  School  of  Mines,9  who  has  examined  the  locality 
and  studied  rock-sections  from  it,  thinks  that  this  diorite  rock 
probably  underlies  the  basic  volcanics  which  form  the  rest  of 

8  It  was  found  impossible  to  separate  augite  from  hornblende  completely  by  the 
use  of  heavy  liquids  ;  but  since  no  gold  or  silver  was  found  in  either,  this  fact  did 
not  affect  the  practical  results  of  this  investigation.     The  same  remark  applies 
more  or  less  to  all  the  minerals  thus  isolated  for  analysis.     The  writer  knows  of 
no  method  which  will  perfectly  isolate  considerable  quantities  of  one  mineral  from 
other  minerals  not  widely  removed  in  specific  gravity.     In  Table  L,  therefore, 
the  terms  "  hornblende,"  "augite,"  etc.,  simply  designate  the  greatest  part  of  the 
mineral  samples  to  which  they  are  applied. 

9  I  desire  at  this  point  to  express  my  grateful  thanks  to  our  respected  chief, 
Professor  Ulrich,  for  much  kipd  encouragement  and  practical  assistance. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


167 


TABLE  I.  (Table  XVIII.  of  original  paper). — Analyses  of  Various 
Minerals  Isolated  from  the  Older  Crystalline  and  Newer  Erup- 
tive Rocks  of  New  Zealand,  Victoria,  and  Queensland. 


A.     KOCKS  OF  NEW  ZEALAND. 


D 

"3. 

Locality. 

is 

n 

•    'g'S 

II 

SJ 

Ill 
lil 

Method  of 
Separation. 

Sulphides. 

Results. 

1... 

2 

From  the  "Staircase," 
on    the  Sutherland 
Falls  road,  Mil  ford 
sound,    W.    coast    of 
Otago. 
Do 

Gm. 

200 

150 

Mica. 
Mica 

Gm. 
200 

150 

Picked 
by  hand. 

Do 

None. 
None 

No  gold  or 
silver. 

Do 

3... 
4... 
5... 

6 

Clinton  gorge,  N.  W.  of 
Lake    Te    Anau,   on 
Milford  sound  road. 
Roaring  creek,  Arthur 
River    valley,    near 
Milford  sound. 
On  the  track  between 
Milford  sound  and 
Lake  Ada,  W.  coast  of 
Otago. 
Duskv  sound   W   coast 

150 

100 
100 

Mica. 
Mica. 
Mica. 

Hornblende. 

150 

100 
100 

Do. 
Do. 
Do. 

Do 

None. 
None. 
None. 

See  note 

Do. 
Do. 
Do. 

7 

of  Otago. 
Do 

500 

Hornblende. 

113 

Somtadt  s 

below. 

below. 

8... 
9... 
10... 
11 

Milford  sound,  W.  coast 
of  Otago. 
Preservation   inlet,  W. 
coast  of  Otago. 
West   Jacket   Arm,  W. 
coast  of  Otago. 
George  sound   W  coast 

100 
100 
140 
500 

Hornblende. 
Hornblende. 
Hornblende. 

100 
100 
140 

solution. 
Picked 
by  hand. 
Do. 

DO. 

None. 
None. 
None. 

silver. 
Do. 

Do. 
Do. 

12 

of  Otago. 
Do 

200 

Hornblende. 

200 

Picked 

below. 

below. 

13 

Do  

1,000 

Hornblende. 

by  hand. 
Do 

silver. 

14... 
15. 

Skipper's  creek,  central 
Otago. 
Shotover  river,  central 

Magnetite. 
Magnetite. 

250 
150 

Magnet. 
Magnet 

below. 
None. 

None 

below. 
No  gold  or 
silver. 
Do 

16  . 

Otago. 
Do  

Magnetite. 

180 

Magnet 

None 

Do 

17 

Portobello    Otago  Pen- 

18 

insula,  near  Dunedin. 
Do 

500 

Horn- 

Sonstadt's 

below. 

below. 

19 

Do 

500 

blende,  57 
Mica.  43 
Biotite  38 

solution. 
Sonstadt's 

silver. 

Dn 

20 

Near  Dunedin  

Magnetite 

Horn- 
blende, 26 
60 

solution. 
Magnet 

Do 

21... 

22... 
23... 

24... 
25... 

26... 

Water  of    Leith,   near 
Dunedin 

Near  Oamaru,  Otago. 
Cape   Foulwind,  W. 
coast  of  Nelson. 
Inangahua  river,  Reef- 
ton. 
Cape   Foulwind    quar- 
ries, W.  coast  of  Nel- 
son, N.  Z. 
Rangitoto,  Westland 

500 
500 

Hornblende, 
2.8  to  3 
Augite, 
3  to  3.  2 
Magnetite. 
Mica. 

Mica. 
Mica. 

16 
25 

80 
200 

84 
43 

Klein's' 
solution. 

Magnet. 
Picked 
by  hand. 
Klein's 
solution. 
Sonstadt's 
solution. 

Klein's 

None. 

None. 
None  . 

None. 
None. 

Do. 

Do. 
Do. 

Do. 
Do. 

See  note 

27... 
28... 
29... 

30 

N.  Z. 

Bed  of  Hokitika  river, 
Westland,  N.  Z. 
Bligh  sound,  W.  coast 
Otago. 
Moanataiari    tunnel, 
Thames  district 

Do 

500 
500 
1,000 

1  000 

Mica. 
Mica. 

Pyroxenes  of 
sp.gr.  2.9  to 
3.2 

48 
61 
73 

56 

solution. 
Do. 

Do. 
Do. 

Do 

below. 
None. 

None. 
None. 

below. 
No  gold  or 
silver. 
Do. 

Do. 

F)n 

and   chlo- 
rite between 
sp.    gr.    2.8 
and  3.1. 

168 


THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 


TABLE  I. — A.     Hocks  of  New  Zealand. —  Continued. 


1 

Locality. 

,C  fi 

11 

'^'S'O 

Sis 

*< 

11 

t 
g 

% 

2 

I 

A 

£H 

ij 

gSS 

"SH. 
*£ 

1 

Qi 

H 

Gm. 

Gm. 

31... 

Waitekauri    creek 

1,000 

Hornbl  e  n  d  e 

65 

Klein's 

None. 

No  gold  or 

Thames  district. 

and  chlo- 

solution. 

silver. 

rite  between 

sp.    gr.    2.8 

and  3.1. 

32... 

Moanataiari    tunnel, 

1,000 

Pyroxen's  be- 

43 

Do. 

None. 

Do. 

Thames  district. 

tween  sp.  gr. 

2.  9  and  3.  2. 

33... 

Fame  and  Fortune  G. 

1,000 

Do. 

84 

Do. 

None. 

Do. 

M.  Co.,  Thames. 

34... 

Do  

500 

Do. 

27 

Do. 

None. 

Do. 

33... 
34... 

Fame  and  Fortune  G. 
M.  Co.,  Thames. 
Do  

1,000 
500 

Do. 
Do. 

84 
27 

Do. 
Do. 

None. 
None. 

Do. 
Do. 

B.     ROCKS  OF  VICTORIA. 

35... 
36... 

37 

900-ft.  level,  Long  Tun- 
nel G.  M.  Co. 
Thomson    river,   near 
Walhalla,  Gippsland, 
Viet. 
Do 

1,000 
1,000 

1,000 

Hornblende. 

73 

Klein's 
solution. 

None. 

See  note 
below. 

None. 

See  note 
below. 
None. 

None. 
None. 

None. 
None. 

No  gold  or 
silver. 
See  note 
below. 

No  gold  or 
silver. 
See  note 
below. 
No  gold  or 
silver. 
Do. 
Do. 

Do. 
Do. 

Hornblende. 
Hornblende. 
Mica. 

Mica. 
Hornblende. 

Magnetite. 
Magnetite. 

38 

Klein's 
solution. 

38... 
39... 
40 

Big  hill,  Bendigo,  near 
the  Silurian  boundary. 
Do 

500 

500 
1,000 

53 

84 
96 

50 
40 

Klein's 
solution. 
Do. 
Do. 

Magnet. 
Magnet. 

Do 

41... 

42... 
43... 

From  Gabo  Island,  S.  E. 
of  Viet.,  used   as   a 
building  stone  in  Mel- 
bourne. 
Ballarat  East,  Victoria. 
Sunbury,  near  Mel- 
bourne, Victoria. 

C.     ROCKS  OF  QUEENSLAND. 


44... 
45... 
46 

The  1.070-ft.  level,  Bril- 
liant and  St.  George 
G.    M.   Co.,    Charters 
Towers,  Queensland. 
Do  

The  950-ft  level  of  the 

500 
500 
1  000 

Sp.  gr.  2.75  to 
3  (biotite). 
Sp.  gr.  3  to  3.2 
(hornblende) 
Sp.gr.  2.  75  to 
3  (biotite). 
Sp.  gr.  3  to  3.2 
(hornblende) 

21 

% 

40 
36 

Klein's 
solution. 

Klein's 
solution. 

None. 
None. 
See  note 

No  gold  or 

silver. 

Do. 
See  note 

47 

No.  5  North  Phoenix 
G.  M.  Co.,  Gympie. 
Do 

1  000 

25 

below. 
Do 

below. 
Do 

1, 2.  Gneiss,  containing  veins  of  mica,  about  0.5  in.  wide,  mixed  with  quartz.    Several  pounds' 
weight  of  mica  were  easily  obtained. 

3.  Granite,  with  muscovite  in  large  plates,  easily  picked  out  of  sample. 

4,  5.  Gneiss ;  contained  veins  of  muscovite,  from  which  pieces  2  in.  square  were  easily  picked 

out. 

6.  Syenitic  gneiss,  consisting  of  quartz,  feldspar,  and  hornblende,  with  a  little  biotite,  the 

hornblende  in  a  seam  about  2  in.  wide.  Pyrrhotite  and  chalcopyrite,  with  minute  specks 
of  native  copper,  associated  with  the  hornblende ;  500  g.  of  the  rock  gave  53  g.  of  sul- 
phides, mostly  pyrrhotite,  which  contained  0.0053  of  silver. 

7.  Syenite. 

8.  Syenitic  gneiss.    A  vein  of  hornblende  about  2  in.  wide  occupied  the  greater  part  of  the 

sample  analyzed. 

9, 10.  Syenite-porphyry,  showing  large  patches  and  crystals  of  hornblende. 
11.  Syenitic  gneiss,  consisting  of  quartz,  feldspar,  and  biotite,  with  patches  of  hornblende. 

Sample  showed  pyrrhotite  and  pyrite ;  500  g.  gave  18.56  g.  of  these  minerals  chiefly,  but 

no  gold  or  silver  was  found. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  169* 

12.  "  Granite,"  a  rock  containing  pink  feldspar,  quartz,  muscovite,  and  bands  of  hornblende.. 

13.  "Granite,"  a  rock  containing  orthoclase,  quartz,  muscovite,  and  hornblende  in  veins; 
1,000  g.  gave  12.18  g.  pyrrhotite  and  arsenopyrite,  which  yielded  no  gold  or  silver. 

14.  Chlorite-schist,  containing  numerous  octahedral  crystals  of  magnetite. 

15.  Hornblende-schist,  containing  numerous  octahedral  crystals  of  magnetite. 

16.  Heavy  "black  sand,"  result  of  erosion  of  mica-schist. 

17.  "Diorite,"  consisting  of  triclinic  feldspar,  hornblende,  biotite,  magnetite,  and  a  little 
quartz  ;  1,000  g.  gave  4.934  g.  of  pyrite,  containing  0.037  grain  of  gold  and  0.0041  grain  of 
silver. 

18, 19.  Diorite,  like  No.  17. 

20.  Phonolite. 

21.  Basalt,  very  much  decomposed,  with  large,  undecomposed  crystals  of  augite  and  horn- 
blende. 

22.  Hard,  solid  basalt,  from  a  quarry. 

23.  Gneiss-granite,  with  large  folia  of  mica,  easily  picked  out  of  sample. 

24.  25.  Fine-grained  granite. 

26.  Granite,  with  a  pyritous  vein  ;  1,000  g.  gave  28.92  g.  of  arsenopyrite  and  pyrrhotite,  with  a 
little  galena,  and  this  yielded  0.0032  grain  of  gold  and  0.0019  grain  of  silver. 

27.  Granite. 

28.  Gneiss. 

29.  Nepheline-andesite,  hard,  very  little  decomposed. 
oO.  Hard  blue  hornblende-andesite. 

31.  Hornblende-andesite,  slightly  altered. 

32.  Augite-andesite,  with  much  chlorite. 

33.  34.  Hard  blue  unaltered  augite-andesite. 

35.  "Diorite"  dike,  near  auriferous  reef,  Walhalla,  Gippsland,  Victoria. 

36.  "  Diorite,  associated  with  copper-lode.    Showed  chalcopyrite,  of  which  there  were  ob- 
tained from  1,000  g.  of  the  rock  16.48  g.  (with  a  small  quantity  of  bournonite),  yielding 
0.407  grain  of  silver  and  no  gold. 

37.  "  Diorite,"  fike  No.  36. 

38.  Syenitic  granite  (quartz,  orthoclase,  and  muscovite,  with  large  crystals  of  hornblende) ; 
1,000  g.  gave  16.03  g.  of  pyrite,  yielding  neither  gold  nor  silver. 

39.  Syenitic  granite,  like  No.  38. 

40.  Granite. 

41.  Syenite. 

42.  Very  dense  basalt,  overlying  auriferous  slates. 

43.  Vesicular  basalt. 

44.  45.  Quartz-mica  diorite  (tonalite:  the  "granite  "  of  Charters  Towers). 

46.  Diorite-aphanite,  with  much  carbonate  of  lime  (calc-aphanite) ;  a  very  much  altered  rock  ; 
effervesces  strongly  with  acid  (the  "greenstone  "  of  the  Gympie  field) ;  it  contains  pyrite 
and  sphalerite  in  small  quantities  ;  1,000  g.  gave  8.42  g.  of  pyrite,  yielding  no  gold  or  silver. 

47.  Diorite-aphanite,  like  No.  46;  1,000  g.  gave  42.7  g.  of  pyrite  and  galena,  which  yielded 
0.0016  grain  of  gold  and  0.0037  grain  of  silver. 


the  peninsula.  In  that  case,  it  would  be  allied  rather  to  the 
dikes  of  the  Upper  Silurian  in  Victoria  than  to  the  newer  vol- 
canic rocks  of  its  immediate  neighborhood. 

A  prepared  thin  section  of  this  rock  was  microscopically 
examined  by  a  German  mineralogist,  who  says  of  it: 

"  This  rock  is,  without  doubt,  one  of  the  older  volcanic  rocks.  It  consists  of 
feldspar,  mica,  and  hornblende,  with  a  little  quartz  and  magnetite.  Mica  is  to  a 
great  extent  absorbed,  and  magnetite  has  taken  its  place.  The  rock  is  difficult 
to  classify,  but  would  be  best  described  as  an  elseolite-syenitic  rock." 

2.  Samples  29  to  34  are  from  the  Thames  district.  It  was 
found  difficult  to  get  samples  of  the  Thames  andesites  in  which 


170      THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 

the  analysis  of  5  g.  would  show  no  trace  of  sulphides — this 
being,  as  already  explained,  a  requisite  condition  for  the  par- 
ticular investigation  in  hand.  A  large  number  of  samples  had 
to  be  rejected  on  this  account;  but  in  Kos.  29  to  34  no  trace  of 
sulphides  was  found.  .  .  . 

3.  Nine  samples  in  Table  I. :  namely,  NOB.  6,  11,  13,  17, 
26,  36,  38,  46,  and  47— contained  sulphides.  The  results  of 
further  examination  were  as  follows : 

No.  6.  Sample  of  500  g.  gave  53  g.  of  sulphides,jnostly  pyr- 
rhotite  arid  chalcopyrite,  which  contained  0.0053  grain  of  silver. 

No.  11.  Sample  of  500  g.  gave  18.56  g.,  chiefly  pyrrhotite. 
No  gold  or  silver. 

No.  13.  Sample  of  1,000  g.  gave  12.18  g.  of  pyrrhotite  and 
arsenopyrite.  No  gold  or  silver. 

No.  17.  Sample  of  1,000  g.  gave  4.934  g.  of  pyrite,  contain- 
ing 0.037  grain  of  gold  and  0.0041  grain  of  silver. 

No.  26.  Sample  of  1,000  g.  gave  28.92  g.  of  arsenopyrite 
and  pyrrhotite,  with  a  little  galena,  containing  0.0032  grain  of 
gold  and  6.0019  grain  of  silver. 

No.  36.  Sample  of  1,000  g.  gave  16.48  g.  of  chalcopyrite, 
with  a  small  quantity  of  bournonite,  carrying  0.407  grain  of 
silver  and  no  gold. 

No.  38.  Sample  of  1,000  g.  gave  16.03  g.  of  pyrite.  No 
gold  or  silver. 

No.  46.  Sample  of  1,000  g.  gave  8.42  g.  of  pyrite.  No  gold 
or  silver. 

No.  47.  Sample  of  500  g.  of  pyrite  and  sphalerite,  contain- 
ing 0.0016  grain  of  gold  and  0.0037  grain  of  silver. 

Conclusions. — The  results  summarized  in  Table  I.  were 
greatly  surprising  to  the  writer.  In  view  of  the  usually  tedi- 
ous character  of  the  operation  of  isolating  the  various  con- 
stituents of  a  rock,  he  would  not  have  examined  so  large  a 
number  of  samples  had  he  not  expected,  at  each  new  analysis, 
that  he  might  succeed  in  discovering  gold  in  some  mineral 
other  than  a  sulphide. 

It  is,  perhaps,  comparatively  easy  to  conceive  why,  in  a 
stratified  area,  gold  may  occur  only  in  connection  with  sul- 
phides ;  but  that  in  such  a  rock  as  gneiss,  granite,  syenite,  or 
diorite,  it  should  form  no  part  of  the  crystalline  constituents, 
but,  on  the  contrary,  should  occur  only  in  the  sulphides  found 
in  these  rocks,  seems  more  remarkable  and  significant. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  171 

CHAPTER  VI. — THE  VADOSE  REGION. 

Professor  Posepny 10  advances  the  sweeping  proposition  that 
the  formation  of  ore-deposits  could  have  taken  place  by  descen- 
sion  and  lateral  secretion  in  the  vadose  region  of  circulation 
only,  and  must  have  been,  in  the  deep  region,  the  product  of 
ascending  currents.  This  distinction  is,  perhaps,  too  sharply 
drawn  by  him.  It  seems  to  the  writer  that  the  lateral-secre- 
tion theory  can  scarcely  be  put  out  of  court  by  assuming  a 
lateral  secretion  to  be  impossible  below  the  ground-water  level. 
Yet  the  marked  difference  everywhere  observed  in  the  con- 
tents of  auriferous  lodes  above  and  below  that  leVel  required 
that  the  rocks  of  the  two  zones  should  be  distinguished,  and 
separately  analyzed  in  this  investigation. 

From  an  economic  stand-point,  this  difference  is  expressed  by 
the  almost  universal  experience  in  the  Australasian  gold-fields, 
that  the  average  yield  of  gold  is  much  smaller  below  the  water- 
level  than  near  the  surface.  This  statement,  which  will  doubt- 
less be  controverted  in  some  quarters,  is  based  on  the  concur- 
rent testimony  of  a  large  number  of  mine-managers  and  others, 
having  long  experience  in  the  auriferous  deposits  of  Australia 
and  New  Zealand.  The  almost  unanimous  evidence  is  in 
favor  of  the  greater  richness  of  vadose  deposits.  Several  men 
of  great  experience  have  even  given  the  opinion  that,  for  ounces 
per  ton  above  the  ground-water  level,  only  pennyweights  per 
ton  have  been  found  below  it. 

This  important  economic  question  is  naturally  discussed  in 
treatises  on  ore-deposits.  Phillips,11  for  example,  gives  a  num- 
ber of  reasons  why  the  results  in  the  vadose  region  may  seem 
to  be,  while  they  are  not  really,  higher  than  those  of  deep  levels. 
Even  after  taking  these  considerations  into  account,  however, 
the  evidence  of  greater  richness  in  the  vadose  region  in  Aus- 
tralia seems  overwhelming. 

In  this  connection,  reference  may  be  made  to  the  exhaustive 
work  of  K.  Brough  Smyth,12  and  to  a  very  interesting  little 
work,13  dealing  with  the  yield  of  the  auriferous  deposits  of  Yic- 

10  Trans.,  xxiii.,  262  (1893). 

11  A  Treatise  on  Ore-Deposits,  pp.  60  to  62  (1884). 

12  G old-Fields  of  Victoria,  pp.  233  to  281  (1889). 

13  The  Gold-Fields  of  Victoria  in  1862,  by  a  Special  Keporter  of  the  Argus,  Mel- 
bourne (1863). 


172  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

toria  from  1851  to  1862.  The  reader  of  the  latter  book  may 
suspect  the  anonymous  author  of  overstating  the  facts ;  but  a 
comparison  of  the  average  yields  noted  in  it  with  those  of  mines 
now  working  in  the  same  reefs,  with  the  aid  of  the  latest  gold- 
saving  appliances,  can  hardly  fail  to  carry  conviction,  even  to 
those  who,  permitting  "  the  wish  "  to  be  "  father  to  the  thought," 
deny  the  impoverishment  of  auriferous  lodes  in  depth.14 

This  greater  richness  of  the  vadose  region  might  be  explained 
in  either  of  two  ways. 

1.  If  the  auriferous  contents  of  the  lodes  are  derived  from 
some  deeper  source,  and  have  been  deposited  from  warm  as- 
cending waters,  the  decrease  of  pressure  on  approaching  what 
was,  at  the  time   of  the   lode-formation,  the   surface,  might 
account  for  the  precipitation  of  the  precious  metals  in  greater 
quantities  near  that  surface. 

2.  If  the  reefs  and  their  auriferous  contents  are  due  to  the 
leaching  action  of  solutions  traversing  the  country-rock  on  each 
side  of  the  fissures,  such  leaching  action  would  naturally  be  far 
more  intense  near  the  surface,  because  the  oxidizing  action  of 
the  surface-water  would  naturally  be  much  greater  in  the  vadose 
region.  • 

Either  of  these  hypotheses  might  account  for  the  greater 
richness  of  the  vadose  region.  In  the  first  case  we  might  have 
in  the  present  deposits  of  that  region  an  example  of  the  re- 
solution and  precipitation  of  gold  which  had  been  previously 
brought  up  from  greater  depths ;  while  in  the  second  case  we 
might  expect  to  trace  a  leaching  action  similar  to  that  occurring 
in  depth,  only  augmented  by  the  effect  of  the  oxidizing  vadose 
waters. 

The  question  is  naturally  suggested,  whether  natural  re- 
agents capable  of  dissolving  gold 15  are  to  be  found  in  the  vi- 
cinity of  auriferous  lodes.  And  this  inquiry  suggests  the 
further  questions :  Does  gold  exist  in  solution  in  mine-waters 
of  either  the  vadose  or  the  deep  circulation  ?  Does  the  gold 
of  the  vadose  circulation,  in  any  particular  mine,  contain  a 

14  The  gold-field  of  Bendigo  is  often  cited  as  an  instance  to  the  contrary,  good 
yields  having  been  there  obtained  in  some  eases  from  great  depths  (2,000  to  2,800 
ft. ) ;  but  the  reason  for  this  is  indicated  in  the  remarks  of  E.  J.  Dunn,  in  his  report 
on  the  Bendigo  Gold-Fields,  pp.  6  and  9. 

15  Gold  is  so  easily  precipitated  from  solution  that  an  investigation  as  to  possible 
precipitating-agents  is  scarcely  necessary. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  173 

smaller  percentage  of  silver  than  that  of  the  deep  circulation  ? 
Is  any  evidence  of  re-solution  and  re-precipitation  to  be  obtained 
by  analyzing  samples  of  country-rock  from  the  vadose  region, 
corresponding  in  position  with  samples  from  the  deep  region 
of  the  same  district? 

Natural  Solvents  of  Gold. 

The  chief  solvents  of  gold  at  all  likely  to  occur  in  the  neigh- 
borhood of  lodes  are  bromine,  iodine,  ferric  chloride,  ferric  sul- 
phate, and  chlorine. 

Bromine  and  Iodine. — The  action  of  iodine  as  a  solvent  for 
gold  in  nature  has  been  emphasized  by  some  writers ; 16  but, 
whatever  may  have  taken  place  in  the  past,  the  present  inves- 
tigation seems  to  show  that  iodine  is*  not  at  all  abundant  in  au- 
riferous rocks.  The  partial  or  complete  analysis  of  53  samples 
of  mine-water  from  both  the  vadose  and  the  deep  circulation 
has  detected  no  bromine,  and  only  in  one  instance  any  trace  of 
a  soluble  iodide.  If,  however,  bromides  and  iodides  do  exist 
in  the  vadose  region,  the  agents  which  liberate  chlorine  (con- 
sidered below)  would  also  liberate  bromine  and  iodine. 

Ferric  Chloride  and  Ferric  Sulphate. — Henry  Wurtz 17  remarks 
that  as  early  as  1859  he  called  attention  to  the  solubility  of  gold 
in  these  salts ;  but  he  does  not  state  the  strength  of  the  solvent 
solutions  employed.  The  same  is  true  of  many  other  assertions 
of  this  reaction,  encountered  in  technical  literature.18  It  was 
therefore  deemed  necessary  in  the  present  investigation  to  test 
the  solubility  of  gold  in  solutions  of  the  above  salts  of  various 
strengths,  not  greatly  exceeding,  however,  the  degree  of  con- 
centration actually  found  in  the  most  highly  mineralized  waters 
analyzed.  Solutions  of  ferric  chloride  and  ferric  sulphate,  con- 
taining from  1  to  20  g.  per  liter,  were  prepared,  and  finely 
divided  (1)  metallic  gold  and  (2)  auriferous  sulphides  were 
treated  in  these  solutions,  being  freely  exposed  to  the  air  at 
ordinary  temperature  for  several  months ;  but  no  gold  was  dis- 

16  For  example,  T.  A.  Rickard,  On  the  Origin  of  the  Gold- Bearing  Quartz  of 
the  Bendigo  Keefs,  1  Vans.,  xxii.,  309  (1893). 

ir  Gold  Genesis,  Scientific  American  Supplement,  vol.  xxxviii.,  No.  979,  p.  15,644 
(Oct.  6,  1894). 

18  It  is  highly  desirable  that  in  all  such  statements  of  solubility,  the  precise 
strength  of  the  reagents  should  be  given.  Most  of  the  accounts  of  the  solution  of 
gold,  for  instance,  employ,  at  best,  only  the  vague  terms  "strong,"  "dilute,"  etc. 


174  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

solved,  even  by  the  strongest  solutions.  As  the  highest  strength 
above  named  considerably  exceeded  that  of  the  most  highly 
mineralized  mine-waters  analyzed,  no  experiments  were  made 
with  still  stronger  solutions  of  the  ferric  salts. 

The  negative  result  of  these  experiments  is,  of  course,  not 
conclusive  proof  that  gold  may  not  have  been  dissolved  by  these 
reagents  in  the  vadose  circulation  in  a  longer  time  and  under 
other  conditions  than  those  supplied. 

Chlorine. — Possibly  many  reactions  in  nature,  not  easily  re- 
produced in  the  laboratory,  may  liberate  chlorine,  even  at  ordi- 
nary temperatures.  We  know,  however,  that  it  is  produced  by 
the  action  of  hydrochloric  acid  on  the  higher  oxides  of  manga- 
nese, or  by  the  action  of  sulphuric  acid  on  the  same  oxides  in 
the  presence  of  chlorides.  • 

The  question  whether  agents  for  the  re-solution  of  gold  exist 
in  the  vadose  region  is  thus  practically  narrowed  to  a  search,  in 
the  waters  and  rocks  of  that  region,  for  (1)  free  hydrochloric 
acid ;  (2)  free  sulphuric  acid ;  (3)  the  higher  oxides  of  manga- 
nese ;  and  (4)  ferric  chloride  and  ferric  sulphate. 

It  was  desirable,  at  the  outset,  to  determine  the  most  dilute 
solution  of  hydrochloric  acid  which  will,  in  the  presence  of  the 
higher  oxides  of  manganese,  liberate  sufficient  chlorine  to  be 
detected  by  ordinary  tests.  Experiment  showed  that  1  part  of 
hydrochloric  acid  of  1.16  sp.  gr.  in  2,500  of  water  would  give 
a  distinct  chlorine  reaction,  while  1  part  of  the  same  acid  in 
1,250  of  water  produced  chlorine  enough  to  dissolve  an  amount 
of  gold  appreciable  by  delicate  tests.  As  the  proportion  of 
pure  HOI  to  water  is  in  the  first  case  only  about  1  to  8,000, 
and  in  the  second  case  1  to  4,000,  it  is  evident  that  extremely 
dilute  acid  will,  in  the  presence  of  manganese  oxides,  dissolve 
gold. 

Cause  of  Acidity  in  Mine-  Waters. — The  chief  cause  of  acidity 
in  mine-waters  (see  examples  below)  is  without  doubt  the  oxi- 
dation of  pyrite,  which  yields  ferric  sulphate  and  sulphuric 
acid.  The  latter,  acting  on  the  chlorides,  which  are  always 
present  to  greater  or  less  extent  in  mine-waters,  frees  hydro- 
chloric acid.  The  writer  has  never  found  a  water  containing 
free  acid  in  which  there  was  not  also  a  large  percentage  of  fer- 
ric salts. 

The  Occurrence  of  Oxides  of  Manganese  in  Mining-Districts. — 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  175 

In  some  mining-districts  (notably  in  Karangahake,  in  the 
Thames  gold-field)  the  oxides  of  manganese  often  form  a  great 
part  of  the  lode-filling.  While  this,  however,  is  exceptional  in 
Australia  and  New  Zealand,  the  presence  of  the  higher  oxides 
of  manganese  in  the  ferric  oxides  of  the  vadose  circulation  is 
surprisingly  general.  Twenty  analyses  of  such  material  from 
various  localities  showed  in  17  cases  manganese,  representing 
from  0.012  to  43.59  per  cent,  (reckoned  as  Mn304).  To  one 
sample,  containing  only  0.38  per  cent,  of  Mn304,  dilute  hydro- 
chloric acid  and  precipitated  gold  were  added,  and  gold  was 
found  to  be  dissolved. 

If,  therefore,  the  vadose  mine-waters  are  found  to  contain 
free  hydrochloric  acid,  it  is  evident  that  agents  for  the  re-solu- 
tion of  gold  in  that  zone  are  not  lacking. 

The  Acidity  of  Vadose  Mine-  Waters. — An  acid  reaction  with 
test-paper  does  not  prove  the  presence  of  free  acid.  Every 
water  examined  which  contained  an  appreciable  quantity  of 
ferric  salts  gave  a  distinct  acid  reaction,  though  in  a  number 
of  cases  examination  proved  the  absence  of  free  acid. 

Seventeen  samples  of  vadose  waters  were  examined  for  free 
acid ;  care  being  taken  to  collect  the  water  as  it  ran  from  the 
rock  or  vein,  before  any  considerable  exposure  to  oxidizing 
agencies  other  than  the  oxygen  held  in  solution  by  the  water 
itself. 

In  calculating  the  results  from  those  samples  which  carried 
much  free  acid,  if  both  sulphates  and  chlorides  were  present, 
and  the  amount  of  free  acid  exceeded  the  amount  represented 
by  the  chlorine  radical  in  the  water,  the  whole  of  the  chlorine 
radical  was  taken  as  combined  with  H  to  form  free  hydro- 
chloric acid,  and  the  remainder  of  the  free  acid  found  was 
reckoned  as  sulphuric  acid.  The  results  are  shown  in  Table  II. 
The  amount  of  ferric  chloride  and  sulphate  can  be  approxi- 
mately calculated  from  the  proportion  of  iron  present  as  ferric 
salts.  Even  after  complete  oxidation  by  exposure  to  the  air, 
the  total  weight  of  ferric  salts  could  never  exceed  12  g.  per 
liter.  For  this  reason,  in  the  experiments  previously  described 
(see  p.  173),  I  did  not  use  solutions  of  ferric  salts  containing 
more  than  20  g.  per  liter. 

Table  II.  shows  the  considerable  increase  in  acidity  caused 
by  exposure  to  the  air.  It  is  noteworthy  that  all  the  samples 


176 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


marked  *,  when  taken  from  the  mine,  precipitated  gold  from 
solution,  but  that  the  same  waters,  after  thorough  oxidation, 
dissolved  metallic  gold  when  the  higher  oxides  of  manganese 
were  added  to  them. 


TABLE  II. — Examination  of  Mine-Waters  of  the   Vadose  Region 
for  Free  Acid  and  Ferric  Salts. 


1 

, 

og 

3- 

a* 

,2 

0  «J 

Free  Acid  in 

Free  Acid  in 

"be*  S 

Bra 

els 

'*P« 

Country-Rock. 

Reaction  t 
Pape: 

Grams  per 
Liter  before  Ex- 
posure to  Air. 

Grams  per 
Liter  after  Ex- 
posure to  Air. 

||| 

Iron  Pres< 
Ferric  S 

i 

|| 

a*... 

Propylite,   highly 
pyritous. 

Strongly 
acid. 

HC1. 
0.446 

H2SO4. 
7.901 

HC1. 
0.446 

H2S04. 

8.650 

3.198 

2.431 

0.767 

b*... 

Do.  

Do. 

0.287 

Nil. 

0.592 

1.3842 

2.471 

0.946 

1.525 

c*... 

Do  

Acid. 

0.065 

Nil. 

0.208 

Nil. 

1.086 

0.731 

0.355 

d*... 

Do 

Strongly 

0.506 

6.078 

0.506 

8.921 

2.017 

0.896 

1.111 

acid. 

€* 

Do 

Acid. 

0.079 

Nil 

0.361 

Nil. 

0.968 

0.834 

0.134 

/*... 

Propylite  and  rhyo- 

Acid. 

0.216 

Nil. 

0.465 

0.380 

0.758 

0.210 

0.548 

lite. 

0*... 

Propylite,  pyritous. 
Mica-schist. 

Acid. 
Neutral. 

0.409 
Nil. 

1.063 

Nil. 

0.605 
Nil. 

1.582 
Nil. 

1.903 
0.095 

1.127 

0.027 

0.776 
0.068 

j  

Mica-schist. 

Neutral. 

Nil. 

Nil. 

Nil. 

Nil. 

0.872 

0.305 

0.567 

i  

Slate  and  sandstone. 

Highly 

Nil. 

Nil. 

Nil. 

Nil. 

0.569 

0.481 

0.088 

acid. 

A;  

Mica-schist. 

Do. 

0.087 

Nil. 

0.105 

Nil. 

1.007 

0.783 

0.224 

1  

Mica-schist. 

Strongly 
acid. 

0.658 

Nil. 

0.816 

Nil. 

1.569 

1.406 

0.163 

m.... 

Mica-schist. 

Slightly 

0.064 

Nil. 

Nil. 

Nil. 

0.987 

0.639 

0.348 

acid. 

n  

Mica-schist. 

Neutral. 

Nil. 

Nil. 

Nil. 

Nil. 

0.640 

0.379 

0.261 

0  

Mica-schist. 

Acid. 

Nil. 

Nil. 

0.406 

Nil. 

1.206 

0.217 

0.989 

P  

Slate  and  sandstone. 

Neutral. 

Nil. 

Nil. 

Nil. 

Nil. 

0.489 

0.426 

0.063 

*  

Do  

Neutral. 

Nil. 

Nil. 

Nil. 

Nil. 

0.602 

0.578 

0.024 

<i.  From  the  Whau  mine,  Thames,  N.  Z.  Contained  a  large  quantity  of  iron  in  solution. 
Color,  wine-red.  Sp.  gr.,  1.021. 

*.  From  Maria  reef,  Karangahake,  Thames,  N.  Z.  Deposited  a  large  quantity  of  ferric  hy- 
droxide on  standing. 

c.  From  Woodstock  reef,  Thames,  N.  Z.    Behaved  on  standing  like  sample  6. 

d.  From  the  Alburnia  mine,  Thames,  N.  Z.    In  appearance  like  sample  a.    Sp.  gr.,  1.019. 

€.  From  the  Grace  Darling  mine,  Thames,  N.  Z. '  Nearly  clear ;  slight  deposit  of  ferric  hy- 
droxide on  standing. 

/.  From  the  Martha  mine,  Waihi,  Thames,  N.  Z.  Appearance  and  behavior  on  standing  like 
sample  e. 

g.  From  the  Crown  mine,  Karangahake,  Thames,  N.  Z.    Like  samples  e  and/. 

h.  From  the  Tipperary  mine,  Macetown,  Otago.    Clear. 

i.  From  the  Premier  mine,  Macetown,  Otago.    Clear. 

j.  From  the  Long  Tunnel,  Walhalla,  Victoria.    Clear. 

k.  From  the  Bonanza  mine,  Nenthorn,  Otago.    Clear. 

I.  From  a  quartz  reef  near  Roxburgh,  Otago.  Reddish  ;  deposited  a  good  quantity  of  .ferric 
hydroxide  on  standing. 

m.  From  the  Bella  reef,  Waipori,  Otago.    Clear. 

n.  From  the  Gabriel's  Gully  reef,  Lawrence,  Otago,    Clear. 

o.  From  the  Game  Hen  reef,  Hindon,  Otago.    Clear. 

p.  From  the  reef  on  Sovereign  hill,  Ballarat,  Victoria.    Clear. 

q.  From  the  reef  on  Big  hill,  Bendigo,  Victoria.    Clear. 


THE    GEKES1S    OF    CERTAIN    AURIFEROUS    LODES.  177 

The  results  shown  in  Table  II.  point  to  the  following  con- 
clusions: 

1.  In  districts  like  the  Thames,  N.  Z.,  where  the  country- 
rock  is  highly  charged  with  sulphides,  the  vadose  water  may 
often  contain  free  hydrochloric  acid  sufficient  (when  the  higher 
oxides  of  manganese  are  present)  to  re-dissolve  gold.     Though 
the  Thames  samples  were  incapable  of  holding  ordinary  salts 
of  gold  in  solution,  they  acted  as  solvents  of  gold  when  they 
were  thoroughly  oxidized  and  manganese  oxides  were  present. 

2.  The  great  majority  of  the  mine-waters  analyzed  contained 
no  free  acid  which  could  liberate  chlorine  by  acting  on  the 
oxides  of  manganese  that  are  abundant  near  quartz  reefs. 

3.  The  higher  salts  of  iron  are  not  present  in  any  samples  of 
water  analyzed  by  me,  in  sufficient  quantity  to  dissolve  gold  at 
ordinary  temperatures.    (Stronger  solutions  of  these  salts  failed 
to  dissolve  gold.)     It  may  be  added,  that  in  every  case  in  which 
much  iron  was  present,  free  acids  were  also  found ;  so  that  in 
any  solution  of  gold  that  might  be  effected,  the  more  powerful 
solvent,  chlorine,  might  also  be  acting. 

Notwithstanding  these  conclusions,  I  must  point  out  that  the 
re-solution  of  gold  has  probably  gone  on,  and  is  still  going  on, 
in  the  vadose  region,  even  where  the  vadose  waters  contain 
neither  free  hydrochloric  acid  nor  notable  quantities  of  ferric 
salts.  The  analyses  of  samples  from  the  vadose  regions  of 
Walhalla  and  Ballarat  (see  Tables  III.  and  IV.,  and  Figs.  1 
and  2  [Tables  XX.  and  XXL  and  Diagrams  8  and  9  of  original 
paper]  ),  the  vadose  waters  of  which  contained  no  free  acid  and 
were  very  poor  in  dissolved  minerals,  show  that  such  re-solu- 
tion has  probably  been  considerable,  though  we  find  no  agen- 
cies now  existing  which  would  account  for  it. 

Does  Gold  Exist  in  Mine-  Waters  of  Either  or  Both  Circulations  ? 
Prof.  A.  Liversidge19  has  pointed  out  that  the  search  for  gold 
in  meteoric  and  mine-waters  has  not  proved  its  presence  in  so- 
lution. It  has  been  detected,  but  it  may  have  been  in  mechani- 
cal suspension.  So  far  as  I  know,  Messrs.  Norman  T.aylor  and 
•Cosmo  Newbery,  of  the  Victorian  Geological  Survey,  are  the 
•only  persons  who  have  experimentally  investigated  this  subject 

19  On  the  Origin  of  Gold  Nuggets,  Proceedings  of  the  Royal  Society  of  New  South 
.Wales,  vol.  xxvii.,  p.  303  (1893). 

12 


178  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

in  these  colonies.  Mr.  Newbery,  who  made  the  most  experi- 
ments, said  before  the  Victorian  Royal  Commission  on  Gold- 
Mining  20  that  whenever  he  got  gold,  he  got  also  angular  frag- 
ments of  quartz,  which  could  find  its  way  wherever  gold  could 
find  its  way,  and  both  might  have  been  conveyed  mechanically. 

The  evidence  for  the  existence  of  gold  in  mine-waters  rests, 
so  far  as  I  am  aware,  on  the  discovery  of  gold :  (1)  in  boiler- 
scale  from  boilers  fed  with  mine-water ;  and  (2)  in  wood  taken 
from  old  mine-workings,  where  it  has  been  covered  for  some 
time  with  mine-water — the. latter  being  assumed  to  have  car- 
ried dissolved  gold  into  the  timber,  to  be  precipitated  by  the 
organic  matter  of  the  wood.  But  the  finding  of  gold  under 
such  circumstances  does  not  prove  that  it  was  in  solution  in 
mine-waters  at  deep  levels.  In  the  first  case,  the  gold  may 
have  been  carried  into  the  boiler  in  suspension,  along  with  the 
silt  which  all  mine-waters  contain.  In  the  second  case,  even 
though  gold  may  have  been  dissolved  in  the  water  surrounding 
the  old  timbers,  it  may  have  been  brought  into  such  solution 
by  the  action  of  air  in  the  mine-workings,  oxidizing  sulphides 
of  the  rock  to  sulphates  and  setting  free  sulphuric  acid,  which, 
in  turn,  acting  on  the  chlorides  always  present  in  mine-waters, 
would  liberate  hydrochloric  acid.  This  acid,  acting  on  oxides 
of  manganese,  would  free  chlorine,  which  would  dissolve  gold. 
This  statement  applies  particularly  to  all  mines  the  waters  of 
which  contain  considerable  iron.  Every  sample  of  chalybeate 
mine-water  analyzed  by  me  acted  as  a  precipitant  of  gold  when 
taken  fresh  from  the  workings,  but  as  a  solvent  of  gold  at  ordi- 
nary temperatures,  in  the  presence  of  the  oxides  of  manganese, 
when  it  had  been  exposed  to  the  air  for  a  week  or  two. 

Mr.  Newbery,  however,  distinctly  said,  in  his  testimony 
already  cited,  that  he  found  angular  quartz  which  had  been 
soaked  up  into  the  timber  examined,  and  that  the  gold  might 
have  been  mechanically  introduced  in  the  same  way. 

With  regard  to  the  suspension  of  gold  in  mine-waters,  the 
following  evidence,  obtained  by  me  last  year,  may  be  of  interest. 

In  the  Long  Tunnel  G.  M.  Co.'s  mine  at  Walhalla,  Gipps- 
land,  Victoria,  one  of  the  most  productive  mines  in  Australia, 2l 

20  Report  of  the  Commission,  p,  68  (1893). 

21  Ramsay  Thompson,  the  general  manager,  to  whom  I  am  indebted  for  much 
kind  assistance,  informed  me  that  up  to  December,  1894,  this  mine  had  produced 
over  22  tons  of  gold,  and  had  paid  £1,200,000  in  dividends. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  179 

the  water  pumped  from  various  depths,  down  to  about  2,300 
ft.  below  the  surface,  is  run  into  two  large  settling-tanks,  be- 
fore using.  At  the  time  of  my  visit  one  of  these  tanks  con- 
tained a  large  quantity  of  fine  silt,  which  had  been  suspended 
in  the  mine-water.  I  analyzed  three  samples  of  about  2  Ib. 
each,  first  panning  off  the  lighter  part,  and  then  assaying  the 
residue.  The  first  sample  gave  0.0063  grain  of  gold;  the  sec- 
ond, no  trace  ;  and  the  third,  0.0175  grain. 

These  results  show  that  assays  of  boiler-scale  do  not  neces- 
sarily prove  that  gold  was  dissolved  in  the  water  depositing  it ; 
and,  also,  that  in  all  analyses  even  of  samples  from  the  vadose 
circulation,  to  test  the  presence  of  dissolved  gold,  care  must  be 
taken  to  free  the  water  beforehand  from  every  trace  of  sus- 
pended matter. 

I  have  tested  many  old  mine-timbers  for  gold.  In  every  case 
the  outside  wood  was  chipped  off  to  the  depth  of  about  0.5  in.; 
and,  when  cracks  appeared  in  the  timber,  about  0.5  in.  on  each 
side  of  the  crack  was  also  chipped  off.  These  parts  were 
burned,  and  analyzed  separately  from  the  inner  portions.  The 
results  of  several  such  analyses  are  shown  in  the  table  on  p.  180. 

Search  for  Gold  in  Mine-  Waters. — It  was  soon  found  useless 
to  examine  mine-waters  which  contained  much  iron,  and  in 
which  the  ferrous  salts  had  not  been  oxidized  to  ferric  salts  by 
exposure  to  the  atmosphere.  The  analyses  were  consequently 
restricted,  for  the  vadose  region,  to  waters  containing  a  very 
small  percentage  of  iron-salts,  and  chalybeate  waters  which 
had  been  thoroughly  oxidized  (the  latter  being  apparently  ex- 
ceptional, even  in  that  region),  and,  for  the  deep  circulation,  to 
waters  containing  so  little  iron  that  they  do  not  act  as  precipi- 
tants  of  gold. 

This  chapter  treats  of  mine-waters  under  the  conditions  of 
temperature  and  pressure  now  -encountered.  What  might  be 
effected  by  these  waters  under  other  conditions  does  not  concern 
us  at  this  stage. 

If  gold  be  present  in  mine-waters  at  all,  it  is  likely  to  be  in 
very  minute  proportions.  Hence  large  quantities  of  water 
must  be  operated  upon.  The  method  of  evaporation  for  the 
assay  of  the  residue  was  too  tedious,  especially  in  view  of  the 
limited  time  at  my  disposal  in  each  locality.  I  therefore 
availed  myself  of  the  well-known  action  of  sulphides  and  or- 
ganic matter  in  precipitating  gold  from  solution. 


180  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


Analyses  of  Old  Mine-Timbers. 


Sample. 

Description  and  Locality. 

Part  Analyzed. 

Gold  Found. 

I. 

Prop  from  the  Tipperary  Gold  Mining 
Co.,  Macetown.  Otago,  much  decom- 
posed. The  part  analyzed  had  been 
under  water  for  many  years 

Outside  of  the 
prop. 

None. 

II. 

Do. 

Inside  of  prop. 

None. 

III. 

Prop  from  an  old  tunnel  in  an  alluvial 
terrace,  near  Skipper's  Point,  Otago. 
The  part  analyzed  had  been  under 
water  for  probably  20  years. 

Outside  of  prop. 

None. 

IV. 

Do. 

Inside  of  prop. 

None. 

V. 

A  prop  from  the  Premier  mine,  Mace- 
town,  Otago.  Water  had  been  run- 
ning over  it  for  2  years  at  least. 

Outside  of  prop. 

0.0038  grain. 

VI. 

Eotten  wood  from  the  lower  part  of  a 
rejected  prop  from  the  Long  Tunnel 
Gold  Mining  Co.,  Walhalla.  From  a 
part  of  the  mine  where  a  richly  auri- 
ferous reef  had  been  worked. 

Outside  of  prop. 

0009  7  grain. 

VII. 

Do. 

Inside  of  prop. 

None. 

VIII. 

Decayed  portion  of  lath  brought  up  from 
the  deep  workings  of  the  Northern 
Star  Gold  Mining  Co.,  Ballarat.  Had 
evidently  been  saturated  with  water 
for  many  years. 

No  portion  was 
sound  ;  all 
was  burned 
and  analyzed. 

None. 

IX. 

Portion  of  sleeper  used  in  a  tramway, 
Northern  Star  Gold  Mining  Co.,  much 
decayed.  A  large  quantity  of  water 
had  been  running  over  it  for  at  least 

Do. 

0.0129  grain. 

a  year. 

A  filter  was  constructed,  consisting  of  a  tinned-iron  cylinder, 
about  3  in.  in  diameter  and  6  in.  long,  terminating  below  in  a 
funnel,  inside  of  which  was  placed  a  filter  of  glass-wool,  and 
above  this  the  reduciug-agents  (animal  charcoal,  artificial  iron 
and  lead  sulphides,  roughly  powdered).  The  upper  part  was 
connected  by  a  rubber  tube  with  the  tap  supplying  the  water 
to  be  tested. 

The  following  preliminary  test  proved  the  efficiency  of  this 
filter :  A  solution  in  400  gal.  of  water  (from  the  Dunedin  water- 
mains)  of  28  Ib.  of  common  salt,  8  oz.  of  magnesium  sulphate, 
8  oz.  of  ferric  chloride,  and  0.1  grain  of  gold  in  the  form  of  auric 
chloride,  was  allowed  to  trickle  slowly  through  the  filter,  the 
operation  taking  about  48  hr.  The  mixture  of  sulphides  and 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  181 

charcoal  was  then  removed,  roasted,  and  assayed,  when  0.0926 
grain  of  gold  was  recovered,  showing  that  practically  all  the 
gold  had  been  precipitated. 

In  examining  mine-waters,  the  water  was  first  collected  in 
an  iron  tank,  and  powdered  alum  was  added  to  it,  completely 
precipitating  all  suspended  matter.  After  standing  some  hours, 
it  was  tapped  from  2  or  3  in.  above  the  bottom  of  the  tank,  and 
filtered  as  described. 

Four  samples  were  thus  treated;  but  in  no  case  was  gold 
found. 

The  first  sample  (about  500  gal.)  was  water  from  the  high- 
level  tunnel  of  the  Tipperary  G.  M.  Co.,  which  had  percolated 
down  from  the  surface  through  the  lode-fissure  for  from  200 
to  500  ft.,  and  flowed  in  a  large  stream  from  the  tunnel-mouth. 
This  practically  represented  the  vadose  circulation  only. 

The  second  sample  (about  500  gal.)  was  from  the  pump-dis- 
charge of  the  New  Chum  Railway  Co.,  Bendigo,  Victoria,  and 
represented  the  whole  drainage  of  the  mine  from  the  surface  to 
a  depth  of  2,850  feet. 

The  third  sample  (about  700  gal.)  was  from  the  Long  Tunnel 
G.  M.  Co.'s  mine,  Walhalla,  Victoria,  near  a  very  rich  lode,  and 
represented  the  whole  drainage  between  the  adit  (700  ft.  below 
the  summit  of  the  hill)  and  a  level  about  2,300  ft.  below  the 
surface,  or  over  1,500  ft.  below  the  adit. 

The  fourth  sample  (about  500  gal.),  from  a  deep  tunnel  of 
the  Premier  mine,  Advance  Peak,  Otago,  driven  on  a  lode 
which  had  proved  richly  auriferous  in  places,  represented  the 
whole  drainage  from  the  surface  to  probably  2,000  ft.  below  it. 

The  negative  results  of  these  tests  are  the  more  surprising 
to  me,  since  other  examinations,  hereinafter  described,  afforded 
strong  evidence  that  solution  and  re-precipitation  of  gold  have 
taken  place  in  the  vadose  region. 

It  is,  of  course,  possible  that  gold  may  have  existed  in  these 
samples  in  some  form  from  which  it  was  not  precipitated  by 
the  reagents  used.  This  is  suggested,  indeed,  by  my  experi- 
ence (see  Chapter  VII.)  in  attempting  to  precipitate  gold  from 
sea-water.  The  question  can  only  be  decided  by  the  evapora- 
tion of  samples  (first  freed  from  suspended  matter)  in  larger 
amount  and  number  than  mine,  and  the  assay  of  the  residues. 
I  venture  to  recommend  such  an  inquiry  to  those  who  live  in 
the  vicinity  of  rich  mines  and  have  time  for  the  work. 


182  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

Does  the  Gold  of  the  Vadose  Region  Contain  Generally  Less 
Silver  than  That  of  the  Deep  Circulation  in  the  Same  District  ? 

Several  investigations  have  seemed  to  prove  that,  on  the  aver- 
age, the  gold  of  the  alluvial  deposits  in  Australia  and  elsewhere 
is  appreciably  finer  in  quality  than  the  vein-gold.  The  matter 
has  been  discussed  chiefly  in  connection  with  the  origin  of 
nuggets; 22.  but,  so  far  as  I  know,  no  comparison  as  to  fineness 
has  been  made  between  the  vadose  and  the  deep  vein-gold. 

The  observed  difference  between  placer-  and  vein-gold  may 
be  held  to  show,  either  that  the  oxidized  mineral-bearing  waters 
running  in  the  ancient  drift-deposits  dissolved  out  part  of  the 
silver  with  which  the  gold  was  alloyed,  or  else  that  these 
waters  dissolved  both  gold  and  silver,  the  gold  being  again 
precipitated,  alloyed  with  less  silver  than  before.  Similar  rea- 
soning might  be  applied  to  an  observed  difference  between  the 
vadose  and  the  deep  zone,  in  the  quality  of  vein-gold.  I  have 
therefore  made  comparative  assays  of  this  character  in  a  num- 
ber of  cases. 

The  fineness  of  the  gold  may  vary  considerably  even  in  the 
same  level,  and  within  a  few  feet.  This  is  true  even  in  such 
districts  as  Bendigo,  Ballarat,  and  Otago,  where  the  percent- 
age of  silver  is  comparatively  low,  while  in  districts  like  the 
Thames,  N".  Z.,  the  variation  observed  is  sometimes  extraordi- 
nary. On  the  whole,  however,  the  average  quality  of  the  gold 
won  in  districts  of  the  former  class  varies  little. 

Five  localities  were  chosen  (chiefly  by  reason  of  facilities  for 
obtaining  specimens  from  near  the  surface),  namely,  (1)  the 
Nenthorn  gold-field,  in  mica-schist,  in  eastern  Otago;  (2)  the 
Tipperary  and  Premier  mines,  in  mica-schist,  Macetown,  cen- 
tral Otago;  (3)  the  Dart  river,  in  northern  Gippsland,  repre- 
senting the  Upper  Silurian  of  Victoria;  (4)  the  Bendigo  field,23 
representing  the  Lower  Silurian ;  and  (5)  the  Thames  district 
of  the  North  Island,  in  altered  Lower  Tertiary  andesite. 

In  a  few  instances  the  analyses  were  made  of  gold  picked 
out  of  the  reef;  but  the  majority  were  assays  of  vein-stone. 

22  Professor  Liversidge,  in  the  paper  already  cited,  gives  a  convenient  summary 
of  the  literature  of  this  subject. 

23  Surface-samples  are  hard  to  get  in  Bendigo.     Nearly  all  the  companies  are 
mining  in  the  deep  region,  and  have  long  ago  exhausted  the  pay-quartz  above. 
I  took  many  samples  from  outcrops  of  reefs,  but  found  in  the  majority  little  or  no 
gold.     The  results  given  below  are  those  in  which  a  prill  of  appreciable  size  was 
obtained  by  assaying  1,000  grains  of  vein-stone. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  183 

The  percentage  of  silver  was  in  each  case  obtained  by  differ- 
ence, and  represents  the  loss  per  cent  of  the  prill  after  quarta- 
tion.  The  results  were  as  shown  in  the  table  on  p.  184. 

These  analyses  of  76  samples  go,  on  the  whole,  to  prove  that 
the  average  fineness  of  the  gold  in  the  vadose  region  is  appre 
ciably  greater  than  in  the  deep  circulation  in  the  same  district, 
and  also  that  the  vadose  gold  is  considerably  more  regular  in 
quality. 

It  seems  to  be  indicated  that  considerable  solvent  action 
must  have  been  exercised  by  water  percolating  through  the 
rocks  of  the  vadose  region,  as  the  denudation  of  the  surface 
has  gradually  lowered  the  water-level,  converting  the  deep  cir- 
culation of  former  times  into  the  vadose  of  to-day. 

Analyses  of  Vadose  Country-Rock,  etc.,  at  Different  Distances  from 

Auriferous  Lodes. 

At  the  beginning  of  this  chapter  I  have  pointed  out  the  im- 
portance of  separate  rock-assays  in  the  vadose  region.  It  was 
relatively  difficult  to  obtain  good  samples  (other  than  surface- 
samples)  of  this  class,  because  most  of  the  mines  are  now  deep, 
and  the  former  long  cross-cuts  run  on  upper  levels  into  the 
country-rock  are  abandoned  and  closed.  The  samples  there- 
fore comprise  chiefly  oxidized  rock  from  pretty  near  the  lodes, 
and  10  to  100  ft.  below  the  surface,  and  surface-samples  taken 
at  all  distances  from  the  lodes.  Particular  interest  attaches  to 
samples  of  (1)  oxide  of  iron  and  manganese  deposited  along 
bedding-planes  or  fractures ;  (2)  solid  rock  as  little  altered  as 
possible  by  the  action  of  percolating  water;  and  (3)  secondary24 
sulphides,  abundant  in  the  vadose  region  of  many  mines. 

The  remarks  covering  the  methods  of  concentration  and  as- 
say pursued  with  samples  from  the  deep  levels,  apply  here  also. 

24  In  calling  these  vadose  sulphides  "  secondary,"  I  mean  that  they  have  prob- 
ably been  formed  through  the  oxidization  of  the  sulphides  of  the  deep  circulation 
by  surface-water,  followed  by  a  reduction  of  the  sulphates  and  re-precipitation  of 
the  sulphides  by  orgmic  matter.  I  do  not  mean  to  say  positively  that  the  sul- 
phides of  the  deep  zone  are  not,  as  many  observers  believe,  also  secondary  in  this 
sense,  that  is,  due  to  the  reducing  action  of  carbonaceous  matter  upon  soluble  sul- 
phates. This  is  Sandberger's  view  (Untersuchung,  etc.,  vol.  i.,  p.  21).  Yet  so 
far  as  my  experience  of  the  deep  sulphides  goes,  it  certainly  favors  the  theory  of 
their  formation  by  the  action  on  the  silicates  of  metals  of  hydrogen  sulphide,  dis- 
solved in  ascending  water. 


184       THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 

Relative  Fineness  of  Vadose  and  Deep  Vein- Gold. 


A.    Surface-Samples  from  Nenthorn  Gold- 
Field,  Otago,  N.  Z. 

B.    From  Deeper  Levels  of  Nenthorn  Dis- 
trict (the  Bulk  of  the  Gold  was  Held 
by  Pyrite). 

No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

1 

91.85 
89.27 
90.43 
89.19 
92.01 
89.38 
91.46 
90.79 
90.07 
92.00 

7.15 
10.73 
9.67 
10.81 
7.99 
10.62 
8.54 
9.21 
8.53 
8.00 

1           

89.86 
91.43 
87.17 
90.45 
89.07 
92  01 

10.14 
8.57 
12.83 
9.55 
10.93 
7.99 
9.83 
11.25 
8.97 
9.70 

2 

2 

3 

3  

4 

4 

5 

5  

c 

6 

90.17 
88.75 
91.03 
90.30 

g 

8         

9           

9  

10 

10  

Average  fineness  of  10  samples,  90.645  per 
cent.    Range  of  fineness,  89.19  to  92.01  = 
2.827  per  cent. 

Average  fineness  of  10  samples,  90.024  per 
cent.    Range  of  fineness,  87.17  to  92.01  = 
4.  84  per  cent. 

C,    Surface-Samples  from  Tipperary  Pre- 
mier, and  Sunrise  Gold  Mining  Companies. 
All  near  Macetown,  Central  Otago,  N.  Z. 


D     From  Deep  Levels  (1,000  to  1,500  Ft. 

Below  Surface)  in  Tipperary  and  Premier 

Mines,  Macetown. 


No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

1 

96.12 
U3.37 
94.19 
92.87 
95.00 
94.58 
93.23 
95.84 
95.93 
94.89 

3.88 
6.63 
5.81 
7.53 
5.00 
5.42 
6.77 
4.16 
4.07 
5.11 

1  
2  

95.39 
94.48 
91.87 
96.29 
93.06 
94.31 
93.80 
94.73 
93.90 
94.10 

4.61 
5.52 
8.13 
3.71 
6.94 
5.69 
6.20 
4.27 
6.10 
5.90 

2                      

3 

3    

4 

4 

5 

5  

6 

g 

7 

8 

9 

10            ... 

10 

Average  fineness  of  10  samples,  94.602  per 
cent.    Range  of  fineness,  92.87  to  96.12  = 
3.  25  per  cent. 

j 

.Average  fineness  of  10  samples,  94.293  per 
cent.    Range  of  fineness,  91.87  to  96.29  = 
4.42  per  cent. 
NOTE.—  A  sample  taken  from  a  bar  of  194  oz. 
from  deep  levels  of  Premier  Gold  Mining 
Co.  contained  94.45  per  cent. 

E.    Surface-Specimens  from  Richly  Aurif- 
erous Lode  in  the  Vicinity  of  the  Dart 
River,  North  Gippsland,  Victoria. 

F.    Unoxidized  Specimens  from  the  Same 
Reef,  Dart  River,  North  Gippsland, 
Victoria. 

No. 

Percentage 
of  Gold. 

Percentage  ; 
of  Silver. 

No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

1 

91.87 
94.96 
93.08 
92.00 
92.63 
94.73 
93.45 
95.01 
94.91 
92.84 

8.13 
5.04 
6.92 
8.00 
7.37 
5.27 
6.55 
4.99 
5.09 
7.18 

1  

91.50 
90.43 
87.69 
96.28 
91.17 
84.64 
88.93 
95.03 
90.37 
90.80 

8.50 
9.57 
12.31 
3.72 
8.83 
15.36 
11.07 
4.97 
9.63      . 
9.20 

2           

2  

3 

3  

4              

4«  

5 

5  

g 

6  & 

7                  

7  

8 

8             

9                  

9  

10 

10  

Average  fineness  of  10  samples,  93.548  per 
cent.    Range  of  fineness,  91.87  to  95.01  = 
4.  14  per  cent. 

Average  fineness  of  10  samples,  90.984  per 
cent.    Range  of  fineness,  84.64  to  96.28  = 
12.36  percent. 
a  Sample  assayed  consisted  of  arsenopyrite 
and  pyrite. 
6  Sample  assayed  composed  chiefly  of  galena. 

THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


Relative  Fineness  of  Vadose  and  Deep  Vein-Gold. —  Continued. 


G.    Surface-Samples  from  Bendigo  Gold- 
Field,  Victoria. 

H. 

Samples  from  Deep  Levels  (1,200  to 
3,000  Ft.)  of  Bendigo  Gold-Field. 

No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

Te.                 Percentage 
of  Gold 

Percentage 
of  Silver. 

] 

94.76 
95.03 
94.05 
94.27 
94.10 
95.00 

5.24 
4.97 
5.95 
5.73 
5.90 
5.00 

1 

93  08 

6.92 
4.96 
6.00 
8.73 
5.70 
5.81 
6.04 
7.05 
7.63 
5.30 

9 

2... 
3 

9o.04 

3 

94  00 

4  

4... 

91.27 

5 

91  30 

6  

6... 

94.19 

7 

93  % 

g 

Q2  95 

9... 

..   .                            92  37 

10... 

91.70 

Average  fineness  of  6  samples,  94.535  per  cent.  ;  Average  fineness  of  10  samples,  93.586  per 


Range  of  fineness,  94.05  to  95.03 
cent. 


0.98  per 


cent.    Range  of  fineness,  92.37  to  95.04  = 
2.64  per  cent. 


I.    Samples  from  Vadose  Region  of  Various 
Parts  of  Thames  District,  N.  Island,  N.  Z. 


K.    Samples  from  Deep  Circulation  of  the 
Thames  District. 


No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

No. 

Percentage 
of  Gold. 

Percentage 
of  Silver. 

1 

63  72 

36  28 

\ 

63  76 

56  °4 

2  

79  34 

20  66 

2 

71  14 

28  86 

3 

52.90 

47.10 

I    3       

59  93 

40  07 

4  

57.39 

•   42  61 

4 

53  01 

46  99 

5   ..    . 

67  01 

39  99 

5 

64  25 

35  75 

6  

59  98 

40  02 

6 

43  17 

56  83 

7  

65.55 

34.45 

7... 

66  98 

33  02 

8  

73  07 

36  93 

1    g 

51  30 

48  70 

9  .    . 

60  08 

39  9'> 

1    9 

69  04 

30  % 

10  

51  19 

48  81 

!  jo 

48  75 

51  25 

Average  fineness  of  10  samples,  60.023  pen!  Average  fineness  of  10  samples,  59.133  per 
cent.  Range  of  fineness,  51.19  to  79.34=  \\  cent.  Range  of  fineness,  43.17  to  71.14  = 
28.15  per  cent.  27.97  per  cent. 


[In  the  majority  of  cases  the  samples  taken  weighed  7  or  8  lb.;  the  samples 
tested,  4.48  lb. ;  and  the  assays  were  made  from  concentrates  of  the  latter,  but  some- 
times 4.48  lb.  was  the  actual  sample  for  assay  ;  in  which  case  the  total  quantity 
was  pulverized  to  pass  a  No.  60  sieve,  and  divided  into  12  parts  of  about  2,500 
grains  each,  and  to  each  part  3,000  grains  of  purified  litharge,  2,000  grains  of  car- 
bonate of  soda,  and  1,000  to  1,500  grains  of  borax  were  added  for  the  assay,  with 
sufficient  argol  to  reduce  about  400  grains  of  lead.] 

But  concentration  of  an  oxidized  rock  is  much  more  diffi- 
cult, because  oxidation  destroys  the  heavy  sulphides,  and  also 
liberates  very  finely  divided  gold,  which  there  is  danger  of 
losing.  Hence  my  results  with  vadose  country-rock  are  not 
quantitatively  correct.  To  minimize  the  probable  error,  the 
samples  were  not  concentrated  nearly  as  far  as  those  from  deep 
levels  had  been. 


186 


THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 


TABLE  III. — Analyses  of  Country-Hock  from  the  Vadose  Region 
of  Walhalla  Gold-Field,  G-ippsland,  Victoria. 


.2  -  o 

i 

!• 

^  *t*  ^V-** 

£ 

s 

2 

&•  ;- 

• 

Q)       VH  T% 

'g 

f. 

3 

t^    £ 

»2 

"3  3  a;  ^ 

3 

3 

0 

Jt- 

1 

1*8* 

X 

H 

Weight  of  Concentrates  Obtained. 

c  p. 

1 

o«~5 

flP 

1 

I1 

I 

U 

Feet. 

Pounds. 

Grains. 

Grains. 

Grains. 

o  

3  West. 

4.48 

1,904  Chiefly  oxide  of  iron,  showing  a 

Trace. 

Nil. 

Nil. 

little  mica. 

6  

10  West. 

4.48 

1  650                                   .     . 

Trace. 

Nil. 

Nil. 

c  

16  West. 

2.24 

1  824  

Nil. 

0.027 

27. 

d*... 

100  West. 

2.24 

All  assayed       .  .           ...        

Nil. 

Nil. 

Nil. 

240  West. 

2  24 

1  463 

Nil. 

0.0183 

18.3 

*  

360  West. 

1  000  g 

All  assayed          

Nil 

Nil. 

Nil. 

9  

540  West. 

4.48 

1,280  Chiefly  quartz,  ferric  oxide,  with 

Nil. 

0.0027 

1.35 

a  little  mica. 

h.  ... 

1,200  West. 

2  24 

1  640                                                    

Nil. 

0.0076 

7  6 

i.'.  .. 

6  East.' 

2.24 

1,356  Mostly  ferric  oxide,  with  a  little 

Nil. 

0.029 

29. 

magnetite. 

i*   . 

75  East. 

2.24 

All  assaved  

Trace. 

0.0017 

1.7 

i.:." 

360  East. 

2.24 

1  748  Chiefly  ferric  oxide        

Nil. 

Nil. 

Nil. 

a.  Very  hard,  coarse-grained,  solid  sandstone,  much  stained  with  oxide  of  iron. 

b.  Fine-grained,  hard,  solid  slate,  very  little  altered  in  any  respect. 

c.  Oxide  of  iron  from  a  cavity  between  sandstone  and  slate.    The  country  much  broken 

near  where  sample  was  taken. 

d.  Slate,  fine-grained,  very  little  altered,  very  soljd  and  hard. 

€.  Broken  sandstone,  slate,  and  oxide  of  iron,  from  a  small  fault  in  the  rock,  exposed  to  the 

surface. 

/.  White  quartz,  slightly  iron-stained,  from  small  reef-formation  about  4  in.  wide. 
g.  Hard,  fairly  coarse-grained  sandstone,  with  seams  of  ferric  oxide  along  the  bedding-planes. 
h.  Slate,  sandstone,  and  ferric  oxide  from  broken  country,  filling  a  slight  fault. 
i.  Ferric  oxide,  coating  slate  and  sandstone. 
j.  Hard,  solid,  fine  grained  slate,  little  altered. 
k.  Hard  sandstone,  much  stained  with  ferric  oxide. 
In  the  case  of  samples  marked  *  the  whole  of  the  sample  left  after  concentration  was  assayed 

after  the  concentrates  had  been  examined. 

Walhalla. — A  good  cross-section  of  the  gold-bearing  rocks  of 
Walhalla  is  extended  along  both  sides  of  the  Walhalla  creek, 
where  the  cliffs  rise  steeply  from  300  to  600  ft.  Analyses  of 
specimens  are  given  in  Table  III. 

Ballarat. — A  deep  cutting,  about  0.25  mile  long,  running 
east,  across  the  strike  of  the  rocks,  from  the  summit  of  Sov- 
ereign hill,  in  this  district,  presented  a  good  cross-section  of 
the  country-rock  near  the  surface.  Table  IV.  gives  the  result 
of  analyses. 

Otago. — Examinations  of  country-rock  from  the  deep  region 
in  Otago  were  confined  to  one  district,  Macetown  ;  but  quartz 
•reefs  have  been  worked  at  various  depths  in  different  parts  of 
the  province;  and  vadose  samples  were  taken  from  three  other 
Otago  districts  besides  Macetown,  namely,  Waipori,  ISTenthorn 
and  Saddle  Hill.  In  every  case  the  country-rock  is  either  phyl- 
lite  or  mica-schist.  Table  Y.  gives  the  analyses  of  13  samples. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


187 


TABLE  IV. — Analyses  of  Country- Rock  from  the  Vadose  Region  of 
the  Ballarat  Gold-Field,  Victoria. 


&*« 

•c 

*-t     i 

2  >• 

°5  0 

c 

o 

jg 

.2 
& 

®^  V 

ss« 

6£§ 

1 

Weight  of  Concentrates  Obtained. 

|« 

-2J3 
G  O, 

o 
O 

<tH 

O 

T3  C 

?°P 

I 

£o>2 
2«<2 

2 

g3 
COO 

2 

0 

<=^« 

'O  « 

s§-= 

'£ 

£ 

?-l 

<u  o 
£H 

Feet. 

Pounds. 

Grains. 

Grains. 

Grains. 

<i  
b  

8  East. 
60  East 

1.12 
2  24 

684  Mostly  ferric  oxide  and  quartz  
1  050        

Nil. 

Nil 

0.037 
0  017 

74 
17 

c 

140  East 

4  48 

Nil 

0  0063 

3  15 

d 

186  East 

4.48 

1  4S5     .         

Nil 

0  0023 

1  15 

€ 

240  East 

4  48 

2  116 

Nil 

0  0016 

0  8 

f 

360  East 

2  24 

1,642  

Nil' 

0  0058 

2  9 

g 

500  East 

1  12 

856 

Nil 

Nil 

Nil 

a.  Oxide  of  iron,  with  a  little  quartz  and  loose  sand,  formed  by  the  disintegration  of  sand- 

stone. 

b.  Oxide  of  iron,  from  a  joint  separating  two  adjacent  strata  of  sandstone. 

c.  Soft  sandstone,  pure  white. 

d.  White  pipe-clay,  with  yellow  streaks.    A  product  of  the  decomposition  of  slate. 

e.  Soft,  fine-grained  pipe-clay,  colored  from  red  to  purple  by  oxide  of  iron. 
/.  Oxide  of  iron,  mixed  with  soft  sandstone  and  clay  from  broken  country. 
g.  Oxide  of  iron,  forming  clay  parting  between  two  beds  of  pipe-clay. 

Otago. — Samples  from  Districts  Remote  from  Auriferous  Lodes. 
— Vadose  samples  were  also  taken  in  Otago,  far  from  any  au- 
riferous lodes.  Previous  assays  having  shown  that  the  mate- 
rials most  likely  to  contain  gold  were  the  broken  rock,  iron 
oxide,  etc.,  filling  fault-fissures,  the  samples  were  taken  of  such 
materials  only.  If  all  the  mica-schists  of  the  Otago  gold-field 
contained  gold,  some  of  it  would  be  carried  by  percolating 
water  into  such  crevices,  and  lodge  there  with  the  ferric  oxide. 
The  analysis  of  samples  at  a  long  distance  from  any  auriferous 
reef  is  specially  interesting,  since,  as  will  be  seen  in  the  last  three 
tables,  deposits  of  ferric  oxide  in  the  vadose  region,  even  at  a 
considerable  distance  from  a  reef,  were  nearly  always  auriferous. 

A  good  section  of  the  favorable  rock  (the  middle  division  of 
the  foliated  schists  already  mentioned),  in  which,  however,  for 
several  miles,  no  gold-bearing  reef  has  yet  been  discovered,  is 
exposed  by  the  "  Skipper's  "  road  from  Queenstown  to  Skip- 
per's creek.  This  road  is  cut  around  almost  vertical  cliffs  for 
several  miles,  on  the  north  side  of  the  Skipper's  range.  Nine 
samples  of  broken  rock  and  ferric  oxide  from  joints,  cracks,  and 
faulted  country  in  these  cuttings  were  analyzed,  with  the  results 
shown  in  Table  VI. 

Lake  Wakatipu. — Fourteen  vadose  samples  of  little-altered 
Upper  Devonian  and  Carboniferous  rocks  were  taken  from  the 
western  shore  of  Lake  Wakatipu.  No  gold  was  found  in  them. 
The  examination  is  reported  later  on,  under  the  head  of  "  Gold 
in  Marine  Sediments." 


188 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


TABLE  Y. — Analyses  of  Rocks  from  the  Vadose  Region  of  Otago  y 

New  Zealand. 


,2 

la 

Distance  from  Au- 
riferous Reef. 

II 
^ 

P 
^ 

Locality. 

Weight  Taken. 

Weight  of 
Concentrates. 

Percentage  of 
Sulphur. 

Yield  of  Gold. 

Yield  of  Gold  per 
Ton  of  Country- 
Rock. 

a  
ft     , 

Feet. 
4 

20 

Feet. 
40 

40 

From  a  tunnel  driven 
along  the  Bella  reef, 
Waipori,  Otago. 

Do.... 

Pounds. 

4.48 

4.48 

Grains. 
643  Mostly 
mica  and 
oxideof 
iron. 
1,246  

Nil. 
Nil. 

Grains. 
0.0016 

0.0107 

Grains. 

0.8 

5.35 

r  
d  

g 

3 

60 

35 

50 
30 

60 

Do  
Near   the  mouth  of  the 
low-level    tunnel,  Tip- 
perary  G.  M.  Co..  Mace- 
town,'  Otago. 

4.48 
4.48 

2  24 

1,675  
1,217  

1  176 

Nil. 
Nil. 

Trace 

0.065 
Nil. 

0  0179 

32.55 

Nil. 

17  9 

f 

20 

70 

but  25  ft.  nearer  the  reef. 

2  24 

1  030 

Trace 

0  0086 

8  6 

n 

1GO 

35 

ft.  nearer  the  reef. 
From  near  the  mouth  of 

1  12 

774  ' 

Nil 

0  0018 

8.6 

h 

90 

85 

the    low-level    tunnel, 
Premier  G.  M.  Co.,  Mace- 
town,  Otago. 
From   the   same  tunnel 

2  24 

617        

Trace 

Nil. 

Nil. 

i 

65 

95 

but  nearer  the  reef  and 
at  a  greater  depth. 

2  24 

612 

Nil 

0  0013 

2.6 

3  
It 

6 
3 

40 
40 

but  15  ft.  nearer  the  reef. 
From  the  Bonanza  reef, 
Nenthorn,  Otago,  with- 
in 6  ft.  of  a  rich  auri- 
ferous reef. 

From  the  same  mine   at 

2.24 
2.24 

1,738  Princi- 
pally 
mica  and 
ferric 
oxide. 
1  217  

0.027 
Nil. 

0.0016 
0.0073 

n.e 

7.3 

I  . 

600 

20 

the    same    depth,   but 
nearer  the  reef. 
From  a  cliffwest  of  Saddle 

1  V> 

726        

0  008 

Nil. 

Nil. 

m 

200 

20 

Hill  reef,  near  Duned  in. 
From  the  same  locality 

224 

1  078  

Nil. 

0.0005 

0.5 

but  nearer  reef. 

a,  b,  c.  Mica-schist,  yellowish  color,  soft,  very  much  decomposed. 

d.  Hard  mica-schist,  with  quartz  bands  0.5  in.  wide,    Specimen  much  stained  with  oxide  of 

iron. 

e.  Ferric  oxide  from  a  slight  fault  in  mica-schist,  showing  a  little  quartz  in  veins. 
/.  Quartz  and  ferric  oxide  from  broken  country. 

g.  Solid  mica-schist,  much  stained  by  ferric  oxide. 

h.  Ferric  oxide  and  broken  mica-schist,  from  a  small  fault. 

i.  Solid  mica-schist,  much  discolored  by  ferric  oxide. 
j,  Jc.  Much  decomposed,  very  soft  mica-schist,  stained  brown  with  ferric  oxide. 

I.  Ferric  oxide  filling  the  space  in  joint-planes  of  phyllite,  which  forms  the  country-rock  of 

this  reef. 
m.  Decomposed  phyllite,  much  stained  with  ferric  oxide. 

Ohinemuri  District,  Thames. — The  samples  collected  for  me 
from  the  vadose  region  in  the  Ohinemuri  district,  in  the  south- 
ern part  of  the  Thames  gold-field,  differ  somewhat  from  the 
oxidized  samples  of  other  gold-fields.  All  those  analyzed  are 
highly-altered  andesites ;  and,  in  many  cases,  even  when  most 
oxidized,  they  contain  much  pyrite.  This  sometimes  doubtless 
represents  the  pyrite  found  in  the  propylites  of  the  deep  region 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


189 


TABLE  VI. — Analyses  of  Samples  from  Skipper's  Road,  near 
Lake  Wakatipu,  Otago. 


oJ 

"p. 

Distance  from  Au- 
riferous Reef. 

|| 

Locality. 

Weight  Taken. 

Weight  of 
Concentrates. 

Percentage  of 
Sulphur. 

Yield  of  Gold. 

Ig 

1  

i 

At  least  2  or  3 
miles. 

About  0  25 

Feet. 
50 

80 

All  these 
samples  were 
taken  from  a 
deep  cutting 
on  the  Skip- 
pers' road. 

Pounds. 
2.24 

2.24 

Grains. 
1,127  Chiefly 
ferric  oxide 
and  mica. 

1,416  With  a  little 

Nil. 
Nil. 

Grains. 
Nil. 

Nil. 

Grains. 
Nil. 

Nil. 

i" 

mile  from  a. 
At  least  1  mile. 
About  1  000 

so 

2.24 
•)  04 

pyrite. 
1.723..!..  
1  096  With  a  good 

Nil. 
1  384 

Nil. 
Nil 

Nil. 

Nil 

e  .... 

yd.  from  c. 
From  near 

40 

2.24 

percentage 
of  sulph'd's. 
834  Showed  no 

Nil. 

Nil. 

Nil. 

f 

sample  d. 
About  3  miles 

20 

224 

pyrite. 

1  568                . 

Nil 

Nil 

Nil 

40 

0  24 

817 

Trace 

Nil 

Nil 

sample/. 

10 

1  12 

716 

Nil 

Nil 

Nil 

i* 

15 

618 

Nil 

Nil 

Nil 

a.  Ferric  oxide  from  joint-planes. 

6.  Broken  rock;  quartz  and  mica,  with  much  contorted  mica-schist,  filling  a  fissure  18  in. 
wide. 

c.  Broken  rock  ;  quartz  and  mica. 

d.  Broken  rock,  but  the  sample  contained  a  few  large  crystals  of  pyrite,  somewhat  decom- 

posed to  ferric  oxide. 

e.  Broken  rock,  but  showed  no  pyrite. 

f.  Quartz  and  broken  mica-schist  and  ferric  oxide,  from  a  fault-fissure  or  lode-formation, 

about  1  ft.  wide,  in  mica-schist. 

g.  Quartz  and  broken  mica-schist. 

h.  Ferric  oxide,  filling  joint-planes  in  broken  mica-schist. 

i.  Quartz-interlaminations,  about  2  in.  wide,  in  mica-schist,  much  stained  with  ferric  oxide. 
In  the  case  of  sample  marked  *  the  whole  of  the  sample  left  after  concentration  was  assayed 
after  the  concentrates  had  been  examined. 


in  this  district ;  but,  from  the  mode  of  its  occurrence,  I  am  in- 
clined to  think  the  greater  part  of  it  is  due  to  the  oxidation  of 
the  older  pyrite  to  ferrous  and  ferric  sulphate,  and  the  subse- 
quent reduction  of  such  sulphates  by  organic  matter.  I  have 
therefore  called  it  "  secondary"  pyrite.  (The  bullion  associated 
with  it  does  not  carry  the  abnormally  high  percentage  of  silver 
which  was  noticed  in  the  bullion  from  the  sulphides  of  the 
deep  region — a  fact  which  should  repay  further  investigation, 
and  might  throw  important  light  upon  the  solution  and  re-pre- 
cipitation of  gold  and  silver  by  natural  agents.)  Table  VII. 
gives  the  results  of  the  analyses  of  these  samples. 


190 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


TABLE  VII. — Analyses  of  Samples  from  the  Vadose  Region  of  the 
Ohinemuri  District,  Thames,  New  Zealand. 


g 

i 

1                             I 

. 

fe 

fl 

Q 

*o 

'O 

£> 

a> 

d 

A 

s 

^o   . 

J=  J; 

~  t4_; 

Locality. 

1 

Weight  of 
Concentrates. 

i 

Id 
If 

02 

1 

S* 

el 

2 

2 

2  | 

0)   — 

2 

2  §. 

Q 

6T 

to 
'5 

H         £ 

S 

> 

^ 

£ 

FeetT 

Feet. 

Pounds. 

Grains.               Grains. 

Grains. 

Grains.1  Grains. 

a.... 

10 

30 

From  a  cliff  on;      4.48 

1,634  

0.0014 

0.7 

0.0018 

(1   Q 

the    tramway    be-| 
tween   the   Crown 

mine   and   Karan- 

gahake,  Thames. 

6  

20 

180 

From  a  fault. 

1.12 

All  assayed. 

0.009 

18 

0.0036  i       7.2 

c  

20 

350 

From  a  fault. 

4.48 

1,065  With   a 

0.0062 

3.18 

0.0054 

2.7 

good  per- 

cent age 
of  pyrite. 

d.... 

30 

120 

East  of  the  Ma- 
ria  reef,  Karanga- 

4.48 

873  With  a     Nil. 
good  pro-  i 

Nil. 

Nil. 

Nil. 

hake,  Thames. 

portion! 

of  pyrite.( 

e  

80 

3         Great  Woodstock 

1.12 

All  assayed. 

0.0095 

19 

0.0034 

6.8 

tunnel,  Karanga- 
hake,  Thames. 

/•..... 

10 

60    !  From  a  cliff  on  the       2.24 

All  assayed.       0.0013 

1.3 

0.0042  !      4.2 

Waitawheta   river, 

' 

near  the  Crown 

mine,  Thames. 

fir  

60 

24 

Near    the   Grace       4.48 

1,372  0.0063  |    3.15 

0.0048 

2.4 

Darling  reef,  Wai- 

tekauri,  Thames. 

h  

60 

30 

Foot-wall  side  of 

4.48 

846  With  a     Nil. 

Nil. 

Nil. 

Nil. 

Crown  reef. 

large  pei-! 

centage  of 

sulphides.1 

i  

25 

600 

200  yd.  off  hang- 

2.24 

617  Nearly   0.0093 

9.3 

0.0126 

12.6 

ing-wall  side  of  the 

all  pyrite. 

Crown  reef,  10  ft. 

above  the  Waita- 

wheta river. 

3  

10 

660 

From  a  fault  ex-       1.12 
posed  on  the  tram- 

All  assayed. 

0.0071 

14.2 

0.0014         2.8 

way  between  the 
Crown  mine  and 

Karan  gah  ake  , 

Thames. 

a.  Nearly  white  propylite  ;  showed  a  good  percentage  of  pyrite. 

5.  Ferric  oxide  and  higher  oxides  of  manganese,  with  a  little  quartz. 

c.  Solid,  hard  andesite,  oxidized  to  brown  color  on  outside.    Showed  a  good  deal  of  pyrite. 

d.  Hard,  greenish  hypersthene-andesite.    Showed  a  good  deal  of  pyrite. 

e.  Ferric  oxide  and  higher  oxides  of  manganese,  from  a  vein  near  the  foot-wall  of  the  Great 

Woodstock  reef. 

/.  Andesite  ;  brown,  much  decomposed.    No  pyrite  visible. 
g.  Decomposed  andesite  and  ferric  oxide,  from  a  fault. 
h.  Grayish-white  andesite,  much  oxidized  on  the  outside,  but  showing  pyrite  freely  when 

broken. 

i.  Nearly  white,  very  siliceous  rhyolite.    Showing  pyrite  freely. 
j.  Ferric  oxide  and  higher  oxides  of  manganese. 

Remarks. — These  examinations  show  a  striking  difference  in 
gold-contents  between  the  vadose  and  the  deep  region  of  the 
same  district.  Figs.  1  and  2  show  this  difference  graphically, 
in  curves  plotted  for  the  vadose  samples  and  for  samples  from 
the  deep  region  (900-ft,  and  1,422-ft.  levels)  of  the  Walhalla 
Long  Tunnel  mine. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  191 

In  the  deep  region,  as  has  been  shown,  gold  was  obtained 
only  when  pyrite  was  present  in  the  rock ;  and  when  such  py- 
rite  occurred  at  a  considerable  distance  from  the  reef,  it  was 
seldom  gold-bearing.  In  the  vadose  region,  on  the  contrary, 
the  country-rock  was  found  to  be  impregnated  with  gold  to  a 
much  greater  distance  from  the  reef,  and  to  a  much  greater 
degree. 

It  is,  of  course,  possible  that  some  of  the  gold  found  in  the 
vadose  country-rock  was  carried  into  it  mechanically  by  per- 
colating surface-water,  and  its  presence  may  therefore  be  no 
proof  of  the  solution  and  re-precipitation  of  gold.  But  in  view 
of  the  positions  from  which  most  of  the  samples  were  taken,  I 
think  the  results  indicate  that  such  solution  and  re-precipitation 
have  gone  on  to  a  considerable  extent  in  the  vadose  region — 
the  gold  being  in  all  probability  derived  from  higher  parts  of 
the  lode,  which  have  long  since  disappeared  through  surface- 
detrition. 

CHAPTER  VII. — THE  ORIGIN  OF  GOLD  IN  STRATIFIED  DEPOSITS. 

The  country-rocks  of  nearly  all  the  chief  Australian  gold- 
fields  are  more  or  less  altered  sedimentaries,  originally  depos- 
ited in  marine  basins.  Hence,  writers  on  the  origin  of  the  gold 
in  the  reefs  have  laid  much  stress  on  the  presence  of  minute 
quantities  of  gold  and  silver  in  sea-water.  The  argument  is 
briefly : 

Gold  exists  in  sea-water.  Palaeozoic  marine  sediments  there- 
fore contained  gold,  either  mechanically  entangled  in  them,  or 
precipitated  with  them  by  organic  matter,  which  undoubtedly 
existed  in  the  ancient  eeas.  These  horizontal  deposits  being 
subsequently  tilted  and  fractured,  their  gold  and  silver  were 
re-dissolved  by  percolating  waters  and  re-precipitated  in  the 
lode-fissures  where  they  are  now  found. 

This  has  been  the  thesis  of  not  a  few  ingenious  speculations, 
backed  sometimes  by  chemical  equations,  but  not  by  chemical 
analyses. 

In  1851,  Malaguti  and  Durocher  announced  the  discovery 
of  silver  in  sea-water,  and  made  a  quantitative  estimation  of  it, 
namely,  1  mg.  in  100  1.  (or  0.155  grain  per  ton).  But  they  did 
not  report  any  gold.  , 


192 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


In  1872,  E.  Sonstadt25  discovered  gold  ill  sea-water  from 
Ramsey  bay,  on  the  coast  of  the  Isle  of  Man.  He  did  not  de- 
termine the  quantity,  but  said  it  was  certainly  less  than  1  grain 
per  ton.  Strange  to  say,  many  writers  who  have  used  this  dis- 
covery as  a  basis  for  theoretical  speculation  have  represented 
Sonstadt  as  having  found  1  grain  per  ton.26 


30 


10 


1200 
West 


1000 


800 


600 


400 


200 


200 


Feet  400 
East 


FIG.  1. — YIELD  OF  GOLD  PER  TON  OF  COUNTRY-ROCK  IN  VADOSE  KEGION. 

(From  Diagram  8  of  Original  Paper,  Comparison  of  Yield  of  Vadose  Region  of 

Walhalla,  Victoria,  with  Deep  Circulation.     See  Tables  III.  and  IV. ) 

So  far  as  I  am  aware,  no  attempt  has  been  made  to  verify 
Sonstadt's  discovery,  and  to  determine  accurately  the  amount 
of  gold  in  sea-water,  or  to  test  his  statement  that  this  gold  is 

25  On  the  Presence  of  Gold  in  Sea- Water,  Chemical  News,  vol.  xxvi.,  No.  671, 
p.  159  (Oct.  4,  1872). 

26  Thus  James  Park  in  his  report  on  the  Thames  Gold-Field  [New  Zealand 
Mining  Report  for  1893,  Appendix]  says  (p.  65)  :  "Sonstadt  was  the  first  to  show 
that  every  ton  of  sea-water  contains  a  grain  of  gold."     A  later  writer,  noting, 
perhaps,  that  Sonstadt  found  "less  than  a  grain,"  is  very  scrupulous,  and  fixes  the 
amount  at  0.9  grain  ! 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


193 


not  precipitated  by  ordinary  reducing-agents,  by  reason  of  the 
presence  in  sea-water  of  iodate  of  calcium.27 

Methods  of  Detecting  Gold  in  Sea-  Water. 

Sonstadt's  Methods. — Sonstadt  gave  three  methods  for  the  de- 
tection of  gold  in  sea-water,  two  of  which  he  recommended  as 
easily  applicable.  In  the  first  of  these,  150  to  200  cc.  of  sea- 


d± 


150 


100 


50 


*?• 


Feet 


FIG.  2. — YIELD  OF  GOLD  PER  TON  OF  COUNTRY-ROCK  AT  900-FT.  LEVEL 

AND  1,422-FT.  LEVEL. 

(From  Diagram  9  of  Original  Paper,  Comparison  of  Yield  of  Vadose  Region  of 
Walhalla,  Victoria,  with  Deep  Circulation.     See  Tables  III.  and  IV.) 

water  is  acidulated  with  hydrochloric  acid,  ferrous  sulphate  is 
added,  and  the  water  is  concentrated  by  boiling.  The  film  of 
ferric  oxide  found  in  the  bottom  of  the  dish  is  treated  with 

i7  Since  my  experiments  were  made,  I  have  learned  from  Mr.  Eickard's  paper 
On  the  Origin  of  the  Gold-Bearing  Quartz  of  the  Bendigo  Reefs  (Trans.,  xxii., 
308)  that  Miinster  has  found  gold  in  the  sea-water  of  Christiania  fiord,  and  has 
estimated  the  amount.  I  find  also  that  Prof.  A.  Liversidge  has  estimated  that  the 
sea- water  off  the  coast  of  N.  S.  Wales  contains  0.5  grain  of  gold  to  the  ton.  (See 
his  paper,  read  before  the  N.  S.  W.  Royal  Society,  Oct.  2,  1895,  On  the  Amount 
of  Gold  and  Silver  in  Sea- Water. ) 

13 


194  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

chlorine-water,  and  the  solution  obtained  is  tested  for  gold  with 
tin  chloride.  In  the  second  method,  a  small  quantity  of  baric 
chloride  is  added  to  the  sea-water,  and  both  gold  and  silver  are 
found  to  be  precipitated. 

The  first  method  I  tried  upon  water  from  the  Pacific,  at  St. 
Clair  head,  near  Dunedin,  and  obtained  with  tin  chloride  a  dis- 
tinct coloration,  doubtless  due  to  gold.28  But  I  found  it  im- 
possible to  obtain  beads  of  gold  by  fusing  with  borax  and  pure 
lead,  as  Sonstadt  directs.  (This  is  not  surprising,  since  my 
subsequent  determinations  would  give,  as  the  quantity  of  gold 
in  200  cc.  of  this  sea-water,  less  than  0.000012  grain.)  The 
necessity  of  boiling  makes  this  method  unsuitable  for  the  treat- 
ment of  samples  large  enough  to  yield  a  weighable  bead  of  gold. 

I  therefore  tried  the  precipitation  with  baric  chloride.  Son- 
stadt makes  the  remarkable  assertion  that  in  order  to  precipi- 
tate the  gold,  the  baric  chloride  does  not  need  to  be  added  in 
sufficient  quantity  to  precipitate  as  baric  sulphate  all  the  solu- 
ble sulphates  in  the  sea-water,  but,  on  the  contrary,  that  the 
amount  added  to  a  liter  of  sea-water  need  not  exceed  that  re- 
quired to  form  about  1  grain  of  precipitate.  Baric  sulphate 
being  one  of  the  least  soluble  of  salts,  this  statement  seems  in- 
explicable ;  nevertheless,  I  have  been  convinced,  whatever  be 
the  explanation,  that  Sonstadt's  method  is  as  effective  as  if  the 
whole  of  the  soluble  sulphates  were  precipitated  as  baric  sulphate. 

He  explains  the  precipitation  by  baric  chloride  by  supposing 
the  gold  to  be  present  as  an  aurate.  To  test  this  question,, 
artificial  sea-water  was  prepared,  and  the  aurate  of  potassium 
was  added  to  it.  Subsequent  treatment  with  baric  chloride 
precipitated  no  gold.  The  experiment  was  repeated,  with  the 
same  result. 

It  seems  unlikely,  therefore,  that  the  gold  exists  in  sea-water 
as  an  aurate.  I  confess  that  I  can  form  no  conception  of  its 
state  of  combination.  The  subject  would  repay  a  more  thor- 
ough investigation. 

The  Author's  Method. — Having  been  led,  by  evidence  which 
I  will  not  here  repeat,  to  doubt  whether  the  precipitation  with 
baric  chloride  was  complete,  I  tried  a  different  one,  which,  if 

28  The  experiment  is  more  successful  with  the  modification  of  the  tin  chloride 
test  prepared  by  T.  K.  Rose,  Chemical  News,  vol.  Ixvi.,  No.  1723,  p.  271  (Dec.  2, 

1892). 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


195 


successful  at  all,  would  certainly  precipitate  all  the  gold  present. 
All  ordinary  salts  of  gold  are  reduced  to  the  metallic  state  by 
moderate  heating.  Applying  this  principle  first  to  an  artificial 
solution,  I  added  to  112  Ib.  of  artificial  sea- water29  ten  times 
as  much  calcic  iodate  as  Sonstadt  found,  and  a  solution  of 
auric  chloride  in  sodium  chloride,  containing  0.005  grain  of 
gold,  so  that  the  water  would  contain  0.1  grain  of  gold  per  ton. 
This  solution  was  allowed  to  stand  in  a  dark  place  for  a  week, 
that  the  gold  might  have  time  to  form  possible  new  combina- 
tions. The  whole  was  then  evaporated ;  the  mixed  salts  (over 
4  Ib.)  were  heated  dull  red  and  lixiviated  with  water ;  the  in- 
soluble residue  (123  grains)  was  fused  with  borax  and  pure 
litharge,  and  0.0043  grain  of  gold  was  obtained.  The  experi- 
ment was  repeated,  the  gold  being  added  as  an  iodate,  dis- 
solved in  excess  of  potassic  iodate;  and  in  this  case  0.0052 
grain  of  gold  was  recovered.  (The  slight  excess  may  have 
been  due  to  a  small  particle  of  the  cupel  remaining  in  the  but- 
ton. It  was  not  due  to  silver  in  the  litharge.) 

The  method  was  then  applied  to  actual  sea-water;  only  the 
sample  was  doubled  in  weight,  to  allow  for  the  smaller  propor- 
tion of  gold.  The  mixed  salts  (about  8  Ib.)  resulting  from  the 
evaporation  of  0.1  ton  of  sea-water  were  heated  dull  red  and 
lixiviated,  and  the  residue  (principally  sand,  with  a  little  oxide 
of  iron)  was  fused  and  cupelled  as  before.  The  weight  of  pure 
gold  obtained  from  0.1  ton  of  sea- water  was,  in  the  first  ex- 
periment 0.0065,  and  in  the  second  0.9071  grain.  In  both 
cases,  the  prill  contained  absolutely  no  silver. 

The  following  table  summarizes  the  experiments  above  de- 
scribed : 

Determinations  of  Gold  in  Sea-  Water. 


Method. 

Sea- 
Water. 

Gold  Ob- 
tained. 

Gold  per 
Ton  . 

1.  Sonstadt's  (baric  chloride)  : 
a.   All  sulphates  precipitated           ..                 \ 

Pounds. 
224 

Grain. 
0.0061 

f\  AAOQ 

Grain. 
0.061 

Or\na 

b.  Small  proportion  of  sulphates  precipitated  -< 

224 
224 

0.0074 
0.0078 

0.074 
0.078 

2.  Evaporation  and  reduction   of  gold  in  residue  f 
by  heating                                                                \ 

224 
224 

0.0065 
0  0071 

0.065 
0  071 

Average  per  ton.... 

0.071 

'9  Prepared  according  to  the  analysis  by  Roscoe  and  Schorlemmer. 


196  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

I  have  said  nothing  concerning  the  silver  in  sea-water.  Pre- 
cipitation by  baric  chloride  certainly  saves  some  silver,  but 
only  about  one-fourth  as  much  as  was  reported  by  Malaguti 
and  Durocher.  Probably  the  precipitation  is  not  complete. 

The  Precipitation  of  Gold  in  Marine  Sediments. 

Since  gold  exists  in  sea-water,  it  seems  reasonable  to  believe 
that  it  is  precipitated  at  the  present  time  by  natural  reducing- 
agents.  Those  writers  who  trace  the  metallic  contents  of  lodes 
to  metals  dissolved  in  sea-water  assume,  indeed,  that  such  a 
precipitation  is  constantly  going  on ;  but  experimental  proof  of 
this  assumption  is  lacking.  I  have  attempted  to  investigate 
the  question  in  two  ways : 

1.  By  the  examination  of  coast-sediments,  now  being  depos- 
ited under  conditions  favorable  to  the  reduction  of  gold  from 
the  sea-water. 

2.  By  the  introduction  into  sea-water  of  reducing-agents  such 
as  naturally  occur  along  the  coasts  at  the  present  time,  and  a 
subsequent  examination  for  precipitated  gold. 

Examination  of  Coast-Sediments. — To  secure  trustworthy  re- 
sults, the  whole  of  the  drainage-basin  to  the  erosion  of  which 
the  sediments  are  due  should  consist  of  non-auriferous  rocks,  so 
that  we  may  be  sure  that  any  gold  detected  did  not  come  from 
the  land.  Otago  harbor,  on  the  upper  part  of  which  Dunedin 
is  located,  satisfies  tjiis  requirement.  The  Leith  and  other 
small  streams  entering  the  harbor  flow  wholly  through  basic 
Tertiary  volcanic  rocks  which  contain  no  gold.  At  the  same 
time  the  shores  are  more  or  less  covered  with  timber,  so  that 
organic  matter  is  abundant  in  the  sediments  of  the  streams. 
The  volcanic  rocks  contain  much  iron.  Beds  of  hematite  and 
limonite  abound  along  the  shores.  The  conditions  for  the  re- 
duction of  gold  from  sea-water  are  therefore  very  favorable. 
Besides  organic  matter,  there  is  sulphide  of  iron,  produced  by 
the  action  of  the  sulphates  in  sea-wa*ter  upon  iron-salts,  forming 
sulphate  of  iron,  reducible  to  sulphide  by  organic  matter.  (As 
will  be  seen,  some  such  action  does  in  fact  take  place.  In  every 
case  the  concentrates  contained  insoluble  sulphides.) 

Analyses  were  made  of  mud  and  silt  from  different  parts  of 
Otago  harbor,  where  the  circumstances  seemed  most  favorable. 


THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 


197 


In  each  case,  from  1  to  2  cwt.  of  the  silt  was  carefully  panned 
off,  till  a  residue  of  about  1,000  grains  was  left.  This  residue 
consisted  chiefly  of  magnetite,  augite,  and  hornblende,  derived 
from  the  volcanic  rocks  of  the  coast.  The  percentage  of  sul- 
phur (insoluble  sulphides)  in  the  concentrate  was  determined 
upon  a  small  portion,  and  the  remainder  was  roasted  (giving  in 
every  case  a  strong  reaction  of  sulphur  dioxide).30  The  roasted 
material  was  then  assayed.  The  details  of  four  assays  are  given 
in  the  following  table  : 

Examination  of  Marine  Sediments. 


Sample. 

Concentrates. 

Sulphur 
in  Non- 
Magnetic 
Concen- 
trates. 

Gold 
Obtained. 

Total. 

Extracted 
by  Mag- 
net. 

a     

Grains. 
438 
1,678 

875 
586 

Grains. 
365 
916 
418 
307 

Per  Cent. 
12.38 
7.03 
16.19 
4.61 

Nil. 
Nil. 
Nil. 
Nil. 

b  :  

c    

d  

a.  Over  1   cwt.  of  black  mud,  containing  much  organic  matter,  from  Upper 
Otago  harbor,  taken  at  low  tide  near  Logan's  Point. 

b.  About  2  cwt.  of  black  mud,  containing  much  putrefying  organic  matter,  from 
the  upper  harbor,  near  the  outlet  of  a  main  sewer. 

c.  Over  1  cwt.  of  silt  from  Pelichet  bay,  where  a  small  stream  of  highly-ferru- 
ginous water  runs  into  the  bay  from  a  bed  of  hematite. 

d.  About  1  cwt.  of  silt  from  the  upper  end  of  the  harbor,  near  the'  outlet  of  a 
main  sewer  from  South   Dunedin.      It  contained   much   decomposing  organic 
matter. 


Examination  of  Wood  That  Had  Been  Lying  Under  Sea- 
Water  for  a  Long  Time.  —  Several  samples  of  wood,  which  had 
been  buried  many  years  under  sea-water  and  mud  in  Otago 
harbor  and  elsewhere  on  the  New  Zealand  coast,  were  analyzed 
for  gold.  In  each  case  from  '10  to  30  Ib.  of  the  wood  was 
burned,  and  the  ashes  were  fused  with  pure  litharge. 

The  results  are  given  in  the  following  table  : 

0  When  the  magnetite  was  removed  by  means  of  a  magnet,  the  remainder  did 
not  show,  under  the  microscope,  recognizable  crystals  of  pyrite  ;  but  the  presence 
of  pyrite  was  certainly  proved  by  roasting,  and  by  the  sulphur-determination. 


198 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 


Analyses  of  Wood  for  Gold. 


Sample. 

Description. 

Weight 
Burned. 

Results. 

a. 

Kauri  plank,  which  had  lain  in  Dunedin  harbor  at 

Pounds. 
12 

Nil. 

least  15  years.     Other  parts  much  decomposed. 

6. 

Pine  plank  from  Catlin's  estuary,  east  coast  of  Otago. 

20 

Nil. 

c. 

Part  of  a  ship  wrecked  20  years  ago. 
Remnant  of  manuka  pile  from  Otago  harbor.    Under 

12 

Nil.   , 

water  20  years. 

d. 

Do.,  the  decayed  part. 

10 

Nil. 

e. 

Part  of  a  pile  from  the  Vauxhall  baths,  Anderson's 

18 

Nil. 

bay,  Otago  ;  in  the  water  30  years. 

f. 

Driftwood  imbedded  in  the  mud  at  Madagascar  beach, 

16 

Nil. 

west  coast  of  Otago. 

Attempts  to  Precipitate  Gold  from  Sea-  Water. 

These  experiments  were  confined  to  such  natural  reducing- 
agents  as  might  naturally  occur  along  the  coast  at  the  present 
day,  namely,  sulphides  of  iron  (chiefly  formed  by  the  reduction 
of  the  sulphates  of  sea-water),  and  carbonaceous  matter  of 
various  kinds. 

To  make  a  suitable  filter,  an  earthenware  pipe  4  in.  in  diam- 
eter and  1  ft.  long  was  closed  at  the  ends  with  strong  cloth. 
Next  the  cloth  was  placed  a  loose  plug  of  asbestos,  about 
2  in.  in  thickness,  wrapped  in  linen,  and  the  middle  part  of  the 
pipe  was  filled  with  coarsely-broken  earthenware,  with  which  the 
reducing-agent  was  mixed.  The  reducing-agents  used  were 
animal  charcoal,  wood-charcoal,  soot,  and  sulphides  of  iron, 
copper,  and  lead — the  latter  being  prepared  by  precipitating 
sulphates  of  iron  and  copper  and  the  nitrate  of  lead,  in  order 
to  make  sure  that  they  should  contain  no  gold. 

Pelichet  bay  is  separated  from  the  upper  reaches  of  Otago 
harbor  by  an  embankment,  in  which  an  opening  about  20  ft. 
wide  has  been  left.  Through  this  passage  the  sea  runs  with 
considerable  force  at  most  states  of  the  tide.  The  apparatus 
above  described  was  fixed  beneath  the  bridge  which  spans  this 
opening,  so  that  both  the  ebbing  and  the  flowing  current  might 
pass  through  it.  The  filter  was  kept  thus  immersed  for  periods 
varying  from  one  to  two  months.  The  reducing-agents  were 
then  taken  out,  roasted,  and  assayed. 

The  results  are  given  in  the  following  table : 


THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 


199 


Experiments  in  Reducing  Gold  from  Sea- Water. 


Experi- 
ment. 


Reducing-Agent. 


Animal  charcoal,  in  fine  pow- 
der. 


Mixture  of  pounded  charcoal 
and  soot. 

Animal  charcoal  in  lumps. 
Sulphide  of  iron. 


Remarks. 


The  greater  part  of  the  animal 
charcoal  had  been  washed 
through  the  filter,  a  The  re- 
mainder was  assayed. 

The  smaller  particles  washed 
away.  Charcoal  remained. 


The  sulphide  was  much  oxi- 
dized ;  the  whole  apparatus 
being  coated  with  ferric 
oxide. 

Very  little  altered. 

Carbonate  of  copper  found  in 
the  asbestos  filter  and  other 
parts  of  the  apparatus. 

Mixture  of  animal  charcoal,  j  Very  little  oxidation,  even  of 
soot,  sulphide  of  lead,  sul-  i  the  artificial  sulphide  of 
phide  of  copper,  and  sul-  iron,  was  noticed, 
phide  of  iron. 


Sulphide  of  lead  in  lumps. 
Sulphide  of  copper  in  lumps. 


Gold 
Found. 


Nil. 

Nil. 

Nil. 
Nil. 

•Nil 
Nil. 

Nil. 


«  After  the  first  two  attempts  the  reducing-agents  were  put  in,  not  as  powder, 
but  in  lumps  from  0.25  to  0.5  in.  in  diameter,  it  having  been  found  that  the 
strong  current  carried  the  finer  stuff  through  the  asbestos  filter. 

A  very  large  quantity  of  sea-water  must  have  passed  through 
the  apparatus  in  each  of  the  above  cases,  but  there  was  no  way 
of  estimating  it  with  precision.  In  view  of  the  negative  results 
of  all  the  experiments,  an  attempt  was  made  to  precipitate  gold 
and  silver  from  a  measured  quantity  of  sea-water.  Ten  thou- 
sand grains  of  artificial  sulphides  of  iron,  copper,  and  lead,  with 
animal  charcoal  and  wood-charcoal — all  in  fine  powder — were 
mixed  in  a  barrel  with  60  gal.  of  sea-water  taken  from  the 
Pacific  ocean  at  Tomahawk  Head,  near  Dunedin.  The  reduc- 
ing-agents were  stirred  in  the  water  for  half  an  hour,  and  the 
sediment  was  allowed  to  settle  for  some  hours.  The  clear 
water  above  was  then  decanted  off,  and  the  barrel  was  again 
filled.  This  operation  was  repeated  14  times  in  the  same  bar- 
rel, or  until  over  4  tons  of  sea-water  had  been  treated.,  The 
sediment  was  then  collected  and  roasted  at  a  dull  red  heat,  to 
incinerate  the  charcoal  and  get  rid  of  the  sulphur.  On  assay- 
ing the  residue,  no  gold  was  obtained ;  but  the  result  was  a 


200  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

bead  of  pure  silver  weighing  0.0014  grain.  I  cannot  say  cer- 
tainly whether  this  silver  (which  contained  no  gold)  came  from 
the  sea-water  or  from  the  litharge  used.  I  do  not  think  the 
latter.  If  it  came  from  the  sea-water,  however,  it  is  note- 
worthy that  the  amount  from  4  tons  represents  only  0.00035 
grain  per  ton,  or  one  five-hundredth  part  of  the  quantity  found 
in  sea-water  by  Malaguti  and  Durocher  in  1851. 

All  my  experiments  have  thus  signally  failed  to  show  any 
precipitation  of  gold  (and  have  practically  failed  as  to  silver) 
from  sea-water  by  natural  reagents.  So  far '  as  they  go,  they 
lend  no  support  to  the  theory  that  the  deposition  of  gold  and 
silver  by  such  reagents  in  marine  sediments  is  now  going  on. 

If  such  deposition  had  been  the  rule  in  former  periods,  and 
if  this  be  the  origin  of  the  gold  in  stratified  formations,  why 
should  only  a  comparatively  small  proportion  of  such  formations 
be  traversed  by  auriferous  veins  ?  This  point  has  not  escaped 
the  attention  of  Posepny.31  It  seems  to  me  that  important  evi- 
dence may  be  drawn  from  the  examination  of  stratified  rocks 
known  to  be  consolidated  marine  sediments,  but  the  lodes  in 
which  have  not  proved  auriferous.  Table  VI.  gives  an  exam- 
ination of  nine  samples  from  Skipper's  road,  east  of  Lake 
Wakatipu,  Otago,  an  area  in  which  the  rocks  are  known  to 
belong  to  the  middle  division  of  the  foliated  mica-schists  (the 
favorable  country-rock  for  gold  in  Otago),  but  in  which  no  au- 
riferous reefs  had  hitherto  been  discovered.  Only  those  parts 
(e.  g.,  fillings  of  veins  and  seams,  etc.)  particularly  favorable  to 
the  deposition  of  gold  were  examined,  but  no  gold  was  found 
in  any  of  the  samples. 

A  second  series  of  examinations  was  made  on  samples  from 
the  west  shore  of  Lake  Wakatipu,  which  is  largely  occupied 
by  rocks  of  the  Maitai  (Carboniferous)  and  the  Te  Anau  (Upper 
Devonian)  series.  These  rocks  (mostly  sandstones  and  slates) 
are  undoubted  marine  sediments,  but  no  gold  has  been  found 
in  this  area. 

If  the  gold  of  the  lodes  in  the  foliated  mica-schists  east  of 
this  lake  was  originally  deposited  from  sea-water  and  has  since 
been  collected  by  lateral  segregation,  it  is  difficult  to  under- 
stand why  gold  should  not  have  been  deposited  in  the  marine 
sediments  west  of  the  lake  also. 

31  Genesis  of  Ore-Deposits,  Trans.,  xxiii.,  307  (1893). 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  201 

I  therefore  examined  16  samples  of  quartz,  ferric  oxide,  etc., 
from  the  two  series  above  named,  where  they  are  exposed  north 
and  south  of  the  Greenstone  river.  There  were  4  samples  of 
fine-grained  blue  slate;  6  of  ferric  oxide  from  joints  and  fis- 
sures; 4  of  small  quartz  veins,  none  of  which  contained  sul- 
phides ;  2  of  slate  containing  large  crystals  of  pyrite,  amount- 
ing in  weight  to  254  grains  for  the  two  samples. 

No  trace  of  gold  or  silver  was  found  in  any  of  these  samples. 

CHAPTER  VIII. — SUMMARY  OF  RESULTS. 
[The  recapitulation  of  the  various  results  recorded  in  the 
preceding  chapters  is  here  omitted,  to  save  space.] 

Bearing  of  these  Results  on  the  Origin  of  Auriferous  Lodes. 

When  I  began  this  work,  seven  years  ago,  I  was  strongly 
inclined  to  believe  that  the  lateral-secretion  theory  afforded 
the  most  reasonable  explanation  of  the  origin  of  auriferous 
deposits  in  these  colonies ;  but,  as  the  result  of  each  series  of 
examinations  appeared,  I  was  forced  to  the  following  conclu- 
sions : 

If  any  reliance  can  be  placed  on  the  examinations  detailed 
in  the  foregoing  chapters,  they  seem  to  indicate  that  the  gold 
of  many  lodes  of  the  chief  mining-districts  of  New  Zealand, 
Victoria,  and  Queensiland  is  due,  not  to  lateral  segregation  from 
the  adjacent  country-rock,  but  to  solutions  ascending  from  some 
rock  deeper  than  any  now  exposed  at  the  surface  in  any  part  of 
these  colonies. 

I  am  not  concerned  with  the  question  whether  this  source  is 
the  vague  "  barysphere,"  with  its  somewhat  apocryphal  con- 
tents of  heavy  metals.  I  have  simply  to  note  that  a  series  of 
laborious  and  careful  examinations  has  failed  to  find  it  in  the 
rocks  of  the  "  lithosphere." 

What  may  be  the  value  of  these  investigations  in  the  study 
of  the  general  question  of  the  origin  of  ore-deposits  I  leave  the 
reader  to  judge,  being  myself  content  to  quote  the  opinion  of 
Professor  Stelzner,  of  Freiberg,  no  mean  investigator  of  that 
larger  question,  that 

"Each  increase  of  our  positive  knowledge  of  the  nature  and  mode  of  origin  of 
ore-deposits,  each  explanation  of  any  question  connected  with  such  deposits  or 
with  their  associated  country-rocks,  is  a  distinct  gain,  not  only  to  science,  but  also 
to  mining  practice."  32 

32  Concluding  sentence  of  Die  Lateraisecretionstheorie  (1889). 


202  THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 

DISCUSSION. 

(Trans.,  xxvii.,  993.) 

JOSEPH  LE  CONTE,  Berkeley,  Cal. :  I  have  read  with  some 
care  and  with  extreme  interest  the  work  of  Dr.  Don,  and  have 
no  hesitancy  in  expressing  my  high  estimate  of  its  value.  We 
have  here  an  example  of  laborious  work  undertaken  in  the  true 
scientific  spirit  and  by  right  methods.  Loose  statements  and 
rash  conjectures  are  here  brought  to  the  test  of  chemical  an- 
alyses. By  such  work  only  may  we  hope  to  reach  reliable  con- 
clusions and  finally  to  solve  our  complex  problems  presented 
by  the  concurrence  of  ore-deposits. 

Such  work  as  this  is  not  only  scientific  but  is  in  the  highest 
degree  practical;  for  while  a  crude  and  imperfect  science,  by 
interfering  with  the  results  of  approved  empirical  methods, 
may  be  positively  hurtful,  a  more  perfect  science  must  eventu- 
ally become  the  only  sure  guide  to  practice.  Such  a  more  per- 
fect science  can  only  be  reached  by  such  work  as  Dr.  Don's. 

I  am  sure  every  member  of  the  Institute  will  unite  with  me 
in  the  hope  that  Dr.  Don  will  continue  his  work,  and  that  his 
example  will  incite  others  to  similar  work. 

S.  F.  EMMONS,  Washington,  D.  C. :  I  desire  to  bear  my  hum- 
ble testimony  to  the  great  value  of  Dr.  Don's  paper  to  the  sci- 
ence of  ore-deposits,  the  thoroughness  and  accuracy  of  his 
work,  and  the  immense  amount  of  care-taking  and  tedious 
labor  which  it  represents.  The  only  regret  with  regard  to  it 
is  that  it  could  not  have  been  published  in  full.  No  more 
important  paper  in  its  line  has  ever  appeared  in  the  Transac- 
tions. Indeed,  this  is  a  line  in  which  far  too  little  has  been 
done  anywhere.  Geologists  are  not  often  sufficiently  trained 
chemists  to  carry  on  such  work,  if  they  had  the  time ;  and  for 
mining-geologists  in  our  country  the  press  of  work  in  other 
directions  is  so  great  that  they  could  not  give  the  necessary 
time  involved  in  this  class  of  work,  if  they  were  so  inclined. 
The  chemist,  on  the  other  hand,  is  rarely  enough  of  a  geolo- 
gis",  or  so  placed,  as  to  get  sufficient  field-experience  to  keep 
thoroughly  in  touch  with  the  processes  of  nature  as  shown  in 
mine-workings.  By  an  organization  like  the  U.  S.  Geological 
Survey,  where  the  chemist  and  the  geologist  might  work  in 
harmony  for  a  common  purpose,  it  would  seem  that  investiga- 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  203 

tions  into  terrestrial  chemistry  might  best  be  carried  on ;  and 
15  years  ago,  in  connection  wich  Mr.  Hillebrand,  one  of  the 
most  thorough  inorganic  chemists  of  the  day,  I  had  planned 
such  a  line  of  experimental  work,  which  I  hoped  might  be  con- 
tinued as  part  of  the  regular  chemical  work  of  the  Survey. 
But  the  powers  that  were  willed  it  otherwise.  My  colleague, 
Mr.  Becker,  has  made  some  important  researches  in  this  line, 
especially  with  regard  to  the  natural  solvents  of  gold,  which 
do  not  appear  to  have  come  under  Mr.  Don's  notice.  Such 
work  is  necessarily  very  slow,  and  Mr.  Don's  paper,  as  he  tells 
us,  covers  the  results  of  seven  years'  labor. 

I  do  not  propose  to  discuss  Mr.  Don's  paper  from  a  chemical 
point  of  view,  but  only  to  consider  the  deductions  that  may  be 
made  from  it  from  the  geological  side ;  and  I  do  this  with  some 
hesitation,  because,  not  being  able  to  read  his  statements  in 
detail,  I  may  not  infer  correctly  what  his  actual  conclusions 
were.  I  must  say,  however,  that  he  seems  to  be  most  broad- 
minded  in  this  respect,  and  his  work  presents  a  pleasing  con- 
trast to  parts  of  the  great  paper  of  the  lamented  Posepny, 
where  the  effects  of  the  latter's  recent  contest  with  Sandberger 
seemed  to  make  him  look  at  Nature  through  ascensionistically 
colored  glasses. 

Dr.  Don's  first  and  most  important  conclusion  from  his  tests 
is  that  gold  does  not  occur  in  the  rocks  of  the  regions  investi- 
gated by  him  as  an  original  constituent  of  the  bisilicates,  and 
that  where  it  is  found  in  these  rocks  it  is  associated  with  sul- 
phides, mainly  of  iron.  His  inference  seems  to  be  that  it  can- 
not be  original  in  the  rock,  because  pyrite  is  necessarily  a  sec- 
ondary constituent,  that  is,  one  introduced  after  the  rock 
consolidated.  Now,  my  work  for  the  past  ten  years  has  been 
bringing  me  more  and  more  to  doubt  the  adequacy  of  the 
bisilicates  of  eruptive  rocks  as  a  source  of  the  metals  for  our 
ore-deposits,  and,  especially  in  the  case  of  gold,  to  look  to  the 
pyrite,  if  not  as  a  source,  as  the  visible  accompaniment.  Where 
there  is  no  pyrite  in  the  neighboring  eruptive  rocks,  I  have 
not  found  that  the  veins  are  usually  rich.  But  I  have  not, 
therefore,  abandoned  my  belief  that  eruptive  rocks,  similar  to 
those  we  see  at  the  surface,  are  the  source  of  supply  from  which 
the  great  majority  of  our  ore-deposits  have  been  concentrated. 
Pyrite  is  not  necessarily  a  secondary  constituent  in  such  rocks, 


204  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

as  seems  to  be  tacitly  assumed  by  many.  On  the  contrary, 
most  petrographers  admit  the  existence  of  primary  pyrite,. 
though  they  do  not  generally  appreciate  its  importance  in  the 
study  of  ore-deposits.  .Lindgren  has  lately  discussed  primary 
pyrites  as  a  product  of  magmatic  consolidation  in  the  gold- 
bearing  rocks33  of  California.  I  cannot  even  feel  absolutely 
sure,  in  spite  of  the  apparent  conclusiveness  of  Mr.  Don's  in- 
vestigations for  his  regions,  that  the  bi silicates  of  our  Rocky 
Mountain  eruptives  may  not  contain  some  of  the  metals,  but 
must  wait  until  similarly  exhaustive  tests  have  been  carried  on 
here.  Lead  and  cobalt  have  been  found  by  Mr.  Hillebrand  in 
the  bisilicates  of  some  of  the  eruptive  rocks  of  the  Ten-Mile 
district,  and  lead  and  silver  similarly  by  Mr.  Eakins  in  the  bi- 
silicates of  granite  at  Silver  Clifi',  Colo. 

It  seems  important  to  note  that  the  lateral-secretion  theory 
which  Mr.  Don's  tests  seem  to  disprove  is  not  the  one  that  has 
been  generally  advocated  in  the  United  States ;  for  I  fancy  few 
American  geologists  believe  in  the  narrower  view  advocated  by 
Sandberger,  that  the  metals  are  derived  necessarily  from  the 
immediately  adjacent  country-  or  wall-rock.  Dr.  Don  says  that 
he  believes  the  gold  of  New  Zealand  is  derived  from  rocks 
deeper  than  any  now  exposed  at  the  surface  there,  but  adds 
that  he  "is  not  concerned  with  the  question  whether  this 
source  is  the  vague  barysphere,  with  its  somewhat  apocryphal 
contents  of  heavy  metals."  While,  therefore,  no  longer  a  be- 
liever in  Sandberger,  he  is  apparently  not  willing  to  subscribe 
to  the  extreme  views  of  Posepny.  It  has  been  the  fashion  for 
some  time  to  decry  Sandberger ;  but  I  think  his  work  has  been 
of  the  utmost  value  to  the  study  of  ore-deposits,  even  if  hi& 
ultimate  conclusions  are  not  admitted ;  for  he  aroused  us  from 
the  unthinking  belief  that  the  metals  necessarily  came  from 
unknown  depths,  which  it  was  fruitless  to  speculate  about  or  to 
try  to  investigate.  He  started  in  movement  the  pendulum  of 
thought,  which  had  so  long  been  stationary  at  that  point ;  for 
a  while  it  swung  on  his  side,  then  back  again  to  the  ascen- 
sionist  side.  Now,  with  some  geologists,  it  has  taken  a  very 
strong  impetus  in  the  direction  of  the  long-ago  abandoned  sub- 
limation theory,  or  something  very  like  it.  The  Swedish  geolo- 

33  Gold  Quartz  Veins  of  Nevada  City  and  Grass  Valley,  by  W.  Lindgren., 
Seventeenth  Annual  Report,  U.  S.  Geological  Survey,  Part  II.,  p.  94  (1895-96). 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  205 

gists  represented  by  Vogt,  a  disciple  of  the  great  petrographer 
Brb'gger,  consider  certain  workable  masses  of  iron  and  other 
ores  as  segregations  from  the  still  molten  mass,  or  direct  prod- 
ucts of  magmatic  differentiation.  Other  minerals  occurring 
in  pegmatite  veins,  and  some  metallic  oxides,  like  tin,  for  in- 
stance, they  consider  to  have  been  deposited  in  the  last  stages 
of  consolidation  of  a  molten  magma  by  a  mixed  process,  which 
they  call  pneumatolysis,  and  which  brings  in  the  agency  of 
water  expelled  during  cooling  from  the  igneous  magma.  This 
comes  back  to  the  old  French  theory  of  aqueo-igneous  fusion 
in  the  presence  of  certain  substances,  such  as  fluorine,  boron, 
chlorine,  etc.,  which  were  called  agents  mineralisateurs ;  but  it 
is  less  purely  theoretical,  in  that  it  is  founded  on  certain  facts 
of  observation  in  nature. 

Vogt  is  at  present  preparing  a  new  book  on  ore-deposits,  in 
which  he  will  doubtless  extend  very  widely  the  scope  of  his 
pueumatolytic  processes.  But  the  applicability  of  either  the 
French  or  the  Swedish  theory  must  be  limited  by  a  very  sinlple 
geological  condition,  which  is — whether  the  fissures  in  which 
ore-deposition  has  taken  place  could  have  been  formed  during 
the  final  consolidation  of  the  eruptive  magma.  In  most  of  the 
important  ore-deposits  which  I  have  had  opportunities  of  study- 
ing, the  fissures  or  fractures  which  have  served  as  ore-channels 
were  the  result  of  earth-movements  that  took  place  long  after 
the  entire  consolidation  of  the  eruptive  magmas.  In'  some 
cases,  even,  there  is  evidence  of  several  such  movements  before 
the  ore-deposition.  My  belief,  as  I  have  had  occasion  to  state 
already,  is  that,  by  reason  of  some  process  which,  for  want  of  a 
better  name,  we  may  call  magmatic  differentiation,  certain  por- 
tions of  an  eruptive  mass  are  richer  in  metals  than  the  average ; 
and  that  from  such  portions  circulating  solutions  have  ab- 
stracted these  diffused  metals  and  deposited  them  in  a  more 
concentrated  form  in  favorable  situations  in  rocks  in  the  vicin- 
ity. The  original  bringing  up  of  the  metals  from  the  bathy- 
sphere was,  however,  accomplished  by  the  eruptive  magma  be- 
fore consolidation.  Present  ore-deposits  are  in  this  sense  the 
result  of  a  secondary  concentration  at  only  moderate  depths. 

Dr.  Don's  investigation  of  the  processes  going  on,  or  that  may 
go  on,  in  the  vadose  region  affords  interesting  and  useful  data. 
He  first  assumes  that  deposits  are  generally  richer  in  the  pre- 


206  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

cious  metals  above  than  below  the  water-line — a  perfectly  justi- 
fiable assumption,  in  my  opinion — and  then  presents  alterna- 
tive explanations,  one  based  on  the  ascension,  the  other  on  the 
lateral-secretion,  theory;  but  he  does  not  mention  the  most 
obvious  explanation  of  this  fact,  namely,  that  the  baser  metals, 
which  are  usually  in  far  greater  amount  than  the  precious 
metals,  form  by  oxidation  more  readily  soluble  compounds,  and 
are  therefore  to  a  much  larger  extent  removed  in  the  vadose  or 
oxidizing  region,  while  the  precious  metals  are  for  the  most 
part  either  not  dissolved  or  are  re-precipitated.  Hence,  the 
specific  gravity  of  the  whole  mass  of  vein-material  is  decreased 
in  the  vadose  region;  and  a  given  bulk,  though  it  may  have 
absolutely  no  more  of  the  precious  metal  in  it  than  before  oxi- 
dation, contains  a  relatively  higher  percentage,  by  weight,  of 
the  precious  rnetals.  There  may  also  be  in  places  an  actual 
enrichment,  due  to  the  ready  precipitability  of  the  precious 
metals.  I  have  myself  seen  cases  where,  in  a  zone  immediately 
above  the  water-line,  the  ore-body  was  not  only  very  much 
richer  than  in  the  unoxidized  portion  below,  but  also  richer 
than  the  average  of  the  oxidized  ore  above,  showing  that  the 
precious  metal  had  been  in  a  measure  leached  down  and  re- 
precipitated.  Dr.  Don  himself  shows  various  ways  in  which 
gold  might  be  dissolved  in  the  vadose  region  and  re-precipi- 
tated lower  down ;  he  also  thinks  it  may  have  been  carried 
down  mechanically;  the  result  of  his  investigations  of  mine- 
waters  being  that,  where  they  are  found  to  contain  gold,  it  is 
usually  in  mechanical  suspension  rather  than  in  solution. 

One  of  the  most  interesting  parts  of  Dr.  Don's  investigations 
is  that  relating  to  the  gold-content  of  sea-water,  in  which  he 
has  not  contented  himself  with  the  vague  statement  that  the 
metal  does  occur,  but  has  made  a  quantitative  estimate  of  its 
amount,  which  must  be  translated  into  the  metric  system  in 
order  to  become  intelligible  to  any  but  English  chemists.  The 
average  content  as  determined  by  him  is  0.0071  grain  to  the 
ton,  which  means,  if  I  have  calculated  correctly,  something  like 
twelve  million  dollars'  worth  to  the  cubic  mile — a  large  sum,  if 
it  could  be  gotten  out.  But  Dr.  Don  has  shown  by  a  pretty 
exhaustive  series  of  experiments  that  there  is  no  probability 
that  any  natural  precipitant  would  throw  down  any  measurable 
portion  of  it. 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  207 

GEORGE  F.  BECKER,  Washington,  D.  C. :  Dr.  Don's  paper  is 
an  extremely  important  contribution  to  mining-geology,  and 
worth  the  vast  amount  of  labor  which  it  has  manifestly  cost. 
I  trust  that  the  paper  in  the  Transactions  will  prove  to  be  only 
a  preliminary  abstract,  and  that  the  entire  memoir  will  soon 
appear. 

The  greater  part  of  the  conclusions  which  Dr.  Don  reaches 
are  quite  in  line  with  those  to  which  Mr.  Lindgren  and  I  have 
been  led  by  studies  of  the  gold-deposits  in  this  country.34  I 
have  been  greatly  impressed  of  late  years  with  the  character  of 
the  auriferous  wall-rocks  of  gold-quartz  veins.  It  seems  to  be 
true  in  most  cases,  for  deep  mines,  that  the  gold  in  the  walls  is 
contained  in  the  sulphurets ;  that  it  is  of  smaller  fineness  than 
the  vein-gold;  that  the  sulphurets  are  pyrites;  and  that  gold 
and  sulphurets  diminish  rapidly  in  quantity  as  the  distance 
from  the  vein  increases.  Sometimes  the  wall-rock  pyrite  is 
almost  barren.  There  appear  to  me  to  be  two  sorts  of  wall- 
pyrite.  One  seems  to  be  the  result  of  the  action,  on  ferro-mag- 
nesian  silicates,  of  the  sulphides  of  hydrogen  or  of  the  alkalies, 
as  I  pointed  out  in  treating  of  the  Comstock  lode.  This  variety 
is  sometimes,  and  I  suspect  usually,  almost  worthless.  There  are 
other  impregnations  of  pyrite  which  seem  to  me  to  have  per- 
meated from  the  vein-fissures,  in  solution,  as  double  sulphides 
of  the  alkalies  and  iron.  I  have  studied  such  solutions  in  a 
memoir  on  quicksilver-deposits,  and  shown  that  solutions  of 
alkaline  carbonates,  partly  charged  with  hydrogen  sulphide, 
will  take  up  notable  quantities  of  many  sulphurets,  and  also  of 
gold.  Dr.  Don  has,  I  think,  overlooked  this  investigation. 
Mr.  Dolter  has  since  succeeded,  where  I  failed,  in  dissolving 
lead  and  silver  sulphides  in  a  similar  menstruum. 

Wall-rocks  appear  to  be  much  more  permeable  by  solutions 
of  some  substances  than  by  those  of  others.  Native  gold, 
quartz,  and  all  the  sulphurets  excepting  pyrite,  are  for  the 
most  part  retained  in  the  veins,  while  carbonates  seem  to  pene- 
trate freely  into  the  wall-rock.  This  indicates  an  osmotic  sep- 
aration of  the  metal-bearing  solution,  as  I  pointed  out  years 
ago. 

34  Parts  of  these  studies  have  been  printed  in  the  Fourteenth  to  Eighteenth  Annual 
Reports,  U.  S.  Geological  Survey  (1892-96). 


208  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

That  some  undecomposed  rocks  (granite,  andesite)  contain 
free  gold  in  clearly-visible  particles  appears  to  be  quite  certain. 
There  is  also  strong  evidence  for  the  strange  hypothesis  that 
some  sulphurets  in  massive  rocks  are  original  constituents.  I 
entertain  no  doubt  that  some  eruptive  rocks  associated  with 
veins  are  truly  metalliferous.  Nevertheless,  the  possibility 
presents  itself  that  in  such  cases  vein  and  rock  each  derived 
its  metallic  contents  from  a  common  source,  miles  beneath  the 
surface.  Such  a  hypothesis  is  not  without  difficulties  of  its 
own,  but  accords  better  with  the  osmotic  phenomena  than  the 
theory  of  derivation  from  wall-rock. 

Dr.  Don's  remarks  on  secondary  re-crystallization  are  inter- 
esting. That  sulphurets  are  regenerated  is  certain.  The  ques- 
tion of  the  re-crystallization  of  gold  needs  more  research. 

ARTHUR  WINSLOW,  Kansas  City,  Mo. :  Dr.  Don's  work,  even 
as  presented  in  the  abridged  form  of  his  Institute  paper,  is  a 
notable  example  of  painstaking,  conscientious  research,  for 
which  the  author  deserves  great  credit.  The  field  and  literary 
work  alone  must  have  been  very  great ;  but,  in  addition,  the 
investigation  involved  many  special  experiments  on  a  large 
scale,  and  the  testing  and  assaying  of  over  400  bulky  samples, 
with  more  than  100  other  assays  and  analyses,  which,  to  any  one 
familiar  with  such  tasks,  seems  a  stupendous  labor.  The  re- 
suits  are  especially  of  quantitative  value,  furnishing  many  exact 
facts  and  definite  data  which  will  control  speculation,  and  upon 
which  theories  can  be  built  up.  Therefore,  in  whatever  esti- 
mation one  may  hold  Dr.  Don's  methods  and  results,  or  how- 
ever one  may  diiFer  in  the  conclusions  to  be  drawn,  all,  I  think, 
will  agree  in  admiring  the  courage  and  entire  disregard  for 
labor  which  prompted  and  sustained  his  inquiries. 

The  investigation  is,  first  and  principally,  one  to  determine 
whether  the  ores  of  certain  auriferous  lodes  of  New  Zealand, 
Victoria,  and  Queensland  were  formed  by  lateral  secretion  or 
by  ascension.  Secondarily  and  incidentally,  it  is  a  valuable 
-contribution  to  the  general  subject  of  the  genesis  of  ore-deposits. 

The  work  is  of  special  interest  when  considered  in  connec- 
tion with  the  hypothesis  advanced  by  T.  A.  Rickard 35  for  the 
origin  of  the  ores  of  the  Bendigo  reefs  of  Australia.  Indeed, 

35  Trans.,  xxii.,  289  (1893). 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  209 

it  would  appear  as  if  Mr.  Don  must  have  had  this  hypothesis 
immediately  in  mind  in  planning  his  work,  so  directly  does  he 
meet   the    questions  which    arise    in    reading    Mr.   Rickard's 
paper.     Passing  by  his  experiments  and  conclusions  as  to  the 
precipitation  of  gold  in  marine  sediments,  and  also  allied  in- 
quiries of  somewhat  negative  value,  the  results  of  most  posi- 
tive and  emphasized  importance  are  his  analyses  of  the  country- 
rocks  for  the  detection  of  gold.     These  are  principally  inter- 
esting in  the  uniformity  with  which  they  show  that  the  metal 
was  not  detected,  or  was   found  to  be  present   only  in  very 
minute  quantities  in  the  normal  country-rock;  also  that,  where 
its  presence  was  detected,  it  was  associated  with  sulphides,  and 
that  both  the  quantity  of  the  sulphides  and  the  richness  in  gold 
increased  as  the  lode  or  other  form  of  deposit  was  approached. 
The  question  which  arises,  and  which  to  me  seems  of  great 
significance,  is  as  to  the  sufficiency  of  the  evidence.    Dr.  Don's 
assay-results  marked  "  Nil "  as  to  gold-content  must  be  con- 
sidered as  relative.     They  mean  simply  that  no  gold  was  de- 
tected by  the  method  he  used.     It  is  probable  that  gold  and 
other  metals  are  generally  diffused  through  the  rocks  of  the 
earth's  crust,  and  are  represented  normally  by  amounts  pro- 
portional to  their  abundance  and  the  solubilities  of  their  natu- 
rally-formed compounds.     The   researches  of  Forschhammer, 
Dieulafait,  Bischof,  Sandberger,  Malaguti,  and  others,  referred 
to  in  my  report  on  the  lead-  and  zinc-deposits  of  Missouri,  M 
show  the  frequent  diffusion  of  copper,  lead,  and  zinc  in  rocks, 
minerals,  and  waters.     Mr.  Robertson's  analyses  of  crystalline 
-and  clastic  rocks  of  Missouri,  in  connection  with  the  same  re- 
port, 87  sustain  this  belief.    Proof  that  such  diffusion  is  general 
would  seem  purely  a  question  of  the  amount  of  rock  used  and 
of  the  refinement  of  method.     The  refinement  of  Dr.  Don's 
methods  may  be  inferred  from  the  fact  that  0.1  grain  per  ton 
is  the  lowest  result  given  in  figures.    There  is  nothing  between 
this  and  the  "  Nil "  results.     Gold  to  the  amount  of  more  than 
0.1  grain  he  shows  to  be  frequently  present  in  the  country- 
rock,  remote  from  lodes,  and  even  amounts   of  over  1  grain 
were  found.     On  the  assumption  that  the  gold  has  been  de- 
rived from  these  rocks,  such  gold  now  found  to  be  present  must 

36  Reports  Missouri  Geological-  Survey,  vol.  vi.,  p.  30  et  seq.  (1894). 

37  Reports  Missouri  Geological  Survey,  vol.  vii.,  p.  479  et  seq.  (1894.) 

14 


210  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

be  a  residuum  after  the  process  of  leaching.  The  question 
arises,  what  gold-content  is  required  in  a  country-rock  that  it  may 
be  regarded  as  a  source  of  the  ores  in  the  veins  traversing  it. 
Assuming  0.1  grain  to  the  ton,  it  would  take  just  4,800  tons  of 
rock  to  supply  the  gold  for  1  ton  of  1-oz.  ore,  if  all  the  gold 
were  removed  from  the  country-rock  into  the  veins.  On  this 
basis  1  cu.  mile  of  rock  would  supply  2,300,000  tons  of  such 
ore.  Mr.  Rickard's  hypothesis,  which  ascribes  the  gold  to 
sea-water  retained  in  the  sediments,  would  hardly  call  for  a 
greater  original  concentration,  seeing  that  he  allows  only  -jig- 
grain  per  ton  to  the  sea-water  of  the  present  day. 

The  conception  of  lateral  secretion  as  a  process  whereby  the 
contents  of  the  ore-body  simple  trickle  in  from  the  sides  or 
walls  can,  of  course,  not  be  sustained,  even  though  the  name 
may  seem  to  justify  it.  To  harmonize  with  the  ideas  now 
more  generally  held,  the  flow  and  transmission  of  solutions 
must  have  been  in  devious  directions,  according  to  hydrostatic 
and  thermal  conditions,  and  according  to  the  structure  of  the 
rocks.  The  solutions  would  naturally  follow  fissures,  and  flow 
into  open  spaces,  either  in  ascending  or  descending  currents. 
They  would  at  the  same  time  penetrate  the  wall-rocks  of  such 
openings,  and  when  they  contained  gold  these  wall-rocks  would 
be  enriched.  Thus,  an  increase  of  the  mineralization,  or  of 
the  gold-content,  as  the  vein  is  approached,  is  not  incompatible 
with  the  large  conception  of  lateral  secretion. 

It  is  true  that  such  an  expansion  of  the  original  idea  of  lat- 
eral secretion  appears  to  rob  it  of  its  distinctive  features,  so 
that  it  seeing  in  fact  to  embrace  the  rival  process  of  ascension, 
and  to  leave  no  room  for  the  separate  existence  of  the  latter. 
This  is  not,  however,  the  case.  The  essential  idea  of  the  as- 
cension theory  is  that  metals  and  other  constituents  of  lodes 
are  derived  from  a  deep-seated  source  of  supply — a  sort  of 
treasure-house  of  nature — whence  they  were  transported  for  the 
use  of  man  by  the  agency  of  ascending  solutions  or  vapors 
which  followed  the  paths  of  profound  fissures.  The  opposed 
idea  of  lateral  secretion,  as  developed,  if  not  precisely  so  ex- 
pressed in  recent  writings,  is  that  these  constituents  of  lodes 
are  distributed  and  diffused  in  greater  or  less  quantities 
throughout  the  rocks  of  the  earth's  crust — in  such  rocks  as 
are  or  have  been  exposed  at  the  surface — that  they  have  been 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  211 

gathered  from  these  rocks  and  concentrated  in  ore-deposits  by 
the  action  of  percolating  waters  of  various  compositions,  as- 
sisted by  chemical,  l^drostatic,  thermal,  and  structural  condi- 
tions, such  as  are  brought  about  by  sedimentation,  by  earth- 
movements,  by  injection  of  volcanic  rocks,  etc.  In  cases  of 
the  more  abundant  metals,  such  as  iron  and  manganese,  this 
process  is  plainly  recognized,  and  the  requisite  conditions  are 
commonly  presented.  In  the  case  of  less  common  metals,  such 
as  copper,  lead,  and  zinc,  the  process  is  not  so  simple  or  so  gen- 
erally to  be  observed.  In  the  case  of  the  precious  metals, 
which  are  rare  and  difficult  of  solution  and  transportation, 
more  powerful  factors  and  special  or  stronger  reagents,  such  as 
highly-heated  solutions,  seem  necessary  to  produce  the  result. 
Thus,  according  to  the  lateral-secretion  theory,  our  own  home 
country-rocks  are  our  treasure-houses,  and  we  are  not  depen- 
dent upon  the  foreign  depths  of  the  earth  for  our  metals. 
Such  may  be  in  some  cases  the  source  of  supply,  but  the  ag- 
gressive secretionist  is  disposed  to  throw  the  burden  of  the 
proof  upon  the  ascensionist,  and  to  maintain  that  his  rule  is 
the  more  satisfactorily  proved  by  the  removal  of  successive 
supposed  exceptions. 

W.  P.  BLAKE,  Tucson,  Arizona :  As  appropriate  to  the  dis- 
cussion on  the  origin  of  quartz-lodes  and  the  deposition  of  gold, 
I  desire  to  direct  attention  to  the  very  general  association  in 
California,  especially  in  the  Jura-Trias  and  Carboniferous 
slates,  of  gold  with  slates  containing  a  large  amount  of  carbo- 
naceous matter.  This  association  is  particularly  noticeable  in 
the  Princeton  mine,  on  the  Mariposas  estate ;  in  the  Keystone 
mine,  Amador  county;  in  the  Plumas  mine,  and  in  many 
other  mines  in  the  main  gold-belt  of  the  State.  It  has  been 
noted  also  by  Ross  E.  Browne,  who,  in  a  recent  article,  gives 
three  cross-sections  showing  the  mother-lode  traversing  soft 
black  slate.  He  describes  the  lode  as  a  "  continuous  series  of 
parallel  quartz  veins,  following  more  or  less  persistently  a  nar- 
row belt  of  soft  black  slate."  M 

At  the  Arizona  School  of  Mines  a  sample  of  coal  has  been 
received  from  Wyoming,  which  is  said  to  contain  gold.  Pre- 
liminary assays,  made  with  great  care,  show  an  appreciable 

38  Mining  and  Scientific  Press,  vol.  Ixxvi.,  No.  5,  p.  105  (Jan.  29,  1898). 


212  THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES. 

amount  of  the  metal ;  but  further  investigation  of  the  source 
of  the  coal  and  assays  upon  other  samples  are  desirable  before 
attaching  special  value  to  this  form  of  association  of  gold  and 

carbon. 

(Trans.,  xxviii.,  799.) 

DR.  DON  :  I  have  to  express  my  grateful  thanks  to  Messrs. 
Le  Conte,  Emmons,  Becker,  and  Winslow,  for  their  very  kiad 
remarks,  presented  at  the  Atlantic  City  meeting,  on  my  paper. 
An  investigator  works  practically  alone  and  under  many  dis- 
couragements, at  this  end  of  the  world;  and  nothing  has 
encouraged  me  so  much  in  my  research  as  to  find  my  work 
appreciated  by  men  whose  wide  knowledge  of  the  subject  and 
whose  eminent  services  to  science  entitle  their  opinions  to  my 
deepest  respect. 

Professor  Le  Conte's  last  sentence  gives  me  an  opportunity 
to  express  the  hope  that  chemical  analysis  may  in  future  be 
more  generally  used  as  an  aid  to  observation.  If  any  degree 
of  finality  is  ever  to  be  reached  with  regard  to  this  most  puz- 
zling question,  such  finality  will  only  be  attained  by  the  com- 
bination of  the  experimental  work  of  the  chemist  with  the 
skilled  observation  of  the  mining-geologist. 

Mr.  Emmons,  in  his  highly-valued  criticism,  says  : 

"Dr.  Don's  first  and  most  important  conclusion  from  his  tests  is  that  gold  does 
not  occur  in  the  rocks  of  the  regions  investigated  by  him  as  an  original  constitu- 
ent of  the  bisilicates,  and  that  where  it  is  found  in  these  rocks  it  is  associated  with 
sulphides,  mainly  of  iron.  His  inference  seems  to  be  that  it  cannot  be  original  in 
the  rock,  because  pyrite  is  necessarily  a  secondary  constituent,  that  is,  one  intro- 
duced after  the  rock  consolidated.  ' 

I  confess  that  I  had  not  in  my  mind  as  clearly  as  I  could 
wish  the  fact  that  in  the  case  of  crystalline  eruptive  and  plu- 
tonic  rocks  the  pyrite  and  other  sulphides  may  be  as  much  a 
primary  constituent  of  the  rocks  as  the  bisilicates. 

This  distinction  between  primary  and  secondary  sulphides 
need  not,  however,  be  observed  in  the  great  majority  of  the 
country-rocks  examined  by  me.  These  country-rocks  may  be 
roughly  divided  into  four  classes : 

a.  Those  that   are    unmistakable    sediments,  more   or   less 
altered.     These  form  the  great  majority  of  the  samples  ana- 
lyzed; and  in  these  cases,  all  sulphides  must  be  "secondary." 

b.  Dike-rocks  from  the  Upper  and  Lower  Silurian  of  Vic- 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  213 

toria.     NOUQ  of  these  rocks  could  be  obtained  in  the  unaltered 
state ;  but  those  that  were  least  altered  contained  no  sulphides. 

c.  The  remarks  under  b  apply  also  to  the  andesites  of  the 
Thames  gold-field,  and  the  tonalite  of  the  Charters  Towers 
field  of  Queensland. 

d.  In  the  case  of  the  gneissoid  rocks  of  the  Manipori  forma- 
tion of  New  Zealand,  and  the  granite  that  probably  underlies 
the   sedimentaries   of  Victoria,  the  sulphides  found  in   some 
samples  may  have  been  primary. 

Mr.  Emmons  says : 

.  "It  seems  important  to  note  that  the  lateral-secretion  theory  which  Dr.  Don's 
tests  seem  to  disprove  is  not  the  one  that  has  been  generally  advocated  in  the 
United  States ;  for  I  fancy  few  American  geologists  believe  in  the  narrower  view 
advocated  by  Sandberger,  that  the  metals  are  derived  necessarily  from  the  imme~ 
diately  adjacent  country-  or  wall-rock." 

The  introduction  to  Chapter  Y.  (omitted  in  the  condensed 
form  of  my  paper)  included  a  discussion  of  this  point,  and 
showed  that  the  analysis  of  underlying  granites  and  other  crys- 
talline rocks  had  been  undertaken  with  a  view  to  testing  this 
later  extension  of  the  lateral-secretion  theory.  By  reference  to 
my  paper  [p.  162,  this  volume],  it  will  be  seen  that  the  crystal- 
line rocks  were  chosen  because  they  afforded  an  opportunity 
for  testing,  not  the  actual  country-rock  bounding  the  lodes,  but 
the  crystalline  rock-mass  that  probably  underlies  many  of  the 
rocks  in  which  our  lodes  occur. 

The  majority  of  the  results  noted  in  Table  I.,  J.,  J5,  and  C 
(Table  XVIII.  of  original  paper),  come  under  this  heading. 
Owing  to  the  great  labor  involved  in  isolating  some  of  the 
crystalline  constituents  of  such  rocks,  the  number  of  these 
analyses  is  comparatively  small ;  but  so  far  as  these  results  are 
conclusive,  they  point  to  a  source  for  the  gold  below  even  the 
crystalline  rocks  that  may  be  assumed  to  underlie  our  gold- 
bearing  sedimentaries. 

I  have  to  thank  Mr.  Emmons  for  his  criticism  pointing  out 
a  weakness  in  my  statement  of  the  two  alternatives  on  p.  172  of 
my  paper.  The  second  alternative  should  certainly  have  been 
extended  in  the  direction  suggested  by  him.  On  page  182, 
however,  the  action  of  the  oxidizing  vadose  waters,  in  enrich- 
ing vein-gold  by  dissolving  out  part  of  the  silver,  is  taken  into 
account. 


214      THE  GENESIS  OF  CERTAIN  AURIFEROUS  LODES. 

Mr.  Becker  draws  a  clear  distinction  between  the  two  kinds 
of  pyrite  associated  with  country-rock.  This  distinction  seems 
to  me  to  be  of  very  great  interest,  and  of  the  first  importance. 

Granted  this  distinction,  and  the  selective  osmotic  action 
exercised  by  the  wall-rock,  a  new  light  is  thrown  on  many  of 
the  results  obtained  in  my  analyses.  The  apparently  abnormal 
results  obtained  in  some  cases — more  particularly  in  the  Thames 
andesites  and  the  country  bounding  the  Reefton  lodes — become 
much  clearer  in  the  light  of  Mr.  Becker's  remarks. 

Mr.  Becker  refers  also  to  the  presence  of  visible  particles  of 
gold  in  undecomposed  crystalline  and  eruptive  rocks.  Such 
instances  are  by  no  means  rare;  but  is  it  not  possible  that 
the  samples  in  which  these  occurrences  are  noticed  may  have 
been  taken  from  the  vicinity  of  lodes,  so  that  the  gold  found 
may  have  been  an  impregnation  from  the  lode  itself?  An  in- 
teresting example  of  such  an  occurrence  lately  came  under  my 
notice.  In  a  sample  of  syenitic  rock  taken  from  the  vicinity  of 
a  copper-lode  in  Dusky  sound,  on  the  west  coast  of  Otago, 
minute  specks  of  metallic  copper  were  observed,  apparently . 
forming  a  constituent  of  the  hornblende  of  the  rock.  In  this 
instance  there  seemed  to  be  no  doubt  that  the  copper  was 
derived  from  the  lode.  I  should  be  much  interested  if  any 
members  of  the  Institute  could  give  authentic  instances  of  the 
occurrence  of  visible  particles  of  gold  actually  forming  part  of 
crystalline  or  eruptive  rocks  at  long  distances  from  lodes. 

Mr.  Winslow's  criticism  raises  the  whole  question  as  to  the 
possibility  of  obtaining  any  experimental  evidence,  other  than 
that  founded  on  observation  alone,  with  regard  to  the  genesis 
of  auriferous  deposits,  where  the  amount  of  metal  to  be  looked 
for  is  extremely  minute.  This  is  a  difficulty  that  must  have 
presented  itself  to  any  honest  worker  who  has  made  a  study  of 
the  subject.  The  question  is  not  so  much  whether  the  methods 
used  by  any  particular  investigator  have  been  sufficiently  re- 
fined, as  whether  any  possible  test  may  be  delicate  enough  to 
give  reliable  results. 

Now,  while  it  is  quite  true  that  the  results  obtained  by  me 
do  not  show  any  difference  between  -fa  grain  to  the  ton  of  coun- 
try-rock (or  one  part  in  156,800,000)  and  ml,  and  while,  in  my 
opinion,  it  is  not  possible  to  carry  the  refinement  much  further 
with  safety,  one  must  not,  I  think,  lose  sight  of  the  fact  that  if 


THE    GENESIS    OF    CERTAIN    AURIFEROUS    LODES.  215 

the  gold  of  any  lode  had  been  derived  by  segregation  from  the 
country-rock  or  from  associated  and  subjacent  rocks  (it  will  be 
observed  that  lateral  secretion  is  here  indicated  in  its  wider 
sense),  such  segregation  must  have  been  accompanied  by  local 
deposition  at  many  points,  as  the  auriferous  solutions  made 
their  way  to  the  lode-fissure.  It  is  a  matter  of  common  obser- 
vation that  the  country,  even  at  considerable  distances  from 
lodes,  is  in  many  cases  a  network  of  miniature  lodes,  where  de- 
position might  reasonably  be  expected  to  take  place.  In  col- 
lecting samples  for  analysis,  care  was  taken  to  include  many 
such  places  of  possible  deposition ;  yet  the  evidence  obtained 
by  me  would  almost  justify  the  general  statement  that  in  solid 
country,  where  the  possibility  of  impregnation  from  a  lode  or 
dike  was  reduced  to  a  minimum,  no  trace  of  gold  was  present, 
even  in  the  sulphides  found.  Numerous  illustrations  in  sup- 
port of  this  generalization  are  to  be  found  in  most  of  the  tables. 


216  INFLUENCE    OF    COUNTRY-HOCK    ON    MINERAL    VEINS. 


No.  9. 
Influence  of  Country-Rock  on  Mineral  Veins. 

BY   WALTER  HARVEY   WEED,*   WASHINGTON,    D.    C. 

(Mexican  Meeting,  November,  1901.     Trans.,  xxxi.,  634.) 

AMONG  the  many  causes  of  that  perplexing  feature  of  mine- 
exploitation,  the  unequal  distribution  of  the  ore,  the  influence 
of  the  country-rock  upon  the  vein-contents  has  long  been  ac- 
cepted as  an  important  factor  in  certain  districts,  but  the  gen- 
eral application  of  the  theory  has  not  been  proved.  It  is  now 
possible  to  obtain  trustworthy  data  with  which  to  test  the 
theory,  and  either  to  confirm  or  to  overthrow  this  time-honored 
tradition.  By  the  searching  methods  of  modern  petrography 
and  chemistry,  rock-determinations  are  now  scientifically  made, 
while  the  examination  of  thin  sections  of  ores  supplements 
field-  and  laboratory-study,  and  affords  conclusive  evidence  of 
the  paragenesis  of  the  ore-minerals. 

In  the  great  mass  of  data  regarding  mineral  deposits  accu- 
mulated during  the  past  century,  there  are  some  facts  which 
stand  the  test  as  to  reliability ;  but  the  greater  part  are  not 
available  for  use  in  this  discussion.  Within  the  last  20  years, 
however,  many  able  workers  have  contributed  careful  and 
accurate  accounts  of  various  ore-deposits;  and  it  is  by  the 
facts  given  in  such  papers,  and  by  personal  experience,  that  I 
have  become  convinced  that  there  is  in  some  districts  a  true 
relation  between  the  country-rock  and  the  mineral  contents  of 
the  veins. 

My  own  interest  in  the  subject  arose  from  the  observation  of 
a  number  of  striking  instances  of  the  variation  of  vein-con- 
tents with  the  nature  of  the  inclosing  rock.  Having  already 
recorded  certain  observations  of  this  kind,  I  venture  (to  present 
in  this  paper  further  notes,  together  with  a  few  facts  from  the 
literature  of  the  subject,  which  seem  to  prove  the  correctness 
of  my  view.  It  is  apparent  that  if  the  relation  holds  true, 
though  in  limited  districts  only,  it  will  be  of  great  practical  in- 

*  U.  S.  Geological  Survey. 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS.  217 

terest  to  the  miner,  and  will  confer  upon  the  geological  survey 
of  a  mining-district  a  new  value,  rendering  it,  in  fact,  an  almost 
indispensable  preliminary  to  the  extensive  working  of  large 
properties. 

The  influence  of  the  inclosing  rocks  upon  mineral  veins  evi- 
dently affects  both  the  vein-structure  and  the  vein-filling.  The 
first  effect  is  physical ;  the  second  is  mineralogical  or,  primarily, 
chemical.  The  first  has  been  but  lightly  touched  upon,  if  no- 
ticed at  all,  by  writers  on  mining-geology.  The  second  has 
long  been  recognized  as  a  fact  in  a  few  well-known  examples ; 
but,  although  many  attempts  have  been  made  to  show  a  rela- 
tionship between  certain  ores  and  definite  rock-types,  the  corre- 
lations have  been  of  local  value  only. 

I.  INFLUENCE  OF  ROCKS  ON  VEIN-STRUCTURE. 

It  is  self-evident  that  in  most  mineral  deposits  the  rocks  must 
have  been  either  porous  or  so  fractured  as  to  permit  the  circula- 
tion of  underground  waters  as  a  preliminary  to  vein-formation* 
It  is  also  evident  that  according  to  the  varying  hardness,  tough- 
ness, etc.,  of  the  rocks,  the  fissures  found  in  them  will  vary  in 
character,  and  the  physical  aspect  of  any  resultant  ore-deposit 
will  be  governed  by  the  nature  of  the  rock. 

Fissure-veins,  and,  indeed,  all  forms  of  ore-deposits,  are  af- 
fected in  size  and  shape,  and  probably  to  some  extent  in  rich- 
ness, by  the  character  of  the  fissure  or  fracture  in  which  the 
vein  was  formed.  Experience  shows  that  a  vein  often  varies 
greatly  in  structural  characters,  such  as  width,  uniformityr 
presence  of  splits  and  horses,  etc.,  in  passing,  whether  horizon- 
tally or  vertically,  from  one  rock  into  another.  Thus  the  vein 
may  pinch  out  in  a  very  tough  rock,  expand  in  a  more  easily 
shattered  material,  become  dissipated  into  a  stockwork  in 
brittle,  shattered  rock,  or  become  lost  entirely  in  a  shale.  In 
easily-soluble  rocks,  like  limestones  and  dolomites,  the  original 
character  of  the  fissure  may  be  modified  by  solution,  and  thus 
the  original  effects  of  its  force  may  be  masked.  This  case  stands 
in  such  intimate  connection  with  the  mineralogical  effects  due  to 
the  nature  of  the  rock  that  it  is  best  considered  in  the  .second 
part  of  this  paper.  The  irregular  deposits  formed  in  limestones 
show  the  influence  of  the  inclosing  rock  on  the  form  of  the 
deposit  to  an  even  more  marked  degree  than  fissure-veins. 


218 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS. 


The  fissures  which,  in  traversing  a  tough  rock,  are  clean  cut, 
may,  in  passing  into  a  more  easily  fractured  rock,  or  one  netted 
by  fine  jointing,  produce  a  mass  of  shattered  material  in  which 
the  mineral  is  so  disseminated  in  minute  and  numerous  fissures 
that  the  entire  mass  must  be  extracted.  Often  the  vein,  solid 
and  continuous  in  one  rock,  splits  up,  forming  horses  or  drop- 
pers, or,  if  very  extensive,  becomes  a  zone  traversed  by  many 
small  parallel  threads  and  stringers,  too  small  to  be  worked. 
This  is  discussed  by  Professor  Beck,  in  his  recent  book,1  from 
which  Fig.  1  is  taken. 

In  the  Guadalupe  mine,  Chihuahua,  Mexico,  a  vein,  carrying 
a  solid  ore  from  10  to  40  ft.  wide,  changes  eastward  into  many 
small  branches,  too  small  to  be  worked,  though  the  richness  of 
the  ore  in  them  may  be  unchanged. 


FIG.  1. — SCATTERING  OF  THE  GOTTLOB  VEIN  IN  QUARTZ-PORPHYRY,  IN  THE 
DAVID  SHAFT,  NEAR  FREIBERG,  SAXONY,  g,  GRAY  GNEISS  ;  p,  QUARTZ- 
PORPHYRY  ;  m,  VEIN. 

Where  veins  traverse  foliated  rocks,  such  as  gneisses  and 
schists,  the  original  fissures  may  have  been  due  to  a  very  slight 
movement  along  the  plane  of  schistosity,  and  the  result  may  be 
linked  veins,  composed  of  numerous  connected  lenses,  such  as 
are  commonly  found  in  the  Piedmont  area  of  the  Carolinas.  If 
the  movement  is  distributed  over  several  folia  the  vein  is  not  a 
simple  one,  but  consists  of  a  series  of  lenticular  masses  over- 
lapping each  other,  and  these  may  occur  in  a  zone ;  so  that  the 
"  vein  "  may  be  several  hundred  feet  wide. 

It  is  evident  that,  since  different  rocks  break  in  different  ways, 
the  character  of  the  fissures  formed  in  them  will  depend  on 
the  country-rock.  Excellent  examples  of  the  various  effects 

1  Lehre  von  cten  Erzlagerstatten,  p.  135  (1901). 


INFLUENCE    OF    COUNTRY- ROCK    ON    MINERAL    VEINS. 


219 


due  to  the  texture,  cleavage,  hardness,  and  other  properties  of 
the  rocks,  are  to  be  seen  in  the  silver-lead  mines  of  Neihart, 
Mont.,  where  steeply-dipping  metamorphic  rocks  are  cut  by  a 
large  and  very  irregular  intrusion  of  diorite,  and  both  are  cut 
by  later  intrusions  of  rhyolite-porphyry.  Well-defined  fissure- 
veins  cross  all  these  rocks.  The  metamorphic  rocks  consist  of 
alternating  bands  of  feldspathic  gneiss  with  softer,  more  schist- 
ose micaceous  rocks,  and,  more  rarely,  tough  amphibolites. 
The  veins  cross  these  rocks  at  nearly  right  angles  to  the 
schistosity.  The  underground  workings  show  the  veins  to 
vary  somewhat  in  width  and  in  the  relative  abundance  of  in- 
cluded rock-fragments,  when  they  pass  from  one  belt  of  feld- 
spathic gneiss  to  another,  and  more  markedly  when  they  pass 
into  the  more  schistose  rocks ;  but  the  change  is  so  abrupt 


Roof  of  level 


1  clay  selvage 
\  no  trace  of  ore 


FIG.  2.— SECTION  OF  LEVEL,  SHOWING  THE  FLORENCE  VEIN,  NEIHART,  MONT., 
CROSSING  AN  AMPHIBOLITE  DIKE  IN  METAMORPHIC  SCHISTS. 

where  the  amphibolites  are  encountered  that  the  miners  say 
the  vein  is  faulted.  In  fact,  the  tough  nature  of  this  rock  has 
sometimes  deflected  the  vein,  and  has  always,  in  the  instances 
observed,  narrowed  it  from  7  to  8  ft.  in  width  of  good  ore  to  a 
foot  or  more  of  barren  gangue.  Fig.  2 2  is  an  example  from 
Neihart,  where  the  veins,  passing  from  schist  into  Pinto  dio- 
rite, a  peculiar  igneous  rock  of  coarse  grain  and  texture,  are 
invariably  narrowed,  but  well  defined.  In  the  rhyolite-por- 
phyry the  same  fissures  lose  their  compact  character,  ramifying 
into  a  network  with  shattered  rock  between,  which  dissipates 
the  ore ;  so  that,  while  the  surface- workings  are  commonly 
rich,  the  ore-body  does  not  pay  in  depth,  owing  to  the  large 
amount  of  waste. 

2  From  the  Twentieth  Annual  Report,  U.  S.  Geological  Survey,  Part  III.,  p.  421 
(1900). 


220    INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS. 

The  same  phenomenon  is  described  by  De  la  Beche.3  The 
vein  shown  in  Fig.  3  encounters  an  elvan  dike,  6,  in  passing 
from  d  to  e,  and  passes  up  the  wall  of  the  dike,  scarcely  show- 
ing as  a  vein  alongside  of  the  dike  until  it  crosses  the  dike  at  c, 
and  continues  on  through  the  slates. 

At  Butte,  Mont.,  the  veins  occur  in  a  coarse-grained  gran- 
itic rock  (a  quartz-monzonite)  with  intrusions  of  aplite-granite, 
and  dikes  of  porphyry.  Where  the  veins  cross  the  porphyry 
they  are  narrower  to  a  marked  degree ;  and  the  same  is  true 
of  the  aplite.  In  part  this  is  due  to  a  more  intense  metaso- 
matic  replacement  of  the  granite  than  of  the  other  rocks, — a 
fact  which  will  be  discussed  in  describing  the  influence  of  the 
wall-rocks  on  the  tilling.  It  is  quite  evident  that  rock  char- 
acter has  influenced  the  fissure. 

The  copper-veins  at  Yirgilina,  Ya.,  which  occur  in  meta- 
morphic  schists  formed  from  old  igneous  rocks,  show  a  struc- 
tural feature  common  in  the  veins  of  the  Southern  States  where 


6 
FIG.  3.— FISSURE  DEFLECTED  BY  DIKE  (DE  LA  BECHE). 

the  fissure  crosses  the  rocks  at  less  than  90°  to  the  schistosity. 
In  such  cases  the  veins  show  many  spurs  running  off  for  short 
distances  from  the  vein  along  the  planes  of  the  schist.  The 
Blue  Wing  mine,  at  the  locality  mentioned,  shows  a  diabase 
dike  cutting  the  schists ;  and  where  the  vein  crosses  this  rock 
it  is  narrowed  and  becomes  a  mere  zone  of  plated  rock.  The 
spurs  seen  in  some  veins  in  granite  are  evidently  the  result  of 
cross-fissures  or  joints,  and  not  to  be  considered  as  a  function 
of  the  rock  itself. 

Where  the  veins  pass  from  schists  into  quartzite,  as  may  be 
seen  at  Neihart,  there  is  a  marked  change  in  their  character. 
This  is  well  seen  at  the  Big  Seven  mine,  where  a  well-defined 
vein  changes  to  many  small  fissures  with  shattered  rock  be- 
tween. At  French  town,  a  small  settlement  east  of  Deer  Lodge, 
Mont.,  the  veins  in  andesite-porphyry  are  strong  and  well-de- 

3  Geological  Observer,  p.  657  (1851  ed. ). 


INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS.     221 

iined  fissures,  but  do  not  cut  any  other  rock;  hence  direct 
comparison  cannot  be  made.  At  the  Porphyry  Dike  mine, 
south  of  Rimini,  Mont.,  the  veins  are  small  and  tight  in  the 
granite,  and  open  out  in  the  rhyolite  into  wide  fissures,  ill-de- 
fined, and  really  more  like  bands  of  shattered  rock. 

This  variation  of  fissures  in  different  rocks  is  especially  well 
shown  at  Cripple  Creek,  Colo.,  as  described  by  Penrose,4  and 
alluded  to  by  Van  Hise.5  In  hard  rock  the  fissures  are  sharp 
and  clean-cut  breaks,  but  in  the  soft  rock  they  are  ordinarily 
mere  series  of  very  small  cracks,  constituting  what  Van  Hise 
calls  "  distributive  "  faults. 

In  slates  the  vein  is  commonly  well  defined,  as  at  Copper- 
opolis  in  Montana,  and  Parral,  Mexico.  In  the  Cceur  d'Alene, 
in  Idaho,  the  veins  cross  slates  and  quartzites,  and  present  only 
those  minor  peculiarities  which  might  be  expected  in  passing 
through  such  rocks — in  fact,  there  is  less  change  than  one 
would  naturally  look  for. 

Throughout  the  Appalachians  the  veins  show  a  clustering  of 
quartz  lenses  whose  ends  overlap.  These  have  been  called 
"linked  veins"  by  Becker,  and  "compression-veins"  by  Stretch. 
That  they  are  the  result  of  the  foliation  of  the  schists  is  gener- 
ally accepted.  Where  the  lenses  are  parallel  to  the  foliation 
there  is  reason  to  believe  that  they  are  a  result  of  the  spreading 
apart  of  the  folia  by  movement.  When  the  quartz  lenticules  lie 
across  the  vein,  as  they  often  do  in  the  Carolinian  veins,  present- 
ing the  structure  figured  by  Rickard 6  for  the  Victorian  veins,  it 
seems  that  the  quartz-filled  spaces  result  from  a  rending  of  the 
rock  between  two  parallel  fissures.  Many  of  the  minor  pecu- 
liarities of  vein-walls  are  due  to  the  character  of  the  rocks,  but 
these  are  not  intended  to  be  treated  here.  Rickard  has  already 
described  many  features  of  vein-walls  due  to  varying  rocks. 

The  study  of  a  large  number  of  mines  all  over  the  country 
shows  that,  although  no  rule  can  be  laid  down  for  all  localities, 
each  district  will  present  certain  peculiarities.  In  Montana, 
the  rhyolites  are  not  favorable  for  well-defined  constant  veins, 
as  the  rock  is  too  easily  shattered.  The  granular  rocks  vary  in 

*  Mining  Geology  of  Cripple  Creek   District,  Sixteenth  Annual  Report,  U.  S. 
Geological  Survey,  Part  I.,  p.  144  (1894-95). 

5  "Some  Principles,"  etc.,  Trans.,  xxx.,  35  (1900). 

6  Trans.,  xxi.,  686-713  (1892-93). 


222    INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS. 

effect;    and   the  more  basic  forms,  carrying   augite  or  horn- 
blende, are  favorable  for  well-defined  fissures. 

As  it  is  not  my  intention  to  do  more  than  call  attention  to 
the  differences  in  fissuring  in  varying  rocks,  no  further  men- 
tion of  such  peculiarities  will  be  presented  here.  It  is  evident, 
however,  that  where  a  single  mass  of  rock  varies  in  texture,  as, 
for  example,  the  granite  core  of  Castle  Mountain,7  Mont.,  in 
which  continuous  exposures  show  the  rock  passing  from  gran- 
ite through  intermediate  gradations  into  rhyolite-porphyry,  the 
vein-fissures  will  vary  with  the  physical  characters  of  the  rock. 

II.  INFLUENCE  OF  COUNTRY-ROCK  ON  VEIN-FILLING. 

Where  a  vein,  passing  through  two  different  rocks,  carries 
one  set  of  ore-  and  gangue-minerals  in  one  rock,  and  another 
set  in  the  other,  there  is  a  strong  presumption  that  the  varia- 
tion in  the  inclosing  rock  has  caused  the  variation  in  the  vein- 
materials.  Similarly,  if  in  given  districts  one  set  of  vein-min- 
erals always  occurs  with  a  certain  kind  of  country-rock,  and 
another  set  with  another  kind,  it  is  probable  that  such  associa- 
tion is  genetic,  and  not  accidental. 

For  many  years  there  has  been  a  widespread  belief  among 
mining-geologists  and  engineers  that  igneous  rocks  are  an  al- 
most invariable  accompaniment  of  productive  ore-deposits  of 
the  precious  metals.  Whether  the  igneous  rocks  be  regarded 
as  the  actual  source  of  the  metal,  or  as  the  cause  of  fissuring 
and  ore-deposition  by  reason  of  dynamic  disturbance,  the  re- 
sult is  genetically  due  to  the  volcanic  forces.  Professor  Yogt 
has  recently  given  us,  in  his  able  and  instructive  paper,8  a 
resume  of  his  studies,  and  Professor  Kemp  has  shown 9  both  the 
competency  of  the  igneous  rocks  themselves  as  a  source  of 
supply  and  of  the  intrusives  as  a  source  of  energy.  It  is  not 
this  phase  of  the  subject  that  I  propose  to  discuss,  but  the  time- 
honored  question  of  the  influence  of  wall-rock  upon  the  mineral 
contents  of  the  vein.  Many  students  of  ore-deposits,  familiar 
with  the  common  occurrence  of  galena-ores  in  limestone,  and 
the  changes  in  mineral  character  of  the  Cornish  veins  with 

7  Weed  and  Pirsson,  Geology  of  the  Castle  Mountain  Mining  District,  Bulletin 
No.  139,  U.  S.  Geological  Survey  (1896). 

8  Problems  in  the  Geology  of  Ore-Deposits,  Trans.,  xxxi.,  125  (1901). 

9  K61e  of  the  Igneous  Rocks,  etc.,  Trans.,  xxxi.,  159  (1901). 


INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS.     223 

change  of  rock,  have  sought  to  establish  a  relation  between 
certain  rocks  and  certain  ores.  While  such  a  relation  seems  to 
prevail  in  a  few  districts,  no  general  law  has  been  established 
by  these  attempts. 

Conditions  Governing  the  Relation  of  Country-Rock  to  Vein- 
Contents. 

In  considering  the  relations  between  country-rock  and  vein- 
contents,  the  following  premises  are  assumed  : 

1.  Vein-filling  may  be  the  result  (a)  of  the  filling  of  open 
fissures,  (b)  of  replacement,  or  (c)  of  both  filling  and  replace- 
ment. 

2.  The  ore-  and  gangue-minerals  of  all  these  types  vary. 
Lindgren  has  divided  veins  filled  by  metasomatic  replacement 
into   11   classes,   and   shows  that  the  chemical  processes  in- 
volved were  very  different  in  each  case.     It  is  made  certain  by 
the  study  of  altered  wall-rocks  and  of  mine-waters  that  the 
mineral-forming  solutions  have  varied  greatly  in   character. 
Moreover,  some  veins  have  been  opened  after  formation,  and 
new  minerals  have  been  introduced  by  later  solutions. 

In  veins  the  material  of  which  is  well  crustified,  or  is  known 
to  be  the  result  of  the  filling  of  open  fissures,  a  marked  influ- 
ence of  the  wall-rock  on  the  contents  of  the  vein  would  not  be 
expected.  In  the  majority  of  veins,  however,  there  is  evidence 
of  more  or  less  metasomatic  replacement;  and  it  is  evident 
that  the  nature  of  the  wall-rock  will  be  an  important  factor  in 
the  chemical  reactions  of  the  processes  of  replacement.  It  should 
be  remembered,  however,  that  the  evidence  of  many  districts 
shows  that  veins  of  different  kinds  and  ages  may  form  in  the 
same  rock,  and  hence  it  is  not  to  be  expected  that  any  general 
conclusions,  applicable  to  all  veins,  can  ever  be  reached. 

Examples. 

Butte,  Mont. — In  the  typical  silver-veins  of  this  district  the 
filling  consists  of  quartz,  showing  well-marked  "  comb  "-struc- 
ture, with  rhodonite,  rhodochrosite,  pyrite,  zinc-blende,  and  sil- 
ver sulphides.  The  structure  is  clearly  that  of  the  filling  of 
open  fissures.  These  veins  occur  in  the  normal  Butte  granite, 
a  quartz-monzonite,  and  in  the  Bluebird  granite,  which  is  an 
aplite.  There  is,  however,  no  perceptible  difference  in  either 


-224  INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS. 

the  character  or  the  tenor  of  the  ore  between  the  veins  in 
the  aplite  and  those  in  the  normal  granite,  or  in  the  parts  of 
the  same  vein  where  it  cuts  the  two  rocks.  In  the  copper- 
veins,  on  the  other  hand,  there  is  a  marked  difference.  These 
-are  of  undoubted  metasomatic  origin,  and  were  formed  by  the 
replacement  of  the  rock  along  fracture-planes.  In  the  copper- 
area,  the  veins  cut  both  the  two  rocks  previously  mentioned 
and  also  a  quartz-porphyry,  which  I  have  named  the  Modoc 
porphyry.  In  the  Butte  granite,  the  veins  are  commonly  rich 
in  copper;  in  the  Bluebird  granite,  they  are  almost  equally 
wide  and  strong,  but  are  lean,  and  composed  chiefly  of  quartz, 
with  comparatively  little  pyrite  and  copper.  In  the  porphyry, 
the  veins  are  narrow  and  lean.  There  are  so  many  instances 
in  which  the  same  veins  can  be  seen  cutting  all  three  rocks 
that  there  can  be  no  doubt  as  to  the  correctness  of  these  con- 
clusions. The  vein-filling  consists  of  quartz  which  shows  no 
comb-structure,  with  pyrite  and  various  copper-minerals,  of 
which  chalcocite,  enargite,  and  bornite  are  the  most  common. 
The  walls  on  each  side  are  much  altered,  and  the  less  altered 
rocks  at  some  distance  from  the  veins  show  the  ferro-magnesian 
silicates  altered  to  pyrite.  The  relative  richness  of  the  veins 
in  the  Butte  granite  is  believed  to  be  due  to  the  basic  character 
of  the  rock,  and  its  greater  content  of  the  easily-replaceable  iron 
silicates.  The  rock  is  a  quartz-monzonite,  the  composition  of 
which  has  been  carefully  calculated  from  chemical  analyses  of 
the  rock,  and  of  the  biotite  and  hornblende  isolated  from"  it, 
and  from  microscopic  analysis  of  the  rock  as  well.10  These 
show  it  to  contain  15.26  per  cent,  of  hornblende  and  4.22  of 
biotite.  There  is  a  little  augite  also.  The  aplite  contains  over 
10  per  cent,  more  silica  than  the  rock  just  noted,  no  hornblende, 
and  very  little  biotite.  The  Modoc  porphyry  also  has,  when 
fresh,  a  very  little  mica,  and  is  as  high  in  silica  as  the  aplite. 
H.  Y.  Winchell  has  called  my  attention  to  the  condition  shown 
in  the  diagram,  Fig.  4.  In  the  case  here  given  as  a  general 
type,  the  vein  is  workable  only  in  the  Butte  granite. 

A  study  of  thin  sections  of  the  rock  adjacent  to  the  ore  shows 
that  the  hornblende  is  the  first  mineral  to  be  altered  into  ore, 
-and  that  the  bunches  of  this  mineral  form  the  nucleus  for  a 

10  Granite  Kocks  of  Butte,  Mont.  W.  H.  Weed,  Journal  of  Geology,  vol.  vii., 
JNo.  8,  p.  737  (Nov. -Dec.,  1899). 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS. 


225 


more  or  less  complete  replacement  of  the  entire  rock.  The 
general  principles  of  this  metasomatic  replacement  are  those 
given  by  Lindgren.11  It  is  probable  that  the  alteration  now 
seen  in  the  wall-rock,  with  its  nests  of  pyrite  replacing  the 
biotite  and  the  hornblende,  may  present  the  earlier  stages  of 
the  metasomatic  process,  and  that  the  pyrite  thus  formed  was 
not  only  the  nucleus  for  a  further  deposition  of  pyrite,  but  that 
the  pyrite  itself  was  the  '  precipitating-agent  for  the  copper- 
minerals,  as  has  been  shown  to  be  the  case  in  the  secondary 
enriched  ores.  In  the  aplite  there  is  more  quartz  and  less 
pyrite,  and  the  latter  mineral  is  noticeably  poor  in  copper.  The 
same  general  statement  also  holds  true  for  the  porphyry. 


Granite 


K**v/~;l  Aplite 

FIG.  4. — IDEAL  PLAN  OF  CONDITIONS  IN  A  COPPER- VEIN  AT  BUTTE,  MONT., 

PASSING  FROM  BASIC  GRANITE  INTO  APLITE  MASSES. 
The  solid  black  represents  high-grade  copper-ore,  when  the  vein  is  in  basic  granite. 

The  Dolcoath  mine  of  Cornwall  is  perhaps  the  best-known 
example  of  a  vein,  the  mineral  contents  of  which  vary  with  the 
nature  of  the  inclosing  rocks.  As  described  by  many  writers, 
the  veins  carry  copper-ores  in  slate  and  tin-ores  in  granite. 
Stretch  12  gives  a  further  example  of  argentiferous  galena  with 
its  usual  associated  blende  and  pyrite  in  a  decomposed  plagio- 
•clase  porphyry,  changing  to  auriferous  arsenopyrite  in  the 
underlying  granite. 

Cornwall. — Fissures  crossing  the  contact  of  granite  or  other 
intrusive  rock  with  sedimentary  rocks  are  not  uncommonly 
productive,  when  the  district  is  metalliferous.  This  is  very 
marked  in  the  Cornwall  mines,  where  bunches  of  ore  occur  at 

11  Metasomatic  Processes  in  Fissure- Veins,  Trans.,  xxx.,  578  (1900). 

12  Prospecting,  Locating,  and  Valuing  Mines,  p.  135  (1899). 

15 


226 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS. 


the  junction  of  granite  and  schist.  De  la  Beche  13  mentions 
fissures  traversing  schists  and  passing  through  a  dike  of  por- 
phyry (elvan)  some  300  ft.  thick.  The  vein  above  the  dike 
carried  little  ore ;  in  the  elvan,  ore  was  abundant  and  rich,  but 
became  poor  again  in  the  slates  beneath  (Fig.  5).  This  occur- 
rence of  ore-bunches  where  fissure-veins  cross  such  dikes  has 
always  been  known  to  the  Cornish  miners.  When  the  lodes 
pass  into  the  dikes,  they  are  often  branched  and  split,  as  shown 
in  Figs.  3  and  6  (after  De  la  Beche);  and  in  such  cases,  though 
the  total  amount  and  richness  of  ore  be  the  same,  the  vein  may 
not  pay  to  work,  on  account  of  the  large  amount  of  waste. 

Pontgibaud,  France. — Here  the  silver-lead  veins  occur  along 
fractures  within  granulite  dikes,  and  on  the  line  of  contact 
with  the  gneiss  country. 


FIG.  5.  —  SECTION  ACROSS  WHEAL 
ALFRED  GWINEAR,  CORNWALL. 
RICH  ORE  OCCURS  IN  THE  DlKE 
ONLY.  (FROM  DE  LA  BECHE.  ) 


FIG.  6. — VEIN  SPLIT  IN  TRAVERSING 
JOINTED  "  ELVAN  "  DIKE  (Ds  LA 
BECHE). 


"  When  the  dike  diminishes  in  size  the  vein  decreases  in  width  ;  when  the 
vein  penetrates  the  gneiss  the  ore  disappears.  The  best  ore  is  associated  with  the 
kaolinization  of  the  feldspar  of  the  granulite  ;  when  the  latter  becomes  hard,  un- 
altered in  depth,  the  ore  pinches  out."  u 

Rico,  Colo. — Bickard  also  mentions  the  veins  of  rich  gold- 
and  silver-ores  at  Newman  hill,  Rico,  Colo.,  as  "  noticeably 
affected  by  the  character  of  their  rock-walls."  There  is  a 
marked  change  in  passing  from  limestone  into  sandstone ;  and 
generally  the  veins  are  richest  in  the  darker-colored  sedi- 
mentary rocks.  The  interdependence  between  country-rock 
and  ore  is  briefly  discussed  by  Bickard,  who  adopts  Cotta's  ex- 
planation that  the  physical  texture  and  chemical  composition 

13  Geological  Observer,  p.   678  (1851  ed. ). 

14  T.  A.  Rickard,  Vein  Walls,  Trams.,  xxvi.,  200  (1897). 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS. 


227 


of  the  country-rock  affect  the  deposition  of  ore,  and  declares 
that  it  was  undoubtedly  the  carbonaceous  matter  of  the  rock 
at  Rico  which  acted  as  a  precipitant.  This  example  differs, 
therefore,  from  that  of  Pontgibaud,  where  feldspar  has  been 
replaced  by  silver-bearing  galena. 

Neihari,  Mont. — At  this  locality  the  veins  show  a  remark- 
able variation  in  richness,  corresponding  to  differences  in  the 
wall-rock.  Robert  H.  Raymond,  the  former  manager  of  the 
Diamond  R.  properties,  found  that  the  veins  were  barren  in 
the  dark-colored  gneisses,  and  held  ore-bodies  in  the  pink  or 
white  feldspathic  gneiss.  My  own  observations  enabled  me  to 
confirm  this  in  a  general  way,  and  also  showed  that  in  amphib- 
olite  the  vein  was  barren  as  well  as  narrow,  and  that  no  work- 


Pinto  diorite;  no  ore. 


Gray  gneiss:  pay  ore. 


Black  gneiss;  no  ore. 


3d  gneiss;  good  ore. 


Dark-gray  schist;  no  or^, 


FIG.  7. — DIAGRAM  (PLAN)  SHOWING  KOCKS  TRAVERSED  BY  THE  NEIHART 
VEINS,  AND  RELATION  OF  PAY-OKE  TO  COUNTRY-ROCK.  (The  veins  are 
indicated  by  simple  parallel  lines. ) 

able  ore-bodies  had  been  found  in  the  diorite.  In  quartzite 
and  in  the  intrusive  rhyolite-porphyry  the  veins  have  proved 
rich  near  the  surface,  but  the  values  have  gone  down  but  a  few 
yards.  It  is  believed,  however,  that  this  is  because  of  struc- 
tural conditions,  with  secondary  enrichment  of  a  shattered 
zone,  rather  than  because  of  a  mineralogical  condition  due  to 
the  nature  of  the  inclosing  rock.  These  conditions  are  indi- 
cated in  Fig.  7,  reproduced  from  the  report  on  the  district.15 

Furstenburg. — A  similar  example  is  quoted  from  Fournet  by 
De  la  Beche.16     The  Wenzal  vein   at  Furstenburg  is   nearly 

15  Geology  of  the  Little  Belt  Mountains,  Montana,  Twentieth  Annual  Report,  U. 
S.  Geological  Survey,  Part  III.,  p.  419  (1900). 

16  Geological  Observer,  p.  680  (1851  ed.). 


228  INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS. 

vertical  and  cuts  down  through  many  beds  of  gneiss,  about  60 
ft.  thick,  that  dip  east.  In  the  micaceous  gneiss  the  vein  is  a 
nearly-imperceptible  string  of  clay.  In  argillaceous  slates  it 
suddenly  becomes  from  12  to  18  in.  thick,  consisting  of  baryta, 
ruby-silver,  large  masses  of  antimonial  silver,  and  argentiferous 
gray  copper.  In  the  hornblende-gneiss  it  continues,  but  the 
silver-ores  are  wanting  and  galena  is  the  only  ore.  In  the 
fourth  series,  of  slightly  micaceous  beds  of  gneiss,  the  silver- 
ores  are  as  abundant  as  in  the  argillaceous  slates ;  but  they 
gradually  disappear  in  depth,  being  replaced  by  selenite  and 
galena. 

It  will  be  noted  that  the  Neihart  veins  present  several  con- 
tradictions to  the  rule  observed  in  the  Butte  district.  The  ores 
occur  in  the  feldspathic  rocks,  carrying  little  ferro-magnesian 
minerals.  The  basic  amphibolite  and  the  diorite  are  both  bar- 
ren. It  should  be  noticed  also,  in  this  connection,  that  the  ore- 
depositing  solutions  were  markedly  different  in  the  two  cases. 
In  the  Neihart  veins  the  gangue  is  mainly  a  mixture  of  carbon- 
ates of  lime,  iron,  and  manganese.  The  ores  are  also  markedly 
different,  as  they  consist  primarily  of  galena  with  sphalerite 
and  pyrite,  which  is  secondarily  enriched  in  the  upper  parts  of 
some  veins.  The  solutions  have  been  of  such  a  character  as  to 
react  with  the  feldspars  rather  than  with  the  ferro-magnesian 
silicates. 

Other  Montana  Localities. — In  the  silver-lead  camp  of  Barker 
in  the  Little  Belt  mountains,  near  Neihart,  as  at  the  mines  at 
Castle,  Mont.,  and  a  score  of  other  places  where  the  ores  occur 
in  limestone,  it  is  evident  that  different  action  has  taken  place. 
Here,  as  is  so  very  commonly  the  case,  the  ore-bodies  occur  in 
limestone  near  the  contact  with  igneous  intrusions.  The  heat 
of  the  latter  and  the  vapors  of  the  cooling  magma  have  altered 
these  limestones  to  more  or  less  coarse-grained  marbles,  if  the 
limestones  were  pure,  or  to  mixtures  of  garnet,  epidote,  and 
other  silicates,  if  the  limestones  were  impure.  The  latter  is 
the  case  at  the  Trout  mine  and  other  contact  ore-bodies  near 
Philipsburg,  Mont.,  where  the  Granite  Mountain  vein  (of  ^quite 
different  and  drier  ore,  without  lead)  occurs  in  the  granite. 
In  this  case  the  gangue  is  largely  silica;  and  it  is  probable  that 
similar  solutions  circulating  as  a  result  of  the  heat  supplied  by 
the  igneous  intrusion,  and,  in  part,  at  least,  in  fissures  formed 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS.          229 

in  rocks  by  the  intrusion,  formed  one  set  of  ores  in  the  lime- 
stone and  another  in  the  granite. 

Another  instance  of  the  difference  of  mineral  contents  in 
the  same  ore-deposit  in  different  rocks  is  shown  by  the  Elk- 
horn  mine  at  the  town  of  that  name,  Jefferson  county,  Mont. 
This  deposit  is  peculiar  in  its  structural  relations,  being  similar 
to  the  well-known  saddle-reefs  of  Australia  in  that  it  occurs  in 
a  saddle-shaped  mass  along  the  axis  of  a  steeply-pitching  anti- 
clinal fold.  The  rocks  are  sedimentary,  of  probable  Cambrian 
age,  and  dip  at  steep  angles  towards  the  contact  of  a  great  mass 
of  granite  and  other  intrusive  igneous  rocks.  The  ore  occurs 
at  the  contact  between  an  altered  shale  and  a  massive  crystal- 
line limestone,  and  both  rocks  have  been  changed  by  contact- 
metamorphism.  The  bedding-plane  is  ore-bearing  only  where 
the  general  dip  of  the  rocks  is  disturbed  by  flexures.  In  addi- 
tion to  the  ore  found  along  the  contact,  a  number  of  very  large 
ore-bodies  have  been  found  at  some  little  distance  in  the  dolo- 
mite, though  always  in  the  same  structural  position.  The  ore 
found  along  the  altered  shale-dolomite  contact  is  essentially  a 
"dry"  quartzose  milling-ore;  that  of  the  dolomite,  mainly 
galena,  with  accessory  sphalerite  and  pyrite.  Both  ores  are 
connected  by  "  pipes  "  and  stringers,  and  both  the  field-  and 
the  microscopic  evidence  shows  that  they  were  formed  by  the 
same  solutions  and  at  the  same  time.  There  is  no  escape  from 
the  conclusion  that  the  difference  in  the  mineralogical  char- 
acter of  the  ores  is  the  result  of  the  different  nature  of  the  in- 
closing rock. 

It  would  be  tedious  to  enumerate  all  the  familiar  deposits  in 
limestone.  Those  of  Leadville,  Colo.,  and  Eureka,  Nev.,  have 
been  thoroughly  studied  'and  described.  Tombstone,  Ariz., 
presents  quartzose  veins  filling  fault-fissures,  cutting  slightly- 
tilted  sedimentary  rocks,  with  the  workable  ore-bodies  formed 
by  replacement  of  limestone  along  bedding-planes,  and  pre- 
sumably by  the  same  solutions  that  filled  the  fissures. 

Derbyshire. — The  Derbyshire  lead-mines  of  England  are  also 
well-known  examples  of  veins  carrying  galena  in  limestone,  and 
barren  when  in  the  intercalated  intrusive  trap-rocks  (toadstone). 
Fig.  8,  from  De  la  Beche,  illustrates  the  occurrence  of  galena 
in  the  limestones  above  and  below  an  intrusive  sheet  in  one  of 
the  Derbyshire  mines.  The  leader  or  fissure  traverses  the 


230    INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS. 

"  toadstone "  as  well  as  the  lime-rock,  but  it  is  only  in  the 
limestone  that  galena  occurs  in  the  altered  area.  The  channels 
or  rakes  (g  i,  a  k,  c  m,)  were  fissures,  through  which  solutions 
reached  the  pipes  or  ore-bunches,  p  p,  the  bedding-plane  de- 
posits,//, and  the  joint-deposits,  h  h. 

Contact-Deposits. 

As  Lindgren  has  remarked  in  discussing  the  formation  of 
contact-deposits,  a  chemical  reaction  seems  to  take  place  be- 
tween the  substances  leaving  the  magma  and  the  carbonate  of 
lime,  causing  the  deposition  of  new  minerals  and  the  liberation 
of  carbon  dioxide.  In  the  cases  mentioned  in  this  paper,  the 
evidence  shows  that  the  veins  were  probably  formed,  not  by 
true  pneumatolytic  action,  but  by  hot  circulating  waters  which 
were  as  truly  a  result  of  the  igneous  intrusion  as  the  vapors 
and  gases  of  pneumatolytic  action.  The  escaping  vapors  and 
gases  from  the  magma  were,  it  is  believed,  taken  up  by  circu- 


FIG.  8. — LIMESTONE  BEDS  OF  DERBYSHIRE,  WITH  INTERCALATED  BEDS  OF 
IGNEOUS  ROCK  (TOADSTONE)  TRAVERSED  BY  VEINS.     (Ds  LA  BECHE.) 

lating  waters  of  either  deep-seated  or  meteoric  origin,  so  that 
the  "  mineralizing-agents "  which  had  taken  up  and  formed 
the  volatile  compound  of  various  metals,  as  supposed  by  Lind- 
gren, passed  into  solution.  Concerning  the  occurrence  of  this 
class  of  deposits  in  limestone,  Mr.  Emmons's  description  of  the 
Greenwood  ores  is  quite  significant.  He  says:  "  The  ore- 
bodies  are  cut  by  eruptive  dikes  that  do  not  apparently  disturb 
or  exert  any  metamorphic  influence  on  the  ore,  and  yet  are  not  at 
all  mineralized  themselves;"  At  a  number  of  localities  seen 
by  the  writer,  the  veins,  if  traced  into  the  granite  or  diorite, 
would  be  found  to  be  barren  of  galena,  and  generally  without 
value.  On  the  other  hand,  at  Marysville,  Mont,  the  veins 
show  no  appreciable  change  in  character  in  passing  through 
the  altered  shales  or  hornstones  into  the  granite.  It  should 
be  noted,  however,  that  the  ores  at  this  place  are  .not  kad- 


INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS.     231 

bearing.  Moreover,  I  am  told  by  G.  H.  Robinson,  the  former 
manager  of  the  mine,  that  in  the  earlier  workings  the  veins 
showed  a  marked  tendency  to  be  richer  in  approaching  the 
granite  (or  rather  diorite)  contact,  and  were  poor  when  they 
passed  into  the  granite. 

Thunder  Bay  Silver- Veins. — H.  V.  Winch  ell  tells  me  that 
the  Thunder  Bay  district  of  Canada  affords  excellent  examples 
of  vein-variation  in  different  rocks.  The  basaltic  caps  and  sills 
of  that  region  overlie  Animikie  slates  and  argillites,  resting  in 
turn  upon  taconites  and  several  hundred  feet  of  cherts.  These 
rocks  rest  upon  the  basal  quartzite  overlying  the  Archaean  com- 
plex. The  silver-veins  are  often  from  8  to  10  ft.  wide  in  the 
slates,  and  carry  native  silver  and  argentite  with  small  amounts 
of  blende,  galena,  and  pyrite,  in  a  gangue  of  quartz,  barite, 
calcite,  fluorite,  etc.  They  are  wide  and  productive  in  the 
slates,  but  split  up  into  narrow  and  barren  seams  in  the  over- 
lying trap-rock,  and  are  barren  in  the  underlying  cherts  and 
Archaean  rocks.  The  Rabbit,  Silver  Mountain,  Beaver,  and 
other  mines  have  been  noted  producers. 

Kemp 17  describes  the  Silver  Islet  mine  as  a  fissure-vein  car- 
rying native  silver,  argentite,  tetrahedrite,  galena,  blende,  and 
nickel  and  cobalt  compounds  in  a  calcite  gangue.  The  vein  is 
in  flags  and  shales  of  the  Animikie  series  (Algonkian)  and  cuts 
a  large  trap  dike  (gabbro),  within  which  alone  the  vein  is  pro- 
ductive. 

Influence  of  Carbonaceous  Matter  on  the  Formation  of  Ore. 

The  well-known  reducing  action  of  carbon  has  long  been  an 
accepted  explanation  of  the  occurrence  of  ore-bodies  in  car- 
bonaceous shales.  The  silver-veins  of  the  Animikie  slate  are 
often  cited  as  examples.  The  Australian  veins,  which  carry 
rich  gold-ores  only  where  they  cross  "  indicators,"  are  a 
well-known  instance,  and  the  Fahlbands  of  Norway  another. 
Rickard  ascribes  the  Australian  ore-bodies  to  the  reducing 
action  of  the  carbonaceous  shales.  All  the  descriptions  show, 
however,  that  although  these  indicator-reefs  are  strata  of  car- 
bonaceous shale,  they  are  remarkable  for  the  amount  of  pyrite 
they  contain,  while  other  shale-beds  crossed  by  the  veins  are 
also  carbonaceous,  but  not  pyritic.  In  previously-published 

17  Ore-Deposits,  3ded.,  p.  283  (1900). 


232    INFLUENCE  OF  COUNTRY-ROCK  ON  MINERAL  VEINS. 

papers  I  have  called  attention  to  the  reducing  action  of  pyrite 
on  solutions  carrying  copper-salts ;  and  believe  that  this  min- 
eral is  the  real  precipitating-agent  in  both  the  Australian  and 
Norwegian  ores  cited.  This  view,  based  upon  field-observa- 
tions and  laboratory-experiments,  in  connection  with  the  work 
of  the  U.  S.  Geological  Survey,  is  strengthened  by  the  experi- 
ments made  under  the  direction  of  my  friend,  H.  V.  Winchell, 
geologist  of  the  Anaconda  Copper  Co.,  who  finds  that  the 
mine-waters  of  that  company's  properties,  though  strongly 
charged  with  cupric  sulphate  and  ferric  sulphate,  also  contain 
large  amounts  of  carbonaceous  matter  from  the  old  mine-tim- 
bers. It  is  evident  that  if  the  carbon  were  an  active  reducing- 
agent,  it  would  reduce  the  ferric  iron  to  the  ferrous  condi- 
tion. On  the  other  hand,  experiments  show  that  pyrite  from 
the  Butte  veins  left  for  several  weeks  in  the  natural  mine- 
waters  became  coated  with  copper-glance  (Cu2S). 

Dependence  of  Vein-Minerals  on  the  Character  of  Wall-Rock,  Due 
to  Metasomatic  Chemical  Reactions. 

The  examples  given  show  that  a  variation  of  mineral  contents 
coincides  with  the  change  of  country-rock  in  many  places  and 
in  many  kinds  of  veins.  A  study  of  the  vein-  and  gangue- 
minerals  and  of  the  rock  contiguous  to  the  ore-bearing  fissures 
is  therefore  essential  to  a  complete  understanding  of  the  origin 
of  ore-deposits.  The  rocks  forming  the  vein-walls  are  com- 
monly altered.  Where  no  such  alteration  is  observable,  it  will 
usually  be  found  that  the  veins  are  the  result  of  the  filling  of 
cavities,  and  are  thus  excluded  from  the  category  discussed  in 
this  paper.  Nevertheless,  some  metasomatic  alteration  of  the 
rock  adjacent  to  the  fissure  is  usually  present;  and  it  must  be 
admitted  that  many  veins  show  evidence  both  of  the  filling  of 
open  cavities  and  of  deposition  by  replacement. 

As  already  indicated,  the  coincident  variation  of  mineral 
contents  and  wall-rock  is  due  to  metasomatic  action,  whereby 
there  is  a  chemical  interchange  between  the  rock  and  the  vein- 
producing  solutions.  The  metasomatic  process  varies  greatly 
because  the  solutions  vary.  Lindgren  18  has  treated  the  subject 
fully,  and  has  indicated  the  chemistry  of  the  process,  so  that  a 
detailed  account  of  the  reactions  involved  is  unnecessary  here. 

18  Metasomatic  Processes  in  Fissure- Veins,  Trans.,  xxx.,  578  (1900). 


INFLUENCE    OF    COUNTRY-ROCK    ON    MINERAL    VEINS.  233- 

According  to  his  clear  demonstration,  the  alteration  of  the  same 
kind  of  wall-rock  shows  that  the  vein-forming  solutions  have 
varied  greatly  in  their  chemical  effect  upon  vein-contents,  even 
where  the  veins  are  of  metasomatic  origin. 

The  most  frequent  process  seems  to  be,  in  granitic  rocks,  a 
reaction  between  the  ferro-magnesian  minerals,  such  as  augiter 
hornblende,  biotite,  etc.,  and  the  vein-forming  solutions,  with 
the  formation  of  pyrites  and  other  sulphides.  If  later  recon- 
centration  occurs,  bonanzas  are  formed  by  reaction  of  the 
pyrites  on  later  solutions.  This  process  I  have  treated  quite 
fully  in  a  monograph  now  in  preparation  on  the  Butte  ore- 
deposits. 

In  other  cases,  the  feldspars  are  attacked,  and  the  iron-min- 
erals of  the  rock  are  not  replaced.  Such  a  case  is  described  by 
R.  C.  Hills ; 19  and  Rickard  ascribes  the  silver-lead  ores  of 
Pontgibaud,  France,  to  the  replacement  of  the  feldspars  of 
granulite,  as  already  quoted. 

The  attempt  to  tabulate  the  relation  between  vein-contents 
and  country-rock  has  been  made  by  various  writers,  and  lately 
by  Stretch.  The  latter  author,  in  his  very  interesting  essay,20 
has  given  139  occurrences,  and  attempted  to  eliminate  the  per- 
sonal equation  of  the  observer.  It  is  evident,  however,  that 
existing  literature  is  not  adequate  for  such  work.  Too  often 
the  rocks  are  wrongly  named,  or  receive  generic  terms  only. 
The  words  "granite"  and  " porphyry"  have  long  been  used 
in  a  textural  sense  by  mining  engineers,  and  by  many  geolo- 
gists unfamiliar  with  petrographic  distinctions ;  and,  as  is  well 
known,  shales,  limestones,  and  sandstones  grade  into  one  an- 
other. For  the  careful  study  of  metasomatic  replacement, 
which  must  be  made  to  establish  scientifically  a  relation  be- 
tween country-rock  and  vein-filling,  finer  distinctions  must  be 
made.  The  granitic  rocks  of  some  writers  include  gabbros, 
diorites,  granite,  and  aplite,  with  a  wide  range  of  mineral  and 
chemical  compositions.  The  most  that  can  be  attempted  at 
present  is  to  present  the  known  facts  of  occurrence  in  deposits 
about  which  there  can  be  no  doubt,  or  which  have  been  care- 
fully studied.  The  facts  here  set  forth  show  the  advantages  of 
geological  examination  of  the  district  about  a  mine,  especially 

19  Proceedings  of  the  Colorado  Scientific  Society,  vol.  i.,  p.  20. 

20  Pocket-Book  for  Prospecting,  Locating,  and  Valuing  Mines  (1900). 


234  INFLUENCE    OF    COUNTRY-BOCK    ON    MINERAL    VEINS. 

of  the  area  containing  the  vein.  It  is  evident  that  it  is  im- 
portant to  ascertain  the  extent  laterally  and  the  probable  extent 
vertically  of  the  rock  in  which  the  ore  occurs ;  and,  if  other 
rocks  occur,  what  they  are  and  what  effect,  if  any,  they  will 
have  on  the  vein-fissure  and  vein-filling.  Such  associations 
have  long  been  recognized  in  a  rough  way  by  the  miners,  who 
say  "that  mineral  will  not  live  long  in  such  a  rock."  The  in- 
stances noted  in  the  literature  of  ore-deposits  are  few,  compared 
to  those  actually  encountered  in  mining-operations,  where  the 
character  of  the  vein  has  changed  in  depth.  Such  change  is, 
it  is  true,  very  often  due  to  secondary  alteration,  with  or  with- 
out reconcentration  and  enrichment  of  material,  but  in  many 
cases  it  is  probably  due  to  change  of  rock. 

CONCLUSIONS. 

From  the  evidence  presented  the  following  conclusions  are 
drawn : 

1.  The  structural  characters  of  vein-fissures,  such  as  course, 
width,  etc.,  vary  with  the  nature  of  the  country-rock. 

2.  The  mineral  contents  of  veins  formed  wholly  by  the  fill- 
ing of  open  fissures  are  not  affected  by  the  nature  of  the  vein- 
walls. 

3.  The  mineral  contents  of  ore-deposits  formed  by  metaso- 
matic  replacement  vary  with  the  nature  of  the  inclosing  rock. 

4.  As  metasomatic  processes  vary  in  character  with  the  na- 
ture  of  the  solutions,  no  invariable  general   relation  can  be 
established  between  certain  rock-types  and  rich  ore-deposits. 


IGNEOUS    ROCKS    AND    CIRCULATING    WATERS.  235 

No.  10. 

Igneous  Rocks  and  Circulating  'Waters  as  Factors  in  Ore- 
Deposition. 

BY  J.  F.  KEMP,  NEW  YORK,  N.  Y. 
(New  Haven  Meeting,  October,  1902.     Trans.,  xxxiii.,  699.) 

IN  submitting  an  additional  contribution  to  the  discussion  on 
ore-deposits  in  the  recent  volumes  of  the  Transactions,  it  is  my 
desire  to  adhere  closely  to  matters  of  material  importance  as 
affecting  the  actual  processes.  Judging  from  the  discussion  by 
Professor  Van  Hise,  and  from  one  or  two  reviews  or  other  arti- 
cles by  associates  of  his  in  geological  work,  the  impression 
seems  to  prevail  that,  in  so  far  as  my  paper*  referred  to  his 
masterly  essay, f  I  was  guilty  of  misconceptions  regarding  both 
the  part  attributed  by  him  in  it  to  the  igneous  rocks  and  the 
ubiquitous  presence  of  the  ground-water.  I  should  regret  ex- 
tremely to  be  wanting  in  these  particulars  or  to  have  misun- 
derstood one  for  whose  great  services  in  this  and  other  branches 
of  geology  no  one  has  a  higher  esteem  than  myself.  I  have, 
however,  in  the  most  careful  way,  and  with  these  points  in 
mind,  read  his  essay  again,  and,  taking  it  as  a  whole,  I  can- 
not gain  any  different  impression  of  relative  magnitudes  than 
the  one  first  received.  The  importance  of  the  igneous  phe- 
nomena and  the  restrictive  influence  of  the  processes  described 
by  "  cementation  "  in  their  effect  upon  the  ground-water,  as  set 
forth  in  Professor  Van  Hise's  "  Discussion  "  (  Trans.,  xxxi.,  292), 
impress  me  as  being  in  very  marked  contrast  with  the  same 
things  in  his  first  essay.  If  the  point  seems  to  anyone  of  suffi- 
cient importance,  it  can  easily  be  decided  by  reading  the  origi- 
nals. My  paper  was  the  result  of  some  years  of  observation, 
reading  and  reflection,  and  was  meant  to  be  an  independent 
contribution,  controversial  only  in  some  subordinate  particu- 
lars. In  depicting  the  drama  of  the  deposition  of  ores,  I  can- 
not but  feel  that  Professor  Van  Hise  assigned  to  the  chorus  and 
the  scene-shifters  some  characters  which,  it  seems  to  me,  should 

*  "The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins,"  by  J.  F. 
Kemp,  Trans.,  xxxi.,  169,  and  Genesis  of  Ore-Deposits,  p.  681. 

f  "Some  Principles  Controlling  the  Deposition  of  Ores,"  by  C.  R.  Van  Hise, 
Trans.,  xxx.,  27,  and  Genesis  of  Ore-Deposits,  p.  282. 


236  IGNEOUS    ROCKS    AND    CIRCULATING   WATERS. 

have  been  among  the  leading  parts.  This  is  not  to  imply  that 
the  chorus  or  the  supernumeraries  are  unimportant  or  unessen- 
tial members  of  the  cast.  On  the  contrary,  no  presentation  could 
be  given  without  them ;  and  the  earnest  student  of  the  text  of 
dramas  will  quite  invariably  find  them  mentioned  in  the  incon- 
spicuous way  appropriate  to  their  modest  station. 

Still,  psychology  on  the  surface  of  the  earth  does  not  ma- 
terially affect  the  production  of  veins  in  the  depths ;  and,  with 
this  preliminary  clearing  of  the  ground,  points  of  more  conse- 
quence may  be  taken  up.  All  veins  and  replacements,  and  the 
greater  number  of  contact-deposits,  must  have  been  produced 
through  the  agency  of  underground  water  aided  by  auxiliary 
reagents  and  heat.  No  sensible  man  can  doubt  this.  Unques- 
tionably, moreover,  where  there  is  a  continuous  column  of 
water  possessing  "  head "  and  operating  through  sufficiently 
open  channels,  circulation  will  ensue.  The  underground  water 
and  related  solvents  must  be  derived  either  (A)  from  the 
emissions  of  eruptive  rocks  or  (B)  from  meteoric  sources,  pos- 
sibly during  sedimentation.  When  the  latter,  the  heat  which 
is  essential  to  promote  circulation  must  come  (IB)  from  the 
crushing  and  frictional  rubbing  of  particles  or  similar  dynamic 
causes  in  rocks,  or  from  chemical  reactions ;  (2B)  from  the 
normal  increase  of  temperature  with  depth ;  or  (3B)  from  igne- 
ous intrusions.  (Compare  "Principles,  etc.,"  Trans.,  xxx.,  49. 
Much  the  same  appears  in  the  writer's  "  Ore-Deposits  of  the 
U.  S.  and  Canada,"  3d  ed.,  pp.  26  and  27,  1901.)  The  discus- 
sion of  these  several  topics  will,  I  believe,  cover  the  debatable 
points. 

A.  Emissions  of  eruptive  rocks.  This  point  has  been  dis- 
cussed briefly  in  the  first  part  of  my  former  paper,  and  I  am 
led  to  believe  that  it  deserves  all  the  importance  which  is  there 
given  it.  A  citation  from  the  Zeitschrift  fur  praktische  Geologic 
for  October,  1901,  p.  383,  bears  on  this  point.  The  original  in 
the  "  Echo  "  is  inaccessible  to  me. 


"The  gases  which  are  emitted  by  the  plutonic  rocks,  when  the  latter  are 
strongly  heated,  present  a  subject  of  notable  interest  in  so  far  as  it  is  necessary  to 
believe  that  a  part  of  them  were  enclosed  in  the  rocks  at  great  pressure  at  the 
time  of  consolidation.  According  to  the  '  Echo,'  Armand  Gautier  has  submitted 
to  strong  ignition  a  number  of  rocks  which  had  crystallized  at  high  temperatures 
and  pressures.  From  each  100  volumes  of  the  following  varieties  he  obtained  at 


IGNEOUS    ROCKS    AND    CIRCULATING    WATERS.  237 

a  red  heat  the  stated  volumes  of  gases :  granite,  670  ;  ophite,  760  ;  porphyry, 
740.  8ince  we  must  believe  that  these  rocks,  while  beneath  the  surface,  were 
often  heated  to  similar  temperatures,  which  are  below  those  prevailing  at  their 
time  of  consolidation,  it  is  clear  that  the  results  possess  an  important  bearing 
upon  the  question  of  the  production  of  the  volcanic  gases  and  of  those  dissolved 
in  hot-springs.  If  we  give  due  weight  to  the  expansive  power  which  these  rock- 
•gases  must  develop  whenever  the  pressure  upon  the  heated  rock  in  the  interior  of 
the  earth  permits,  we  see  that  the  old  theory  of  the  production  of  volcanic  out- 
breaks by  the  introduction  of  water  is  no  longer  necessary.  By  a  stall  stronger 
ignition  the  volume  of  the  emitted  gases  appreciably  increases.  At  1000  degrees 
(centigrade)  granite  affords,  according  to  the  calculation,  20  times  its  own  volume 
of  various  gases,  besides  89  times  its  volume  of  steam  ;  that  is,  more  than  100 
times  its  own  volume  of  gases  and  vapors.  When  one  realizes  the  explosive  power 
which  this  implies,  one  may  dismiss  the  introduction  of  surface  waters  into  the 
glowing  reservoirs  of  rock  from  the  theories  of  volcanic  action." 

I  will,  however,  bring  these  matters  in  as  important  factors  in 
the  production  and  circulation  of  underground  waters  and  the 
formation  of  ores  ;  and,  so  long  as  their  original  presence  in  the 
igneous  rocks  is  admitted,  it  is  a  matter  of  small  moment,  in 
this  connection,  whether  the  magmas  are  brought  up  into  the 
zone  of  circulating  waters  by  gravity,  according  to  the  views 
of  Dutton,  Gilbert  and  Van  Hise,  or  by  the  exhaustive  force  of 
the  once  occluded  vapors  themselves,  as  other  authorities  of 
•equal  weight  maintain. 

The  general  conception  also  gains  much  support  from  what 
we  know  of  the  contact-deposits  which  are  found  on  the  bor- 
ders of  eruptive  rocks  and  limestones.  Mr.  Lindgren's  paper* 
bears  on  this  subject.  I  have  recently  had  the  opportunity  to 
study  one  of  the  largest  of  the  Mexican  cases,  and  it  seems  to 
corroborate  the  derivation  of  ores  directly  from  a  magma.  In 
the  course  of  the  intrusion  of  a  series  of  eruptives  at  San 
Jose,  Tamaulipas  (which  will  be  soon  described  in  detail  by 
my  assistant,  Mr.  George  I.  Finlay),  about  midway  in  time, 
there  came  a  laccolithic  mass  of  andesitic  rock  which  embraced 
in  itself  huge  masses  of  Cretaceous  limestone.  It  has  produced 
contact-zones  of  garnet-rock,  with  magnetite,  a  little  specular 
hematite,  and  great  quantities  of  pyrite  and  chalcopyrite.  All 
these  must  be  considered  to  be  the  products  of  contact-meta- 
morphism,  and,  except  in  the  matter  of  certain  minor  re- 
arrangements, there  is  no  reason  to  think  that  meteoric  waters 

*  "  The  Character  and  Genesis  of  Certain  Contact-Deposits,"  by  W.  Lindgren, 
Trans.,  xxxi.,  226,  and  Genesis  of  Ore-Deposits,  p.  716. 


238  IGNEOUS    ROCKS    AND    CIRCULATING    WATERS. 

have  had  any  share  in  their  production.  The  limestone,  which 
is  quite  pure,  yielding  over  50  per  cent,  of  CaO,  as  I  under- 
stand from  the  smelter-records,  has  been  changed  to  garnet 
with  something  like  15  per  cent,  of  CaO.  There  must  have, 
therefore,  been  an  enormous  emission  of  SiO2  and  other  sub- 
stances from  the  magma.  Certainly  a  million  tons  would  be  a 
small  estimate  of  the  garnet-rock  actually  in  sight  within  an 
area  of  2  or  3  square  miles.  Let  us  suppose,  now,  that  a 
magma  charged  with  these  materials  were  intruded  in  some 
other  rock  than  limestone,  such  as  sandstone  or  granite,  or 
some  intractable  material.  The  same  emission  of  silica,  of 
sulphur  and  of  metallic  bases  would  certainly  take  place ;  but 
not  being  able  to  react  on  the  walls,  and  not  being  held  by  them 
next  to  the  eruptive,  they  must  migrate  upward  through  fissures. 
It  is,  moreover,  inconceivable  that  they  should  be  emitted 
otherwise  than  in  association  with  much  more  steam  or  poten- 
tial water  than  their  own  mass,  and  one  must  believe  that  they 
would  be  yielded  under  such  pressure  and  with  such  a  vis  a 
tergo  that  they  would  not  need  any  other  motive  power  to  drive 
them  upward.  In  higher  levels,  metallic  veins  with  prevailing 
quartz-filling  and  all  the  common  varieties  of  ore-deposits 
wTould  result.  They  might  mingle  with  meteoric  waters  to  a 
certain  degree,  and  beyond  question  would;  but  the  latter 
would  play  no  necessary  or  essential  part  in  the  process. 
The  original  deposits  might  be  later  rearranged  by  the  circula- 
tions of  meteoric  waters,  and  I  realize  perfectly,  from  the 
recent  observations  of  Messrs.  Emmons,  Weed,  Van  Hise, 
De  Launay  and  others,  that  there  is  every  reason  to  believe  that 
they  would  be ;  but  it  is  not  necessary  to  assume  such  arrange- 
ments in  order  to  yield  an  ore-body. 

Mr.  Lindgren's  paper  on  contact-deposits  refers  to  a  number 
of  others  similar  to  this  Mexican  one,  wrhich,  in  fact,  he  also 
cites,  quoting  a  very  brief  reference  to  it  by  Ordonez ;  but  there 
are  many  more.  There  is  a  very  large  one,  for  example,  at 
San  Pedro,  N.  M.,  a  detailed  description  of  which  has  been 
given  by  two  members  of  the  Institute,  Messrs.  Yung  and 
McCaffery.*  I  have  had  the  privilege  of  going  over  the 
ground  with  them  the  past  summer.  Notes  upon  still  ad- 

*  "The  Ore-Deposits  of  the  San  Pedro  District,  New  Mexico,"  Trans.,  xxxiii., 
350.  ; 


IGNEOUS  ROCKS  AND  CIRCULATING  WATERS.        239 

ditional  cases  have  been  received  from  other  old  students  and 
friends.  The  very  valuable  contributions,  moreover,  of  Messrs. 
Weed  and  Barrell*  upon  the  Elkhorn  district,  Montana,  have 
served  to  show  the  important  preparatory  work  of  contact- 
metamorphism  in  producing  porous  rock  wherein  ores  may 
later  be  deposited.  Mr.  Weed  has  shown  that  the  Cananea 
mines,  Sonora,  Mexico,  are  of  this  type;  and  informally,  from  Dr. 
W.  L.  Austin,  the  writer  has  learned  of  many  additional  cases. 

The  recent  exhibitions  of  vulcanism  in  the  West  Indies  must 
bring  the  force  of  these  statements  home  to  any  one  who  re- 
flects upon  them.  That  the  sea  or  any  form  of  meteoric  water 
could  have  contributed  more  than  a  small  portion,  which  was 
caught  up  as  the  explosive  vapors  progressed  toward  the  sur- 
face, seems  to  me  contrary  to  sound  principles  in  physics.  In 
fact,  I  cannot  resist  the  conviction  that  in  the  study  of  vul- 
canism and  its  effects  lies  the  promising  field  of  investigation 
which  will  throw  additional  light  upon  the  production  at  least 
of  the  first  deposits, f  which  may  afterwards  experience  en- 
richment in  their  upper  portions  from  the  action  of  meteoric 
waters. 

The  pegmatites  and  at  least  their  limiting  quartz-veins  were 
certainly  produced  in  very  much  the  way  just  outlined.  They 
are  very  widespread.  Mr.  Lindgren  mentions  the  general  ex- 
perience that  they  are  barren  of  ores,!  and  I  have  likewise  re- 
marked this  feature  ;§  but  Dr.  0.  A.  Derby  has  recently  con- 
tributed to  the  Institute  some  notes  on  Brazilian  gold-veins  in 
which  he  describes  a  very  extensive  series  of  rather  richly  pro- 
ductive veins  of  this  character.  || 

If,  now,  we  add  to  the  above  considerations  the  further  one 
of  the  almost  constant  association  of  eruptive  rocks  with  veins, 

*  "Geology  and  Ore-Deposits  of  the  Elkhorn  Mining  District,  Jefferson  Co., 
Mont.,"  by  W.  H.  Weed  ;  "  Petrography, "  by  Joseph  Barrell,  22d  Ann.  Rept. 
U.  S.  G$ol  Survey,  Part  II.,  p.  399.  "Physical  Effects  of  Contact-Meta- 
morphism,"  by  Joseph  Barrell,  Am.  Jour.  Sci.,  April,  1902,  p.  279. 

f  A  very  suggestive  essay  bearing  on  this  point  is  that  of  L.  De  Launay, 
"Contribution  a  1' Etude  des  Gites  Me*tallif  eres, "  Annales  des  Mines,  August, 
1897,  p.  119. 

J  "Character  and  Genesis  of  Certain  Contact-Deposits,"  Trans.,  xxxi.,  243,  and 
Gene»is  of  Ore-Deposits,  p.  732. 

%  "Hole  of  the  Igneous  Rocks,  etc.,"  Trans.,  xxxi.,  133",  and  Genesis  of  Ore- 
Deposits,  p.  694. 

II   "Notes  on  Brazilian  Gold-Ores,"  Trans.,  xxxiii.,  282. 


240  IGNEOUS    ROCKS    AND    CIRCULATING    WATERS. 

and  the  usually  very  restricted  occurrence  of  the  latter,  it 
seems  to  me  that,  areally  considered,  we  have  adequate  reason 
to  attribute  to  the  former,  and  especially  when  there  is  no  posi- 
tive contradictory  evidence,  very  great  importance  in  vein-pro- 
duction. It  is  reasonable,  efficient,  demonstrated  in  important 
cases,  and  in  no  respect  more  speculative  than  the  inferred 
deep  circulations  of  descending  meteoric  water.  I  do  not  state 
this  controversially,  but  as  a  claim  for  its  recognition. 

When  ore-formation  is  referred  to  pneumatolytic  or  fumarolic 
action,  I  understand  that  practically  these  processes  are  meant. 
Under  these  names,  or  with  a  general  statement  similar  to  the 
one  given  above,  the  processes  have  been  often  appealed  to.* 
Nevertheless,  such  unquestioning  faith  has  generally  been  felt 
in  meteoric  waters  that  the  possibilities  of  this  general  cause 
have  received  comparatively  little  attention. 

B.  Regarding  the  general  question  of  the  descent  of  mete- 
oric waters  into  the  earth,  there  developed  in  our  two  papers 
considerable  difference  of  opinion  between  Professor  Van  Hise 
and  myself.  I  am  entirely  frank  to  admit  that  I  gained  from 
his  "  Principles  "  the  idea  that  he  believed  the  meteoric  waters 
to  be  everywhere  descending,  migrating  laterally  through  the 
smaller  waterways,  and,  although  guided  by  relatively  impervi- 
ous beds,  pitching  anticlines,  etc.,  to  be  then  returning  to  the 
surface  by  the  trunk-channels.  This  is  certainly  the  concep- 
tion of  the  ground-water  hitherto  held  by  the  lateral-secretion- 
ists.  I  have  again  and  repeatedly  read  the  parts  of  the  essay 
bearing  on  this  subject,  and  I  cannot  blame  myself  for  reaching 
this  conclusion.  I  therefore  laid  stress,  and  with  entire  justifi- 
cation, upon  the  dryness  of  deep  mines,  in  order  to  delimit  or 
disprove  it.  Professor  Van  Hise's  rejoinderf  to  my  arguments 
strikes  me  as  a  great  restriction  upon  what  I  believed  to  be  his 
conception,  and,  were  it  not  for  his  statement  to  the  contrary, 
I  should  conclude  that  his  attitude  had  been  much  modified. 
The  latter  expression  makes  it  less  difficult  for  us  to  attain 

*  For  instance,  by  von  Richthofen  for  the  Comstock  lode ;  by  J.  S.  Curtis  for 
Eureka,  Nev.,  Monograph  VII.,  U.  S.  Geol.  Survey,  p.  89  ;  and  by  Arnold  Hague, 
Monograph  XX.,  294;  by  J.  E.  Spurr  for  Mercur,  Utah,  IQth  Annual  Report, 
U.  S.  Geol.  Survey,  Part  II.,  p.  402  ;  and  by  the  last  named,  again,  in  the  18th  An- 
nual Report,  Part  III.,  pp.  297  to  316. 

f  Trans.,  xxxi.,  300  and  301. 


IGNEOUS  ROCKS  AND  CIRCULATING  WATERS.        241 

approximate  agreement.  I  am  quite  free  to  admit  that  it  is 
possible  that  the  advance  of  "  cementation  "  may  plug  up  cav- 
ities so  as  seriously  to  impede  circulation.  This  would  be  es- 
pecially effective  in  the  larger  channels  where  the  main  ore- 
bodies  such  as  we  mine  are  precipitated.  If,  then,  a  mine 
went  down  on  a  filled  and  plugged  vein,  water  might  reason- 
ably diminish  and  disappear  with  depth.  It  is  less  easy  to 
believe  that  the  same  results  would  take  place  in  the  smaller 
and  tributary  conduits  which  feed  downward  and  into  the 
larger  up-takes,  because  they  must  be  kept  open  in  order  to 
bring  in  material  wherewith  to  plug  the  latter.  If,  then, 
deep  shafts  in  a  district  of  heavy  rainfall  like  the  copper 
region  of  Keweenaw  Point,  before  reaching  the  ore-body,  cut 
nearly  a  mile  of  strongly  inclined  lava  sheets,  a  hundred  or 
more  in  number,  and  many  of  them  amygdaloidal,  without  find- 
ing water  below  a  comparatively  shallow  depth,  it  proves  that 
rocks  are  ordinarily  much  more  impervious  than  has  been  sup- 
posed in  most  discussions  in  the  past  regarding  the  descent  of 
meteoric  waters.  I  learn  from  friends  who  have  been  in  the 
Transvaal  gold  regions  that  the  deep  shafts  there,  which,  as  we 
.all  know,  are  sunk  through  one  flank  of  a  syncline  of  sedimen- 
tary strata,  likewise  find  dry  ground  at  a  depth  of  about  250 
ft.  Aside  from  any  bearing  upon  Professor  Van  Hise's  essay,  I 
think  it  is  important  to  emphasize  these  points.  I  am  frank 
to  admit  that  I  did  not  fully  appreciate  the  force  of  this  obser- 
vation myself  until  I  came  to  prepare  the  paper  on  the  "  Role 
of  the  Igneous  Rocks;"*  and  yet,  despite  the  force  of  Professor 
Van  Hise's  reply,  I  cannot  say  that  I  believe  that  the  damaging 
effects  of  experience  in  deep  .and  dry  mines  upon  our  older 
conceptions  of  the  descent  of  the  meteoric  waters  (conceptions 
which  I  have  held  in  common  with  geologists  in  general)  have 
been  satisfactorily  met  by  Professor  Van  Hise  in  advancing  the 
idea  of  the  zone  of  cementation.  The  dryness  of  deep  mines 
destroys  for  a  large  part  of  the  earth  the  very  foundations  of 
Professor  Van  Hise's  main  contention ;  and  in  meeting  this  ob- 
jection with  the  conception  of  the  zone  of  cementation  he  may 
well  be,  as  it  seems  to  me,  merely  opposing  a  damaging  ma- 


Trans.,  xxxi.,  169,  and  Genesis  of  Ore- Deposits,  p.  681. 
16 


242       IGNEOUS  ROCKS  AND  CIRCULATING  WATERS. 

terial  fact  with  a  largely  subjective  conception.  I  am  led  rather 
to  have  the  more  confidence  in  the  intrusive  rocks  and  their 
emissions.  In  this  connection  it  may  be  of  interest  to  remark 
that  in  a  paper  in  vol.  vi.  of  the  Transactions,  pp.  544  and 
545,  1877,  Dr.  Raymond  has  outlined  briefly  both  sides  of  this 
discussion. 

Let  us,  however,  admit  that,  after  periods  of  upheaval  and 
special  fracturing,  the  meteoric  waters  descend  with  all  the 
facility  and  in  all  the  abundance  required  by  the  conception 
formulated  by  Professor  Van  Hise.  According  to  this,  as  I 
understand  it,  the  cause  of  their  return  to  the  surface  from  the 
depths,  which,  as  the  extreme,  are  about  10,000  meters,  is  the 
"  head,"  or  the  amount  by  which  the  pressure  at  the  base  of 
the  descending  columns  exceeds  that  at  the  base  of  the  corre- 
sponding ascending  columns.  The  head  is  chiefly  due  to  the 
greater  length  of  the  former  column,  because  it  is  fed  from 
entrance-points  which  are  above  the  points  of  emergence  of  the 
returning  waters ;  but  the  head  is  reinforced  by  the  expansion 
produced  in  the  ascending  and  hotter  column  because  of  in- 
crements of  heat  absorbed  at  a  greater  or  less  depth  within  the 
earth.  The  motive  power  is,  however,  the  head  in  all  cases; 
that  is,  it  is  gravity.  I  do  not  for  a  moment  question  the  force 
or  attractiveness  of  this  conception,  nor  the  able  way  in  which 
it  has  been  presented  by  Professor  Van  Hise,  even  though  I 
have  not  the  same  faith  in  its  efficiency  which  he  evidently 
feels. 

It  is  clear  that  if  "  head  "  is  at  all  active,  there  must  be  a 
continuous  and  unbroken  column  of  water  from  the  surface,  or 
from  very  near  the  surface,  to  the  ultimate  depths  reached  by 
the  meteoric  waters,  and  back  again  to  their  point  of  emer- 
gence. This  pressure  or  head  must  be  transmitted  through  all 
the  cavities,  small  and  large,  capillary,  subcapillary  and  supra- 
capillary,  which  the  waters  traverse.  It  seems  to  me  to  de- 
mand, where  it  operates,  practical  saturation  of  the  crust  of  the 
earth  with  water, — a  condition  which  experience  in  deep  mines 
proves  to  exist,  so  far  as  I  know,  in  no  mining-region  to-day  r 
except,  perhaps,  in  one  or  two  of  obvious  expiring  vulcanism. 
Despite  the  conception  of  the  zone  of  cementation,  earlier  re* 
ferred  to,  I  am  influenced  by  this  experience. 


IGNEOUS    ROCKS    AND    CIRCULATING    WATERS.  243 

In  discussing  the  transmission  of  pressure  through  cavities 
of  capillary  size  by  the  descending  waters,  I  regret  that  I  did 
do  Professor  Van  Hise  an  unintentional  injustice,  as  he  re- 
marks in  his  closing  discussion,  in  that  I  confused  the  passage  of 
the  descending  waters  under  pressure,  through  capillary  tubes, 
with  capillarity  or  capillary  attraction.  The  interposition  of  the 
latter  would  destroy  "  head,"  but  the  interposition  of  the  former 
would  only  greatly  reduce  it  because  of  friction, — a  point  em- 
phasized by  Professor  Van  Hise. 

There  is  no  question  that,  if  meteoric  waters  enter  a  frac- 
tured and  open-textured  portion  of  the  earth,  descend,  migrate 
laterally  in  unbroken  course,  and  meet  uprising  fissures  which 
reach  the  surface  at  lower  points  than  the  place  of  entry,  they 
must  emerge  and  establish  a  circulation.  The  points  open  to 
argument  are,  first,  the  extent  and  relative  amounts  by  which 
the  different  sources  of  internal  heat  may  aid  them  or  substi- 
tute a  source  of  energy  even  greater  than  "  head  "  or  gravity ; 
second,  whether  they  are,  on  the  whole,  as  efficient  causes  of 
vein-formation  as  intruded  rocks  and  their  emissions;  and, 
third,  whether  the  general  geological  relations  of  veins  support 
one  view  or  the  other,  and  to  what  extent.  In  taking  up  the 
first  point,  I  revert  to  the  blocking  out  of  the  sources  of  inter- 
nal heat  mentioned  above  as  IB,  2B  and  3B,  which  are  essen- 
tially the  same  as  those  mentioned  by  Professor  Van  Hise  in 
his  "Principles"  (Trans.,  xxx.,  49).  The  second  and  third 
points  I  have  already  discussed  in  my  previous  contribution. 

IB.  Doubtless  the  crushing  of  rocks  under  dynamic  stress 
and  chemical  reactions  develops  heat,  but  to  what  extent  I  do 
not  know,  nor  does  this  source  seem  to  me  to  be  capable  of 
more  than  this  general  expression.  The  development  of  in- 
terior heat  by  chemical  reactions  shares  the  same  indefinite- 
ness. 

2B.  As  to  the  part  which  the  normal  increase  of  temperature 
plays  in  aiding  terrestrial  circulations,  it  is  possible  to  reach  a 
more  accurate  quantitative  expression.  The  heat  which  will 
raise  the  temperature  of  a  column  of  water  from  4°  C.  to 
100°  C.  will  produce  an  expansion  of  about  4  per  cent,  and  a 
consequent  diminution  of  density.  This  calculation  is  used, 
with  subsequent  general  modification  to  meet  terrestrial  condi- 


244       IGNEOUS  ROCKS  AND  CIRCULATING  WATERS. 

tions,  by  Professor  Van  Hise.*  I  brought  against  it  the  objec- 
tion that  this  expansion  would  be  neutralized  by  the  pressure 
of  the  accumulating  column  of  water,  which,  to  a  height  of 
about  10,000  ft.,  would  rest  upon  that  portion  which  would 
attain  a  depth  in  the  earth  where  the  temperature  would  be 
100°  C.  While  I  did  not  have  at  hand  the  data  for  an  exact 
expression,  I  had  submitted  the  proposition  to  a  friend  who 
could  give  an  authoritative  opinion  and  had  been  assured  that 
the  modification  was  well  grounded.  I  stated,  therefore,  that 
it  would  practically  prevent  effective  expansion  and  loss  of 
density.  This  statement  is  too  sweeping,  and  Professor  Van 
Hise's  objection  in  the  Discussionf  is  well  taken.  Professor 
William  Hallock  has  kindly  given  me  the  following  references,^ 
in  which  it  is  stated  that  the  cubical  compression  of  water 
at  4°  C.  is  0.0000469  per  atmosphere.  Assuming  that  this 
holds  good  for  all  temperatures  up  to  100°  C.,  it  means,  in 
a  column  of  10,000  ft.  in  height,  which  would  create  a  pres- 
sure of  about  5000  Ibs.  to  the  square  inch,  a  compression  of 
about  1.6  per  cent,  at  the  base,  leaving  2.4  per  cent,  of  the 
original  4  there  effective.  If,  again,  the  data  given  by  Dr. 
Carl  Barus,  and  cited  by  Professor  Van  Hise,§  are  taken,  the 
results  are  not  greatly  modified.  Dr.  Barus  determined  the 
compression  of  a  capillary  column  of  water,  17.4  c.m.  in 
length  and  at  a  temperature  of  23°  C.,  to  be,  for  83  atmospheres, 
.0037;  for  160  atm.,  .0075;  for  226  atm.,  .0108.  If  we  con- 
tinue it  at  the  same  rate  for  340  atm.  (or  10,000  ft),  it  is  .0165 
or.  1.65  per  cent.  At  100°  C.,  on  a  capillary  column  18.1  c.m. 
long,  Dr.  Barus  determined  it  to  be,  for  83  atm.,  .0046 ;  for 
180  atm.,  .0098  ;  for  244  atm.,  .0133.  Continuing  at  the  same 
rate,  it  would  be,  for  340  atm.,  1.84  per  cent,  at  the  base. 

Since  we  assume  that  the  increment  of*  temperature  and  the 
increment  of  pressure  are  each  uniform  in  descent,  we  may  say 
that  for  an  increment  of  96°  C.  we  have  an  expansion  of  4  p«r 
cent,  or  -fa  of  1  per  cent,  for  1°.  At  the  same  time  we  have 

*  Trans.,  xxx.,  49,  and  Genesis  of  Ore-Deposits,  p.  304. 
f  Trans.,  xxxi.,  296. 

J  W.  Watson,  Textbook  of  Physics,  p.  182.     Wiillner,  Lehrbuch  der  Physik,  vol.  i., 
p.  275.     Johann  Miiller,  Lehrbuch  der  Physik,  vol.  i.,  p.  139. 
I  Trans.,  xxxi.,  296. 


IGNEOUS  ROCES  AND  CIRCULATING  WATERS. 


245 


a  compression  of  1.6  per  cent.,  or,  expressed  in  the  rate  per' 
degree  of  increased  temperature,  -fa  of  1  per  cent.  The  net 
expansion  per  degree  expressed  in  per  cents  is  therefore  -^ 


mnus 


or 


It  is  now  not  difficult  to  reach  a  quantitative  expression  of 
the  actual  efficiency  of  the  normal  increase  in  temperature  in 
promoting  hot-springs.  We  may  assume  a  mean  annual  tem- 
perature at  the  surface  of  the  earth  of  10°  C.  For  comparison, 
at  New  York  it  is  10.6.  If  a  descending  column  starts  at  10° 
and  ends  at  100°,  its  mean  temperature  will  be  55°.  Mr.  G. 
K.  Gilbert  has  found,  as  quoted  by  Professor  Van  Hise,  that  the 
waters  of  the  hot-springs  in  the  Cordilleran  region  range  from 
37°  C.  to  100°  C.,  and  that  those  of  the  much  more  abundant 
warm  springs  range  from  18°  to  37°.  There  is  little  doubt 
that  many  of  these,  and  probably  all  the  hotter  ones,  are  con- 
nected with  expiring  vulcanism  and  have  no  bearing  upon  this 
immediate  discussion.  If,  therefore,  we  assume  springs  emerg- 
ing at  20°,  30°,  40°,  and  so  on  to  100°,  we  shall  cover  the  essen- 
tial cases  in  Nature.  In  the  calculation  we  must  use  the  mean 
temperatures  of  ascending  columns  which  start  at  100°  C.  and 
reach  the  surface  at  the  above  temperatures,  and  we  may  ex- 
press the  whole  matter  in  a  small  table,  recalling  that,  for  each 
increase  of  1°  in  the  mean  temperature  of  the  uprising  column, 
as  compared  with  that  of  the  descending  one,  there  results  an 
expansion  of  -^  of  1  per  cent.,  which,  expressed  in  feet  for  a 
10,000-ft.  column,  is  2.5  ft. 


TABLE  I. — Mean  Temperature  of  Descending  Column,  55°  C. 


Temp,  of 
Emergence. 
Centigrade 
Degrees. 

Mean  Temp,  of 
Ascending 
Column. 
Cent.  Deg. 

Excess 
of 
Temp. 
Cent.  JDeg. 

Increase  of  Head. 

Per  Cent. 
Expansion. 

Feet. 

20 

60 

5 

i 

12.5 

30 

65 

10 

25. 

40 

70 

15 

37.5 

50 

75 

20 

50. 

60 

80 

25 

62.5 

70 

85 

30 

75. 

80 

90 

35 

87.5 

90 

95 

40 

1 

100. 

100 

100 

45 

It 

112.5 

246  IGNEOUS    ROCKS    AND    CIRCULATING    WATERS. 

When  we  consider  how  slight  an  increase  this  amounts  to  in 
a  10,000-ft.  column,  which  is  fed  by  all  sorts  of  small  tributa- 
ries with  high  friction ;  and  when  we  compare  the  results  with 
the  vastly  greater  head  resulting  from  inequalities  of  the  ground 
which  would  almost  pass  unnoticed ;  when,  again,  we  recall  the 
rarity  of  hot-springs  having  even  the  moderately  elevated  tem- 
peratures and  not  obviously  in  volcanic  or  eruptive  regions ; 
and  when  we  realize  that  any  ascending  column  would  inevit- 
ably draw  to  itself  by  induced  currents  much  colder  water  in 
the  rocks  toward  the  surface,  I  think  we  are  justified  in  prac- 
tically dismissing  the  normal  increase  of  temperature  in  the 
earth  as  of  any  essential  importance  in  helping  to  force  de- 
scending meteoric  waters  through  the  devious  underground 
passages.  We  must  have  a  head  contributed  by  a  higher 
source  at  the  point  of  entry,  and  therefore  a  continuous  column 
of  water,  or  we  must  have  local  supplies  of  heat  from  recently 
intruded  igneous  rocks. 

Again,  if  we  have  a  region  where  the  rate  of  increase  of  the 
interior  temperature  is  less  than  the  basis  of  the  above  calcula- 
tion, viz.,  1°  C.  for  each  30  meters  (1°  F.  for  each  55  ft.),  as, 
for  instance,  Keweenaw  Point,  where  the  rate  is  very  nearly  1° 
C.  for  60  meters  (1°  F.  for  each  100-110  ft),  or  the  Transvaal, 
where,  as  I  learn  from  Mr.  Pope  Yeatman,  preliminary  experi- 
ments have  shown  an  even  slower  rate,  then  the  force  of  my 
argument  is  doubled.  And  if  the  mean  annual  temperature  is 
higher  than  10°  C.,  the  argument  is  thereby  correspondingly 
strengthened.  Naturally,  also,  a  colder  mean  annual  tempera- 
ture weakens  the  argument,  but  not  proportionately,  since  water 
is  densest  at  4°  C.,  leaving  a  range  of  but  6°  for  mean  annual 
temperature  as  between  this  and  the  10°  assumed  above,  before 
the  limit  is  reached. 

I  realize  that  the  expulsive  action  of  the  normally  heated  in- 
terior was  only  a  minor  point  in  Professor  Van  Hise's  argu- 
ment, and  it  is  not  with  reference  to  his  paper  that  these  con- 
clusions are  specially  urged,  but  because  it  is  probable  that 
generally,  among  geologists,  much  greater  efficiency  is  attributed 
to  this  agent  than  it  would  seem  to  deserve.  All  these  consid- 
erations make  us  fall  back  with  the  greater  reliance  on  igneous 
rocks  as  sources  of  heat  and  energy  for  promoting  circulations 


IGNEOUS    ROCKS    AND    CIRCULATING    WATERS.  247 

which  reach  the  surface.  The  influence  of  the  increase  of  tem- 
perature in  the  normal  ratio  must  be  mainly  one  of  magnifying 
chemical  efficiency  in  those  meteoric  waters  which  come  within 
its  influence. 

In  this  connection  I  cannot  refrain  from  referring  with  the 
greatest  admiration  to  Mr.  Weed's  recent  paper  on  "  Mineral 
Vein-Formation  at  Boulder  Hot  Springs,  Montana."*  It  is  of 
the  highest  significance,  both  in  reference  to  the  topic  here  dis- 
cussed and  to  the  one  next  to  be  taken  up. 

3B.  If  we  imagine  a  mass  of  molten  igneous  rock  injected 
from  below  into  the  upper  regions  where  the  meteoric  ground- 
waters  exist,  a  new  factor  is  introduced  of  enormous  efficiency. 
The  molten  rock  may  be  considered  as  having  a  temperature  of 
about  1200°  C.  (about  2200°  F.).  Its  influence  in  expanding 
to  the  full  limit  of  the  liquid  condition  any  meteoric  waters 
within  the  sphere  of  its  influence  would  be  relatively  abrupt, 
.and  its  effect  in  increasing  normal  head  would  be  pronounced. 
If  it  sufficed  to  change  to  vapor  any  of  these  waters,  their 
density  would  be  enormously  lowered  and  the  head  would  be 
still  more  effective.  But  even  apart  from  the  head  of  the  de- 
scending column,  and  even  without  assuming  its  existence  with 
reference  to  waters  at  the  place  in  question,  for  meteoric  waters 
may  be  present  even  if  not  under  a  continuous  column  to  the 
surface,  the  expansive  force  of  the  steam,  or  even  of  the  disso- 
ciated gases,  reinforced  by  the  copious  emissions  of  the  erup- 
tive, would  start  circulations  toward  the  surface,  and,  as  it  seems 
to  me,  would  be  a  most  efficient  agent.  This  is  what  I  have 
referred  to  in  my  paper  and  elsewhere  as  contributions  of 
energy,  and  the  process  has  been  indicated  by  describing  in- 
trusive rocks  as  stimulators  of  circulation. 

Gradually  the  intrusive  rock  cools  and  becomes  a  less  and 
less  efficient  cause,  and  in  the  end  it  assumes  the  normal  tern- 
perature  for  that  portion  of  the  earth  in  which  it  is  situated. 
Possibly  circulating  waters  continue  their  migrations,  urged  on 
by  head,  and  are  effective  in  depositing  ores.  Possibly,  also, 
they  practically  cease,  and  the  period  of  ore-deposition  corre- 
sponds to  the  period  of  efficiency  of  the  eruptive.  I  am 

'*  Twenty-First  Annual  Report  U.  S.  Geol.  Survey,  II.,  227. 


248  IGNEOUS    ROCKS    AND    CIRCULATING    WATERS, 

strongly  inclined  to  believe  the  latter  view  is  correct,  and  that 
when  the  fires  under  the  boiler  are  quenched,  the  engine  ceases 
to  run. 

Do  we,  then,  find  mineral  veins  provided  with  ores  in  those 
places  where,  once  in  a  million  times,  the  combination  of  pre- 
cipitating agent  and  metalliferous  solution  meet  under  favor- 
able conditions  in  the  circulation  of  the  meteoric  ground- 
waters  ?  or  do  we  find  them  where,  down  under  the  surface, 
some  intrusive  rock  has  entered  charged  richly  enough  with  a 
metallic  burden  to  impart  it  to  uprising  heated  waters  and 
yield  a  series  of  ore-bodies  ?  From  the  experience  gained  in 
western  mining-districts  the  latter  appeals  to  me  the  more 
forcibly,  and  I  am  inclined  to  believe  that  original  ore-deposi- 
tion ceased,  not  so  much  because  cementation  plugged  the  con- 
duits as  because  the  energy  of  the  stimulating  cause  became 
exhausted.  But  even  in  making  this  guarded  statement,  I 
trust  that  I  do  not  fail  to  appreciate  the  extent  to  which  the 
whole  matter  is  speculative  and  inferential, — a  phase  of  the  sub- 
ject adequately  emphasized,  and  I  think  alone  adequately  em- 
phasized,  in  my  previous  paper. 

There  remain  but  one  or  two  other  points  which  seem  to  me 
to  deserve  attention  beyond  the  treatment  given  them  in  the 
"Role  of  the  Igneous  Rocks,  etc."  There  is  some  difference 
of  opinion  between  Professor  Van  Hise  and  myself  regarding 
the  abundance  of  veins.  While  I  have  the  greatest  respect  for 
his  very  wide  experience  and  observation,  I  nevertheless  am 
strongly  of  the  opinion  that,  if  we  leave  out  pegmatites  and 
their  related  quartz-veins,  which  are  so  extensively  developed 
in  metamorphic  districts,  veins  of  any  sort,  commensurate  in 
size  with  those  which  we  mine,  are  quite  rare  phenomena,  and, 
though  locally  abundant,  are  yet,  on  the  whole,  but  seldom 
seen.  This  is  not  alone  my  own  opinion,  but  that  of  friends  in 
the  practice  of  mining  engineering,  and  of  greater  experience 
in  these  matters  than  either  Professor  Van  Hise  or  myself. 
Unless  some  very  restricted  cause  has  occasioned  them,  they 
ought  to  be  far  more  abundant  than  they  are. 

As  to  the  presence  of  the  ground-water  in  all  mining-regions, 
an  additional  word  may  be  of  interest.  There  certainly  are 
localities  in  the  arid  region  of  the  West  where,  at  considerable 


IGNEOUS    ROCKS    AND    CIRCULATING    WATERS.  249 

depths,  it  has  not  yet  been  met  in  notable  amount,  and  where 
its  distribution  is  very  irregular.  At  Tintic,  Utah,  for  in- 
stance, as  I  am  informed  by  Dr.  W.  P.  Jenney,  the  Mammoth- 
Tintic  workings  are  2000  ft.  deep  in  the  limestone.  They 
have  never  used  a  pump  nor  have  had  more  than  a  little  drip  of 
water  in  a  few  places.  The  ores  are  oxidized  and  the  bottom 
levels  are  perfectly  dry.  The  ground-water  may  be  encountered 
in  time,  but  it  is  certainly  very  deep.  One  or  two  miles  away, 
in  the  monzonite,  water  is  met  within  100  or  200  ft.  of  the 
surface — not  in  great  quantity,  indeed,  but  sufficient  to  have 
prevented  the  oxidation  of  the  ore.  Over  the  divide  from  the 
Mammoth,  and  beginning  550  ft.  below  it,  are  the  Bullion-Beck 
and  Gemini  mines.  Their  shafts  are  down  1660  ft,  and  from 
very  large  and  extended  workings,  and  of  course  with  no  at- 
tempt to  impound  the  water  near  the  surface,  they  gather  about 
10  gallons  a  minute, — no  more  than  can  be  readily  removed  by 
a  bailer  once  in  a  while  through  the  day.  The  ores  are  all  oxi- 
dized. 

The  Horn-Silver  mine  at  Frisco  is  down  1600  ft.  and  is  prac- 
tically dry ;  the  ore  is  oxidized.  Water  for  the  camp  is,  of  ne- 
cessity, brought  in  from  a  distance.  I  realize  that  Mr.  Em- 
mons  has  stated  in  his  paper*  that  some  water  is  met,  but  the 
quantity  is  so  small  that  the  present  management  is  sinking  a 
bore-hole  from  the  bottom  of  the  mine  in  the  hope  of  tapping 
enough,  at  least,  to  furnish  a  supply  for  the  boilers. 

My  friend,  Mr.  John  N.  Judson,  has  given  me  some  interest- 
ing notes  on  the  Mapimi  mines  in  Mexico.  The  mines  were 
dry  to  a  depth  of  over  760  meters,  or  about  2400  ft.  Some 
dampness  was  first  observed  in  the  wall-rock,  and  later  some 
water  appeared  in  the  veins,  which  are  chimneys  in  lime- 
stone. Whether  the  workings  will  pass  through  this  wet 
ground  (it  is  not  very  wet)  and  again  reach  dry  rock  will  be 
one  of  the  interesting  things  for  the  future  to  determine. 

In  a  review  of  the  separate  volume  on  "  The  Genesis  of  Ore- 
Deposits,"  recently  issued  by  the  Institute,  Mr.  H.  F.  Bain,  in 
the  Journal  of  Geology,  May-June,  1902,  p.  434,  emphasizes- 


*  "The  Delamar  and  the   Horn-Silver  Mines,"   by  S.   F.   Emmons,   Trans.r 
xxxi.,  658. 


250  IGNEOUS    ROCKS    AND    CIRCULATING    WATERS. 

the  importance  of  considering,  in  this  connection,  only  vertical 
depths,  and  not  the  relatively  flat  inclines,  which,  while  long 
and  perhaps  dry,  may  not  attain  great  depth  nor  be  significant. 
I  believe  all  the  cases  cited  by  me  have  been  of  vertical  shafts. 
Mr.  Bain  also  mentions  experience  in  the  Newhouse  tunnel,  in 
cutting  wet  veins,  as  indicating  the  presence  of  water  at  great 
depths.  To  this,  however,  it  may  be  replied  that  a  tunnel  into 
a  mountain  merely  produces  an  artificial  spring;  that  springs 
exist  along  almost  all  valleys,  and  their  water  at  times  certainly 
comes  from  considerable  depths ;  but  my  contention  is  that,  so 
far  as  actual  experience  goes,  in  very  deep  mining,  water  is 
scarce  or  almost  unknown  unless  there  is  expiring  vulcanism. 
From  this  it  follows  that  the  igneous  rocks  are  probably  the 
important  factors  in  deep  circulations. 

Regarding  points  like  these,  it  is  most  desirable  that  mem- 
bers of  the  Institute  should  place  observations  on  record. 

In  closing,  I  may  add  that,  although  I  apparently  differ  with 
Professor  Van  Hise  regarding  the  relative  importance  of  cer- 
tain factors  in  the  problem,  there  is  no  one  who  has  a  higher 
admiration  for  his  essay  than  myself,  a  feeling  which,  as  a 
matter  of  fact,  I  had  elsewhere  expressed  before  the  Rich- 
mond meeting.  At  the  same  time,  a  somewhat  extended  cor- 
respondence has  shown  that  not  a  few  mining-geologists  in 
America  and  elsewhere  are  in  sympathy  with  the  points  em- 
phasized in  my  paper,  and  with  the  relative  importance  there 
attached  to  the  several  factors. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.       251 

No.  11. 


A  Consideration   of   Igneous    Rocks    and   their  Segregation 
or  Differentiation  as  Related  to  the  Occurrence  of  Ores.* 

BY  J.    E.    SPURR,  CONSTANTINOPLE,  TURKEY,  f 

(New  York  and  Philadelphia  Meeting,  February  and  May,  1902.     Trans.,  xxxiii.,  288.) 

CONTENTS. 

PAGE 

INTRODUCTION, 252 

I.  THE  RELATION  OF  ORE-DEPOSITS  TO  IGNEOUS  ROCKS  IN  GENERAL,  253 

II.  THE  DISTRIBUTION  OF  METALS  IN  SEDIMENTARY  ROCKS,       .         .  254 

III.  THE  SEGREGATION  OR  DIFFERENTIATION  OF  IGNEOUS  ROCKS,        .  259 

IV.  THE  ORDER  OF  CRYSTALLIZATION  OF  MINERALS  IN  IGNEOUS  ROCKS,  263 
V.  THE  FORMATION  OF  MINERAL  SEGREGATIONS  IN  MOLTEN  MASSES,  .  264 

VI.  THE  UNKNOWN  FINER  LAWS  OF  ROCK-SEGREGATION,    .        .        .  265 
VII.  THE  PRESENCE  OF  METALS  IN  THE  IGNEOUS  ROCKS,      .         .        .  266 
"VIII.  THE  CONCENTRATION  OF  COMMERCIALLY- VALUABLE  MINERALS  BY 
SEGREGATION  WITHIN  MOLTEN  MASSES,  PREVIOUS  TO  THEIR  CON- 
SOLIDATION,    .        .        .        .         .        .         .        .        L        ...  267 

1.  Iron, ...'...  267 

2.  Chromium, .         .         .         .         .         .                  .         .  •                 .         .  267 

3.  Nickel, ".     ./,        .         .268 

4.  Cobalt, .  'J69 

5.  Platinum, %       .  269 

6.  Copper, 270 

7.  Gold,. .  271 

IX.  THE  ORIGIN  OF  CERTAIN  GOLD-QUARTZ  VEINS,     ....  271 

1.  Evidence  as  to  the  Origin  of  Quartz- Veins  «.->•  Magmatic  Segreyations,        .  275 

2.  The  Genetic  Connection  of  Gold-Quartz  Veins  with  Siliceous  Igneous  Rocks,  279 

3.  The  Subordinate  Connection  of  Gold-  Quartz  Veins  with  Basic  Igneous  Rocks,  284 
X.  RESUME  OF  THE  EVIDENCE  CONCERNING  THE  PREFERENCE  OF  CER- 
TAIN METALS  TO  ACCUMULATE,  BY  MAGMATIC  SEGREGATION,  IN 
CERTAIN  ROCK-TYPES  OF  THE  ESTABLISHED  CLASSIFICATION;     .  .  284 

1.  Basic  Rocks, 285 

2.  Siliceous  Rocks,   .         .         .         .         .         .  '       .         .         .         .         .  285 

XI.  THE  RELATION  BETWEEN  ORE-DEPOSITS  DUE  TO  MAGMATIC  SEG- 
REGATION AND  OTHER  ORE-DEPOSITS,  ......  236 

XII.  THE  SEQUENCE  OF  VOLCANIC  ERUPTIONS,  CONSIDERED  IN  CONNEC- 
TION WITH  THE  SEQUENCE  OF  METALLIFEROUS  VEINS,        .        .  288 

XIII.  THE  PERSISTENCE  OF  PETROGRAPHIC  PROVINCES,  CONSIDERED  IN 

CONNECTION  WITH  THE  PERSISTENCE  OF  METALLIFEROUS  PROV- 
INCES                       .  291 

XIV.  CONCLUSION, 299 

POSTSCRIPT, •    .  301 

*  Published  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey, 
t  Since  returned  to  the  United  States,  and  now  again  in  the  service  of  the 
IU.  S.  Geological  Survey.— R.  W.  R. 


252    IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

INTRODUCTION. 

IN  a  new  field  like  that  of  the  study  of  ore-deposits,  it  is 
hard  to  keep  all  sides  of  the  question  in  sight  at  once ;  to  real- 
ize that  the  laws  worked  out  for  certain  types  of  ore-deposits 
in  one  region  do  not  apply  to  deposits  of  apparently  similar 
ores  the  world  over.  Thus  have  arisen  our  most  hotly-con- 
tested controversies,  over  such  questions,  for  instance,  as : 
Whether  bedded  ores  are  mechanical  sediments  formed  at  the 
same  time  with  the  enclosing  rock,  or  were  introduced  later  by 
solution;  Whether  metals  have  been  deposited  by  ascending 
or  by  descending  waters ;  Whether  they  are  derived  from  the 
immediate  wall-rock,  from  the  rocks  of  the  whole  district  in 
which  they  occur,  or  from  the  "  barysphere  " ;  Whether  they 
are  deposited  in  pre-existing  cavities  or  are  replacements ;  and 
so  on. 

The  researches  of  the  past  score  of  years  or  so  have  rather 
dampened  the  heat  of  these  discussions.  Investigators  have 
been  led  to  recognize  in  nature  a  complexity  which  permits 
most  of  the  advocated  theories  to  find  their  place  as  factors 
mutually  co-operating  to  constitute  the  intricate  system  which 
determines  the  occurrence  of  ores  as  we  now  find  them.  I 
think  most  of  us  agree  with  Prof.  Van  Hise,*  that  "  for  many 
ore-deposits  a  complete  theory  must  be  a  descending,  lateral-se- 
creting, ascending,  descending,  lateral-secreting  theory."  In- 
deed, all  this — and  more  ! 

Van  Hise's  discussion  of  the  work  of  underground  water  in 
forming  ore-deposits  seems  to  me  the  best  general  contribution 
of  recent  years,  not  excepting  the  famous  treatise  of  Posepny. 
A  masterly  discussion  like  this  fills,  for  the  moment,  the  whole 
mind  of  the  reader,  and  he  might  thus  fail  to  consider  the  im- 
portance of  principles  which  the  author  has  purposely  omitted. 
Kemp,  Lindgren  and  Vogt,  in  their  discussions  of  Van  Hise's 
paper,  have  called  attention  to  certain  of  these  principles,  espe- 
cially those  involving  the  connection  of  igneous  rocks  with  ore- 
deposition,  or  ore-segregation,  as  I  would  like  to  call  it. 

It  is  concerning  this  part  of  the  field  that  I  wish  to  present 
some  considerations,  limited  in  extent  and  detail  by  my  lack  of 

*  "Some  Principles  Controlling  the  Deposition  of  Ores,"  Trans.,  xxx.,p.  173.. 
Genesis  of  Ore-Deposils,  p.  428. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     253 

access  to  a  wide  range  of  literature,  and  by  the  difficulty  of  the 
subject  itself.  With  most  of  Van  Hise's  conclusions,  I  may 
remark,  I  fully  agree. 

For  the  ideas  herein  set  forth  I  can  claim,  of  course,  only  a 
certain  amount  of  originality.  It  will  be  seen  that  my  views 
(which  I  have  previously  announced,  although  not  in  such  com- 
pact form  as  this*)  resemble,  more  or  less,  those  of  Lindgrenf 
and  KempJ  in  this  country,  and  De  Launay,  Beck  and  Yogt§ 
in  Europe,  but  especially  the  last  named. 

I.  THE  RELATION  "OF  ORE-DEPOSITS  TO  IGNEOUS  ROCKS  IN 

GENERAL. 

Two  important  points  have  come  to  be  agreed  upon  by  most 
of  the  best  writers  on  ore-deposits,  namely :  (1)  That  ores  in 
general  were  originally  derived  from  igneous  rocks;  and  (2) 
that  present  ore-deposits  are  closely  associated  with  actually-ex- 
posed eruptives. 

Probably  at  least  nineteen  out  of  twenty  important  ore-de- 
posits (excepting  those  of  iron)  are  acknowledged  to  have  a 
genetic  connection  with  associated  rocks  of  igneous  origin. 
Especially  well-marked  is  the  connection  of  ore-regions  or  zones 
with  areas  or  belts  of  igneous  activity.  ||  The  interdependence 
of  eruptive  rocks,  hot  springs  and  many  ore-deposits  has  at 
last  attained  the  dignity  of  a  general  law. 

The  hot  springs  often  owe  their  heat,  and  hence  their  up- 
ward propulsion,  to  igneous  masses,  while  the  ore-deposits  are 
the  direct  work  of  both  the  other  two,  the  material  being 
largely  derived  from  the  rocks  and  the  concentration  being 
effected  by  the  waters.  Moreover,  the  lines  of  weakness  (of 


*  J.  E.  Spurr,  "Economic  Geology,  Mercur  Mining  District,  Utah,"  IGth  An- 
nual Rpt.  U.  S.  Geol  Surv.,  Part  II.,  pp.  395,  449  (1895);  "  Geology  of  the  Yukon 
Gold-District,"  ISth  Annual  Rpt.  U.  S.  GeoL  Surv.,  Part  III.,  p.  297(1898); 
"  Quartz-Muscovite  Kock,  from  Belmont,  Nevada,"  Am.  Jour,  of  ScL,  4th  series, 
vol.  x.,  Nov.,  1900,  p.  355. 

f  Waldernar  Lindgren,  "  Character  and  Genesis  of  Certain  Contact- Deposits," 
Trans,,  xxxi.,  p.  226,  and  Genesis  of  Ore-Deposits,  p.  716. 

I  J.  F.  Kemp,  "The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins," 
Trans.,  xxxi.,  p.  169,  and  Genesis  of  Ore- Deposits,  p.  681. 

g  J.  H.  L.  Vogt,  "Problems  in  the  Geology  of  Ore-Deposits,"  Trans,  xxxi., 
p.  125,  and  Genesis  of  Ore- Deposits,  p.  636. 

||  J.  F.  Kemp,  "The  R61e  of  the  Igneous  Rocks  in  the  Formation  of  Veins," 
Trans.,  xxxi.,  196,  197,  and  The  Genesis  of  Ore-Deposits,  pp.  707-709. 


254  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

faulting,  etc.)  determined  by,  or  at  least  coextensive  with,  the 
intrusion  of  the  molten  masses,  frequently  form  the  channels 
of  the  springs,  and  thus  operate  to  restrict  the  ore-deposits  to 
the  eruptive  zones. 

The  broad  explanation  of  this  association  is  plainly  contained 
in  the  proof  which  we  now  possess,  that  the  eruptive  rocks  con- 
tain in  varying  amounts  the  rarer  elements  (among  them,  most 
of  the  metals),  in  addition  to  the  common  ones. 

In  the  stratified  rocks,  on  the  other  hand,  the  metals,  though 
present,  seem  to  be  in  general  less  abundant.* 

II.  THE  DISTRIBUTION  OF  METALS  IN  SEDIMENTARY  EOCKS. 

All  sediments  were  probably  derived  in  the  beginning  from 
the  destruction  of  igneous  rocks,  but  the  elements  thus  de- 
rived attain  through  mechanical  and  chemical  surface  agencies 
a  degree  of  concentration  hardly  equalled  in  the  igneous  rocks 
themselves.  Thus  calcium  becomes  concentrated  into  lime- 
stones, and  silicon  into  great  volumes  of  sandstone  or  quartzite. 
Among  the  commercially  valuable  minerals,  salt,  gypsum, 
phosphate  of  lime,  borax  and  others  have  thus  become  con- 
centrated. These  facts  indicate  that  metals  also  must  be  sim- 
ilarly dissolved  out  and  dispersed.  In  the  case  of  some  of  the 
metals,  we  know  that  they  are  re-deposited  in  concentrated 
form.  By  chemical  and  mechanical  action,  iron  is  concen- 
trated in  bogs,  in  greensands,  and  in  ferruginous  shales  and 
sandstones,  there  to  yield,  after  some  further  concentration, 
such  notable  deposits  as  the  iron-ores  of  the  Lake  Superior 
region.  By  chemical  action,  manganese  is  concentrated,  not- 
only  in  bogs,  but  on  a  large  scale  in  marine  sediments,  such 
as  shales  and  limestones,  so  that  most  of  the  commercially  im- 
portant deposits  are  derived,  through  the  medium  of  further 
concentration,  from  these  sources.  By  mechanical  and  chemi- 
cal action  such  rarer  metals  and  minerals  as  gold,  platinum, 
diamond,  tin-ore,  monazite,  garnet,  etc.,  are  very  highly  con- 
centrated in  river  channels  and  in  marine  shore-deposits.  Ex- 
amples of  the  enormous  efficiency  of  surface  concentration  in 
producing  valuable  deposits  of  the  rare  metals  are  furnished 

*  J.  F.  Kemp,  "  The  Kole  of  the  Igneous  Kocks  in  the  Formation  of  Veins," 
Trans.,  xxxi.,  p.  175,  and  The  Genesis  of  Ore-Deposits,  p.  686. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OP    ORES.     255 

by  the  world's  gold-placers,  the  Cape  Nome  beach-sands,  and 
(according  to  some  authorities)  the  South  African  auriferous 
beds.  As  regards  platinum,  nearly  all  the  known  concentra- 
tions, so  complete  as  to  be  commercially  valuable,  have  been 
effected  by  surface-agencies. 

But,  on  the  one  hand,  iron  and  manganese  are  common  ele- 
ments; and,  on  the  other  hand,  gold,  platinum,  tin-stone,  etc.? 
are  relatively  insoluble ;  and  thus  their  concentration  may  be 
explained.  Concerning  the  metals  (such  as  silver,  copper,  leady 
zinc,  arsenic,  antimony,  etc.),  which  are  at  the  same  time  rela- 
tively rare  and  relatively  soluble,  no  such  satisfactory  conclu- 
sion has  been  reached.  That,  upon  disintegration  of  the 
igneous  rocks,  these  metals  largely  go  into  solution  in  sur- 
face-waters, there  is  no  doubt.  These  waters  (apart  from  those 
which  pass  underground,  where  we  know  that  the  metals  are 
frequently  precipitated  in  concentrated  form*)  find  their  way 
into  lakes,  and  especially  into  the  oceans.  What  becomes  of 
the  metals  which  they  hold  in  solution  ? 

Are  they  precipitated  either  in  concentrated  or  in  evenly  dis- 
seminated form,  or  do  they  remain  in  solution  ?  If  it  be  true, 
as  I  think  it  is,  that  a  sedimentary  rock,  as  a  rule,  contains 
much  smaller  proportions  of  the  metals  than  an  igneous  rock,f 
we  must  conclude  that  these  metals  are  not  evenly  precipitated. 
Yet  I  find  it  impossible  to  believe  that  all  of  these  metals  con- 
tained in  the  igneous  rocks  which  have  been,  ever  since  the 
solid  world  began,  going  to  pieces  to  form  the  enormous  bulk 
of  known  sediments,  can  have  been  stored  in  the  sea-water  and 
are  there  'still. 

Most  of  the  elements — especially  silver,  copper,  iron,  man- 
ganese, and  gold — have  been  chemically  detected  in  sea-water; 
but  they  are  present  only  in  minute  traces;  whereas  the 
total  amount  of  metals  which  has  passed  into  the  sea  in 
solution  during  the  ages  of  erosion  and  deposition  must  be 

*  C.  R.  Van  Hise,  "  Principles  Controlling  Deposition  of  Ores,"  Trans.,  xxx., 
p.  138  et  seq.,  and  The  Genesis  of  Ore- Deposits,  p.  393. 

t  J.  F.  Kemp,  "The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins," 
Trans.,  xxxi.,  174,  says  it  appears,  from  analyses  of  both  the  sedimentary  and  the 
igneous  rocks  of  Missouri  for  lead  and  zinc,  that  the  igneous  rocks  are,  as  a  rule, 
richer  by  one  place  of  decimals  than  the  former.  F.  Posepny,  in  The  Genesis  of 
Ore-Deposits,  p.  122,  says  that  innumerable  analyses  of  marine  sediments  and 
precipitates,  especially  of  limestones,  have  failed  to  show  traces  of  metals. 


256     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

many  times  in  excess  of  the  solvent  power  of  the  water  at 
any  one  time,  and  vastly  in  excess  of  the  dissolved  amount 
now  contained  therein.  We  must,  therefore,  confess  that,  be- 
sides the  metals  mechanically  laid  down  in  slates  and  conglom- 
erates, derived  directly  from  the  abrasion  of  igneous  rocks,  the 
same  metals  have  been  chemically  precipitated  somewhere  from 
marine  and  other  surface-waters.  Indeed,  the  researches  of 
Malaguti,  Bibra  and  Forchhammer*  long  ago  established  the 
fact  of  such  precipitation  by  finding  traces  of  metals  in  the 
ashes  of  marine  plants,  and  in  the  hard  parts  of  marine  ani- 
mals, such  as  corals.  Among  the  metals  mentioned  above  as 
having  the  question  of  their  concentration  at  the  surface  still 
undecided,  lead,  zinc,  cobalt  and  nickel  have  been  thus  de- 
tected. 

Since,  therefore,  the  metals  in  question  (notably  lead,  zinc, 
silver  and  copper),  which  are  both  relatively  soluble  and  rela- 
tively rare,  after  being  extracted  from  the  igneous  rocks  during 
the  process  of  weathering,  transportation  and  sedimentation, 
have  neither  been  uniformly  deposited  in  the  sediments  nor 
accumulated  in  solution,  I  am  forced  to  believe  that,  like  the 
commoner  elements  (among  them  the  commoner  metals)  already 
mentioned,  they  have  been  (probably  by  chemical  precipita- 
tion) deposited  in  certain  places  as  concentrations,  which  are,  as 
a  rule,  relatively  richer  than  the  igneous  rocks  in  which  the 
said  substances  were  originally  disseminated. 

The  hypothesis  that  bedded  ores  have  sometimes  been  de- 
posited contemporaneously  with  the  enclosing  sediments  has 
been,  of  late,  distinctly  out  of  fashion,  and  justly  so,  in  the 
exclusive  sense  in  which  it  has  sometimes  been  held.  Bischof, 
reasoning  from  the  traces  of  metals  in  sea-wrater,  believed  that 
their  precipitation  as  sulphides  was  possible,  and  thus  ex- 
plained the  occurrences  of  copper  and  silver  sulphides  in  the 
Permian  Kapferschiefer,  and  of  lead  sulphide  in  the  Buntsand- 
stein. 

Groddeck  advocated  the  same  idea,  and  advanced  the  theory 
that  certain  horizons  are  especially  ore-bearing. f  Hoefer  has 
.applied  this  explanation  to  the  lead-  and  zinc-deposits  of  Upper 

*  Chem.  u.  Phys.  Geologic,  vol.  i.,  Bonn,  1863,  pp.  445-7.     C.  G.  Bischof. 
f  Posepny,  Genesis  of  Ore-Deposits,  first  edition,  p.  112,  etc.  ;  second  edition, 
p.  122. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  257 

Silesia  and  other  districts,  which  occur  in  Triassic  marine 
limestone.  In  Bohemia  and  the  Urals,  as  in  the  German 
Kupferschiefer  district,  the  Permian  rocks  contain  copper  in 
many  places ;  in  Utah  and  New  Mexico  (in  the  Silver  Reef 
and  Nacimiento  districts,  etc.)  the  Triassic  sandstones  con- 
tain copper  and  sometimes  silver;  in  the  Permian  of  Texas 
there  are  three  copper-bearing  zones,  extending  over  three 
counties.* 

These  are  examples  of  numerous  deposits  which  have  been 
described  by  some  able  investigators  as  due  to  deposition  con- 
temporaneous with  the  enclosing  beds,  while,  in  every  case, 
this  conclusion  has  been  repeatedly  and  vigorously  contested. 
The  fact  is  that  in  every  one  of  these  instances  the  ore-deposits 
have  an  evident  genetic  connection  with  fissures,  joints,  dikes, 
etc.,  of  later  age  than  the  rock;  and  hence  it  is  argued  that  the 
ores  (including  those  disseminated  in  the  rock)  have  been  in- 
troduced through  these  fissures. 

I. need  hardly  point  out  that  this  conclusion  is  not  logically 
valid.  I  confess  that,  after  visiting  the  Mansfeld  deposits,  I  was 
so  impressed  by  the  evident  connection  of  the  faults  with  the 
ore-bodies,  and  by  the  frequent  proofs  of  the  formation  of  min- 
erals more  recent  than  the  country-rock,  that  I  came  away  quite 
satisfied  that  the  idea  of  contemporaneous  deposition  was  old- 
fashioned  and  untenable.  Yet  neither  there  nor  elsewhere  does 
this  opinion  certainly  follow  from  the  observed  facts.  The 
present  ore-bodies  in  most  of  these  districts — perhaps  in  all — 
are  largely  secondary  concentrations,  due  to  percolating  waters, 
and  are  hence  found  along  water-channels,  as  held  by  Posepny 
and  others ;  but  this  does  not  affect  the  question  whether  these 
waters  brought  up  the  metals  with  them  "  from  below  "  or  con- 
centrated them  from  disseminations  contemporaneous  in  depo- 
sition with  the  strata.  In  view  of  what  I  have  stated  above,  I 
am  now  inclined  to  hold  the  latter  view. 

Among  the  detrital  rocks,  slates  are  known  to  contain 
marked  quantities  of  the  metals  in  question.  Frick,  Forch- 
hammer  and  Sandberger  found  copper,  zinc,  lead,  arsenic,  anti- 
mony, tin  and  cobalt  in  clay-slates.  These  are,  very  likely  to 
a  large  extent,  mechanical  concentrates  from  the  rocks  by  the 

*  Kemp,  Ore-Deposits  of  the  United  Stales,  third  edition,  p.  224,  etc. 

17 


258  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

destruction  of  which  the  slates  originated ;  yet  they  are  prob- 
ably also,  in  some  degree,  chemical  precipitates. 

The  Mediterranean  has  been  found  to  contain  copper  in  solu- 
tion in  the  proportion  of  at  least  0.01  gramme  to  the  cubic 
meter.  Philips*  says  that  "  the  black  and  usually  very  sul- 
phurous matter  deposited  in  basins  where  sea-water  has  been 
left  to  itself  constantly  contains  copper,  and  the  same  is  gen- 
erally true  with  regard  to  the  dark-colored  gypseous  muds  of 
all  ages." 

Most  chemically  precipitated  rocksf  certainly  seem  to  be  much 
poorer  in  original  metallic  contents  than  the  fragmental  ones. 
The  limestones  of  the  Mississippi  valley  have  been  shown 
to  contain  lead  and  zinc,  disseminated  in  small  quantity ;  and 
it  is  the  conclusion  of  Whitney,  Chamberlin,  Winslow  and 
others  that  the  ore-deposits  have  been  concentrated  from  these 
disseminations.  But  these  limestones  appear  to  contain  the 
metals  in  smaller  quantity  than  do  the  older  igneous  rocks  of 
the  region,  so  that  the  dissemination  in  the  limestones  can 
hardly  be  regarded  as  a  concentration.  (See  footnote,  p.  255.) 

With  these  and  other  facts  in  mind,  we  cannot  safely  give  up 
the  idea  that  metals  have  been  concentrated  by  surface  agencies 
in  favorable  places  and  times,  and,  consequently,  that  certain 
strata  (possibly  also,  and  restrictedly,  certain  geologic  periods) 
are,  by  reason  of  their  original  metallic  contents,  more  favor- 
able than  others  to  the  occurrence  of  ore-deposits.  I  would 
even  hesitate  equally  to  deny  or  to  affirm  that  there  is  a  con- 
nection between  the  Triassic  and  Permian  red  sandstones  and 
certain  copper-deposits.  Yet  we  must  be  careful  not  to  rush 
into  any  such  hasty  generalization  as  that  of  Sir  Roderick 
Murchison,  who  believed  that  most  auriferous  rocks  are  of  Si- 
lurian age,J — an  obsolete  idea  which  I  have  nevertheless  found 
in  one  of  our  latest  works  on  the  metallurgy  of  gold. § 

The  concentration  of  metals  by  surface  agencies,  though  a 
fascinating  study,  is  out  of  place  in  the  special  inquiry  to  which 
this  paper  is  devoted — that  of  concentration  by  segregation 
within  molten  rocks. 


*  Phillips  and  Louis,  Treatise  on  Ore-Deposits,  1896,  p.  132. 
f  This  phrase  is  meant  to  include  limestones  of  organic  origin. 
J  See  Kickard's  "Keview,"  Eng.  Min.  Jour.,  Oct.  19,  1901,  p.  491. 
$  Eissler,  Metallurgy  of  Gold,  1900,  p.  31. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     259 

III. — THE  SEGREGATION  OR  DIFFERENTIATION  OF  IGNEOUS 

ROCKS. 

Having  pointed  out  the  generally-admitted  fact  that  the  larger 
number  of  ore-deposits  have  direct  genetic  connection  with  ig- 
neous rocks,  I  wish  to  describe  one  of  the  chief  processes  by 
which  the  different  kinds  of  igneous  rocks  originate,  which 
I  believe  has  an  important  bearing  upon  the  segregation  of 
ores. 

While  it  is  known  that  igneous  rocks  may  be  formed  directly 
from  the  fusion  of  sediments  (in  which  case  their  composition 
is  determined  by  the  selective  action  of  surface  agencies),  yet 
it  is  now  widely  accepted  that  many,  perhaps  most,  of  them 
owe  their  peculiarities  of  composition  to  a  process  of  segrega- 
tion which  goes  on  within  the  molten  masses  of  the  earth's  in- 
terior. The  evidence  for  this  process,  and  some  of  the  details 
of  it,  have  been  pretty  fully  stated  by  the  writer  elsewhere,*  and 
only  a  few  points  will  be  mentioned  here.  The  line  of  argu- 
ment is  best  seen  if  we  proceed  from  examples  on  a  small  scale 
to  successively  larger  ones.  Thus,  in  the  laboratory,  materials 
intimately  mingled  in  solution  may  separate  into  distinct  crys- 
tals, or  into  segregated  bunches  of  like  crystals ;  and  in  veins 
the  different  minerals  are  often  found  bunched  in  the  same  way. 
Nearly  every  igneous  rock  shows  irregularities  of  composition 
due  to  a  similar  clustering  together  of  like  minerals.  These 
aggregations  increase  from  microscopic  size  to  the  size  of 
a  man's  head;  and  from  these  relatively  small  patches  there 
is  a  gradation  to  larger  rock-masses,  which  have  marked  differ- 
ences in  structure  and  composition  from  the  rest  of  the  igneous 
body,  of  which  they,  nevertheless,  form  integral  portions.  For 
example,  the  borders  of  dikes  are  frequently  less  siliceous,  and 
contain  more  iron  (and  associated  elements)  than  the  interior 
of  the  same  bodies.  In  still  larger  igneous  masses,  it  is  found 
that  different  portions  have  slightly  different  chemical,  miner- 
alogical  and  structural  characters,  while  they  all  grade  into  one 
another.  Again,  it  has  been  observed  that  in  a  given  district 
different  igneous  rocks  (such  as  volcanic  rocks  erupted  at  differ- 
ent times)  are  often  closely  related,  and  pass  into  one  another. 

*  "Geology  of  the  Yukon  Gold-District,"  18th  Ann.  Rep.  U.  S.   Geol.  Surv., 
Part  III.,  p.  SCO. 


260     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

Finally,  modern  petrographic  research  and  comparison  have 
shown  that  the  rocks  of  a  large  region,  taken  collectively,  often 
present  constant  differences  from  those  of  neighboring  regions. 

All  these  phenomena  may  be  explained  by  the  observed  fact 
that  in  the  molten  masses,  as  well  as  in  solutions,  there  is  a  force 
inducing  like  elements  to  group  themselves  together. 

Concerning  the  exact  process  by  which  the  materials  of  the 
molten  rocks  are  enabled  to  make  such  important  migrations 
in  order  to  cluster  together,  there  is  no  certainty;  and,  indeed, 
for  the  purposes  of  this  paper,  it  is  hardly  necessary  to  inquire. 
Until  recently,  it  was  common  to  appeal  to  Soret's  principle  of 
molecular  flowT,  namely,  that  molecular  concentration  maybe 
caused  by  differences  of  temperature.  Mr.  G.  F.  Becker,* 
however,  has  argued  against  the  applicability  of  this  law,  on 
account  of  the  slowness  with  which  it  operates.  Mr.  Beckerf 
and  the  writer,J  independently  and  at  about  the  same  time, 
called  attention  to  the  probable  importance  of  convection  cur- 
rents in  producing  segregation.  By  these  currents  the  miner- 
als which  first  crystallize  (namely,  the  heavier  minerals,  such 
as  magnetite,  olivine,  hornblende,  pyroxene,  etc.)  would  be,  to 
a  greater  or  less  extent,  concentrated  in  the  outer  portions  of 
igneous  rock-masses,  where  they  are  actually  often  found. 

The  small  segregations  in  igneous  rock  are  usually  either 
more  siliceous  or  less  siliceous  (more  "  acid  "  or  more  "  basic  ") 
than  the  enclosing  rock ;  and  extremely  acid  and  extremely 
basic  segregations  are  often  found  in  close  association  This  ten- 
dency of  the  molten  mass  to  segregate  its  highly  siliceous  con- 
stituents from  the  rest  has  also  been  studied  on  a  large  scale, 
chiefly  from  the  order  of  succession  of  lavas  erupted  at  suc- 
cessive periods  in  the  same  district,  or  of  dikes  successively 
introduced.  Brogger  and  Geikie,§  from  extensive  studies  of 
eruptive  rocks  in  Norway  and  in  Scotland,  respectively,  both 
concluded  that  the  rocks  progressed  from  the  more  basic  to  the 
more  acid  varieties. 

i 

r  "Some  Queries  On  Rock  Differentiation,"  Am.  Jour.  ScL,  Jan.,  1897, 
4th  series,  vol.  iii.,  p.  21. 

f  "Fractional  Crystallization  of  Bocks,"  Am.  Jour.  Sci.,  Oct.,  1897,  p.  257. 

t  "Geology  of  the  Yukon  Gold-District,"  18th  Ann.  Rep.  U.  S.  Geol.  Surv., 
Part  III. ,  p.  306. 

I  J.  P.  Iddings:  "The  Origin  of  Igneous  Kocks,"  Bull.  Phil.  Soc.  Wash., 
vol.  xii.,pp.  122,  145,  146. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   261 

Iddings's*  work  goes  to  show  the  normal  law  to  be,  that  a 
rock  of  intermediate  composition  is  followed  by  rocks  progres- 
sively higher  and,  at  the  same  time,  by  others  progressively 
lower  in  silica  (the  more  basic  and  the  more  acid  varieties 
being  associated  and  contemporaneous),  so  that  the  series 
begins  with  a  mean  and  ends  with  extremes.  This  has  been 
considered  by  the  writer  to  hold  good  for  the  dike-rocks  of 
the  Forty-Mile  district,  Alaska,  f  and  (a  problem  on  a  much 
larger  scale)  for  the  petrographic  province  of  which  the  great 
basin  of  Nevada  forms  a  portion.  J  In  the  case  of  the  Forty- 
Mile  dikes,  the  most  siliceous  varieties  were  found  to  be  later 
than  the  most  basic  ones. 

The  laws  thus  deduced  agree  in  this  :  That  a  molten  rock, 
mass,  under  favorable  conditions,  tends  to  separate  (segregate) 
into  a  more  acid  and  a  more  basic  portion  ;  while  the  fact  that 
the  acid  (siliceous)  rocks  characteristically  follow,  rather  than 
precede,  the  basic  (less  siliceous)  at  any  one  period,  joined  with 
the  other  known  principles  of  segregation,  indicates  that  the 
change  is  effected  at  each  stage  by  the  separation  and  crystalli- 
zation of  the  more  basic  constituents,  leaving  the  more  sili- 
ceous residue  unconsolidated. 

That  the  basic  minerals  in  general  crystallize  first  in  a  cool- 
ing rock  has  been  proved  by  microscopic  study.  If  the  segre- 
gation is  limited  in  time,  and  is  broken  into  by  such  an  occur- 
rence as  eruption  and  consolidation,  the  differences  attained 
may  be  comparatively  slight;  but  under  favorable  circum- 
stances extremes  may  be  reached.  Thus,  rocks  consisting 
almost  entirely  of  olivine,  pyroxene,  or  hornblende,  together 
with  iron  oxides  and  sulphides,  may  originate.  On  the 
other  hand,  rocks  made  up  essentially  of  quartz  and  alkali 
feldspars  (alaskites)§  may  be  formed,  and  these  may  pass  by 
gradual  transitions  into  quartz-veins,  as  will  be  dwelt  upon 
later.  An  illustration  of  these  different  results  is  found  in  the 


*  Opcit. 

f  "  Geology  of  the  Yukon  Gold-District,"  18th  Ann.  Rep.  U.  S.  Geol.  Surv., 
Part  III.,  p.  234. 

J  "  Succession  and  Relation  of  Lavas  in  the  Great  Basin  Region,"  Journal 
of  Geology,  vol.  viii.  ,  p.  621. 

%  J.  E.  Spurr:  "Classification  of  Igneous  Rocks,"  Am.  Geologist,  Apr.,  1900, 
vol.  xxv.,  p.  229. 


262     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

dikes  of  the  Forty-Mile  region,*  which  consist  of  rocks  closely 
related,  being  made  up  chiefly  of  hornblende,  quartz  and  feld- 
spar. Yet  by  gradual  changes  in  the  proportions  of  these 
minerals,  rocks  of  all  degrees  of  basicity  and  acidity  are  pro- 
duced, terminating,  on  the  one  hand,  in  hornblendites  (com- 
posed almost  entirely  of  hornblende)  and  pyroxenites,  contain- 
ing pyrite,  pyrrhotite,  ilmenite  and  other  metallic  minerals; 
and,  on  the  other  hand,  in  alaskites,  growing  gradually  more 
siliceous  until  they  pass,  with  no  break,  into  quartz-veins. 

In  the  progress  of  segregation,  we  have  seen  that  in  the 
acid-gaining  portion  there  is  a  continuous  increase  of  silica, 
due  to  the  constant  precipitation  ^nd  removal  of  the  basic  por- 
tions. There  is  also  an  attendant  increase  in  the  amount  of 
water. 

As  is  shown  by  microscopic  and  chemical  study,  all  rocks 
contain  water,  but  the  molten  material  contains  much  more 
than  the  resulting  rock.  Most  of  this  water  is  expelled  at 
the  moment  of  solidification,  together  with  certain  gases  and 
a  great  variety  of  other  materials  held  in  solution,  f  When 
rocks  cool  at  the  surface,  this  escaping  water  forms  the  clouds 
of  steam,  highly  charged  with  gases  and  minerals,  which  issue 
from  fissures  and  other  vents ;  but  when  they  solidify  below  the 
surface  the  waters  and  gases  are  forced  into  the  enclosing  rock, 
producing  the  recrystallization  and  rearrangement  of  its  con- 
stituents, called  contact-metamorphism.  This  is  chiefly  confined 
to  the  contacts  of  siliceous  igneous  rocks,  being  especially  re- 
markable around  intrusive  masses  of  granite,  where  it  occupies 
a  zone  which,  in  extreme  cases,  may  be  several  miles  in  width. 

It  seems,  therefore,  that  the  molten  material  from  which 
siliceous  rocks  solidify  contains  more  water  than  the  basic  ma- 
terial. Therefore,  we  may  believe  that  by  the  progressive  sep- 
arating out  of  the  more  basic  constituents  the  residual  portion 
of  a  molten  mass  becomes  more  aqueous  and  more  siliceous. 
Thus  the  peculiar  form  (often  in  lenses,  not  visibly  communi- 
cating with  large  bodies  of  igneous  rocks)  and  coarse  crystalli- 
zation of  pegmatites  are  explained;  for  these  rocks  are  near 
the  end-product  of  the  siliceous  series;  and  the  pegmatic 

*  "Geology  of  the  Yukon  Gold -District,"  18th  Ann.  Eep.  U.  S.  Geol  Surv., 
Part  III.,  p.  233. 

f  Daubre'e,  Geologic  Experim&ntale,  Paris,  1879,  p.  152. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   263 

rocks,  by  the  disappearance  of  feldspar  and  mica,  grade  into 
pure  quartz-veins,  which  show  by  their  structure  that  they  have 
been  deposited  from  solutions  so  attenuated  that  they  may  best 
be  described  as  waters  highly  heated  and  charged  with  mineral 
matter  in  solution. 

By  this  process  of  rock-differentiation,  concentration  is  con- 
tinually effected  through  the  segregation  of  like  materials. 
Most  of  these  materials  are  not  commercially  valuable.  Thus 
the  frequent  segregation  of  masses  of  nearly  pure  hornblende, 
pyroxene  or  quartz  has  no  lively  interest  for  the  miner.  But 
when  (as  often  happens)  such  segregations  are  feldspar  or  mica, 
they  may  acquire  economic  importance.  And  if  the  commonest 
of  rock-constituents  may  be  thus  concentrated,  other  substances 
may  be,  also.  In  the  basic  Forty-Mile  dikes,  mentioned  above, 
there  was  so  large  a  proportion  of  ilmenite,  magnetite,  pyrrho- 
tite  and  other  metallic  minerals  that  small  pieces  of  the  rock 
were  drawn  by  the  magnet.  A  slight  further  concentration 
would  give  commercially  valuable  masses ;  and  there  is  good 
evidence  that,  in  other  districts,  many  such  masses  have  origi- 
nated in  this  way. 

IV.  THE  ORDER  OF  CRYSTALLIZATION  OF  MINERALS  IN 

IGNEOUS  ROCKS. 

The  process  of  segregation,  which  we  have  considered  on  a 
large  scale,  with  the  progressive  precipitation  of  basic  ingre- 
dients and  the  leaving  behind  of  the  siliceous  ores,  is  recorded 
on  a  small  scale  in  the  internal  structures  of  igneous  rocks,  as 
studied  under  the  microscope. 

Under  this  head  I  cannot  do  better  than  quote  Prof.  J.  F. 
Kemp,*  who  says : 

"  Microscopic  study  of  the  igneous  rocks  has  shown  that,  with  few  exceptions, 
the  rock -making  minerals  separate  from  a  fused  magma  on  cooling  and  crystal- 
lizing in  a  quite  definite  order,  f  Thus  the  first  to  form  are  certain  oxides,  mag- 
netite, specular  hematite,  ilmenite,  rarely  chromite  and  picotite,  a  few  silicates, 
unimportant  in  this  connection  (zircon,  titanite),  and  the  sulphides,  pyrite  and 
pyrrhotite.  Next  after  these  metallic  oxides,  etc. ,  the  heavy,  dark-colored  basic  sil- 
icates, olivine,  biotite,  augite,  and  hornblende,  are  formed.  All  these  minerals  are 
characterized  by  high  percentages  of  iron,  magnesium,  calcium  and  aluminum. 

*  Ore-Deposits  of  the  United  States  and  Canada,  4th  ed.,  p.  33. 

f  H.  Rosenbusch,  "Ueberdas  Wesen  der  kornigen  und  porphyrischen  Structur  bed- 
Massengesteinen,"  Neues  Jahrbuch,  1882,  ii.,  1. 


264     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

They  are  very  generally  provided  with  inclusions  of  the  first  set.  Following  the 
bisilicates  in  the  order  of  crystallization  come  the  feldspars,  and  after  these  the 
residual  silica,  which  remains  uncombined,  separates  as  quartz." 

V.  THE  FORMATION  OF  MINERAL  SEGREGATIONS  IN  MOLTEN 

MASSES. 

It  has  been  shown  that  in  the  process  of  segregation  in 
molten  masses  there  is  a  recognized  tendency  to  split  up  into 
more  siliceous  and  less  siliceous  portions.  The  basic  materials 
thus  concentrated  may  be  the  almost  exclusive  constituents  of 
the  resulting  rocks.  Thus  there  are  not  uncommonly  rocks 
made  up  essentially  of  the  dark,  heavy,  basic,  ferro-magne- 
sian  minerals,  biotite,  olivine,  pyroxene  and  amphibole,  with 
metallic  minerals,  such  as  magnetite,  ilmenite,  etc.,  in  smaller 
amounts.  The  acid  materials  likewise  may  form  rocks  without 
important  admixture  of  the  basic  ones,  as  in  quartz  alkali- 
feldspar  rocks  (alaskite),  or  in  rocks  made  up  almost  entirely 
of  alkali-feldspar  (sanadinite,  albitite,  etc.).  Further,  as  al- 
ready pointed  out,  the  constituent  minerals  may  separate  out 
from  the  mixture  and  the  like  crystals  may  group  themselves 
together.  Thus,  there  are  rocks  consisting  almost  entirely  of 
olivine  alone  (dunite),  of  hornblende  alone  (hornblendite),  of 
pyroxene  alone  (pyroxenite),  of  orthoclase  feldspar  (sanadinite), 
of  soda-feldspar  (anorthosite),  and  of  lime-feldspar  (anorthite 
rock).  This  completes  the  roll  of  the  commonest  rock  con- 
stituents, save  the  micas  and  quartz.  Although  mica  forms 
small  segregations  in  igneous  rocks,  the  writer  is  not  aware 
that  it  occurs  as  the  only  essential  mineral  in  any  considerable 
mass  of  such  rock.  Quartz  also  appears  at  first  sight  to  be  an 
exception ;  but  the  writer  will  try  to  show  later  that  this  is  not 
so,  and  that  many  considerable  masses  and  veins  of  quartz  are 
the  result  of  segregation  •from  the  same  molten  material  that 
produces  other  igneous  rocks. 

Besides  these  commonest  original  or  primary  minerals,  there 
are  others  which  are  commonly  present  in  marked  quantity  in 
almost  every  fragment  of  igneous  rock.  Perhaps  the  most 
important  of  these  is  magnetite,  which  is  found  in  nearly  all 
rocks.  Besides  this,  there  are  other  common  metallic  min- 
erals, such  as  pyrite,  ilmenite  and  pyrrhotite — all  iron  minerals. 
Chromite  is  rarer.  Among  the  non-metallic  accessory  min~ 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  265 

erals,  zircon,  titanite  and  apatite  are  perhaps  the  most  impor- 
tant. All  of  these  less  common  minerals  (as  well  as  others 
not  mentioned)  are  known  to  segregate,  to  a  certain  extent  at 
least,  so  that  they  are  many  times  more  abundant  in  some  rocks 
than  in  others. 

This  being  the  case,  it  is  natural  that  the  still  rarer  minerals 
and  elements  also  should  segregate,  and  should  be  found  in 
certain  rocks  in  far  larger  quantity  than  in  others ;  and,  indeed, 
this  is  known  to  be  the  fact. 

VI.  THE  UNKNOWN  FINER  LAWS  OP  EOCK-SEGREGATION. 

If  there  were  invariable  associations  between  certain  rocks 
and  certain  valuable  minerals,  prospectors  and  miners  would 
probably  have  detected  it  long  ago,  especially  as  regards  the 
metals.  But  in  the  majority  of  cases  the  exceptions,  to  any 
rule  we  may  be  tempted  to  construct,  are  so  numerous  that  we 
abandon  the  attempt.  That  this  fact,  however,  does  not  contra- 
dict the  conclusions  above  reached  in  regard  to  the  preferential 
segregation  of  these  minerals  into  certain  rocks  will  appear  when 
we  consider  how  we  name  and  distinguish  the  rocks  themselves. 
The  existing  classifications  of  rocks  are  all  based  upon  the  rel- 
ative content  of  the  common  constituents,  the  rarer  ones  being 
necessarily  disregarded.  The  divisions,  granite,  syenite,  dunite, 
diabase,  basalt,  phonolite,  and  the  whole  legion  of  others,  are 
(apart  from  considerations  of  structure,  age,  mode  of  occur- 
rence, etc.,  which  have  for  the  moment  no  bearing  on  this  dis- 
cussion) founded  upon  the  presence  and  relative  proportions  of 
the  ordinary  minerals  quartz,  the  various  feldspars  and  felds- 
pathoids,  olivine,  mica,  amphibole  and  pyroxene.  Even  in 
classifications  based  upon  the  chemical  composition  of  the 
whole  rock,  the  component  minerals  being  lumped  together  for 
analysis,  only  certain  ordinary  elements  are  taken  into  account, 
and  the  rock  is  assigned  to  its  place  upon  the  basis  of  the  rela- 
tive proportions  of  silicon,  aluminum,  iron,  calcium,  magne- 
sium, sodium  and  potassium.  Rock-divisions  based  on  these 
elements  do  not  necessarily  connote  the  presence  or  absence  of 
any  others.  For  example,  a  petrographer  finding  a,  certain 
igneous  rock  knows  at  once  that  this  rock  is  unusually  rich 
in  calcium,  sodium,  aluminum  or  silicon ;  but  he  does  not  know 
if  it  contains  more  or  less  than  the  average  quantity  of  lead, 


266    IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

silver  or  mercury.  Each  element  follows  its  own  independent 
law  of  segregation,  and  disregards  the  established  rock  classifi- 
cation. Even  with  the  commoner  minerals  and  elements  upon 
which  this  classification  is  roughly  based,  the  variations  are  so 
wide  as  to  lead  the  petrographer  into  grave  difficulties.  Thus, 
among  the  rocks  which  have  been  called  gabbro  we  may  find 
some  consisting  almost  entirely  of  feldspar,  and  others  made 
up  chiefly  of  pyroxene.  One  of  the  commonest  chemical  divi- 
sions of  the  rocks  is  into  acid,  basic  and  intermediate  kinds, 
essentially  according  to  the  proportion  of  silica  present;  but 
rocks  of  different  mineralogical  composition  may  have  the  same 
acidity.  The  basic  rocks  are  rich  in  ferro-magnesian  silicates, 
and  so  should  be  exceptionally  strong  in  magnesia;  but  occa- 
sionally cases  may  be  found  where  gabbro  shows  less  magnesia 
than  granite. 

We  can  hardly  expect,  therefore,  that  the  identification-  of 
a  rock-species,  under  the  accepted  classification,  will  be  of 
much  help  in  guiding  us  to  a  knowledge  of  the  relative  con- 
tent of  the  rarer  elements.  To  arrive  at  such  a  knowledge,  we 
should  have  a  classification  based  principally  upon  the  content 
of  these  rarer  elements,  and  recognizable  in  practice  by  easy 
physical  and  chemical  marks.  But  this  is  clearly  impracticable. 

In  this  difficulty,  we  may  be  helped  to  some  extent  by  the  prin- 
ciple which  underlies  the  laws  of  chemical  affinity  and  the  asso- 
ciation of  minerals.  Elements  and  minerals  have  tendencies  to 
cluster  in  groups  marked  by  some  common  characteristics ;  each 
element  or  mineral  prefers  to  associate  with  certain  elements  or 
minerals  rather  than  with  others.  This  law  of  selective  asso- 
ciation has  long  been  recognized  by  the  geologist  and  the 
chemist.  So  it  seems  reasonable  that  among  the  rare  elements 
and  minerals  not  considered  in  rock-classification,  some  may 
have  such  strong  preferential  association  with  certain  of  the 
commoner  rock-constituents  on  which  this  classification  is 
based  that  WQ  may  be  able  to  see  some  connection,  even  if  a 
rude  one,  between  these  rarer  constituents  and  the  established 
rock-types. 

VII.  THE  PRESENCE  OF  METALS  IN  THE  IGNEOUS  ROCKS. 

Iron  is  present — often  in  high  percentage — in  nearly  every 
igneous  rock.  It  occurs  not  only  in  the  dark  ferro-magnesian 


IGNEOUS    HOCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     267 

silicates,  but  also  as  oxides  and  sulphides,  as  hematite,  magne- 
tite, ilmenite,  pyrite  and  pyrrhotite. 

Chromium,  in  the  form  of  chromite  and  picotite,  chrome- 
diopside,  etc.,  occurs  in  marked  quantities  as  an  original  con- 
stituent of  many  basic  igneous  rocks.  Manganese  is  present 
in  nearly  every  igneous  rock,  as  a  not  unimportant  constituent' 
of  the  ferro-magnesian  silicates.  The  rarer  metals,  lead,  cop- 
per, zinc,  tin,  antimony,  arsenic,  nickel,  cobalt,  silver,  gold,  and 
the  still  rarer  ones,  have  all  been  repeatedly  found  in  fresh 
igneous  rocks,  particularly  in  the  dark  bisilicates. 

VIII.  THE  CONCENTRATION  OF  COMMERCIALLY- VALUABLE  MIN- 
ERALS BY  SEGREGATION  WITHIN  MOLTEN  BASSES,  PREVIOUS 
TO  THEIR  CONSOLIDATION. 

1.  Iron. 

The  fact  that  iron  is  unequally  distributed  in  igneous  rocks 
is  well  known.  Many  highly  siliceous  rocks  (acid  granites, 
alaskites,  etc.)  have  only  a  trifling  quantity  (often  1  per  cent, 
or  less),  while  the  basic  rocks  may  contain  10,  15,  and  even  20 
per  cent,  of  iron  oxide.  Of  this  iron,  a  part  is  generally  in 
the  form  of  magnetite,  a  mineral  shown  by  the  microscope  to 
be  thickly  disseminated  in  many  basic  rocks.  It  is  generally 
titaniferous,  and  grades  into  ilmenite.  From  the  highly  mag- 
netiferous  phases  of  ordinary  basic  rocks  to  a  phase  where  the 
magnetite  becomes  the  principal  constituent  is  an  easy  step. 
Such  are  the  occurrences  at  Cumberland,  Rhode  Island,  at 
Taberg,  in  Sweden,  and  in  many  other  places.  At  some  of 
these  localities  the  iron  mineral  may  gradually  increase  so  as 
almost  to  exclude  the  other  constituents,  as  at  Taberg;  or  it 
may  quite  do  so,  as  in  the  anorthosites  of  Minnesota  and  else- 
where, forming  masses  of  iron-ore.  As  to  the  origin  of  these 
ores  by  segregation  within  the  molten  masses  previous  to  cool- 
ing, there  is  a  practical  unanimity  of  opinion. 

2.    Chromium. 

Like  iron,  chromium  has  a  very  manifest  uneven  distribution 
in  igneous  rocks,  being  rare  in  the  siliceous  ones,  while  in  many 
of  the  basic  ones  it  forms  a  not  insignificant  constituent,  espe- 
cially in  rocks  containing  olivine.*  In  these  rocks  its  relations 

*  Zirkel,  Lehrbuch  der  Petrographie,  2d  ed.,  vol.  i.,  p.  426. 


268  IGNEOUS  HOCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

to  other  minerals  show  that,  like  magnetite,  it  is  one  of  the  earli- 
est to  crystallize  during  consolidation.  That  the  chromite  may, 
in  some  portions  of  these  rocks,  become  so  abundant  as  to  form 
the  principal  constituent,  the  rock  being  nevertheless  in  nearly 
the  state  in  which  it  cooled  from  fusion,  is  an  occurrence  which 
we  might  expect  from  our  knowledge  of  the  selective  segregation 
of  other  constituents,  and  one  which  has  been  repeatedly  ob- 
served. Yogt*  has  described  a  fresh  peridotite  from  Norway 
which  was  almost  or  quite  rich  enough  in  chromite  to  be  worthy 
of  exploitation.  The  most  important  occurrences  of  chrome- 
ore  occur  in  serpentines,  which  can  generally  be  shown  to  be 
the  product  of  decomposition  of  basic  igneous  rocks,  chiefly 
peridotites  (olive  rocks);  and  these  deposits  are  considered 
by  Yogt  to  be  the  result  of  segregation  while  the  mass  was 
molten  (magmatic  segregation),  although  they  had  been  ex- 
plained by  others  as  due  to  after-actions  which  took  place  dur- 
ing the  alteration  of  the  fresh  rock  to  serpentine,  or  even  to 
pneumatolytic  (vaporous)  action  at  the  time  of  the  rock's  con- 
solidation. J.  H.  Pratt,  after  studying  the  chrome-ores  of 
North  Carolina,  arrived  at  the  same  conclusion  as  Yogt  for 
other  regions,  namely,  that  the  ores  were  actually  magmatic 
segregations.  Kempf  favors  the  same  origin  for  other  chromite- 
deposits  in  the  United  States.  The  writer,  after  examining  the 
chromite-deposits  near  Saloniki,  Turkey  (Macedonia),  and  also 
in  Asia  Minor,  inclines  to  the  belief  that  most  of  these  deposits 
have  originated  as  magmatic  segregations  from  the  enclosing 
peridotitic  rock. 

3.  Nickel. 

Nickel  occurs  as  an  original  constituent  of  some  olivinesj  in 
basic  igneous  rocks.  It  is  also  found  in  more  considerable 
amount  in  pyrrhotite,  an  iron  sulphide  which  is  frequently  a 
primary  mineral  in  igneous  rocks  and  one  of  the  first  to  crys- 
tallize on  consolidation.  Nickel  occurs  also  as  an  alloy  with 
native  iron,  in  meteorites  and  in  basalt. 

In  certain  igneous  rocks — as,  for  example,  in  the  peridotites 
of  Douglas  county,  Oregon,  and  of  Webster,  North  Carolina — 
nickel  is  much  more  abundant  than  in  others  of  the  same  petro- 

*  Quoted  by  J.  F.  Kemp,  Ore- Deposits  of  the  U.S.  and  Canada,  4th  ed., p.  413. 
f  Op.  tit.,  p.  415.  J  Dana,  System  of  Mineralogy,  6th  ed.,  p.  453. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   269 

graphical  character.  In  the  instances  named,  the  nickel,  upon 
the  weathering  of  the  rock,  separated  out  as  nickel  silicate,  and 
became  concentrated  sufficiently  to  be  of  possible  economic  im- 
portance. 

Although  these  ore-deposits  are  immediately  due  to  circulat- 
ing surface-waters,  which  have  accomplished  a  second  concen- 
tration, the  first  and  most  important  concentration  was  that 
which  brought  together  unusual  quantities  of  nickel  in  these 
particular  rocks,  and  this  was  plainly  done  by  magmatic  segre- 
gation. 

It  has  already  been  noted  that  pyrrhotite,  like  the  other 
early  crystallizing  metallic  minerals,  may  become  abundant  as 
a  primary  constituent  of  igneous  rocks — as,  for  example,  in  the 
case  of  the  Forty-Mile  creek  dike,  already  mentioned.*  Cases 
where  niccoliferous  pyrrhotite  in  basic  igneous  rocks,  evidently 
a  primary  constituent,  gradually  increases  so  as  to  form  com- 
pact masses  and  to  become  a  valuable  ore,  have  been  described 
on  the  best  authority. 

Of  such  origin  (partly,  at  least)  seem  to  be  the  niccoliferous 
pyrrhotites  of  Sudbury,  Ontario,  and  those  of  the  Gap  mine, 
Lancaster,  Pennsylvania. f 

4.   Cobalt. 

This  metal  has  the  closest  associations  with  nickel,  and  the 
general  conclusions  arrived  at  for  the  one  are  probably  to  a 
considerable  degree  good  for  the  other.  Like  nickel,  cobalt  is 
present  in  perceptible  quantity  in  certain  basic  igneous  rocks, 
where  it  has  been  identified  as  occurring  in  olivine,J  and,  al- 
loyed with  native  iron,  nickel  and  copper,  in  Greenland  basalt. 

As  yet,  however,  we  have  not  sufficient  reliable  data  to  de- 
termine whether  any  important  cobalt-ores  are  formed  princi- 
pally by  magmatic  segregation. 

5.  Platinum. 

Platinum,  in  perhaps  the  majority  of  cases,  is  found  closely 
associated  with  chromite  or  nickel,  or  both.  Like  these  min- 
erals, it  is  almost  invariably  genetically  connected  with  basic 

*  See  p.  263. 

f  J.  F.  Kemp,  Ore-Deposits  of  the  United  States  and  Canada,  4th  ed.,  p.  431. 

|  Dana,  System  of  Mineralogy,  6th  ed.,  p.  453. 


270  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

olivine  rocks,  or  with  the  serpentine-rocks  arising  from  the 
alteration  of  these.  As  an  original  constituent  in  basic  igne- 
ous rocks,  it  is  said  to  have  been  found  both  by  Daubree  and 
Engelhardt.  More  recently,  native  platinum  has  been  discov- 
ered in  igneous  rocks  in  the  Urals,  in  the  Nizhni-Tagil  district, 
and  the  Goroblagodat  district.  These  are  extremely  basic  peri- 
dotitic  rocks,  containing  large  amounts  of  magnetite  and  chro- 
mite,  besides  platinum.  According  to  Inostranzeff,  the  plati- 
num occurs  as  grains  and  leaves  in  the  chromite.  In  the 
Goroblagodat  district,  while  the  peridotites  contain  by  far  the 
larger  amount  of  platinum,  Saytzeff  found  the  metal  as  an 
original  constituent  in  other  igneous  rocks  also,  such  as  porphy- 
rite,  gabbro-diorite,  and  syenite-gneiss.  Mr.  C.  W.  Purington 
also  obtained,  on  crushing  and  panning  the  peridotite  of  this 
district,  many  fine  colors  of  platinum.*  The  writer  has  also 
had  the  privilege  of  visiting  the  district,  and  of  collecting 
some  of  the  platinum-bearing  peridotite. 

The  Ural  occurrence,  both  by  reason  of  the  presence  of  the 
platinum  disseminated  in  basic  igneous  rocks  and  its  connec- 
tion with  chromite  and  magnetite  of  acknowledged  igneous 
origin,  must  be  admitted  to  be  a  product  of  magmatic  segrega- 
tion; and  how  powerful  this  segregation  has  been  we  learn 
from  the  fact  that  assays  of  the  ferrous  blebs  (the  most  basic 
segregations)  in  the  Nizhni-Tagil  rocks  gave  a  figure  corre- 
sponding to  $50  per  ton.f 

That  in  this  region  the  platinum  has  been  remarkably  con- 
centrated, as  compared  with  similar  rocks  in  other  places,  is 
shown  by  the  observation  of  Saytzeff  that  even  rocks  elsewhere 
not  known  to  be  platiniferous — "  porphyrite,  gabbro-diorite  and 
syenite-gneiss  " — contain  it.  J 

6.   Copper.       ..• 

Copper,  as  an  original  constituent,  is  known  to  enter  into 
the  composition  of  the  dark  ferro-magnesiaii  silicates  of  the 
igneous  rocks.  It  occurs  also  in  meteorites,  and,  alloyed  with 

*  C.  W.  Purington,  "Platinum  Deposits  of  the  Tura  River-System,"  Trans., 
xxix  ,  p.  8.  t  Purington,  op.  tit.,  p.  8. 

J  A  note  in  the  Eng.  and  Min.  Jour.,  November  16,  1901,  p.  632,  says  that 
samples  of  rock  from  the  State  of  Washington  contain,  according  to  Prof.  J.  F. 
Kemp,  from  0.375  to  0. 5  oz.  of  platinum  per  ton.  The  nature  of  the  rock  is  not 
stated. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   271 

native  iron,  in  the  Ovifak  (Greenland)  basalt.  The  segrega- 
tions of  pyrrhotite  before  noted  in  connection  with  nickel,  and 
believed  to  have  formed  in  the  distinctly  ante-consolidation, 
period,  are  frequently  cupriferous,  and  even  contain  copper 
pyrites,  as  at  Sudbury,  Ontario.  The  magmatic  segregation  of 
the  pyrrhotite  being  granted,  the  copper  also  has  probably  been 
chiefly  concentrated  in  the  same  way.* 

According  to  some  observers,  even  high-grade  copper-ores 
in  various  districts  have  had  this  origin,  f 

7.   Gold. 

Pyrrhotite  frequently,  and  chalcopyrite  generally,  contains 
gold.  Some  masses  of  auriferous  pyrrhotite  and  chalcopyrite 
have  been  thought  to  have  originated  like  the  niccoliferous 
pyrrhotite  above  mentioned.  Such  is  the  case  at  Rossland, 
B.  C.,  where  the  ores  have  been  considered  by  many  writers  to  be 
magmatic  segregations,  while  other  observers,  equally  reliable, 
believe  them  to  be  secondary  replacement  deposits  or  fissure- 
veins.  The  hypothesis  of  a  first  concentration  by  magmatic 
segregation  and  a  second  by  circulating  waters  may  possibly 
be  the  key  to  the  problem. 

Native  gold,  probably  as  an  original  constituent,  has  been 
found  in  granite, J  in  eurite§  (alaskite),  in  quartz-trachyte,  || 
and  in  gabbro.^f 

IX.  THE  ORIGIN  OF  CERTAIN  GOLD-QUARTZ  VEINS. 

As  remarked  in  the  preceding  paragraph,  native  gold  has 
been  found  in  both  basic  and  acid  rocks.  It  has  also  been  de- 
tected in  the  dark  ferro-magnesian  silicates  of  rocks  of  all  de- 
grees of  acidity.  The  commercially-valuable  concentrations 
of  gold  are  generally  connected,  now  with  basalt  or  gabbro, 
now  with  diorite,  now  with  phonolite,  rhyolite,  or  granite. 
They  occur  also, in  many  different  forms,  as  replacement-de- 

*  J.  F.  Kemp,  Ore-Deposits  of  the  U.  S.  and  Canada,  4th  ed.,  pp.  436-7. 
f  Vogt  "  Problems  in  the  Geology  of  Ore-Deposits,"  Trans.,  xxxi.,  p.  131.  Gen- 
esis of  Ore-Deposits,  p.  642. 

J  G.  P.  Merrill,  Am.  Jour.  ScL,  April,  1896,  4th  series,  vol.  i.,  p.  309. 

I  G.  W.  Card,  Records  Oeol.  Surveys  of  N.  S.  W.,  1895,  p.  154. 

||  W.  Moricke,  Tscherwak,  Mih.Mitth.,  xii.,  p.  195. 

fl  Cited  by  J.  F.  Kemp,  Ore- Deposits  of  the  United  States  and  Canada,  4th  ed.,  p.  36, 


272     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

posits  in  limestone;  as  disseminations  in  igneous  and  sedi- 
mentary rocks ;  as  contact-deposits  near  intrusive  masses ;  and 
in  fissure-veins.  Most  of  the  known  processes  by  which  ore- 
deposits  are  formed  have  probably  been  active  in  producing  gold- 
ores.  A  possible  case  of  origin  by  segregation  in  a  basic  magma 
has  just  been  noted  (at  Rossland).  But  the  writer  believes  that 
most  frequently  the  metal  is  concentrated  in  siliceous  magmas. 

After  studying  the  Yukon  gold-quartz  veins  in  1896-7,  the 
writer  announced  a  theory  of  their  formation  as  the  end- 
product  of  rock-segregation  in  the  region  where  they  occur.* 
In  this  connection  a  brief  outline  of  the  theory  will  be  given, 
with  a  few  additional  observations,  since  made,  which  tend  to 
strengthen  it. 

Under  a  previous  heading,  in  considering  the  segregation 
(differentiation)  of  igneous  rocks,  the  conclusion  has  been 
reached  that  many  magmas  segregate  by  a  repeated  concentra- 
tion and  consolidation  of  the  basic  constituents,  leaving  a  more 
siliceous  residue. 

Just  as  this  process  may  result  in  rocks  of  extreme  basicity, 
such  as  olivine,  hornblende  and  augite  rocks,  and  even  in  seg- 
regated masses  of  the  metallic  minerals  which  ordinarily  are 
accessory  constituents,  so,  at  the  other  end  of  the  series,  very 
siliceous  rocks  arise.  From  the  siliceous  granites  the  transi- 
tion is  gradual  (and  may  often  be  observed  in  a  single  rock- 
mass)  to  more  siliceous  rocks,  consisting  almost  entirely  of 
quartz  and  alkali-feldspar  without  important  admixture  of  the 
dark  ferro-magnesian  minerals. 

These  rocks  are  regarded  by  the  writer  as  far  more  wide- 
spread and  important  than  has  generally  been  recognized,  and 
to  the  group  he  has  applied  the  general  term  "  alaskite."f 
These  alaskites  may  pass  gradually  into  quartz-veins. 

In  the  multitudinous  and  varied  dike-rocks  of  Forty-Mile 
creek,  Alaska,  where  most  of  the  observations  were  made 
which  led  up  to  the  theory  in  question,  every  stage  in  the  in- 
creasing acidity  was  observed.  J  The  rocks  which  here  occur 

*  J.  E.  Spurr,  "Geology  of  the  Yukon  Gold-District,"  ISth  Ann.  Kept.  U.  S. 
Geol.  Surv.,  Part  TIL,  p.  312. 

f  J.  E.  Spurr,  "Classification  of  Igneous  Rocks,"  Am.  Geologist,  April,  1900, 
p.  229. 

J  J.  E.  Spurr,  "Geology  of  the  Yukon  Gold-f)istrict,"  18th  Ann.  Rept.  U.  S. 
Geol.  Surv.,  PartllL,  p.  232. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   273 

in  greatest  bulk  are  hornblende  granites  and  hornblende  dio- 
rites,  both  of  medium  acidity.  From  these  rocks  the  change 
is  very  gradual  to  the  extremely  basic  rocks  before  mentioned. 
We  -will,  however,  not  dwell  on  this  phase  of  the  segregation, 
but  turn  to  the  development  of  the  siliceous  rocks,  which  is 
equally  well  displayed. 

The  basic  hornblende  granite,  which  forms  the  greatest  rock 
masses,  contains  subordinate  quantities  of  biotite.  By  a  very 
gradual  transition  the  hornblende  diminishes  in  amount  as  the 
proportion  of  biotite  increases,  so  that  the  rock  becomes  a 
biotite-granite ;  and  in  many  dikes  the  amount  of  biotite  be- 
comes less  and  less,  giving  rise  to  an  extremely  siliceous 
granite,  in  which  the  biotite  is  an  insignificant  constituent  as 
compared  with  the  quartz  and  feldspar.  With  further  diminu- 
tion of  the  biotite  the  granites  change  into  essentially  quartz- 
alkali  feldspar-rocks — alaskites.  These  rocks  are  sometimes 
fine-grained,  or  may  be  coarse,  like  granites,  but  have  a  nearly 
uniform  structure  and  composition.  In  the  alaskite  series  the 
change  is  continued  by  a  relative  increase  in  amount  of  quartz 
and  decrease  of  feldspar.  One  remarkable  phase  studied  is  a 
porphyritic  dike-rock  whose  ground-mass  consists  almost  en- 
tirely of  quartz  in  small  interlocking  grains,  giving,  both  in 
the  hand-specimen  and  under  the  microscope,  the  exact  appear- 
ance of  a  quartzite.  Yet  this  rock  contains  scattered,  but  regu- 
larly distributed,  porphyritic  crystals  of  feldspar.  It  is  thus 
not  only  related  by  the  closest  ties  to  similar  slightly  less  sili- 
ceous alaskites  of  the  same  district,  but  it  is  only  removed  by 
its  scattered  porphyritic  crystals  from  being  a  typical  quartz- 
vein.  Moreover,  the  superabundant  quartz  in  these  very  sili- 
ceous dikes  tends  to  segregate  into  bunches,  which  may  become 
large,  and  which  have  all  the  characteristics  of  ordinary  vein- 
quartz.  With  the  progressive  increase  in  silicification  the 
quartz  begins  to  occupy  an  important  portion,  and  finally  the 
larger  portion,  of  the  dike.  The  feldspar  becomes  restricted 
to  certain  places,  sometimes  occurring  irregularly,  sometimes 
collecting  near  the  walls,  while  the  quartz  lies  in  the  center.* 

*  This  distribution  is  in  accordance  with  the  theory  of  segregation  by  the  aid 
of  convection-currents  ("Yukon  Gold-District,"  18th  Ann.  Repi.  U.S.  Geol.Surv., 
Part  III.,  p.  306),  by  which  the  least  siliceous  and  first-precipitated  minerals  are 
concentrated  near  the  cooler  dike-walls. 

18 


274     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

Finally,  by  the  disappearance  of  the  feldspar,  the  dike  becomes, 
an  ordinary  quartz-vein. 

In  one  and  the  same  dike  the  change  from  a  coarse  alaskite 
to  a  typical  quartz-vein  may  be  seen  in  all  its  stages. 

The  quartz-veins  generally  contain  pyrites,  as  do  all  the 
other  dikes  of  the  region ;  they  contain  occasional  biotite,  and 
some  segregated  calcite,  as  do  also  the  coarse  alaskites.  It  may 
be  remarked,  in  connection  with  the  calcite,  that  epidote,  the 
silicate  of  lime,  aluminum  and  iron,  is  a  constant  and  impor- 
tant mineral  in  all  the  rocks  of  the  Forty-Mile  region,  from  the 
hornblendites  and  pyroxenites  to  the  most  siliceous  alaskites. 

These  veins  contain  pyrite,  argentiferous  galena  and  free  gold. 
From  them  a  portion  of  the  Yukon  placer-gold  is  probably 
derived,  much  of  the  remainder  coming  from  older  quartz- 
veins  which,  by  reason  of  the  shearing  and  metamorphosis  they 
have  undergone,  do  not  offer  plain  evidence  as  to  their  origin. 

Therefore  it  has  been  concluded  that  certain  quartz-veins  in 
the  Yukon  district  (part,  at  least,  of  which  are  auriferous) 
have  originated  by  a  process  of  magmatic  segregation,  which 
has  separated  them  from  other  materials  while  in  a  state  of 
aqueo-igneous  fusion  (the  condition  of  molten  rock  in  general), 
and  that  they  represent  the  siliceous  extreme  of  that  process. 
From  this  standpoint,  they  are  a  variety  of  the  igneous  rocks. 
But  it  has  been  shown  that  as  magmas  become  more  siliceous 
they  also  contain  more  water ;  so,  when  the  stage  of  quartz- 
.  veins  is  reached,  the  magma  is  believed  to  be  so  attenuated 
that  it  may  best  be  described  as  water  highly  heated  and 
heavily  charged  with  mineral  matter  in  solution.  There  would 
thus  be  no  great  difference  (save  in  their  associations,  and  very 
likely  in  the  selection  of  the  mineral  matters  which  they  con- 
tain) between  these  solutions  and  others  where  the  water  may 
have  had,  say,  an  atmospheric  origin ;  and  a  quartz- vein  origi- 
nating by  magmatic  segregation  might  often  not  be  distinguish- 
able from  one  formed  in  the  many  other  ways  which  are  possi- 
ble. The  main  point  of  interest,  so  far  as  this  discussion  is 
concerned,  is,  as  the  writer  believes,  that  veins  originating  by 
magmatic  segregation  are  especially  apt  to  contain  gold  (with- 
out the  admixture  of  so  great  proportions  of  the  commoner 
metals  as  is  usual  in  ore-deposits),  and  that  thus  an  important 
class  of  typical  gold-quartz  veins  has  been  formed. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  275 

Having  briefly  stated  the  evidence  and  formulated  the  theory 
for  the  Yukon  district,  let  us  recite  some  of  the  evidence  bear- 
ing on  it  elsewhere. 

1.  Evidence  as  to  the  Origin  of  Quartz-  Veins  as  Magmatic 
Segregations. 

Pegmatites  are  coarsely  crystalline  rocks  which  show  close 
relationships  with  ordinary  igneous  rocks,  such  as  granites,  on 
the  one  hand,  and  with  veins,  such  as  are  known  to  be  due  to 
precipitation  from  aqueous  solution,  on  the  other.  Hence 
there  has  been  much  perplexity  and  contention,  some  referring 
them  to  the  "  igneous  "  rocks  and  calling  them  dikes,  others  in- 
sisting that  they  were  "  aqueous "  and  true  veins.  But  the 
latest  and  best  essays  on  the  subject*  agree  that  pegmatites  are 
formed  under  conditions  intermediate  between  those  which 
govern  the  formation  of  siliceous  "  igneous  "  rocks  like  granite, 
and  those  under  which  quartz-veins  are  formed.  There  is,  in 
short,  no  line  of  demarcation  in  nature,  corresponding  to  our 
artificial  and  arbitrary  one,  between  igneous  rocks  and  certain 
aqueous  veins — between  granites  and  certain  large  masses  of 
quartz. 

Transitions  of  pegmatite-  to  quartz-veins,  showing  absolute 
and  uniform  gradation  from  one  to  the  other,  have  been  noted 
by  Crosby  and  Fuller,  Williamsf  and  Van  Hise,|  and  transitions 
or  evident  close  and  constant  relations  between  pegmatites 
and  granites  have  been  noted  by  Crosby,  Brogger,  Van  Hise 
and  Williams. 

Professor  C.  "W.  Hall§  has  furnished  notes  on  eastern  and 
central  Minnesota,  where,  in  connection  with  intrusions  of 
hornblende-biotite  granite,  are  shown  "  granitic  veins."  These 
are  "  locally  pegmatitic,  with  coarse  and  well-developed  feld- 
spar individuals  imbedded  in  a  matrix  of  hornblende  and  bio- 
tite,  while  elsewhere  they  are  finely  textured,  possess  a  reddish 

*  "Origin  of  Pegmatite,"  by  W.  O.  Crosby  and  M.  L.  Fuller,  Amer.  Geologist, 
vol.  xix.  (1897),  p.  147;  "Die  Mineralien  der  Syenit-pegmatitgdnge  der  sudnorive- 
gischen  Augit-  und  Nephelin-syenite, "  by  W.  C.  Brogger,  Zeitsch.filr  Kryst.,vol.  xvi., 
1890,  pp.  215-235.  "  Origin  of  the  Maryland  Pegmatites,"  by  G.  H.  Williams, 
15th  Ann.  Report  U.  S.  Geol  Sur. ,  1895,  p.  675.  f  Op.  tit.,  p.  679. 

J  16th  Ann.  Report  U.  S.  Geol.  Sur.,  Part  L,  1896,  p.  688. 

g  Keewatin  Area  of  Eastern  and  Central  Minnesota,  Bull.  Geol.  Soc.  Amer.,  voL 
xii.,  pp.  367-8-9  (1901). 


276     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

color,  and  are  highly  siliceous  in  composition."  Associated 
with  these  are  veins  of  quartz.  In  the  St.  Louis  river-district 
the  veins,  when  wide,  become  pegmatitic.  The  veins  some- 
times carry  segregated  sulphides  and  siderite.  One,  on  Kettle 
river,  has  been  explored  for  gold. 

Professor  J.  F.  Kemp*  observes  that  on  the  north  shore  of 
Long  Island  Sound  "  pegmatites  are  abundantly  developed  in 
connection  with  granites,  and  all  grades  are  shown  up  to  prac- 
tically pure  quartz."  One  of  the  largest  quartz-veins,  which 
Professor  Kemp  thinks  belongs  to  the  pegmatitic  series,  car- 
ries, in  portions,  ferruginous  minerals  and  traces  of  gold. 

Dr.  E.  Hussakf  has  described  an  auriferous  quartz-vein  in 
Brazil  which  he  regards  as  an  ultra-acid  granitic  dike.  Mr. 
"Waldemar  Lindgren,  however,  dissents  from  this  conclusion.  J 

According  to  Phillips  and  Louis, §  at  Timbarra,  in  Kew  South 
Wales,  "  gold  is  found  in  granite ;  these  gold-fields  consist  of  a 
granitic  tableland,  traversed  by  dikes  of  eurite||  and  pegma- 
tite, also  occasionally  showing  veins  of  auriferous  quartz,  which 
'may  possibly  be  segregation  deposits." 

At  Silver  Peak,  Nevada,  the  writer  noticed  transitions  from 
the  granitic  rock  (which  is  there  intrusive  in  Cambrian  lime- 
stones) into  quartz-veins.  Mr.  H.  "W.  Turner,  who  studied  this 
region  more  in  detail,  made  the  same  observation  independ- 
ently, and  communicated  it  subsequently  to  the  writer.  Accord- 
ing to  him,  these  segregated  veins  seem  to  be  connected  in 
some  way  with  the  Silver  Peak  ore-deposits,  which  are  gold- 
quartz  veins. 

On  the  Mojave  river,  in  Southern  California,  the  writer  ob- 
served one  of  the  most  rapid  and  complete  transitions  from 
quartz-veins  into  granite  which  he  has  ever  seen.  Here  Pale- 
ozoic limestones  and  quartzites  (considerably  metamorphosed) 
are  cut  by  intrusive  granite,  whose  dikes  grade  into  pegmatite, 
and  these  to  quartz-veins.  In  a  single  dike  he  observed,  within 
the  length  of  not  many  yards,  a  complete  transition  from  a 

*  "  The  Hole  of  the  Igneous  Rocks  in  the  Formation  of  Veins,"  Trans.,  xxxi., 
p.  182.  Genesis  of  Ore-Deposits,  p.  693. 

t  Zeitschriftfiir  prakt.  Geologic,  1898,  p.  345. 

J  "  Metasomatic  Processes  in  Fissure- Veins,"  Trans.,  xxx.,  642,  and  Genesis 
of  Ore-Deposits,  p.  562. 

\   Ore-Deposits,  second  edition,  p.  649.  ||  Alaskite.— J.  E.  S. 


IGNEOUS    ROCKS    AS    BELATED    TO    OCCURRENCE    OF    ORES.      277 

fine-grained  pegmatite  to  a  typical  quartz-vein.  Gold  is  found 
in  this  locality  (Oro  Grande),  but,  unfortunately,  he  did  not 
remain  long  enough  to  find  whether  it  is  in  these  quartz- 
veins. 

The  writer  has  also  studied  the  transition  of  granite  and 
alaskite  through  pegmatitic  stages  to  quartz-veins,  in  the 
"Walker  river  range,  in  northwestern  Nevada,  near  the  Indian 
reservation ;  and  again  in  the  Mojave  desert,  southeast  of  Ran- 
deburg,  California. 

At  Belmont,  in  Nevada,  the  writer  has  made  a  brief  study  of 
an  interesting  dike-rock  and  its  associated  phenomena.*  The 
dike  is  one  of  the  outlying  offshoots  from  a  large  body  of  sili- 
ceous granite ;  it  is  nearly  half  a  mile  wide,  and  cuts  Silurian 
slates  and  limestones.  Near  the  contact  the  slates  and  lime- 
stones have  been  transformed  into  jasperoidf  by  the  introduc- 
tion of  silica;  in  part  they  have  also  been  altered  to  micaceous 
schists,  often  containing  disseminated  small  bundles  of  yellow 
and  red  metallic  oxides.  In  this  rock  occur  quartz-veins  which 
carry  rich  antimonial  silver-ores. 

The  dike-rock  varies  greatly  in  texture  and  composition. 
One  specimen  collected,  classed  as  a  siliceous  muscovite-biotite 
granite,  is  remarkable  for  the  irregular  arrangement  of  its  con- 
stituent minerals,  the  quartz  often  segregating  into  bunches  a 
quarter  of  an  inch  in  diameter,  with  all  the  characteristics  of 
vein-quartz.  A  coarser-grained  biotite  granite  at  some  little 
distance  has  the  same  peculiarity,  and  in  this  place  the  blotches 
of  quartz,  mosaics  of  intergrown  grains,  are  from  one-third  of 
an  inch  to  one-half  an  inch  in  diameter.  But  the  rock  of  chief 
interest  is  one  which  looks  like  a  micaceous  quartzite,  and, 
indeed,  consists  essentially  of  muscovite  and  quartz.  Micro- 
scopic study  reveals  it  in  the  presence  of  the  feldspar  albite, 
and  proves  that  the  muscovite  has  largely  been  derived  from 
the  alteration  of  orthoclase.  Yet  the  rock  is  fresh  and  hard, 
and  the  change  has  not  been  affected  by  surface  weathering. 

"The  process  must  be  regarded  as  one  of  endomorphism,  and  as  connected  and 
probably  contemporaneous  with  the  exomorphism  indicated  by  the  alteration  of 
the  siliceous  limestone  of  the  wall  rocks  to  jasperoid  and  mica  schist. 

*  J.   E.  Spurr,  Am.  J.  Sci.,  4th  series,  vol.  x.,  p.  351  (1900)  :  "Quartz-Mus- 
covite Rock  from  Belmont,  Nev.,  the  Equivalent  of  the  Russian  Beresite. " 
t  J.  E.  Spurr,  "Geology  of  Aspen  District,"  Mon.  xxxi.,  U.  S.  G.S.,  p.  219. 


278     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

"  In  both  the  intrusive  and  the  intruded  rock  the  result  of  the  metamorphism 
has  been  the  same,  producing  quartz  and  muscovite  at  the  expense  of  the  ortho- 
clase  on  the  one  hand,  and  of  the  calcite  and  subordinate  minerals  on  the  other. 
In  the  case  of  the  wall-rock  the  metamorphism,  being  apparently,  from  its  dis- 
tribution, dependent  upon  the  intrusion,  evidently  took  place  after  this  intrusion, 
and  was  brought  about  by  the  solutions  which  accompanied  the  igneous  rock,  or 
were  residual  from  its  solidification.  Within  the  dike  the  similar  alteration  was 
probably  contemporaneous  with  that  in  the  country-rock."* 

White  quartz-veins,  often  several  feet  in  width,  occur  in  the 
immediate  vicinity  of  this  intrusive  mass.  For  these  the  con- 
clusion is  reached  that : 

"These  quartz- veins  are  probably  contemporaneous  with  those  already  de- 
scribed as  occurring  in  irregular  form  within  the  dike-rock  itself,  and  as  evi- 
dently representing  the  final  product  of  the  residual  solution  of  the  general 
magma.  In  these  quartz-veinsf  the  metallic  minerals  [chiefly  stetefeldtite,  an 
argentiferous  ore  of  antimony,  with  some  lead,  copper  and  iron]  are  scattered  in 
branches  or  disseminated  particles,  rarely  in  banded  form.  .  .  . 

"  The  metallic  minerals  being,  from  their  habit,  plainly  contemporaneous  with 
the  quartz-veins  which  enclose  them,  it  is  evident  that  the  deposition  of  these 
minerals,  the  formation  of  the  quartz- veins,  the  metamorphism  of  the  country- 
rock  to  jasperoid  and  muscovite  schist,  and  the  endomorphism  of  the  muscovite- 
granite  to  quartz-muscovite  rock  were  contemporaneous  occurrences,  all  brought 
about  by  the  same  agencies,  which  were  the  solutions  representing  the  end- 
product  of  the  differentiation  of  the  granitic  intrusive  rock." 

This  Belmont  quartz-muscovite  rock  acquires  additional  in- 
terest as  the  equivalent  of  the  so-called  beresite  of  the  Urals, 
which  the  writer  has  had  the  privilege  of  studying  in  the  field. 
After  considerable  investigation  and  discussion,  the  Ural  beres- 
ite (composed  of  quartz  and  muscovite)  has  been  shown  by 
Arzruni  to  be  an  alteration  from  a  muscovite-granite  in  the 
same  way  as  the  Belmont  rock.  The  analogy  between  the  Bel- 
mont phenomena  and  those  of  Berezovsk  is  still  more  striking 
when  we  consider  the  close  connection  of  the  beresite  with 
gold-quartz  veins.  This  rock  forms  intrusive  dikes  from  2  to 
40  meters  wide,  cutting  schists.  Previous  to  all  scientific  in- 
vestigation, these  dikes  were  recognized  by  the  miners  as  the 
surest  guides  to  gold.  The  auriferous  veins  are  found  in  the 
dikes,  and  only  rarely  extend  into  the  country-rock.  They  gen- 
erally stretch  across  the  dikes  at  right-angles  to  the  walls,  and 
have  been  considered  as  filling  "  fissures  of  contraction "  by 

*  Op.  cit.,  p.  355. 

t  According  to  S.  F.  Emmons,  "  Geol.  Expl.  of  4(M  Parallel,"  vol.  iii. 
(Mining  Industry),  p.  398. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   279 

Posepny.*  This  is  probably  correct,  for  the  veins  follow  the 
same  lines  as  the  "  columnar  jointing  "  of  dikes,  which  are  due 
to  contraction. 

At  Belmont  the  important  point  in  determining  the  age  of 
the  quartz- veins  is  their  contemporaneity  with  the  contact- 
metamorphosis  of  the  wall-rocks,  which  fixes  their  period  of 
formation  as  during  the  final  stage  of  the  consolidation  of  the 
granite.  We  have  not  sufficient  data  to  announce  this  same 
criterion  for  Berezovsk,  and  in  the  study  of  ore-deposits  one 
must  ever  beware  of  reasoning  too  closely  from  analogy;  but 
the  fact  that  the  "  beresite  "  has,  like  the  Belmont  quartz-mus- 
covite  rock,  originated  not  by  surface  alterations,  but  through 
deeper-seated  solutions, f  that  this  alteration  seems  a  part  of 
that  which  produced  the  gold-quartz  veins,J  and  that  the  latter 
are  confined  to  the  dikes  or  their  immediate  vicinity, — all  these 
are  in  favor  of  the  hypothesis  of  the  origin  of  the  veins  as  the 
last  and  most  siliceous  and  most  fluid  segregation  product  of 
the  granitic  magma. 

2.   The  Genetic  Connection  of  Gold- Quartz  Veins  with  Siliceous 
Igneous  Rocks. 

We  have  reviewed  a  number  of  cases  of  the  actually  ob- 
served transition  from  siliceous  igneous  rocks  to  quartz-veins, 
with  or  without  a  pegmatic  stage,  and  in  most  of  these  the 
veins  contain  disseminated  metals,  notably  gold.  When  mining 
engineers  and  geologists  begin  to  look  more  carefully  for  such 
transitions,  it  is  probable  that  numerous  others  will  be  found. 
Meantime,  the  number  of  instances  in  which  gold-quartz  veins 
are  intimately  associated  with  siliceous  intrusive  rocks  is  really 
remarkable. 

On  the  Pelly  river,  in  British  Columbia  (a  part  of  the  Yukon 
gold-belt),  Dr.  G.  M.  Dawson§  found  evidence  to  show  that  the 
development  of  quartz-veins  had  occurred  contemporaneously 
with  the  upheaval  of  the  granites,  and  probably  by  some  action 
superinduced  by  the  granite  masses  themselves  while  still  in  a 
formative  condition. 

*  Genesis  of  Ore-Deposits,  first  edition,  p.  70  ;  second  edition,  p.  76. 
t  The  beresite   is  deeply  decomposed  by  surface  agencies,   but  this  is   inde- 
pendent of  the  agency  by  which  the  first  rock  originated. 

J  The  beresite  itself  contains  gold  in  small  quantity  (50  drachms  to  the  ton). 
I  Ann.  Rep.  Geol.  Nat.  Hist.  Survey,  Canada,  vol.  iii.,  Part  L,  p.  35  B. 


280     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

In  the  Cook  Inlet  region,  Alaska,  gold  is  found  in  aplite* 
dikes,  according  to  Mr.  W.  C.  Mendenhall.  In  the  Nome  re- 
gion, Messrs.  Schrader  and  Brooksf  report  veins  containing 
sulphides,  quartz  and  calcite,  cutting  metamorphic  marble  and 
schists.  A  large  area  of  granite  is  also  reported. 

In  the  Slocan  District,  British  Columbia,  according  to  W.  A. 
Carlyle,J  the  typical  gold-quartz  veins,  as  well  as  quartz-veins 
carrying  argentite.  native  silver  and  gold,  appear  to  be  con- 
fined to  granite,  while  veins  containing  argentiferous  galena, 
blende,  siderite,  tetrahedrite,  etc.,  are  found  both  in  stratified 
rocks  and  granites.  In  California,  "Whitney  §  noted  that,  While 
the  granite  itself  is  not  metalliferous,  its  appearance  seems  to 
be  closely  associated  with  the  metamorphisrn  of  the  adjacent 
sedimentary  rocks,  while  this  latter  condition  is,  as  a  general 
rule,  the  concomitant  of  the  occurrence  of  minerals  or  metal- 
liferous veins.  Prof.  J.  F.  KempH  remarks:  "The  enormous 
introduction  of  silica  is  one  of  the  most  extraordinary  features 
of  the  geology  of  the  Sierras,  and  indicates  a  remarkable  ac- 
tivity of  circulating  waters.  The  igneous  intrusions  doubtless 
promoted,  if  they  did  not  cause,  the  circulations."  In  the 
Lake  of  the  Woods  district,  schists,  early  granite,  and  gneiss 
are  cut  by  later  granite.  The  veins  are  found  in  the  schists, 
but  favor  the  portions  near  the  contact  with  the  granite  or 
gneiss.^ 

In  the  gold-bearing  region  of  Nova  Scotia,  metamorphosed 
sedimentary  rocks  containing  quartz-veins  are  cut  by  many 
great  intrusions  of  granite.** 

In  Madison  county,  Montana,  gold-quartz  veins  occur  in 
granite;  in  Beaverhead  county,  at  the  contact  between  lime- 
stone and  granite;  in  Lewis  and  Clarke  county,  in  granite 
and  slates,  etc. ft 

In  Rhode  Island,  quartz-veins  are  frequent  around  the  great 
inclusions  of  granite.  Traces  of  gold  have  been  met.Jt 

*  "Alaskite."—  J.  E.  S.  t  Trans.,  xxx.,  p.  238. 

t  Quoted  by  J.  F.  Kemp,  Ore-Deposits  of  the  United  States  and  Canada,  4th  ed., 
p.  395. 

%   The  Auriferous  Gravels  of  the  Sierra  Nevada,  p.  353. 

||   Ore-Deposits  of  the  United  States  and  Canada,  4th  ed.,  p.  370. 

Tf  Kemp,  op  cit.j  p.  385.  **  Kemp,  op  cit.,  p.  397. 

ft  Kemp,  op  cit.,  p.  320.  JJ  Kemp,  op  dt.,  p.  383. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  281 

In  the  Appalachian  gold-quartz  region  are  numerous  intru- 
sions of  granitic  rocks,  arid  pegmatite  is  abundant.* 

In  British  Guiana,  gold-quartz  veins  "  occur  mostly  in  meta- 
morphic  schists  and  gneiss;  and  nearly  all  the  streams  and 
rivers  that  traverse  regions  occupied  by  the  above  rocks,  or  by 
granite,  are  gold-bearing,  "f 

In  the  Sutherland  gold-fields  in  Scotland,  the  rocks  are  gran- 
ites, gneiss,  mica-schist,  and  quartzite,  and,  in  a  few  localities 
only,  quartz-veins.  On  the  stream  called  the  Kildonan,  "  the 
miners  preferred  working  either  in  the  vicinity  of  masses  of 
granite,  or  in  the  neighborhood  of  a  partially  decomposed 
greenish  schist." 

No  gold  has  been  found  in  situ  in  this  district,  but  the  drift 
is  entirely  composed  of  fragments  of  purely  local  rocks,  while 
quartz  pebbles  are  almost  entirely  wanting. 

Influenced  by  these  and  similar  considerations,  Messrs.  Joass 
and  Cameron  are  disposed  to  ascribe  a  granitic  origin  to  the 
gold  of  this  area.J 

On  the  island  of  Bommel,  in  Norway,  the  chief  country- 
rock  is  "  gabbro,"  in  which  large  dikes  of  "  quartz-porphyry," 
passing  into  granite,  and  of  altered  diorite,  occur ;  on  the  south 
of  the  district  is  a  large  tract  of  slate,  in  which  are  non-aurif- 
erous quartz-veins.  The  "quartz-porphyry"  dikes,  and  those 
of  diorite,  contain  strong  gold-quartz  veins,  whose  general  con- 
temporaneity with  the  period  of  igneous  intrusion  is  shown  by 
their  being  older  than  some  dikes  and  younger  than  others.  § 

In  the  Kotchkar  district,  in  the  Urals,  the  gold-quartz  veins, 
as  seen  by  the  writer  on  the  occasion  of  a  brief  visit,  are  imme- 
diately the  results  of  circulating  waters  subsequent  to  the  con- 
solidation of  the  country-rock ;  but  they  occur  in,  and  are  prob- 
ably primarily  dependent  upon,  the  granite.  There  are  analo- 
gies in  many  ways  between  this  district  and  that  of  Monte 
Cristo,  "Washington  State,  U.  S.  A.,  where,  according  to  the 
writer's  study,  the  ore-deposits  (chiefly  replacements  of  igneous 
rocks  by  auriferous  sulphides),  while  immediately  the  work  of 
ordinary  circulating  waters,  yet  are  closely  dependent  upon 


*  Phillips  and  Louis,  Ore- Deposits,  2d  ed.,  pp.  786-7. 
f  Phillips  and  Louis,  op  cit.,  pp.  887,  888. 
J  Phillips  and  Louis,  op  cit. ,  p.  320. 
$  Phillips  and  Louis,  op  cit.,  p.  519. 


282    IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

great  intrusive  bodies  of  tonalite  in  which  the  first  concentration 
has  probably  been  effected  by  magmatic  segregation. 

In  India,  it  has  been  stated  by  Mr.  King  that  the  so-called 
quartz-reefs  of  the  Travancore  State  "  are  not  really  veins,  but 
merely  the  outcrops  of  beds  of  quartzite,  associated  with  feld- 
spar, which  run  with  the  foliations  of  the  gneiss.  Although 
minute  traces  of  gold  may  sometimes  be  detected  in  these 
rocks  by  assay,  the  amount  present  is  far  too  small  to  render 
them  of  any  commercial  value  as  a  source  of  that  metal." 
The  phrase  "  beds  of  quartzite,  associated  with  feldspar," 
strongly  suggests  fine-grained  siliceous  alaskite  dikes.  In  the 
Wynaad  district,  "  the  gold-bearing  area  consists  of  granite, 
gneiss,  and  various  metamorphic  rocks,  traversed  by  veins  of 
quartz,  which,  with  their  branches,  are  auriferous."  * 

In  China,  the  reported  gold-quartz  veins  occur  almost  en- 
tirely in  granite,  as  at  Ninghai,  the  Chao-Yuen  district,  and 
Yeshui  in  Mongolia. f 

In  Siberia,  the  connection  of  the  gold  with  granite  and  gran- 
ititej  has  been  observed  in  more  than  one  place.  § 

Turning  to  Australia,  we  find  a  relation  of  the  gold  to  sili- 
ceous igneous  rocks  quite  as  striking  as  in  California  and 
Alaska.  In  Victoria, 

"Gold  is  not  only  found  in  veins  traversing  granite,  felsite  and  diorite,  but  is 
also  sometimes  disseminated  throughout  the  rocks  themselves."  || 

I  quote  from  Phillips  and  Louis :  ^f 

II  In  a  paper  read  before  the  Geological  Society  of  London  in  April,  1872,  Mr. 
Richard  Daintree  drew  attention  to  the  fact  that  the  auriferous  Devonian  districts 
of  Queensland  are  entirely  confined  to  such  as  are  penetrated  by  certain  eruptive 
rocks,  principally  pyritous  diorites.    In  these  diorites,  and  near  the  point  of  their 
intersection  with  the  Devonian  strata,  veins  of  quartz,  calc-spar  and  iron-pyrites 
had  been  examined  and  found  rich  in  gold,  while  the  extensions  of  such  veins  at 
any  considerable  distance  from  the  intrusive  rocks  were  found  to  be  barren.     In- 
stances were   also   adduced   to   show   that  the   pyrites  sporadically   distributed 
through  the  diorites  was  occasionally  distinctly  auriferous,  and  had,  by  its  decom- 
position and  disintegration,  produced  drifts  containing  gold  in  paying  quantities. 

"  In  a  subsequent  communication,  Mr.  Daintree  states  that  since  the  date  of 

*  Phillips  and  Louis,  Ore-Deposits,  pp.  562-3. 

f  Phillips  and  Louis,  op.  cit.,  p.  618.  J  "  Alaskite."—  J.  E.  S. 

%  Quoted  by  DeLaunay,  "Contribution  a  F Etudes  des  Gites  Metalliferes, "  An- 
nales  d.  Mines,  August,  1897,  9th  series,  vol.  xii.,  p.  224. 

||  Phillips  and  Louis,  Ore-Deposits,  p.  620.  fl  Op.  cit.,  p.  641-2. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.   283 

his  first  paper  he  had  learned  from  Mr.  C.  Wilkinson,  then  Government  Geolo- 
gist of  New  South  Wales,  that  the  same  facts  hold  good  for  the  New  South  Wales 
gold-fields  lying  in  Upper  Silurian  or  Devonian  areas  ;  and  Mr.  G.  H.  F.  Ulrich, 
the  Curator  of  the  Technological  Museum  in  Melbourne,  in  his  catalogue  of  the 
rocks  in  that  institution,  gives  details  which  go  to  show  that  the  Upper  Silurian 
rocks  of  Victoria  owe  their  auriferous  character  to  the  same  cause. 

"  He  describes  the  diorites  of  Victoria  as  occurring  mostly  as  dikes,  varying  in 
thickness  from  a  few  feet  to  several  hundred,  traversing  Upper  Silurian  strata,  and 
presenting  nearly  all  the  ordinary  varieties  of  structure  and  composition  of  that 
rock.  They  are  nearly  always  impregnated  with  auriferous  pyrites,  and  are 
either  traversed  by  or  associated  with  quartz-veins.  According  to  Mr.  Ulrich, 
by  far  the  greater  proportion  of  the  quartz-gold  furnished  by  the  gold-fields  occu- 
pied by  Upper  Silurian  rocks  is  derived  from  dikes  of  diorite.  .  .  . 

"The  question  as  to  when  the  auriferous  pyrites  was  deposited  in  these  diorites 
is  of  much  interest,  and  one  that  it  will  be  somewhat  difficult  to  solve.  It  is, 
however,  probable  that  in  the  majority  of  cases  the  pyrites  was  contemporaneous 
with  the  consolidation  of  the  rock  in  which  it  occurs,  although  it  is  also  possible 
that  it  may  have  occasionally  owed  its  origin  to  the  subsequent  passage  through 
the  rock  of  metalliferous  solutions.  .  .  . 

"  Below  the  water- level,  which  usually  very  nearly  coincides  with  the  zone  of 
decomposition,  veins  of  a  class  which,  on  the  whole,  have  proved  very  misleading 
to  the  miner,  although  often  rich  in  gold,  usually  disappear.  These  follow  the  lines 
of  jointing  of  the  rock,  and  are  probably  due  to  the  decomposition  of  auriferous 
pyrites  and  the  re-deposition,  from  solution,  of  a  portion  of  its  material  in  local 
fissures.  .  .  .  Besides  the  veins  above  referred  to,  there  are,  associated  with  the 
intrusive  auriferous  rocks,  others  which  Mr.  Daintree  considers  as  being  of  far 
greater  practical  importance,  from  being  generally  of  greater  width  and  more 
likely  to  be  persistent  in  depth.  These  he  regards  as  the  result  of  hydrothermal  agen- 
cies which  preceded  and  accompanied  the  protrusion,*  and  which  in  some  cases  con- 
tinued long  after  the  intrusive  rock  had  cooled  down." 

Again,  I  quote  the  following  :f 

"Daintree,  Racket,  Wilkinson  and  others  have  shown  that  a  large  portion  of 
the  gold  in  Victoria  and  Queensland  is  due  to  the  agency  of  intrusive  dikes  of 
felstone,  el  van  and  diorite,  so  that  reefs  of  quartz  in  Silurian  rocks  are  not,  as  was 
at  one  time  supposed,  the  exclusive  source  of  Australian  gold. 

"  At  Timbarra,  gold  is  found  in  granite  ;  these  gold-fields  consist  of  a  granitic 
tableland,  traversed  by  dikes  of  euritej  and  pegmatite,  also  occasionally  showing 
veins  of  auriferous  quartz,  w hich  may  possibly  be  segregation  deposits.  $  The  weath- 
ered granite  is  sluiced,  and  very  fine  gold,  to  the  extent  at  times  of  5  dwt.  to  the 
ton,  is  obtained.  Gold  has  been  found  to  occur  here  in  unaltered  granite,  and  in  eurite,\\ 
as  well  as  in  the  decomposed  granite." 

In  the  Transvaal,  in  the  Lydenburg  district,  a  quartz-vein  in 
a  diorite  dike  was  worked  at  Waterfall  creek,T  and  at  Ophir 
Hill  is  a  silicified  bed  of  dolomite,  which  has  been — 

*  The  italics  are  mine.— J.  E.  S.  f   Op.  cit.,  p.  649. 

J  "Alaskite."— J.  E.  S.  g  The  italics  are  mine.— J.  E.  S. 

|j  The  italics  are  mine. — J.  E.  S.       \  Phillips  and  Louis,  op.  cit.,  pp.  734-5, 


284     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

"mineralized  by  gold-bearing  solutions,  which  are  in  some  way  connected  geneti- 
cally with  the  numerous  dioritic  dikes  that  traverse  the  district."  In  the  De 
Kaap  district  the  rocks,  "both  stratified  and  granitic,  are  traversed  by  dikes  of 
diorite  and  pegmatite.  ...  In  the  neighborhood  of  the  granite,  these  rocks  occa- 
sionally carry  small  ferruginous  intercalated  deposits,  which  are  generally  aurif- 


3.    The  Subordinate  Connection  of  Gold- Quartz  Veins  with  Basic 

Igneous  Rocks. 

To  avoid  misunderstanding,  I  wish  to  say  here  that  I  recog- 
nize the  fact  that  gold-quartz  veins  may  occur  in  or  near  basic 
intrusives,  and  may,  indeed,  be  genetically  dependent  on  them. 
In  the  Kolar  gold-field  in  India,  for  example,  the  auriferous 
veins  invariably  occur  in  a  band  of  "greenstone  trap."*  In 
Western  Australia  the  veins  are  reported  to  occur  chiefly  in 
diorite  and  biabase.f  But  certainly  an  overwhelming  majority 
of  gold-quartz  veins  occur  in  connection  with  rocks  of  the 
dioritic  and  granitic  families, — that  is  to  say,  with  the  two 
most  siliceous  families  of  the  three  which  make  up  most  igne- 
ous rocks ;  and  of  these  granite-diorite  rocks,  the  veins  show  a 
decided  preference  for  the  more  siliceous  groups,  such  as 
quartz-diorite  (tonalite),  granite  and  alaskite.  On  the  other 
hand,  the  intimate  genetic  connection  of  these  typical  gold- 
quartz  veins  with  distinctly  basic  rocks,  such  as  those  of  the 
diabasic  family,  may  be  safely  called  exceptional. 

Therefore,  the  statement  may  be  formulated  that  although 
gold  is  present  in  all  igneous  rocks,  and  may  be  unequally  distributed 
in  any  of  them,  yet  the  conditions  for  concentration  by  magmatic 
segregation  become  more  favorable  in  proportion  as  the  rock  becomes 
more  siliceous,  and  become  most  favorable  in  what  has  been  shown  to 
be  the  extreme  siliceous  product  of  rock-differentiation — in  quartz- 
veins  and  dikes. 

The  explanation  of  this  is  a  problem  for  future  study. 

X.  RESUME  OF  THE  EVIDENCE  CONCERNING  THE  PREFERENCE 
OF  CERTAIN  METALS  TO  ACCUMULATE,  BY  MAGMATIC  SEG- 
REGATION, IN  CERTAIN  ROCK-TYPES  OF  THE  ESTABLISHED 
CLASSIFICATION. 

I  have  already  pointed  out  that  if  the  rarer  elements,  which 
have  been  disregarded  in  establishing  the  classification  of  igne- 

*  Phillips  and  Louis,  op  cit.,  p.  568.       f  Phillips  and  Louis,  op.  cit.,  p.  700. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     285 

ous  rocks,  find  themselves,  as  a  result  of  magmatic  segregation, 
more  closely  associated  with  certain  of  these  rock-types  than 
with  others,  it  is  not  due  to  any  merit  in  the  classification,  but 
because  of  the  association  of  these  elements  with  the  commoner 
ones  on  which  the  classification  is  based.  In  proportion  as 
this  association  is  strong,  the  preference  of  a  metal  for  a  cer- 
tain rock  becomes  more  marked.  These,  then,  are  some  of  these 
preferences  : 

1.  Basic  Rocks. 

Iron,  as  is  well  known,  is  most  abundant  in  basic  rocks,  and 
iron-ore  deposits  formed  directly  by  magmatic  segregation  are 
mostly  confined  to  such  rocks. 

Chromium  ore-deposits,  due  to  magmatic  segregation,  are 
chiefly  confined  to  the  most  basic  rocks  (peridotites)  and  their 
alteration  products  (chiefly  serpentine). 

Platinum  also  is  characteristic  of  the  most  basic  rocks  (peri- 
dotites and  serpentine). 

Nickel  is  frequently  closely  associated,  as  the  product  of  mag- 
matic segregation,  with  iron,  chromium  and  platinum,  and  is 
especially  found  in  the  most  basic  rocks. 

Vanadium  is  chiefly  found  in  basic  rocks.* 

Copper,  on  account  of  its  easy  mobility,  occurs  in  many  dif-. 
ferent  rocks,  and  as  the  result  of  many  varied  processes.  Yet 
it  seems  to  be  especially  connected  with,  and  at  home  in, 
basic  rocks.  De  Launay  saysrf  "  Copper  is  geologically  close 
to  nickel,  with  which  it  is  frequently  met,  notably  in  the  peri- 
dotites of  Canada,  for,  like  nickel,  it  is,  above  all,  a  metal  of 
the  basic  rocks.  .  .  ." 

2.  Siliceous  Rocks. 

Molybdenum  is  chiefly  found  in  connection  with  the  siliceous 
igneous  rocks. 

Tin  is  seldom  met  with  except  in  connection  with  granite. 

Tungsten  has  practically  the  same  associations  as  tin. 

The  rarer  elements  in  general  seldom  occur  in  notable 
amount,  except  in  pegmatites  and  granitic  rocks.  J 

*  Resume  by  J.  F.  Kemp,  Ore-Deposits  of  the  United  States  and  Canada,  3d  edi- 
tion, p.  36. 

f  ''Contribution  a  1' Etude  des  Gites  Me'tallife'res,"  Annales  des  Mines,  August, 
1897,  9th  series,  vol.  xii.,  p.  191. 

J  Kemp,  Ore- Deposits  of  the  United  States  and  Canada,  3d  edition,  p.  36, 


286    IGNEOUS    ROCKS    AS    BELATED    TO    OCCURRENCE    OF    ORES. 

Gold,  as  has  just  been  argued,  while  a  mobile  metal  and 
widely  distributed,  seems  to  show  a  preference  for  the  siliceous 
igneous  rocks. 

XL  THE  RELATION  BETWEEN  ORE-DEPOSITS  DUE  TO  MAGMATIC 
SEGREGATION  AND  OTHER  ORE-DEPOSITS.  . 

In  nature  there  are  no  hard  and  fast  lines.  So  we  find  that 
ore-deposits  originating,  as  argued,  by  magmatic  segregation, 
pass  by  transition  stages  into  others  whose  characteristics  de- 
mand a  different  interpretation. 

Especially  close  is  the  connection  between  certain  magmatic 
segregations,  certain  contact-deposits,  and  certain  deposits  of 
gaseous-aqueous  (pneumato-hydatogenic)  origin. 

Magmatic  segregations  take  place  while  the  rock,  as  a  whole, 
is  yet  liquid;  they  are  due  to  the  mobility  of  elements  or  crys- 
tallizing minerals  in  this  liquid,  and  may  be  conveniently  con- 
ceived as  taking  place  through  the  action  of  convection-cur- 
rents. 

Upon  the  cooling  of  an  igneous  intrusive  rock,  however, 
what  might  be  called  a  forced  segregation  takes  place.  As  the 
rock  becomes  solid,  those  materials  which  are  "  left-over  "  are 
expelled,  and  find  their  way  into  the  neighboring  rock,  or  along 
the  fissures  of  the  igneous  rock  itself.  These  "left-over"  ma- 
terials consist  chiefly  of  water,  which  is  usually  highly  sili- 
ceous, and  contains  a  great  variety  of  other  mineral  matters  in 
solution,  and  also,  very  commonly,  an  unusual  quantity  of 
gases.  In  these  excretions  the  proportion  of  gaseous  to  liquid 
constituents  appears  to  vary  as  widely  as  possible — dependent, 
probably,  partly  on  the  nature  of  the  cooling-rock,  partly  on 
the  conditions  or  rate  of  cooling,  etc.  According  as  the  gase- 
ous or  the  liquid  elements  preponderate,  there  result  ore-de- 
posits (for  these  expelled  solutions  often  contain  metals),  which, 
from  the  internal  evidence  they  offer  as  to  their  mode  of  for- 
mation, may  be  classed  as  pneumatogenic  (pneumatolytic) 
pneumato-hydatogenic  (gaseo-aqueous),  or  hydatogenic.  To 
the  first  class  belong  the  ores  deposited  by  volcanic  fumaroles, 
and  the  writer  has  referred  the  gold-ores  of  Mercur,  Utah,  to 
the  same  general  division.*  The  second  and  third  classes  are 

*  J.  E.  Spurr,  "  Economic  Geology  of  the  Mercur  Mining  District,"  16^  Ann. 
Kept.  U.  S.  Geol.  Survey,  Part  II.,  p.  452. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     287 

of  great  importance.  To  the  second  belong  the  tin-veins,  and 
to  the  third  the  u  contact-deposits  "  proper.* 

The  gold-quartz  veins,  such  as  have  been  considered  to  be 
formed  by  magmatic  segregation,  the  veins  of  the  tin-group,, 
and  the  contact-deposits  proper,  are  perfectly  distinct  in  char- 
acteristics and  origin;  yet  between  the  first  and  the  second^ 
and  the  second  and  the  third,  there  are  all  transitions,  indicat- 
ing transitions  in  the  conditions  which  produced  them.  In  all 
three  cases  the  mineralizing  agents  may  be  described  as  highly- 
heated  water  heavily  charged  with  silica,  and  containing  metals 
and  other  mineral  matters,  all  being  directly  derived  from  an 
igneous  rock  in  its  last  stages  of  consolidation  from  a  molten 
condition.  All  are  characteristic  of  the  more  siliceous  intru- 
sives.  Tin-veins  seem  to  be  confined  to  granitic  rocks ;  gold- 
quartz  veins  prefer  granite,  and  after  that  diorite ;  while  con- 
tact-deposits, like  contact-metamorphism  in  general,  are  chiefly 
characteristic  of  the  more  siliceous  rocks,  granite  or  diorite. 
Yet  the  first  may  be  conceived  of  as  quietly  segregating  under 
pressure  in  a  mobile  though  probably  slowly  congealing  magma, 
the  second  as  escaping  from  a  cooling-rock  into  fissures  or  other 
channels,  with  relief  of  pressure  and  the  consequent  assump- 
tion of  different  form  and  proportion,  and  the  third  as  also 
escaping  from  a  cooling-rock,  but  under  pressure  and  penetrat- 
ing largely  by  capillary  or  osmotic  action  into  the  rock  in  con- 
tact with  the  igneous  body.  Each  of  these  processes  involves 
a  different  selection  of  elements  by  the  solutions — hence  tin- 
veins  and  gold-quartz  veins  are  generally  quite  distinct. 

Many  pegmatites  are  closely  related  to  tin-veins.  They  not 
infrequently  contain  cassiterite,  and  are  characterized  by  fluorine 
and  boron  compounds,  indicating  gaseo-aqueous  origin.  Such 
pegmatites,  like  the  true  tin-veins,  are  not  likely  to  contain 
gold,  and  cannot  be  taken  as  an  indication  of  probable  gold- 
quartz  veins.  On  the  other  hand,  pegmatites  containing  slight 
evidence  of  pneumatoiytic  origin  may  be  closely  related  to  and 
associated  with  gold-quartz  veins.  In  some  pegmatites  gold 
has  been  found.  But  the  quartz-veins  that  pass  into  relatively 

*  J.  H.  L.  Vogt,  "Problems  in  the  Geology  of  Ore- Deposits,"  Trans.,  xxxi., 
pp.  139,140.  Genesis  of  Ore-Deposits,  pp.  650,  651.  Waldemar  Lindgren,  "Char- 
acter and  Genesis  of  Certain  Con  tact- Deposits,"  Trans.,  xxxi.,  p.  226.  Genesis  of 
Orc-Dcpotils,  p.  716. 


.288  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

fine-grained,  highly  siliceous  igneous  rocks,  with  slight  display 
of  coarse-grained  pegmatite,  have  probably  been  formed  under 
the  most  favorable  conditions  for  the  segregation  of  gold  in 
them,z'.e.,  comparative  freedom  from  the  pneumatolytic  actions 
which  are  so  unusually  important  in  forming  the  cassiterite 
veins.  Yet  the  occasional  presence  of  tin  and  its  close  asso- 
ciate, tungsten,  as  well  as  tourmaline,  fluorite,  etc.,  in  gold- 
quartz  veins  shows  that  one  set  of  conditions  may  pass  gradu- 
ally into  the  other.  The  occasional  presence  of  tourmaline, 
fluorite,  wolframite,  tin,  etc.,  in  zones  of  contact-metamor- 
phosis and  in  contact  ore-deposits,  contrary  to  the  usual  occur- 
rence, is  an  illustration  of  the  same  principle.* 


THE  SEQUENCE    OF  VOLCANIC   ERUPTIONS  CONSIDERED  IN 
CONNECTION  WITH  THE  SEQUENCE  OF  METALLIFEROUS  VEINS. 

It  has  already  been  described  how,  in  a  certain  volcanic  field, 
the  rocks  erupted  or  intruded  at  different  periods  are  of  quite 
different  character,  and  how  dissimilar  rocks  may  be  most 
closely  associated.  Extremely  acid  and  extremely  basic  rocks 
are  often  almost  or  quite  contemporaneously  intruded  or 
erupted  in  the  same  locality.  From  this,  and  from  the  ob- 
served sequences,  rough  laws  of  succession  have  been  de- 
duced. These  differ  somewhat,  according  to  the  district  in 
which  observations  were  made  in  each  case  ;  but  they  practi- 
cally agree  in  indicating  that  magmas  tend  to  segregate  into 
more  basic  and  more  acid  (more  and  less  siliceous)  portions. 
The  writer,  following  Professor  J.  P.  Iddings,  believes  that  an 
initial  rock  of  intermediate  composition  ordinarily  passes,  by 
magmatic  segregation,  into  rocks  which  are  progressively  more 
acid  and  more  basic,  till  extremely  siliceous  and  extremely 
basic  varieties  are  obtained.  According  to  this,  if  the  rocks 
were  regularly  intruded  or  erupted  at  stated  intervals,  we 
might  expect  to  find  the  law  of  segregation  fully  illustrated  in 
the  succession  of  rocks.  -Sometimes,  indeed,  this  is  the  case; 
but  very  often  the  eruptions  have  taken  place  irregularly,  so 
that  the  normal  succession  is  hardly  recognizable. 

Prof.  J.  F.  Kemp  has  called  attention  to  cases  of  successive 

*  Compare  J.  H.  L.  Vogt,  "  Problems  in  the  Geology  of  Ore-Deposits,"  Trans., 
xxxi.,  p.  139.  Genesis  of  Ore-Deposits,  p.  650. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  289 

vein-formations  of  quite  different  characteristics  in  a  single 
district,  and  has  supported  the  idea  that  new  intrusions  of  igne- 
ous rock,  of  a  character  different  from  the  preceding  intrusions 
(rather  than  new  fractures,  as  has  often  been  assumed),  are 
responsible  for  the  differences,  the  metals  extracted  from  one 
igneous  rock  being  different  from  those  derived  from  another.* 
With  this  idea  the  writer  is  in  general  accord,  and  would  add 
the  suggestion  that  also  the  difference  in  the  veins  at  different 
periods  may  often  depend  upon  the  progress  of  rock-segrega- 
tion (differentiation)  in  a  still  unconsolidated  magma,  from 
which  the  metals,  directly  or  indirectly,  are  derived.  By  apply- 
ing the  idea  of  the  change  of  segregated  metals  with  the  prog- 
ress of  general  rock-segregation,  some  light  on  mineral  asso- 
ciation and  succession  may  possibly  be  obtained.  For  example, 
in  many  districts  of  the  world  gold  and  platinum  are  closely 
associated  in  placers.  In  these  districts  it  is  usual  to  find  ex- 
tremely acid  and  extremely  basic  rocks  (complementary  varie- 
ties) intimately  associated,  representing  apparently  an  extreme 
stage  of  rock-segregation ;  and  frequently,  as  in  the  Urals,  the 
platinum  is  found  to  be  derived  from  the  basic  rocks  (perido- 
tites),  and  the  gold  chiefly  from  gold-quartz  veins  in  the  sili- 
ceous ones  (granite).  This  is  one  of  the  simplest  cases.  In  an 
earlier  stage  of  the  rock-segregation,  when  the  extreme  rock- 
types  had  not  originated,  we  would  not  find  any  platinum- 
segregations,  and  the  occurrence  of  gold-quartz  veins  would 
be  less  probable.  A  similar  example  of  mineral  association, 
probably  dependent  upon  rock-segregation,  is  the  occurrence 
in  the  gold-quartz  district  of  Forty-Mile  creek,  Alaska,  of  an 
ore  containing  nickel,  iron,  chromium  and  magnesia,  and  no 
gold.f  Just  as  the  gold-quartz  veins  here  are  intimately  asso- 
ciated with  the  ultra-siliceous  dikes,  so  this  ore  is  probably  con- 
nected with  the  ultra-basic  ones ;  and,  as  the  two  sets  of  dikes 
have  been  considered  complementary  and  due  to  a  single  pro- 
cess of  segregation,  the  contrasted  ore-formations  must  be  con- 
sidered in  the  same  light. 

In  many  districts  it  has  been  noted  that  the  veins  of  different 

*  "  Igneous  Kocks  in  the  Formation  of  Veins,"  Trans.,  xxxi.,  p.  180.      Genesis 
of  Ore-Deposits,  p.  691. 

f  J.  E.  Spurr,  "  Geology  of  the  Yukon  Gold-District,"  18th  Ann.  Rep.  U.  S. 
G.  S.,  Part  III.,  p.  295. 

19 


290  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

periods  have  different  contents..  Professor  Kemp*  has  called 
attention  to  the  San  Juan  region  in  Colorado,  where  the  differ- 
ent veins  have  been  classified  by  T.  B.  Comstock  as  follows : 
1.  The  northwest  system  with  tetrahedrite.  2.  The  east  and 
west  with  bismuth,  and  less  often  nickel  arid  molybdenum.  3. 
The  northeast  with  tellurides  and  antimony,  and  sulphur-com- 
pounds of  the  precious  metals. 

The  same  writer  cites,  in  this  connection,  the  Telluride  dis- 
trict in  Colorado,  where  a  heavy  vein  is  cut  out  and  faulted  by 
a  later  one  of  different  metalliferous  character.  He  also  re- 
calls an  occurrence  near  Freiberg,  Saxony,  where  seven  sets 
of  veins  have  been  recognized,  distinct  from  one  another  min- 
eralogically,  and  probably  introduced  at  different  periods.  At 
Butte,  Montana,  there  are  two  distinct  sets  of  veins,  one  con- 
taining silver  and  no  copper,  and  the  other  containing  copper, 
silver  and  gold. 

At  Mercur,  Utah,  the  writer  has  described  two  ore-bearing 
zones  which  are  parallel  and  lie  about  100  to  150  ft.  from 
one  another,  f  They  are  of  different  ages  :  The  oldest,  the 
"  Silver  Ledge,"  contains  silver  with  only  traces  of  gold,  while 
the  younger,  the  "  Gold  Ledge,"  contains  gold  to  the  exclusion 
of  silver,  together  with  cinnabar  and  realgar,  minerals  not 
found  in  the  Silver  Ledge. 

This  list  might  be  amplified,  but  will  serve  to  show  the  main 
features  of  the  problem. 

It  is  not  safe  or  reasonable  to  refer  such  differences  in  veins 
to  any  one  universal  cause.  In  the  Mercur  case,  the  writer  has 
reasoned  that  the  Gold  Ledge  is  essentially  a  pneumatogenic 
deposit,  due  to  gases  ascending  along  fissures;  and  that  the 
Silver  Ledge  is  a  contact-deposit,  due  to  waters  occluded  in  cool- 
ing from  the  intrusive  sheet  of  rhyolite  porphyry  at  whose 
contact  it  occurs.  In  such  cases  the  different  nature  of  the  min- 
eralizing solutions  is  sufficient  to  produce  entirely  different  com- 
binations of  vein-minerals  derived  from  a  single  magma,  al- 
though a  change  in  this  magma  itself  by  segregation,  or  the 

*  "Igneous  Kocks  in  the  Formation  of  Veins,"  Trans.,  xxxi.,  p.  179.  Also, 
Ore-Deposits  of  United  States  and  Canada,  fourth  edition,  p.  288.  Genesis  of  Ore- 
Deposits,  p.  691. 

f  J.  E.  Spurr,  "  Economic  Geology  of  the  Mercur  Mining  District,  Utah,"  16th 
Ann.  Rep.  U.  S.  Geol.  Survey,  Part  II.,  p.  403. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     291 

intrusion  of  a  rock  of  a  new  kind  is,  of  course,  not  improbable. 
In  other  cases  the  different  character  of  rocks  traversed  by  the 
same  mineralizing  solutions  might  operate  to  cause  the  precipi- 
tation in  one  rock  of  a  different  combination  of  minerals  from 
that  precipitated  by  another.  Where,  however,  the  different 
veins  are  in  the  same  rock,  and  belong  in  the  same  category  of 
ore-deposits  (from  the  standpoint  of  the  process  of  formation), 
the  assumption  of  a  change  in  the  character  of  the  igneous 
rock  below,  whether  by  new  intrusions  (mechanical  change) 
or  by  segregation  (chemical  change),  will  probably  be  often 
justified.  The  fact  that  the  different  veins  often  occupy  frac- 
tures of  different  trend  and  age  is  far  from  opposing  this 
theory,  for  it  is  only  by  the  aid  of  mechanical  accidents  like 
fracturing  that  new  solutions  can  rise,  and  by  their  effects  bear 
witness  to  the  change  that  would  otherwise  not  be  known. 

XIII.  THE  PERSISTENCE  OF  PETROGRAPHIC  PROVINCES,  CONSID- 
ERED IN  CONNECTION  WITH  THE  PERSISTENCE  OF  METAL- 
LIFEROUS PROVINCES. 

While  an  igneous  rock  of  a  certain  kind  is  not  necessarily 
limited  to  a  certain  part  of  the  earth's  surface,  yet  the  rocks  of 
a  given  district  generally  show  marked  and  persistent  differ- 
ences, taken  as  a  whole,  from  the  rocks  of  other,  even  adjoin- 
ing, regions.  To  these  districts,  showing  within  themselves, 
no  matter  how  varied  the  rocks  they  contain,  a  certain  "  kin- 
ship "  or  "  consanguinity"  between  the  different  rocks,  the  term 
petrograpliic  provinces  has  been  assigned. 

For  example,  many  of  the  rocks  of  northern  Minnesota,  es- 
pecially the  granites,  show  a  constant  excess  of  soda  over  pot- 
ash, producing  the  variety  soda-granite,  which  appears  to  be 
characteristic  of  this  region.*  Other  regions  have  a  large  de- 
velopment of  rocks  especially  high  in  the  alkalies, — phonolites, 
nepheline-syenites,  etc.,  rocks  which  in  most  regions  are  want- 
ing. Rocks  characterized  by  an  especially  great  proportion  of 
magnesia,  such  as  peridotites,  occur  in  certain  regions  and  are 
wanting  in  others. 

The  differences  which  give  rise  to  these  petrographical  prov- 
ings  are  evidently  due  to  the  unequal  distribution  of  the  com- 

*  21st  Ann.  Rep.  Minn.  Geol.  and  Nat.  Hist.  Survey,  pp.  41,  42. 


•  292     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

moner  rock-forming  elements,  upon  which  rock-classification 
is  based,  in  different  portions  of  the  earth's  crust.  In  one 
region  sodium  is  especially  abundant,  in  another  both  sodium 
and  potassium,  in  another  magnesium,  in  another  aluminum, 
etc.  Some  petrographic  provinces  show  mineralogical  differ- 
ences which  are  wonderfully  slight,  considering  their  persist- 
ence— in  one  the  granites  may  be  chiefly  hornblende  granites, 
for  example,  and  in  another  almost  entirely  biotite  granites, 
owing  to  constant,  slight  differences  in  the  proportions  of  alu- 
minum, magnesium,  calcium,  potassium,  etc.,  present  in  each. 
The  existence  of  these  petrographic  provinces,  characterized 
by  different  proportions  of  the  commoner  rock-forming  ele- 
ments, has  been  explained  by  extending  the  theory  of  rock- 
segregation  or  differentiation  so  as  to  make  it  applicable  on  a 
large  scale,  and  by  supposing  that  in  great  internal  reservoirs 
(presumably  connecting,  or  at  least  once  connected)  certain  ele- 
ments, by  reason  of  their  affinity,  become  more  or  less  concen- 
trated in  certain  portions.  We  are  quite  in  the  dark  as  to  what 
might  be  a  possible  cause  for  this  (as  yet)  hypothetical  process, 
for  certainly  the  theory  of  concentration  by  convection-cur- 
rents on  cooling  has  slight  application  here ;  but  in  science  the 
apprehension  of  the  fact  very  commonly  runs  ahead  of  the 
explanation,  and  this  idea  is  at  least  a  good  working  hypothe- 
sis, which  has  much  to  recommend  it.  By  this  theory  all  igne- 
ous rocks  (in  so  far  as  they  are  not  formed  by  fusion 'of  sedi- 
mentary rocks  or  by  mixing  of  already  different  magmas)  have 
originated  chiefly  by  segregation  from  an  original  universal 
magma.* 

If  one  accepts  as  a  working  hypothesis  (as  the  writer  has  done) 
this  theory  that  the  unequal  distribution  or  the  relative  concentration 
of  the  commoner  rock-forming  elements  in  certain  parts  of  the  earth's 
crust  (giving  rise  to  distinct  petrographic  provinces  and  rock-types) 
has  been  effected  by  magmatic  segregation,  one  cannot  avoid  accepting 
the  same  theory  for  the  less  common  rock-forming  elements. 

If  one  accepts  this  for  the  distribution  of  sodium,  potassium, 
aluminum,  magnesium,  titanium  and  phosphorus,  he  must  ac- 
cept it  for  manganese,  barium,  chromium,  nickel,  strontium, 
lithium,  chlorine  and  fluorine ;  and  if  he  applies  it  to  these 

*  J.  P.  Iddings,  "The  Origin  of  Igneous  Kocks,"  Bull.  Philosoph.  Soc.  Wash., 
vol.  xii.,  p.  185. 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  293 

latter,  he  must  extend  it  to  tin,  bromine  and  cobalt;  to  lead, 
zinc,  copper,  arsenic,  antimony,  wolfram ;  to  mercury,  silver, 
bismuth,  vanadium,  tellurium  and  thorium;  to  gold  and  plati- 
num, and  even  to  iridium,  ytterbium  and  germanium.* 

Following  this  idea,  and  observing  that  some  regions  are 
especially  rich  in  sodium,  some  in  magnesium,  and  some  in 
titanium  (petrographic  provinces),  we  should  expect  to  find 
some  especially  rich  in  chromium,  some  in  nickel,  some  in  tin, 
some  in  lead,  some  in  copper,  some  in  mercury,  some  in  gold, 
some  in  platinum,  etc.  This  is  well  known  to  be  the  case,  and 
these  regions,  characterized  by  special  combinations  or  amounts 
of  the  rarer,  especially  the  commercially- valuable,  metals,  I  de- 
sire to  call  metalliferous  provinces. 

A  metalliferous  province  does  not  necessarily  coincide  with 
a  petrographic  province,  for  the  reason  that  I  have  already 
pointed  out — namely,  that  the  petrographic  province  and  its 
contained  rocks  is  classified  solely  on  the  basis  of  the  com- 
moner rock-forming  elements ;  while  the  rarer  ones,  upon  the 
distribution  of  certain  of  which  metalliferous  provinces  may  be 
distinguished,  follow  independent  laws  of  segregation,  which, 
nevertheless,  may  sometimes  partly  coincide  with  the  laws  of 
segregation  of  some  of  the  commoner  elements,  by  virtue  of 
an  affinity  or  preferential  association  between  a  rare  element 
and  a  common  one. 

The  helpfulness  (to  the  investigator)  and  yet  the  final  unre- 
liability of  these  affinities  will  be  at  once  seen  upon  considera- 
tion. Platinum,  for  example,  is  undeniably  most  abundant  in 
basic  rocks — peridotites ;  that  is  to  say,  it  prefers  the  company 
of  elements  like  magnesium,  calcium  or  iron,  and  objects  to 
that  of  silicon;  yet  all  peridotites  do  not  contain  platinum,  at 
least  in  equal  amount.  It  is  only  in  certain  metalliferous  prov- 
inces that  platinum  is  sufficiently  abundant  in  peridotites  to  be- 
come commercially  interesting.  The  same  remarks  apply  to 
chromium,  nickel,  etc.  On  the  other  hand,  tin  seems  to  prefer 
the  society  of  silicon,  and  is  always  found  in  close  connection 
with  siliceous  igneous  rocks,  chiefly  granites ;  yet  not  all 
granites  contain  tin  in  notable  quantities.  The  variation  is 

*  For  the  relative  proportion  of  the  elements  in  the  earth's  crust,  see  F.  W. 
Clarke,  Bull.  U.  S.  G.  S.  Nos.  78  and  148  ;  also  J.  H.  L.  Vogt,  * '  Ueber  die  rela- 
tive Verbreitung  der  Elemente,"  Zcitsch.  fur  praktische  GeoL,  1898,  p.  225. 


294     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

enormous.  So  a  study  of  the  distribution  of  granite  gives  only 
a  slight  clue  to  the  distribution  of  tin,  and  a  knowledge  of  the 
occurrences  of  peridotite  is  only  the  first  step  toward  a  knowl- 
edge of  the  occurrences  of  chrome  or  nickel-deposits.  This 
principle  is  of  wide  application.  Igneous  rocks  have  long 
been  recognized  as  the  ultimate  sources  of  many,  if  not  most, 
ore-deposits.  Yet  not  all  igneous  rocks  are  connected  with 
ore-deposits.  One  mass  of  diorite,  for  example,  may  be  con- 
nected with  rich  ore-bodies  (formed,  it  is  needless  to  say,  in 
most  cases,  finally  through  the  concentrating  action  of  circulat- 
ing waters),  while  an  exactly  similar  diorite  in  another  region 
may  have  no  ores  at  all  associated  with  it.  One  may  explain 
this  by  assuming  that  in  the  first-mentioned  case  there  have 
been  abundant  circulating  waters,  especially  heated  ones,  and 
plentiful  faults,  fractures  and  zones  of  weakness  permitting  the 
passage  of  these  mineralizing  agents ;  and  that  in  the  second 
case  these  conditions  for  concentrating  the  disseminated  metals 
have  not  been  so  favorable.  The  writer  recognizes  these  con- 
siderations as  of  vast  and  universal  importance ;  and  yet  a  com- 
parison of  regions  equally  favored  with  igneous  intrusives,  with 
abundant  circulating  waters,  with  the  necessary  channels  for 
circulation  and  permeation,  and  with  rocks  favorable  for  the 
precipitation  of  the  metals  held  in  solution  in  the  circulating 
waters  (such  as  limestones,  carbonaceous  shales  and  porous 
sandstones),  may  show  an  utter  difference  in  the  amount  and 
nature  of  the  minerals  concentrated.  Moreover,  the  same  type 
of  rock — a  diorite,  for  example — may  be  associated  with  chiefly 
silver-ores  in  one  region,  with  copper  in  a  second,  and  with 
gold  in  a  third. 

Detailed  investigations  concerning  the  less  abundant  metals 
in  igneous  rocks,  although  they  have  rendered  the  science  of 
ore-deposits  the  inestimable  service  of  proving  the  presence  of 
these  rarer  elements,  afford  little  ground  for  more  extended 
conclusions,  on  account  of  their  being  so  few  and  (necessarily, 
from  the  minute  quantities  dealt  with)  so  inaccurate. 

Yet  it  seems  that  they  also  corroborate  the  conclusion  that 
the  metals  are  very  unevenly  distributed. 

Professor  J.  F.  Kemp  remarks:* 

*  il  The  Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins,"  Trans.,  xxxi., 
p.  172;  also,  Genesis  of  Ore-Deposits,  p.  684. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     295 

"  Nevertheless,  it  is  a  fact  of  the  greatest  importance  that  the  presence  of  the 
metals*  in  the  igneous  rocks  has  been  established.  Not  all  igneous  rocks  have 
yielded  such  results  on  assay.  The  general  experience  has  been  that  when  sam- 
ples of  several  varieties  have  been  collected  in  a  given  district,  some  have  proved 
barren  ;  and  it  must  be  .admitted  that  some  negative  results  have  been  obtained. 
As  a  rule,  however,  they  are  decidedly  fewer  than  the  positive  results.  It  is 
likewise  true  that  not  all  igneous  districts  contain  veins  of  ore." 

To  this  quotation  the  writer  adds  the  suggestion  that  most 
of  the  assays  made  have  been  of  igneous  rocks  in  metalliferous 
districts,  where  we  should  a  priori  (according  to  the  ideas  pre- 
viously set  forth)  expect  a  greater  proportion  of  the  metals; 
and  that,  if  assays  of  rocks  in  non-metalliferous  districts  were 
made,  the  proportion  of  negative  results  might  be  decidedly  in 
excess — although  then,  as  now,  the  term  "  negative  results  " 
would  probably  only  mean  that  the  metals  sought  for  were  in 
quantities  too  small  to  be  detected  by  chemical  methods. 

The  chemical  determinations  of  the  presence  of  the  more 
abundant  of  the  relatively  rare  metals  give  results  fully  con- 
firming the  conclusions  reached  as  to  their  unequal  distribu- 
tion in  similar  rocks.  Nickel,  for  example,  is  recognized  as 
especially  at  home  in  the  most  basic  rocks — peridotites  and 
pyroxenites ;  but  Vogtf  gives  a  table  of  nickel  determinations 
in  32  rocks  of  this  kind,  which  vary  all  the  way  from  a  trace 
to  0.6  per  cent. 

Petrographic  provinces  may  be  relatively  small  in  extent,  or 
they  may  be  enormous.  The  writer  has  made  a  study  of  the 
volcanic  region  of  the  Great  Basin,!  where  an  area  whose 
limits  are  not  determined,  but  which  extends  as  far  east  as 
Salt  Lake,  west  into  the  Sierra  Nevada,  north  into  Idaho  and 
Oregon,  and  south  into  California,  shows  the  same  types  and 
the  same  general  succession  of  Tertiary  lavas.  From  later 
studies  by  the  writer  in  the  Monte  Cristo  mining  district, 
Washington,  it  appears  that  the  Tertiary  eruptions  here  also 
correspond  in  types,  age  and  general  succession  to  thos'e  of 
Nevada  ;§  similar  rocks,  age  and  succession  have  been  ob- 

*  Referring,  of  course,  to  the  least  abundant  metals. — J.  E.  S. 

f  "Relative  Verbreitung  der  Elemente,"  Zeitsch.  fur  prakt.  GeoL,  July,  1898, 
p.  236. 

J  Journal  of  GeoL,  vol.  viii.,  p.  621. 

$  See  article  by  author  on  "The  Ore-Deposits  of  Monte  Cristo,  Washington," 
22d  Ann.  Rept.  U.  S.  GeoL  Survey,  Part  II.,  pp.  711-865. 


296     IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES. 

served  on  the  Southern  California  coast;*  and  as  far  away  as 
Mexico  the  studies  of  Ordonezf  have  established  the  fact  that 
the  principal  rocks,  their  succession  and  age,  remain  the  same. 
Without  being  in  danger  of  carrying  this  correlation  to  excess, 
I  may  point  out  that  the  Pliocene  olivine-basalts  of  the  Sierra 
Nevada;);  are  abundantly  present  in  .Oregon  and  Washington ; 
that  the  British  Columbia  basalts  are  approximately,  at  least, 
of  the  same  period  ;§  and  that  throughout  the  whole  of  Alaska 
and  into  the  Behring  Sea  occur  olivine-basalts  of  Pliocene  age.|| 

Again,  the  abundance  of  basic  andesites  (typically  augitic, 
often  hypersthene-bearing,  and  verging  towards  basalts),  all 
belonging  to  one  epoch  (very  late  Pliocene-Pleistocene),  in  a 
continuous  belt  in  Alaska,  running  the  whole  length  of  the 
Aleutian  Islands  and  peninsula,  turning  the  same  angle  as  the 
chief  orographic  and  topographic  features,  and  running  down 
the  coast  past  Sitka;T  the  occurrence  of  the  same  rocks,  be- 
longing to  the  same  age,  in  Washington  and  Oregon  (Mt. 
Rainier,  etc.);  the  extension  of  the  belt  through  the  Sierra 
Nevada  and  along  the  western  part  of  the  Great  Basin ;  finally 
its  extension  into  Mexico,** — this  is  all  striking,  and  deserves 
recognition.  Moreover,  this  belt  of  late  Pliocene-Pleistocene 
augite  (hypersthene)  andesites  extends  through  Central  and 
South  America,  in  the  Andes. ft  In  Alaska  and  in  the  Andes 
some  of  the  cones  of  this  epoch  are  still  active ;  but  the  ma- 
jority have  become  extinct. 

It  appears,  then,  that  the  whole  extreme  western  part  of  the 
western  hemisphere  (the  Pacific  coast  of  the  Americ*as)  is  a 
zone  occupied  by  what  (at  some  periods,  at  least)  is  and  has 
been  a  single  petrographic  province. 

It  remains  to  be  seen  whether  this  province  is  not  continued 


*  I  regret  I  have  not  at  hand  the  paper  of  Mr.  Smith  in  a  recent  U.  S.  GeoL 
Survey  Ann.  Report,  in  order  to  give  an  exact  reference.  (Santa  Catalina  Island.) 

f  "'Las  Rhyolitas  de  Mexico,"  Boletin  del  Institute  Geologico  de  Mexico,  No.  14. 

J  J.  E.  Spurr,  Jour.  Geol.,  vol.  viii.,  No.  7,  chart,  p.  643. 

$  G.  M.  Dawson,  Ann.  Hep.  Geol.  Nat.  Hist.  Surv.  Canada,  vol.  iii.,  Part  I.,  p. 
37  B.  ;  also,  Trans.  Royal  Soc.  Canada,  vol.  viii. ,  Sec.  4,  p.  15. 

||  J.  E.  Spurr,  "Geology  of  the  Yukon  Gold-District,"  18th  Ann.  Rep.  U.  S. 
Geol.  Surv.,  Part  III.,  p.  250. 

^[  J.  E.  Spurr,  ''Reconnaissance  in  Southwestern  Alaska,"  20th  Ann.  Rep.  IT. 
S.  GeoL  Surv.,  Part  VII.,  Map  13. 

**  Ezequiel  Ordonez,  op.  ciL,  p.  66. 

ft  Zirkel,  Lehrbuch  der  Petrographie,  2d  edition,  vol.  ii.,  pp.  831-2. 


IGNEOUS    KOCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.      297 

into  Asia  with  the  change  of  orogenic  trends  in  Alaska  from 
northwest  to  southwest.  The  line  of  late  Tertiary-Pleistocene 
volcanoes,  which  extends  along  the  Aleutian  Islands  to  Kam- 
chatka, is  represented  by  15  or  20  cones  in  this  peninsula;  this 
line,  following  the  general  orogenic  trend,  runs  southwest 
through  the  Kuril  e  Islands,  the  Islands  of  Japan,  and  the  Phil- 
ippines, into  the  East  Indies.  Andesites — largely  pyroxene 
andesites,  and  frequently  hypersthene  andesites — are  character- 
istic of  this  chain  also,  as  far  as  the  famous  volcano  of  Kraka- 
tua.  This  investigation  might  profitably  be  carried  still  fur- 
ther, but  this  is  hardly  the  place  for  it. 

Turning  from  these  examples  of  petrographic  provinces  on 
enormous  scales,  we  find  that  metalliferous  provinces  may  also 
be  of  light  extent,  or  may  be  exceedingly  large.  Taken 
broadly,  they  often  coincide  more  or  less  roughly  with  petro- 
graphic provinces,  just  as  these  are  apt  to  show  some  corre- 
spondence in  their  position  and  trends  with  zones  of  folding 
and  fracture  in  the  crust,  with  mountain  ranges  and  the  bor- 
ders of  continents.  A  metalliferous  province  which  I  have  been 
studying  somewhat  lately  is  the  rich  chrome-bearing  province 
of  Turkey,  which,  with  its  center  at  the  western  coast  of  Asia 
Minor,  extends  across  the  ^Egean  Sea  and  includes  Macedonia 
and  eastern  Greece,  and  in  the  other  direction  stretches  over 
the  western  and  southern  portions  of  Asia  Minor.  This  metal- 
liferous province  is  connected  with  a  petrographic  province 
marked  by  ultra-basic  igneous  rocks  and  serpentines,  with 
which  the  ore  is  associated ;  yet  similar  rocks  are  found  in 
other  regions,  without  the  corresponding  abundance  of 
chrome. 

Taking  a  larger  example,  compare,  in  North  America,  the 
Appalachian  with  the  Cordilleran  region.  That  there  is  a  cer- 
tain kinship  among  the  ores  of  the  Appalachian  chain  and 
its  allied  ranges  has  long  been  recognized  by  mining  men.  It 
is  recognized  that  the  metals,  though  present,  are  constantly  far  less 
abundant  than  in  the  Cordilleran  region.  Every  now  and  then 
one  hears  of  veins  found  in  this  region  which  give  rich  results 
on  assay ;  but  the  discovery,  though  heralded  in  the  news- 
papers, makes  no  disturbance  in  the  mining  world,  for  the 
mining  man  knows,  from  long  experience  with  such  discoveries, 
that  the  vein  will  directly  "  peter  out."  Gold-bearing  veins 


298  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

are  pretty  thoroughly  scattered  along  this  zone  from  Nova 
Scotia  to  Georgia;  but  the  uncertainty  and  the  relative  poverty 
of  these  gold-deposits  is  proverbial. 

Taking  the  western  Cordilleras,  on  the  other  hand,  we  may 
remember  that  the  California  miners  followed  new  finds  north- 
westward, along  the  trends  of  the  mountain  ranges,  into  the 
Frazer  river  country,  the  Caribou  district,  the  Omenica,  the 
Cassiar,  the  Pelly,  and  the  Yukon,  until  the  slow  progress  has 
brought  them  to  the  neighborhood  of  the  Behring  Straits  (the 
Nome  district).  It  seems  exceedingly  probable,  also,  that  this 
true  "  mineral  zone  "  extends  into  Siberia.  For  I  do  not  hesi- 
tate to  call  it  a  mineral  zone,  although  the  gold-quartz  veins  of 
the  Yukon  are  far  different  in  age  from  those  of  California. 
In  fact,  the  existence  of  rich  gold-ores  along  this  zone,  in 
deposits  of  various  ages,  and  made  under  various  conditions 
and  in  various  rocks,  only  serves  to  emphasize  the  conclusion 
that  this  zone  is  essentially  a  metalliferous  province,  marked 
by  a  greater  proportion  of  gold  (considering  the  question  of 
the  gold  alone)  than  the  earth's  crust  in  general. 

Concerning  metalliferous  sub-provinces  within  the  Cordil- 
leras, I  quote  the  following  from  Phillips  and  Louis,*  not 
having  access  to  the  original  authorities : 

"Mr.  R.  W.  Raymond,!  in  a  paper  on  the  mining  districts  of  the  United 
States,  recalls  the  fact  that  W.  P.  Blake,  in  a  note  to  his  Catalogue  of  California 
Minerals,  first  pointed  out  that  the  mining  districts  of  the  Pacific  slope  are 
arranged  in  parallel  zones,  following  the  prevailing  direction  of  the  mountain 
ranges.  More  recently,  Clarence  King  has  summarized  these  phenomena  nearly 
as  follows  :  The  Pacific  coast  ranges  carry,  on  the  west,  quicksilver,  tin  and 
chrome  iron-ores.  The  next  belt  is  that  of  the  Sierra  Nevada  and  of  the  Cas- 
cade mountains  of  Oregon,  which,  upon  their  western  slope,  carry  two  distinct 
zones,  a  foot-hill  chain  of  copper-mines,  and  a  middle  line  of  gold-deposits, 
which  extend  into  Alaska.  Lying  to  the  east  of  this  zone,  along  the  eastern  base 
of  the  Sierras,  and  stretching  southward  into  Mexico,  is  a  chain  of  silver  mines 
which  are  frequently  included  in  volcanic  rocks.  Through  Central  Mexico,  Ari- 
zona, Central  Nevada  and  Middle  Idaho  there  is  another  line  of  silver-mines 
which  more  often  occur  in  the  older  rocks.  Through  New  Mexico,  Utah  and 
Western  Montana  lies  another  zone  of  argentiferous  galena  lodes  ;  and  again,  to 
the  east,  the  New  Mexico,  Colorado,  Wyoming  and  Montana  gold-belt  forms  a 
well-defined  and  continuous  chain  of  deposits.  Raymond  agrees  that  this  paral- 
lelism exists,  though  in  a  somewhat  irregular  way,  and  that  it  is  chiefly  referable, 
as  Blake  and  King  have  shown,  to  the  structural  features  of  the  country." 

This  quotation  the  writer  makes  without  deciding  his  belief 

*  Ore-Deposits,  2d  ed.,  p.  740.  f  Trans.,  i.,  p.  33  (1873). 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     299 

for  or  against  the  divisions  as  claimed.  Undoubtedly  the  later 
discoveries  within  this  region  have  been  so  varied  as  to  make 
some  of  the  distinctions  doubtful ;  yet  a  careful  consideration 
of  the  Cordilleran  ore-deposits  of  western  North  America 
would  probably  result  in  the  determination  of  definite  metal- 
liferous sub-provinces,  which  might  or  might  not  coincide  with 
those  specified.  That  Nevada,  in  general,  is  part  of  such  a 
sub-province,  characterized  especially  by  the  abundance  of  sil- 
ver, with  other  minerals  subordinate,  is  strikingly  illustrated 
by  the  fact  that  the  vigorous  mining  industry  of  this  State,  so 
exceedingly  rich  in  ore-deposits,  was  permanently  prostrated 
by  the  decline  in  the  price  of  silver,  while  other  regions,  differ- 
ing from  this  in  the  nature  of  their  metallic  wealth,  have  pros- 
pered. 

XIV.  CONCLUSION. 

Our  inquiries  lead  us  to  the  hypothesis  that  by  magmatic  seg- 
regation the  metals  of  commercial  value,  as  well  as  the  other  rock- 
forming  elements,  are  irregularly  and  to  a  certain  extent  independently 
concentrated  in  certain  portions  of  the  earth's  crust.  Such  portions, 
characterized  by  the  relative  abundance  of  certain  metals,  may  be 
called  metalliferous  provinces.  It  is  in  these  provinces  that  ore- 
bodies  will  generally  occur.  The  provinces  may  or  may  not  be 
closely  identified  with  petrographic  provinces  (divisions  based 
on  the  relative  abundance  of  the  commoner  metals  and  other 
elements),  although,  by  reason  of  the  chemical  affinity  which 
exists  between  certain  of  the  rarer  metals  and  certain  of  the 
commoner  elements,  they  probably  generally  do  so,  to  a  certain 
extent  at  least.  Moreover,  within  these  metalliferous  provinces  (as 
is  the  case  within  the  petrographic  provinces)  magmatic  segregation 
produces  sub-provinces,  secondary,  perhaps,  in  theoretical  importance 
to  the  grander  divisions,  but  of  more  practical  interest  to  miners. 
To  limit,  again,  the  scope  of  our  views,  by  magmatic  segregation 
the  rarer  metals  (like  the  commoner  elements,  again)  are  in  many 
cases  preferentially  concentrated  into  certain  rocks  in.  a  given  sub- 
province.  Finally,  within  these  rocks  the  metals  may  be  segregated 
chiefly  into  certain  portions,  even  producing,  in  the  case  of  the  com- 
moner metals  (iron,  chromium,  nickel,  etc.),  workable  ore-deposits  with- 
out further  concentration  ;  and,  in  the  case  of  the  less  common  ones, 
either  directly  producing  workable  deposits  (certain  gold-quartz  veins, 
certain  tin-veins,  possibly  certain  platinum  segregations — Urals — ) 


300  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

or  producing  rocks  relatively  so  rich  that  it  requires  only  the  concen- 
trating action  of  other  agents  (chiefly  circulating  waters)  to  create 
" ore-bodies"  It  is  the  writer's  belief  that  the  origin  of  metal- 
producing  districts,  as  contrasted  with  barren  districts,  is  in  most  cases 
due  primarily  to  magmatic  segregation,  and  that  an  important  class 
of  ore-deposits  is  due  directly  to  this. 

Added  to  this  initial  process,  there  are  the  varied  effects  pro- 
duced by  gases  and  liquids  occluded  by  cooling  igneous  rocks, 
and  the  enormous  work  of  waters,  surface  and  underground, 
which,  by  continued  solution  and  deposition  as  well  as  by  me- 
chanical concentration,  may,  under  favorable  conditions,  operate 
to  bring  the  disseminated  metals  within  smaller  and  smaller 
compass.  Underground,  these  waters  may  be  hot  or  cold ;  they 
may  be  ascending,  descending,  or  moving  laterally ;  they  may 
transport  their  metallic  load  only  a  fraction  of  an  inch,  a  few 
rods,  or  miles.  Their  final  effect  is  to  create  directly  what  isr 
perhaps,  the  most  important  type  of  ore-deposits.  The  study 
of  ore-deposits  is  a  study  in  concentration — the  concentration 
of  some  of  the  finely-disseminated  rarer  rock-forming  elements 
into  more  or  less  compact  masses.  This  concentration  is  ef- 
fected chiefly  by  these  processes  :  (1)  magmatic  concentration , 
(2)  concentration  by  occluded  gases  and  liquids  from  consoli- 
dating magmas ;  (3)  concentration  by  the  action  of  hot-spring 
waters  (generally  ascending) ;  (4)  concentration  by  the  action 
of  cold  surface-waters  penetrating  underground  (generally  de- 
scending); and  (5)  concentration  by  the  effects  (chiefly  me- 
chanical, though  largely  chemical)  of  surface-waters  at  the 
surface. 

Any  one  of  these  processes  may  be  chiefly  responsible  for  a 
given  ore-body,  but  in  many  cases  two,  three  or  more  of  them 
may  be  important.  Moreover,  the  history  of  an  ore-deposit 
may  comprise  cycles,  or  repetitions  of  the  same  processes  at 
different  intervals,  before  the  final  concentration  is  sufficiently 
complete.  Take,  for  example,  the  Nome  beach-sands,  where 
the  gold  is  concentrated  from  the  concentrates  of  older  beach- 
sands,  now  transformed  into  land  by  a  crustal  uplift.* 

On  Napoleon  creek,  a  branch  of  Forty-Mile  creek,  Alaska, 
there  was  found  a  strip  of  rich  stream  gold-placer  ground  in 

*  Schrader  and  Brooks,  Trans.,  xxx.,  p.  242. 


IGNEOUS    ROCKS    AS    RELATED    TO    OCCURRENCE    OF    ORES.     301 

a  district  where  working  was  not  otherwise  profitable.  The 
gold  was  apparently  derived  from  a  conglomerate  of  probable 
Cretaceous  asre  which  formed  a  belt  crossing  the  stream  at  this 

o  o 

point.  The  composition  of  the  conglomerate  showed  that  it 
was  derived  from  the  rocks  and  quartz-veins  of  the  ancient 
(Algonkian  ?)  gold-bearing  series.  In  this  ancient  series,  as  al- 
ready explained,  the  gold  is  believed  to  have  been  concentrated 
by  magmatic  segregation.  Here,  therefore,  we  have  three  dis- 
tinct processes  of  concentration  :  (1)  magmatic  segregation 
(Algonkian  ?) ;  (2)  mechanical  concentration  by  surface-waters 
(beach-sands — Cretaceous?);  (3)  mechanical  concentration  by 
surface-waters  (stream-placers — Pleistocene).  And  it  was  only 
after  the  third  process  that  the  metal  was  sufficiently  concen- 
trated to  become  workable  with  profit — to  become  an  ore-de- 
posit, properly  speaking. 

POSTSCRIPT. 

Since  the  above  was  written,  the  writer  has  received  the  in- 
teresting paper  of  Mr.  Luther  Wagoner  on  "  The  Detection  and 
Estimation  of  Small  Quantities  of  Gold  and  Silver/'*  Mr. 
Wagoner  gives  a  series  of  delicate  assays  of  California  rocks, 
remote  from  mineral  deposits,  for  gold  and  silver. 

Four  specimens  of  granite  gave  respectively  the  following 
weights  in  milligrams  per  ton:  Gold,  104,  137,  115,  1,130; 
silver,  7,660, 1,220,  940,  5,590.  One  specimen  of  syenite  showed 
gold,  720;  silver,  15,430.  A  sample  of  diabase  contained  gold, 
76 ;  silver,  7,440  ;  and  one  of  basalt,  gold,  26  ;  silver,  547.  The 
sedimentary  rocks  tested  were  three  specimens  of  sandstone 
from  different  localities,  and  two  of  marble  (one  of  the  latter 
from  Italy).  The  sandstones  gave  respectively,  in  gold,  39,  24 
and  21;  in  silver,  540,  450  and  320.  The  California  marble 
showed  gold,  5;  silver,  212;  the  Italian  sample,  gold,  8.63; 
silver,  201.  Several  assays  of  San  Francisco  bay-mud  (contain- 
ing some  organic  material)  gave  gold  from  45  to  125.  Two 
assays  of  sea-water  gave  a  mean  of  gold,  11.1;  silver,  169.5. 

These  results  are  suggestive ;  and,  although  too  few  to  base 
final  conclusions  on,  the  writer  would  like  to  call  attention  to 
some  striking  facts.  On  reckoning  up  the  means  of  the  re- 
sults, we  find  that  the  granite  averaged  371.5  gold  and  3,852.5 

*  Trans.,  xxxi.,  p.  798. 


302  IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

silver;  the  sandstone,  28  gold  and  436.66  silver;  the  marble, 
6.8  gold  and  206.5  silver;  and  the  bay-mud,  85  gold. 

The  relative  proportion  or  the  precious  metals  in  the  sedi- 
mentary and  in  the  igneous  rocks  first  claims  attention.  The 
mean  of  all  the  igneous  rocks  assayed  in  gold  329f ,  and  silver 
5,546^  ;  of  the  sedimentary  rocks  (sandstones  and  marbles,  not 
the  bay-mud),  17.5  gold  and  344.4  silver.  That  is  to  say,  the 
mean  of  the  igneous  rocks  assayed  shows  about  19  times  as 
much  gold  and  16  times  as  much  silver  as  the  mean  of  the 
sedimentary'  rocks. 

The  relative  proportion  of  the  metals  in  the  different  sedi- 
mentary rocks  is  another  point.  The  sandstones  average  four 
times  as  much  gold  and  over  twice  as  much  silver  as  the  mar- 
bles; while  bay-mud  (which  on  hardening  would  become  shale) 
contains  nearly  13  times  as  much  gold  as  the  marbles. 

Take,  next,  the  relative  proportion  of  the  metals  in  the  differ- 
ent igneous  rocks.  We  have  in  the  list^  siliceous  or  acid  rocks 
(granite  and  syenite)  and  basic  rocks  (diabase  and  basalt). 

Diabase  and  basalt  are,  generally  speaking,  chemical  and 
mineralogical  equivalents,  differing  in  their  texture  and  struc- 
ture. If  we  compare  the  average  of  the  granites  with  that  of 
the  diabase-basalt,  we  find  that  the  former  is  371.5  gold  and 
3,852  J  silver,  while  the  latter  is  gold  51  and  silver  4,008J ;  that 
is,  the  granites  contain  nearly  7.5  times  as  much  gold  as  the 
diabase-basalt,  but  only  about  the  same  quantity  of  silver.  If 
we  add  the  syenite  assay  (probably  unusually  high)  to  those  of 
the  granites,  and  again  compare  the  result  with  the  diabase- 
basalt  contents,  we  find  that  the  acid  rocks  contain  9  times  as 
much  gold  and  1.5  times  as  much  silver  as  the  basic  ones. 

In  spite  of  the  small  quantity  of  data,  these  results  are 
in  accordance  with  the  theoretical  conclusions  arrived  at  in 
this  paper.  One  of  these  conclusions  was  concerning  the 
higher  content  of  precious  metals  in  the  igneous  rocks  as  com- 
pared with  the  sedimentaries.  A  second  conclusion  was  in 
regard  to  the  relative  concentration  of  the  metals  in  the  dif- 
ferent sedimentaries — least  in  the  limestones,  which  are  calcium 
concentrations  effected  largely  chemically  from  the  sea-water 
through  organic  agencies;  more  abundant  in  the  sandstones, 
which  are  silica  concentrations,  but  effected  mechanically  and 
containing  much  debris  from  all  sorts  of  rocks ;  and  most 


IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES.  303 

abundant  in  the  bay-mud,  which  is  a  fine  ground-up  mixture 
of  all  rocks,  and  contains,  besides,  organic  matter  which  is 
known  to  be  a  precipitant  of  metals  from  solution.  A  con- 
tinuance of  these  experiments  is  highly  desirable,  to  fix  the 
point  as  to  whether  the  order  of  richness  in  gold  and  silver  of 
the  sedimentary  rocks  is  really  1,  shales;  2,  sandstones;  3y 
limestones. 

Thirdly,  as  regards  the  igneous  rocks,  the  uniformly  superior 
gold  content  of  the  siliceous  or  acid  rocks,  as  compared  with 
the  basic  rocks,  is  noticeable.  One  must  remark,  also,  that  the 
same  does  not  hold  good  for  silver;  for,  although  the  basalt  con- 
tains the  least  and  the  syenite  the  most,  yet  the  diabase  has  a 
large  amount.  This,  as  far  as  it  goes,  is  in  accordance  with 
the  theory  above  advocated,  that  during  the  process  of  mag- 
matic  segregation  the  gold  (not  the  silver)  seeks  the  siliceous 
rocks  by  preference. 

DISCUSSION. 

(Trans.,  xxxiii.,  1063.) 

ALEXANDER  N.  WINCHELL,  Butte,  Mont. :  Mr.  Spurr  calls 
attention  to  the  fact  that  an  ore-deposit  may  be  due  to  a  succes- 
sion of  concentrations  at  different  geological  epochs.  He  cites 
an  example  of  such  a  condition  on  Napoleon  creek,  a  branch 
of  Forty-Mile  creek,  Alaska. 

It  will  perhaps  be  of  interest  to  call  attention  to  another  ex- 
ample of  the  same  general  character,  not  so  remotely  situated. 
The  example  referred  to  is  located  on  Pole  creek,  a  tributary 
of  Cherry  creek,  in  the  extreme  northeastern  part  of  Madison 
county,  Montana.  An  excellent  geological  map  of  this  region 
is  to  be  found  in  the  Three  Forks  folio  (No.  24)  of  the  United 
States  Geological  Survey.  According  to  this  map,  Pole  creek, 
in  its  upper  course,  occupies  the  contact  between  the  "  Flat- 
head  "  formation,  which  Peale  correlates  with  the  Middle  and 
Lower  Cambrian,  and  an  area  of  gneisses  and  schists  supposed 
to  represent  the  Archean.  A  visit  to  the  region  last  summer 
enabled  the  writer  to  determine  the  presence  of  a  thick  con- 
glomerate formation  between  the  Flathead  and  the  Archean. 
The  conglomerate  in  question  has  an  outcrop  along  the  south- 
west side  of  Pole  creek  varying  from  one-half  to  one 


.304    IGNEOUS  ROCKS  AS  RELATED  TO  OCCURRENCE  OF  ORES. 

width;  its  maximum  thickness  in  this  region  is  at  least  500 
feet;  lying  conformably  above  it  are  300  or  400  feet  of  schists, 
fine  sands,  etc.  It  may  probably  be  correlated  with  the  "  Belt " 
formation  of  Peale,  as  it  lies  unconformably  upon  the  schists 
and  gneisses  of  the  Archean,  and  is  overlain  (above  the  fine 
sands),  apparently  unconformably,  by  the  Flathead  formation. 
It  seems  to  be  auriferous  throughout  its  extent,  and  somewhat 
richer  at  the  immediate  surface. 

Let  us  outline,  now,  the  successive  concentrations  of  gold  in 
this  district.  The  igneous  rocks  of  Madison  county  certainly 
belong  to  a  "  metalliferous  province  "  rich  in  gold ;  but  to  con- 
sider that  the  province  is  due  to  segregation  from  an  originally 
homogeneous  magma  seems  to  the  writer  to  be  straining  the 
theory  of  differentiation  considerably  beyond  the  breaking- 
point.  As  pointed  out  by  Fouque,*  we  have  no  evidence  that 
such  a  primitively  homogeneous  magma  ever  existed ;  on  the 
contrary,  the  marked  heterogeneity  of  meteorites  argues  that 
cosmic  materials  are  far  from  homogeneous. 

Omitting,  then,  from  the  series,  Spurr's  concentration  by 
magmatic  segregation,  which  in  this  case  one  would  probably 
have  to  refer  to  Archean  time,  we  have  :  (1)  mechanical  con- 
centration by  surface-waters  (ocean  conglomerates  and  gravels 
: — probably  pre-Cambrian) ;  (2)  residual  concentration  by  sur- 
face-waters due  to  disintegration  and  erosion ;  and  (3)  mechan- 
ical concentration  by  surface-waters  producing  stream  placer- 
deposits. 

It  seems  just  possible  that  the  same  conglomerate  caps  the 
so-called  "  Gravel  Range "  about  the  head-waters  of  Alder 
creek  (about  thirty  miles  distant  as  the  crow  flies),  in  which 
case  it  probably  aided  in  the  formation  of  the  famous  Alder 
Gulch  placer-deposits. 

*  Bull  Soc.  Fr.  'Mineral.,  1902,  xxv.,  p.  349. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  305 


No.  12. 
The  Chemistry  of  Ore-Deposition. 

BY  WALTER  P.    JENNET,    E.M.,    PH.D.,    SALT  LAKE  CITY,  UTAH. 
(New  Haven  Meeting,  October,  1902.     Trans.,  xxxiii.,  445.) 

CONTENTS. 

I.  The  Reducing  Action  of  Carbon  and  of  Hydrocarbons,        .         .         .  305 

II.  Protective  Action  of  Carbon  and  of  Hydrocarbons,       ....  311 

TIL  Contributory  Action  of  Carbonic  Acid  Gas,           .         .         .        *        .  312 

IV.  The  Stability  of  Carbonic  Acid  and  of  Water, 313 

V.  Occurrence  of  Carbon  and  the  Carbon-Compounds,      ....  315 

VI.  The  Occurrence  of  Carbon,  Alone,         .         .         .         .         .         *         .  315 

VII.  The  Occurrence  of  Carbon  Combined  with  Hydrogen,         -4    '    .         .   320 

VIII.  The  Relative  Reducing  Power  of  Minerals,          .        .         .       -.         .347 

I.  THE  REDUCING  ACTION  OF  CARBON  AND  OF  HYDROCARBONS. 

Carbon  has  long  been  recognized  as  one  of  the  most  power- 
ful reducing  agents  in  the  deposition  of  ores.  Investigations, 
made  by  myself,  of  the  zinc-  and  lead-deposits  in  Southwest 
Missouri,  in  the  region  centering  about  Joplin,  where  the 
formation  of  the  metallic  sulphides  has  been  due  to  the  action 
of  bitumen,  carbonaceous  shales  and  bituminous  coal,  have  af- 
forded abundant  evidence  that  the  solid  oxygenated  hydrocar- 
bons, particularly  when  in  fine  powder  and  in  suspension  in 
the  waters  circulating  through  the  ore-bodies,  are  the  most 
energetic  and  powerful  reducing  agents  known. 

Bitumen,  liberated  by  the  decomposition  of  the  ore-bearing 
limestone,  is  found  in  the  Joplin  mines  in  all  degrees  of  fluid- 
ity and  hardness,  dependent  on  the  amount  of  oxidation  it  has 
undergone.  From  semi-fluid  maltha  it  grades  into  partly  oxi- 
dized mineral-pitch,  which,  by  further  oxidation,  changes  to 
hard  asphalt,  finally  breaking  up,  from  continued  absorption  of 
oxygen,  into  a  fine  powder  resembling  in  appearance  powdered 
coal.  In  this  condition  oxidized  bitumen,  from  its  light  grav- 
ity, is  transported  readily  in  suspension  in  the  underground 
circulating-waters. 

Bituminous  coal  and  black  carbonaceous  clays  and  shales 
occur  as  surface  formations,  often  in  intimate  association  with 

20 


306  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

the  ore-deposits,  and  when  broken  up,  crushed,  and  faulted  by 
crustal  movements,  furnish  organic  matter  in  a  state  of  fine 
division.  This  is  borne  by  the  surface-waters  and  redeposited, 
often  in  large  masses,  in  the  channels  and  spaces  in  the  ore- 
bodies. 

Apparently  the  only  pure  form  of  carbon  occurring  in  the 
ore-deposits  of  the  Joplin  region  is  the  charcoal,  which  is  found 
in  inconsiderable  quantity  in  the  bituminous  coal ;  all  other 
carbon  is  combined  with  hydrogen,  oxygen  and  nitrogen. 

All  these  hydrocarbons  readily  absorb  oxygen  from  the  air 
contained  in  the  subaerial  waters,  and  undergo  at  ordinary 
temperatures,  even  below  ground-water  level,  a  slow  combus- 
tion, the  ultimate  product  being  carbonic  acid  and  water.  They 
deoxidize  the  circulating  waters  by  consuming  all  the  free  oxy- 
gen ;  and  they  reduce  to  sulphides  any  sulphates  that  may  be 
in  solution.  Even  ferrous  and  ferric  sulphates,  on  coming  in 
contact,  in  solution,  with  any  of  the  solid  hydrocarbons,  are  at 
once  re-formed  as  pyrite  or  marcasite, — minerals  that  reduce 
all  other  metallic  sulphates,  first,  by  being  oxidized  to  ferrous 
sulphate,  and  then,  by  further  absorption  of  oxygen,  to  ferric 
sulphate  and  limonite. 

Bain,  writing  of  these  mines,  says,  "  The  widespread  presence 
of  bitumen  has  been  already  emphasized.  The  ground-water 
is  one  great  reducing  solution."*  Nearly  every  observer  in 
this  field  has  recorded  the  association  of  bitumen  with  the 
zinc-  and  lead-ores. 

In  my  paper  on  "  The  Lead-  and  Zinc-Deposits  of  the  Missis- 
sippi Valley  "f  I  called  attention  to  the  reducing  action  of 
bitumen  and  bituminous  shales  in  the  formation  of  the  ore- 
deposits  of  the  Joplin  District,  and  noted  the  influence  of  or- 
ganic matter  in  the  rocks  upon  the  selective  deposition  of  the 
ores  in  certain  beds  in  the  Cambrian  and  Silurian  of  Central 
and  Southeastern  Missouri,  and  also  of  the  Upper  Mississippi 
lead-region. 

In  limestones  containing  organic  matter,  especially  if  the 
rock  be  easily  dissolved  by  waters  carrying  carbonic  acid,  the 
efficiency  of  even  so  minute  a  quantity  as  a  fraction  of  one  per 

*  The  Lead-  and  Zinc-Deposits  of  the  Ozark  Region,  by  H.  F.  Bain,  p.  159. 
f    Trans.,  xxii.,  171-225. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  307 

cent,  of  bituminous  substances,  in  inducing  the  precipitation 
and  crystallization  of  the  ores,  is  very  great.  Small  as  the 
proportion  of  the  carbonaceous  matter  may  be,  it  is  liberated 
by  the  rapid  subterraneous  erosion  of  the  lime-strata,  in  quan- 
tity more  than  is  required  to  consume  the  free  oxygen  in  the 
ore-forming  solutions,  and  to  reduce  all  sulphates  to  sulphides. 
In  limestones  highly  soluble  in  carbonated  waters,  two-tenths 
of  one  per  cent,  of  any  strongly  deoxidizing  material,  as  bitu- 
minous coal  or  bitumen,  disseminated  in  the  rock,  appears  to 
be  ample  to  effect  the  reduction  of  the  metals,  and  to  induce 
the  deposition  of  the  ores  in  the  special  geological  formation. 

Compared  with  carbon,  hydrogen  has  far  greater  reducing 
power,  measured  by  the  amount  of  oxygen  consumed,  for  hy- 
drogen, in  the  production  of  water,  combines  with  three  times 
the  weight  of  oxygen  that  unites  with  carbon  in  forming  car- 
bonic acid.  In  fact,  hydrogen  stands  first  in  reducing  power, 
accomplishing  nearly  nine  times  the  work  of  pyrite,  the  most 
efficient  metallic  sulphide  in  the  redeposition  of  ores.  Sulphur, 
oxidizing  to  sulphuric  acid  (S03),  requires  less  than  one-fifth  the 
oxygen  that  combines  with  an  equal  weight  of  hydrogen  in 
forming  water. 

For  illustration,  the  relative  reducing  power  of  hydrogen, 
carbon  and  sulphur  may  be  compared  with  the  heat  generated 
by  their  combustion,  although  their  calorific  values  do  not  run 
parallel  with  their  respective  powers  in  the  deoxidation  of  min- 
eral solutions. 

A  calory  being  the  quantity  of  heat  necessary  to  raise  1  Ib. 
avoirdupois  of  water  1°  C.,  the  heat  generated  by  the  combus- 
tion of  1  Ib.  of  the  following  substances  is : 

Calories. 

Hydrogen, ..'.     34,462 

Carbon,  . 8,140 

Bituminous  coal, 8,750  to  7,800 

Lignite, 7,300  to  4,600 

Sulphur, 2,250 

On  account  of  the  calorific  value  of  the  contained  hydrogen, 
the  heating-power  of  the  highest  grade  of  bituminous  coals  is 
greater  than  that  of  pure  carbon. 

It  is  not  improbable  that  the  bituminous  coals  occurring  in 
association  with  the  ore-deposits  of  the  Southwest,  on  account 
of  their  purity  and  high  percentage  of  hydrogen,  have  a  some- 


308  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

what  greater  reducing  power  than  pure  carbon,  and  are  ex- 
ceeded in  power  and  intensity  of  action  only  by  bitumen.  The 
lignitic  or  finely  divided  coaly  matter,  disseminated  in  the 
black  clays  and  shales,  may  be  regarded  for  the  purpose  of  this 
discussion  as  a  form  of  highly  impure  bituminous  coal.  An- 
thracite may  be  classed  with  the  bituminous  coals,  as  it  con- 
tains from  1  to  3  per  cent,  of  hydrogen  and  1  to  3.5  per  cent, 
of  oxygen. 

The  hydrocarbons  may  be  divided  into  the  petroleums,  or 
fluid  non-oxygenated  compounds  of  carbon  and  hydrogen ;  the 
bitumens  and  asphalts,  solid  oxidized  hydrocarbons,  soluble  in 
chloroform  or  other  solvents  of  the  resins ;  and  the  pyro-bitu- 
mens,  which  also  contain  oxygen  and  nitrogen,  including  an- 
thracite, bituminous  coal,  lignite,  etc. 

The  Oxygenation  of  Petroleum. 

Experiments  made  by  the  author  on  the  oxidation  of  petro- 
leum show  that  the  heavy  hydrocarbon  oils  unite  very  slowly 
with  oxygen,  when  first  exposed  to  its  action,  even  at  tempera- 
tures as  high  as  150°  C. ;  but  after  the  action  is  once  started, 
by  the  combination  of  even  a  little  oxygen  with  the  hydrocar- 
bon, the  further  oxidation  then  proceeds  with  constantly  in- 
creasing energy.  By  aspirating  a  current  of  air  for  ten  days 
through  heavy  petroleum  oil,  at  140°  to  155°  C.,  there  were 
formed  solid  hydrocarbons,  resembling  certain  natural  asphalts. 
Very  little  water  was  formed  ;  the  oil  "  cracking  "  and  the  hy- 
drogen being  removed  in  the  form  of  light  naphthas  and  non- 
condensable  gases,  containing  a  greater  percentage  of  hydrogen 
than  the  original  oil,  and  leaving  oxidized  hydrocarbons,  with 
less  hydrogen  and  a  greater  proportion  of  carbon.*  The 
asphalts  made  in  the  above  experiments  absorbed  oxygen  from 
the  air  at  ordinary  temperatures ;  the  rapidity  of  the  absorption 
being  increased  if  the  asphalt  was  in  a  fine  powder.  Dana 
refers  to  these  results  as  the  manufacture  of  grahamite  from 
petroleum,  f 

The  oxides  of  lead,  zinc  and  manganese,  and  certain  salts  of 

*  "On  the  Formation  of  Solid  Oxidized  Hydrocarbons  Eesembling  Natural 
Asphalts  by  the  Action  of  Air  on  Refined  Petroleum,"  by  W.  P.  Jenney,  American 
Chemist,  vol.  v.  (April,  1875),  pp.  359-362. 

f  System  of  Mineralogy,  edition  of  1898,  p.  1020. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  309 

the  metals,  notably  manganese-borate,  are.  powerful  driers  of 
the  vegetable  oils,  such  as  linseed  oil.  Even  in  solution,  many 
salts  of  the  metals  have  a  drying  action  if  agitated  with  the  oil. 
In  the  case  of  the  vegetable  oils,  these  metallic  oxides  and  salts 
appear  to  exert  a  catalytic  action  in  accelerating  the  combina- 
tion of  oxygen  with  the  hydrocarbon.* 

Experiments  by  the  writer  indicate  that  oxides  of  lead  and 
manganese  have  a  similar  action  in  promoting  the  union  of 
oxygen  with  petroleum  ;  and  that  the  asphalts  produced  retain  2 
per  cent,  or  more  of  lead-oxide,  even  after  treatment  with  boiling 
acetic  acid  and  purification  by  solution  in  chloroform  or  ether.f 

From  this  point  of  view,  it  is  probable  that  the  oxidation  of 
bitumen,  in  effecting  the  re-formation  of  the  sulphides,  is  accel- 
erated, and  the  intensity  of  the  reducing  action  increased,  by 
the  catalytic  influence  of  ferrous  and  ferric  sulphates  and  by 
the  various  sulphates,  carbonates,  chlorides  and  oxides  of  lead, 
zinc,  copper  and  manganese,  which  are  always  present  in 
greater  or  less  amount  in  the  ore-deposits.  With  petroleum 
having  a  paraffin  base,  the  union  with  oxygen  would  be  ex- 
tremely slow,  were  not  the  chemical  activity  stimulated  in  some 
way.  Petro.leum  with  an  asphalt  base,  owing  to  the  heavy  hy- 
drocarbons in  the  oil  being  combined  with  oxygen,  and  ap- 
proaching fluid  bitumen  or  maltha  in  composition,  would  prob- 
ably absorb  oxygen  more  rapidly. 

That  the  natural  asphalts  and  bitumens,  when  wet,  are  more 
subject  to  the  action  of  oxygen  than  when  dry,  has  been  ob- 
served in  the  wear  of  asphalt  pavements,  which  rapidly  disinte- 
grate in  spots  where  surface-water  accumulates. 

The  Chemical  Reactions  that  Take  Place. 

In  the  reduction  of  metallic  sulphates  to  sulphides,  by  car- 
bon, the  action  in  each  case  is  deoxidation,  with  formation  of 
carbonic  acid,  according  to  the  following  reactions  : 

ZnS04  +  2H,0  +  20  =  ZnS  +  2H2C03. 
PbS04  +  2H20  +  2C  =  PbS  +  2H2C03. 

*  Catalytic  action  is  understood  to  be  the  action  of  a  substance  which,  by  its 
presence,  accelerates  or  retards  the  chemical  activity,  and  may  induce  a  chemical 
reaction  that  would  otherwise  not  occur,  or  would  take  place  only  with  extreme 
slowness.  t  Op.  tit.,  pp.  359-362. 


310  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

The  complete  reduction  of  ferrous  sulphate  to  pyrite  or  to 
marcasite  requires  that  free  sulphuric  acid  be  present  : 

2FeS04  +  2H2S04  -f  5H2O  +  7C  =  2FeS2  +  7H2C03. 

The  carbonates  of  lead,  zinc  and  iron,  in  the  presence  of  alka- 
line sulphates,  are  reduced  by  carbon  to  the  corresponding  sul- 
phides, galena,  blende  and  pyrite  : 


PbC03  +  Na2S04  +  2H20  +  20  =  PbS  -f  Na2CO3  +  2H2C03. 

ZnCO3  4-  CaSO4  +  2H20  +  20  =  ZnS  +  CaCO3  -f  2H2C03. 

2FeC08  +  4CaS04  -f  5H20  -f  70  =  2FeS2  +  4CaCO3  +  5H2C03. 

Chalcopyrite,  CuFeS2,  is  formed  by  the  double  reduction  of 
cupric  sulphate  and  ferrous  sulphate  : 

CuS04  +  FeS04  +  4H20  +  40  =  CuFeS2  +  4H2C03. 

The  reactions  which  take  place  where  the  hydrocarbons  form 
the  reducing  agents  are  more  complex.  The  hydrocarbons  at 
first  lose  hydrogen  and  gain  oxygen,  until  disintegration  occurs  ; 
then  they  rapidly  oxidize  to  carbonic  acid  and  water.  With 
bitumen  and  coal,  it  is  probable  that  practically  all  the  carbon 
is  finally  converted  into  carbonic  acid,  and  the  hydrogen  into 
water.  In  the  oxidation  of  petroleum  some  "  cracking  "  may 
occur,  and  a  portion  of  the  hydrogen  and  carbon  may  escape 
in  the  form  of  light  hydrocarbon  gases,  as  did  take  place  in  the 
experiments  described  above.* 

Oxygen  seems  to  be  needed  to  complete  the  reaction  in  the 
reduction  by  petroleum  of  the  paraffin  series  : 

12ZnS04  -f  C16H34  +  0  =  12ZnS  -f  16H2C03  +  H20. 

Where  the  petroleum  is  partly  oxidized,  ferric  sulphate  forms 
pyrite  in  the  presence  of  an  excess  of  free  sulphuric  acid.  The 
reaction  may  be  written  as  follows  : 


3Fe2(S04)3  4-  3H2S04  -f  C16H3002  =  6FeS2  -f  16H2C03 
To  illustrate  the  partial  reduction  of  ferric  sulphate  to  pyrite, 

*  See  p.  308. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  3H 

with  formation  of  ferrous  sulphate,  the  formula  of  an  oxidized 
hydrocarbon  nearly  corresponding  to  humus  acid  is  assumed, 
as  in  the  following  equation: 

4Fe2(S04)3  +  8H20  +  C16H1608  =  4FeS2  +  4FeS04  +  16H2COS. 

The  complete  reduction  of  ferrous  sulphate  to  pyrite  or  to 
marcasite  by  an  oxygenated  hydrocarbon,  such  as  gilsonite, 
O13  H200,  also  requires  the  presence  of  free  sulphuric  acid : 

5FeSO4  +  C13H200  +  5H2S04  +  3H20  =  5FeS2  +  13H2COS 

+  5H20. 

II.  PROTECTIVE  ACTION  OF  CARBON  AND  OF  HYDROCARBONS. 

Hydrogen  and  carbon  have  affinities  for  oxygen  stronger 
than  those  of  any  other  chemical  elements,  under  conditions 
normally  occurring  in  ore-bodies.  By  consuming  the  free  oxy- 
gen in  the  circulating-waters,  they  act  to  preserve  and  shield 
from  decomposition  all  metallic  sulphides.  Otherwise  stated, 
all  forms  of  carbon,  and  of  the  fluid  and  the  solid  hydrocar- 
bons, when  present  in  excess,  owing  to  their  superior  affinity 
for  oxygen,  prevent  the  oxidation  of  the  ores ;  although  many 
of  the  minerals  in  the  ore-bodies  under  other  conditions,  where 
carbon  and  its  compounds  are  absent,  or  present  only  in  a  sub- 
ordinate degree,  are  powerful  deoxidizing  agents. 

In  the  mines  at  Joplin,  Mo.,  the  metallic  sulphide-ores, 
blende  and  galena,  and  the  associated  minerals,  chalcopyrite, 
pyrite,  and  even  marcasite,  are  protected  from  decomposition 
below  ground-water  level  by  the  bitumen  and  the  bituminous 
shale  contained  in  the  wall-rock  and  present  in  the  ore-bodies. 
ISTear  water-level,  on  the  boundary  between  the  zones  of  oxida- 
tion and  reduction,  these  hydrocarbons  are  consumed  in  places; 
although,  a  few  feet  distant  in  the  same  ore-body,  they  may 
occur  in  great  excess.  In  such  places  the  metallic  sulphides 
undergo1  oxidation,  only  to  be  re-formed  anew  on  coming  in 
contact  with  the  hydrocarbon. 

This  protective  action  has  long  been  understood  with  respect 
to  the  rocks  which  contain  organic  matter.  In  the  black-band 
iron-ores,  and  in  many  bituminous  shales,  the  iron  occurs  as  the 
proto-carbonate  (siderite),  and  is  preserved  from  oxidation  by 


312  THE    CHEMISTRY    OF  .ORE-DEPOSITION. 

the  hydrocarbon.  In  the  outcrop,  such  rocks  are  bleached  by 
weathering,  and  the  iron  is  oxidized  to  limonite  or  hematite. 
That  organic  matter  preserves  the  strata  from  oxidation  is  a 
fact  familiar  to  persons  engaged  in  collecting  fossils,  particu- 
larly fossil-plants.  The  beds  of  black  and  gray  shales,  where 
the  iron  occurs  as  carbonate  or  sulphide,  are  carefully  searched, 
while  bright-colored  strata,  in  which  the  iron  is  peroxidized, 
are  given  only  a  slight  examination. 

III.  CONTRIBUTORY  ACTION  OF  CARBONIC  ACID  GAS. 

In  the  formation  of  ore-deposits,  carbonic  acid  gas  may,  un- 
der special  conditions,  displace  and  expel  the  air  from  the  cav- 
ities, channels  and  interspaces  in  the  rocks,  and  in  this  way, 
by  mechanically  excluding  the  air,  materially  aid  the  reduction 
and  precipitation  of  the  ores  by  the  ordinary  deoxidizing  agents. 
Conditions  also  occur  in  the  oxidation  and  re-formation  of  an 
ore-body,  particularly  at  those  points  where  the  zones  of  oxi- 
dation and  reduction  merge  one  into  the  other,  under  which 
carbon  dioxide  would  be  an  efficient  auxiliary  in  the  process  of 
reduction. 

The  specific  gravity  of  carbonic  acid  gas,  compared  with  air 
as  the  standard,  is  1.524.  Its  action  in  displacing  air  is  not 
unlike  that  of  water ;  a  rise  in  the  ground-water  from  any 
cause,  as  is  often  observed,  drives  out  the  air  from  all  the 
openings  in  the  ore-bodies  and  checks  the  oxidation  of  the 
minerals. 

In  the  Parker  mine,  Wood  River,  Idaho,  the  country-rock  is 
a  lime  shale,  heavily  charged  with  graphite.  Above  the  per- 
manent water-level  all  the  seams  and  joints  in  the  rock  are 
filled  with  carbonic  acid  gas,  produced  by  the  oxidation  of  the 
carbon.  Carbon  dioxide  is  found  in  a  zone  reaching  from 
ground- water  level  to  within  100  ft.  of  the  surface ;  in  this 
zone  it  fills  all  .the  rock-openings  as  perfectly  as  water  fills 
similar  openings  below.* 

Sulphuretted  hydrogen  gas,  which  has  a  specific  gravity  of 
1.19,  may  act  in  much  the  same  manner  in  excluding  the  air, 
although  in  itself  it  is  a  strong  precipitating  and  reducing 
agent. 

*  See  pages  319  and  320. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  313 

Natural  gas,  notwithstanding  its  low  specific  gravity  (0.558)r 
may  be  held  under  pressure  in  the  strata  in  much  the  same 
way  as  it  occurs  sealed  in  the  interspaces  of  the  Trenton  lime- 
stone of  the  Ohio  and  Indiana  gas-field. 

At  the  Silver-Islet  mine,  Lake  Superior,  pockets  filled  with 
hydrocarbon  gas  were  struck  in  drifting  on  the  vein  on  the  8th 
(440  ft,  vertical  depth)  and  10th  levels  (610  ft.  depth).  The 
gas  was  held  confined  in  the  seams  of  the  slate  and  in  the 
openings  in  the  vein  under  a  water-pressure  of  from  440  to  600 
ft.,  equal  to  a  pressure  of  from  190  to  265  Ibs.  per  square  inch.* 

Observations  at  many  gas-wells  show  that  the  pressure 
greatly  exceeds  that  which  would  be  due  to  a  water-column 
equal  in  height  to  the  depth  of  the  gas-producing  strata- 
There  is  no  record  of  any  measurement  of  the  gas-pressure  at 
Silver-Islet. 

IV.   THE  STABILITY  OF  CARBONIC  ACID  AND  OF  WATER. 

Carbonic  acid  when  combined  with  a  base  is  a  weak  acidr 
readily  displaced  by  a  stronger,  as  sulphuric,  hydrochloric  or 
phosphoric  acid,  and  also  by  sulphur  and  by  many  of  the 
organic  acids.  But  the  molecule  of  carbonic  acid  is  never 
broken  up,  is  never  separated  into  its  component  elements 
under  conditions  ordinarily  subsisting  in  the  earth's  crust,  at 
least  not  at  the  depths  reached  in  the  underground  circulation 
of  meteoric  water. 

Volcanic  action  alone,  or  an  earth-temperature  far  above 
normal,  furnishes  the  physical  conditions  in  which  carbon 
dioxide  is  dissociated,  or  the  conditions  that  admit  of  its  being 
reduced  to  the  monoxide  by  carbon,  or  by  other  deoxidizing 
agents. 

Carbonic  acid  is  a  permanent  refuge  of  oxygen ;  once  locked 
up  in  combination  with  carbon,  oxygen  remains  inert  for  all 
time,  in  a  condition  of  stable  equilibrium,  inactive,  and  chemi- 
cally indifferent  to  all  the  complex  changes  taking  place  in  the 
depths  of  the  earth. f  Even  in  ore-deposits  undergoing  oxida- 

*  "  The  Silver-Islet  Mine  and  Its  Present  Development,"  by  Francis  A.  Lowe, 
Eng.  and  Min.  Jour.,  vol.  xxxiv.,  pp.  320-323.  See,  also,  p.  346,  this  paper.  "Sil- 
ver-Islet Mine,  Lake  Superior  "  (author  unknown,  with  Supplement  No.  1,  by  W. 
M.  Courtis),  Eng.  and  Min.  Jour.,  vol.  xxvi.,  p.  438. 

f  Carbonic  acid  gas  contains  :  Carbon,  27.27  per  cent.  ;  oxygen,  72.73  per  cent. 


314  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

tion  and  re-formation,  carbonic  acid,  once  formed,  is  itself  in- 
susceptible to  chemical  change.  Neither  hydrogen,  carbon, 
sulphur,  or  the  most  powerful  deoxidizing  metallic  sulphides, 
can  decompose  it  at  ordinary  temperatures.  This  immutability, 
however,  is  maintained  only  under  the  conditions  subsisting  in 
the  depths  of  the  strata,  where  life  does  not  exist ;  the  carbonic 
acid  in  the  soil  and  in  the  atmosphere  readily  gives  up  its  oxy- 
gen and  carbon  to  plant-life. 

Water  almost  equals  carbonic  acid  in  stability.  It  is  true 
that  water  is  decomposed  by  electrolysis  and  in  many  chemical 
reactions  in  the  laboratory;  yet,  at  temperatures  approaching 
the  normal,  water  is  probably  not  dissociated,  except  in  a  very 
limited  way,  in  any  of  the  processes  incidental  to  ore-for- 
mation. 

In  the  complex  chemical  changes  that  take  place  in  the  oxi- 
dation and  re-formation  of  ores,  it  is  possible  that  water  may 
be  decomposed;  but,  quantitatively,  such  dissociation  must  be 
insignificant.  Practically,  wrater  may  be  regarded  as  chemi- 
cally stable  under  ordinary  conditions  and  temperatures.  The 
fact  that,  in  the  presence  of  the  deep-circulating  underground 
waters  that  contain  no  free  oxygen,  the  complex  sulphides 
forming  the  ore-bodies  have  been  preserved  unaltered  for  ages, 
is  evidence  that  water  is  chemically  inert  to  all  the  elements 
present  in  the  depths  of  the  strata. 

Among  minerals,  many  oxygen  compounds,  as,  for  example, 
quartz,  corundum,  cassiterite,  rutile  and  zircon,  resist  decompo- 
sition, as  do  also  the  silica,  the  alumina  and  the  other  acid  rad- 
icals in  silicates,  aluminates,  borates,  phosphates,  titanates,  tan- 
talates,  tungstates  and  chromates.  Minerals  containing  oxides 
of  the  alkalies  and  the  alkaline  earths,  while  usually  perma- 
nent, may  have  their  oxygen  displaced  by  sulphur  and  by  the 
halogens,  chlorine,  bromine,  iodine  and  fluorine.  In  the 
greater  number  of  the  refractory  minerals  and  permanent 
oxygen-compounds,  the  chemical  union  of  the  elements  with 
oxygen  may  probably  date  back  to  the  primal  origin  of  the 
earth. 

Carbon  and  hydrogen  alone,  of  all  the  elements,  unite  with 
oxygen  under  conditions  now  subsisting  in  ore-deposits,  to  form 
fixed  compounds,  that,  sealed  in  the  rocks,  can  endure  to  the 
end  of  time. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  315 

Y.  OCCURRENCE  OF  CARBON  AND  THE  CARBON-COMPOUNDS. 

Carbon  occurs  as  graphite  in  the  metamorphic  rocks  and  in 
the  gangue  of  certain  mineral-veins.  It  is  also  found,  practi- 
cally free  from  hydrogen,  as  graphitic  anthracite,  and,  in  small 
quantities,  as  native  charcoal.  In  all  cases  carbon  is  the  re- 
sidual element  in  the  decomposition  of  the  organic  matter  de- 
posited in  the  original  sediments ;  the  hydrogen,  oxygen,  nitro- 
gen and  sulphur  with  which  it  may  have  been  combined  have 
been  eliminated. 

Far  more  commonly,  carbon,  when  in  association  with  min- 
eral-deposits, is  combined  with  hydrogen  and  oxygen,  usually 
in  the  form  of  bituminous  coal  or  bitumen  in  the  wall-rocks, 
or  filling  the  ore-bearing  fissures;  in  some  instances,  as  in  the 
Joplin,  Mo.,  mines,  it  is  distributed  generally  throughout  the 
ore-bodies.  In  most  carbonaceous  shales,  in  the  mining  re- 
gions, the  organic  matter  is  mainly  in  the  form  of  finely  dis- 
seminated bituminous  coal.* 

It  is  somewhat  remarkable,  considering  the  almost  universal 
distribution  of  petroleum,  that  the  non-oxygenated  hydrocarbon 
oils  are  found  so  seldom,  either  in  the  ore-deposits  or  in  the 
ore-bearing  formations.  In  a  few  instances,  marsh-gas  and 
other  similar  hydrocarbons  which  are  gases  at  ordinary  tem- 
peratures and  pressures  have  been  found  in  association  with 
mineral-deposits. 

VI.  THE  OCCURRENCE  OF  CARBON,  ALONE. 

Graphite. 

In  the  metamorphic  area  of  the  Black  Hills  of  South  Dakota 
many  large,  irregular  deposits  of  pyrrhotite  occur,  associated 
with  belts  of  graphitic  shales.  Masses  of  crystalline  pyrrhotite 
are  encased  in  soft,  black,  shaly  gangue-rock,  carrying  a  large 
percentage  of  graphite.  As  observed  by  the  author,  these 
graphitic  shales  appear  to  form  a  specially  favorable  gangue  for 
pyrrhotite,  associated  with  ores  of  nickel  and  copper,  and  also 
for  pyrite  and  arsenopyrite. 

*  An  analysis  of  the  Hudson-Kiver  slates  (Lower  Silurian)  gave  5  per  cent,  of 
fixed  carbon  and  3  per  cent,  of  volatile  combustible  matter,  or  nearly  in  the  pro- 
portion of  carbon,  62.5  percent.  ;  volatile,  37.5  per  cent.  ;  corresponding  to  the 
composition  of  the  best  gas-coals.  "Classification  of  Coals,"  by  Persifor  Frazer, 
Jr.,  Trans.,  vl,  448. 


316  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

Pyrrhotite  is  mined  in  the  vicinity  of  Deadwood,  S.  D.,  for 
flux  in  pyritic  smelting.  The  mineral  shows  on  assay  an  aver- 
age value  of  $1.00  to  $2.00  per  ton  in  gold,  with  usually  less 
than  0.25  per  cent,  of  copper.  Many  of  the  deposits  of  pyrrho- 
tite  in  the  region  lying  easterly  and  northeasterly  from  Har- 
ney's  Peak  carry  a  small  percentage  of  nickel  and  copper. 
Dr.  Carpenter  says  that  assays  of  the  nickeliferous  pyrrhotite 
from  this  region,  made  at  the  Dakota  School  of  Mines,  show 
an  average  of  1.5  per  cent,  nickel,  though  samples  carrying  8 
per  cent,  have  been  found.* 

F.  M.  F.  Cazin  describes  the  occurrence,  in  the  Vermont 
copper-mine,  of  deposits  of  the  sulphides  of  iron  and  copper  in 
intimate  association  with  graphite. f 

Prof.  J.  F.  Kemp  notes  that  graphite,  or  some  closely  re- 
lated carbon  mineral,  is  not  uncommon  in  the  ore  of  the  Mary 
mine,  at  Ducktown,  Tenn.  He  says,  "  It  must  have  been  in- 
troduced as  some  gaseous  or  very  mobile  liquid  hydrocarbon, 
which  has  penetrated  into  minute  cavities  and  filled  larger 
cracks,  and  has  been  subsequently  changed  to  graphite."J 

Yon  Cotta,  in  his  "  Treatise  on  Ore-Deposits,"  cites  many  in- 
stances of  the  influence  of  carbon  on  the  localization  of  ore-de- 
posits. A  single  quotation  is  selected:  "Near  Freiberg  the 
veins  .  .  .  are  enclosed  in  mica  schist  which  contains  an  irregu- 
lar layer  of  black  graphitic  schist.  .  .  .  The  veins  have  only 
been  found  productive  in  the  black  schist.  In  the  common 
mica  schist  they  are  very  poor."§ 

Silver  Islet. — In  the  Silver-Islet  mine,  Lake  Superior,  graphite 
was  found  associated  with  native  silver,  silver-glance,  tetrahe- 
drite,  argentiferous  galena  and  a  number  of  rare  silver  miner- 
als, in  a  gangue  of  quartz,  calcite  and  rhodochrosite.  The  geo- 
logical formation  is  gray  slate,  nearly  horizontal  in  bedding, 
traversed  by  steeply  dipping,  parallel  dikes  of  diorite  and  other 
igneous  rocks.  The  vein  cuts  vertically  across  the  dikes  and 

*  "  Ore-Deposits  of  the  Black  Hills  of  Dakota,"  by  Franklin  K.  Carpenter, 
Trans.,  xvii.,  582. 

f  Genesis  of  Ore-Deposits,  pp.  207-209  \  Trans.,  xxiii.,  605,  606.     See,  also,  on  ^ 
this  subject,  "The  Origin  of  the  Gold-Bearing  Quartz  of  the  Bendigo  Eeefs,  Aus- 
tralia," by  T.  A.  Kickard,  Trans.,  xxii.,  314,  315. 

J  "The  Deposits  of  Copper-Ores  at  Ducktown,  Tenn,"  by  J.  F.  Kemp, 
xxxi.,  261. 

\  Treatise  on  Ore-Deposits,  Prime' s  Translation,  pp.  46,  47. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  317 

the  belts  of  slate  included  between  them,  but  was  ore-bearing 
only  where  it  faulted  the  main  dike  of  diorite.  This  dike, 
about  200  ft.  in  width,  was  in  certain  places  strongly  impreg- 
nated with  graphite.*  Intersecting  fissures  appear  also  to  have 
had  an  influence  on  the  localization  of  the  ore.  Two  bonanzas 
were  discovered :  (1)  The  main  ore-shoot  (that  produced  over 
|2,000,000)  extending  from  the  surface  to  a  depth  of  330  ft., 
nearly  to  the  7th  level,  and  formed  at  the  intersection  of  a 
cross-vein  with  the  main  lode ;  (2)  the  rich  body  of  native  sil- 
ver on  the  3d  and  4th  levels,  south  (that  yielded  800,000  oz.  of 
silver),  occurring  near  the  junction  of  the  two  branches  of  the 
vein.  Graphite  was  not  found  in  the  slates,  or  in  any  dike  of 
the  igneous  belt  intersected  by  the  vein-fissure,  with  the  excep- 
tion of  this  particular  dike,  which  in  its  limited  outcrop  above 
the  surface  of  the  lake,  at  the  point  where  the  lode  cut  through 
it,  formed  Silver  Islet.  The  vein  in  no  place  carried  workable 
ore-deposits,  either  in  the  slates  or  in  the  normal  diorite.  Be- 
fore the  mine  was  closed  down,  a  small  body  of  ore  (that  pro- 
duced about  $30,000)  was  struck  on  the  13th  level,  south. 
Like  the  larger  ore-bodies  in  the  upper-levels,  the  ore  was 
found  to  occur  in  association  with  graphite.  McDermott,  writ- 
ing of  this  mine,  says :  "  The  fact  most  striking,  to  one  who  ex- 
amines the  parts  of  the  vein  from  which  the  most  valuable  ore 
has  been  extracted,  is  the  evident  connection  of  the  deposit  of 
the  silver  with  the  region  of  graphite  impregnation  of  the  wall- 

rock."f 

Graphitic  Anthracite. 

An  extensive  deposit  of  graphitic  anthracite,  associated  with 
antimonial  silver-lead  ores,  was  found  in  the  Parker  mine,  in 

*  "  The  trap-dike  has  usually  been  called  diorite,  but  is  determined  to  be  norite 
by  Wadsworth,  Bull.  No.  2,  Minn.  Geol.  Sur. ,  p.  92,  and  gabbro  by  Irving,  Mono- 
graph V.,  V.  S.  Geol.  Sur.,  pp.  378,  379."  Ore-Deposits  of  the  U.  S.  and  Canada, 
by  J.  F.  Kemp,  p.  283. 

t  "The  Silver- Islet  Vein,  Lake  Superior,"  by  Walter  McDermott,  Eng.  and 
Min.  Jour.,  vol.  xxiii.,  pp.  54,  55  and  70,  71. 

"The  Silver-Islet  Mine  and  Its  Present  Development,"  by  Francis  A.  Lowe, 
Eng.  and  Min.  Jour.,  vol.  xxxiv.,  pp.  320-323. 

"Silver  Islet,"  by  Thomas  Macfarlane,  Trans.,  viii.,  226-253. 

"  The  North  Shore  of  Lake  Superior  as  a  Mineral-Bearing  District,"  by  W.  M. 
Courtis,  Trans.,  v.,  473-487. 

" Silver- Islet  Mine,  Lake  Superior  "  (author  unknown,  with  longitudinal  sec- 
tion of  the  mine,  Supplement  No.  1,  by  W.  M.  Courtis),  Eng.  and  Min.  Jour., 
vol.  xxvi.,  p.  438. 


318  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

Idaho.  The  vein  occurred  in  a  belt  of  graphitic  lime-shales, 
about  600  ft.  in  width,  included  between  two  intrusive  sheets  of 
andesite;  the  whole  formation — the  vein  and  the  igneous  sheets 
bounding  the  shales  above  and  below — dipping  into  the  moun- 
tain at  an  angle  of  40  degrees.  The  ores  were  galena  and 
polybasite,  averaging  (in  car-lots)  from  75  per  cent,  of  lead  and 
125  ounces  of  silver  to  45  per  cent,  of  lead  and  680  ounces  of 
silver  per  ton.  The  gangue  was  an  intimate  mixture  of  white 
crystalline  calcite  and  quartz.  An  intersecting  vein,  coming  in 
from  the  foot-wall,  carried  crystallized  pyrite  and  blende,  with 
only  traces  of  silver.  The  mine  produced  $365,000.  At  a 
vertical  depth  of  300  ft.  from  the  surface  a  flat  fissure  was  en- 
countered, filled  with  graphitic  anthracite  with  a  little  white 
quartz  intermixed.  It  formed  a  flat  sheet,  2  to  6  ft.  in  thick- 
ness, and  was  explored  over  an  area  200  ft.  square.  The  coal 
was  heavily  slickensided,  crushed  and  compacted  into  a  hard, 
granular  mass.  It  was  mined  with  difficulty  with  a  pick,  and 
often  required  blasting,  owing  to  the  stringers  of  quartz  dis- 
tributed through  it.  Analysis  gave,  excluding  ash,  90  percent, 
of  fixed  carbon  and  10  per  cent,  of  volatile  matter,  mostly 
water  from  the  clay  contained  in  the  ash.  Owing  to  admixture 
of  quartz  and  earthy  material  from  the  walls,  the  ash  varied 
from  10  per  cent,  to  50  per  cent.  This  coal  had  evidently 
been  formed  by  the  destructive  distillation  of  asphalt  or  petro- 
leum, filling  the  fissure.  The  intrusion  of  the  sheets  of  vol- 
canic rock  enclosed  the  shale  stratum  as  if  in  a  retort.  There 
is  evidence,  in  the  large  amount  of  graphite  in  these  shales, 
that  they  were  originally  highly  charged  with  bituminous 
matter.  The  hydrocarbons,  first  distilled  by  the  heat  accom- 
panying the  intrusion,  were  condensed  and  accumulated  in  the 
fissure  as  heavy  petroleum  or  asphalt,  and,  by  further  action  of 
heat,  carbon  was  deposited,  hydrocarbon  oils  being  driven  oft' 
in  the  same  way  as  in  the  distillation  of  petroleum-tar  in  the 
manufacture  of  lubricating  oils.  Subsequently  the  deposit  was 
crushed  by  faulting  movements  of  the  beds,  and  at  a  still  later 
date  the  ore-deposits  were  formed  in  the  intersecting  vein-fissure. 
In  places  the  ore  lies  against  and  extends  into  the  coal.  Natu- 
ral gas  was  not  encountered,  though  conditions  were  favorable 
for  its  formation,  probably  because  the  workings  were  near  the 
surface.  Heavy  flows  of  carbonic  acid  gas  were,  however,  fre- 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  319 

quently  encountered  in  the  mine ;  and  during  occasional  periods 
of  low  atmospheric  pressure  the  outflow  of  gas  from  the  seams 
and  fissures  in  the  country-rock  was  so  much  increased  that  the 
miners  were  often  driven  from  parts  of  the  mine  that  were  not 
well  ventilated.* 

J.  B.  Farish  notes  that  the  seams  in  the  limestones  at  New- 
man Hill,  near  Rico,  Col.,  were  filled  with  carbonic  acid  gas.f 

Charcoal. 

Native  charcoal,  or  mineral-charcoal,  as  it  is  termed,  is  prob- 
ably never  pure  carbon,  yet  the  amount  of  hydrogen  contained 
is  so  small  that  in  the  discussion  of  its  reducing  power  it  may 
be  classed  with  graphite.  Observation  shows  that  charcoal, 
from  its  soft,  porous  structure,  and  from  the  great  surface  it 
exposes  to  chemical  action,  is  one  of  the  most  energetic  deoxi- 
dizing agents  in  the  formation  of  ore-deposits. 

Small  pockets  filled  with  charcoal  were  found  at  a  depth  of 
800  ft.  in  the  ore-chimney  of  the  Bassick  mine,  near  Silver 
Cliff,  Colorado.  This  remarkable  occurrence  of  charcoal  in. 
an  eruptive  formation  is  set  forth  in  detail  in  the  paper  by  Iu 
E.  Grabill.J 

In  the  discussion  of  this  paper,  the  occurrence  of  charcoal 
in  anthracite  was  described  by  C.  A.  Ashburner ;  and  of  char- 
coal in  Oregon,  formed  by  the  carbonization  of  the  leaves  and 
twigs  of  plants  in  the  layers  of  mud  between  successive  over- 
flows of  lava,  by  Dr.  R.  "W.  Raymond.  § 

President  Rothwell  remarked :  "  Charcoal  has  also  been 
found  in  the  silver-bearing  sandstones  of  Southern  Utah.  These 
sandstones  are  a  simple  sedimentary  formation,  and  contain 
trunks  of  trees,  some  finely  silicified.  ...  I  have  also  found 
there  pieces  of  lignite,  with  the  structure  of  the  wood  still 
quite  evident.  .  .  .  Other  portions  of  the  carbonaceous  matter 
have  almost  the  character  of  charcoal;  the  carbon  has  not 
become  hard,  nor  taken  on  the  form  of  lignite.  The  woody 

*  "Graphitic  Anthracite  in  the  Parker  Mine.  Wood  Kiver,  Idaho,"  by  W.  P. 
Jenney,  School  of  Mines  Quarterly  (1888-89),  vol.  x.,  pp.  313-315. 

f  "  On  the  Ore-Deposits  of  Newman  Hill,  near  Rico,  Colorado,"  Proceedings  of 
the  Colorado  Scientific  Society,  vol.  iv. ,  p.  153. 

I  "On  the  Peculiar  Features  of  the  Bassick  Mine,"  by  L.  E.  Grabill,  Trans. , 
xi.,  110-120. 

g  Ibid.,  p.  119. 


320  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

fiber  of  ordinary  charcoal  can  be  traced  in  it  very  clearly.  .  .  . 
In  the  silver-bearing  portions  of  the  beds,  the  charcoal,  the 
lignite,  or  the  silicified  wood,  as  the  case  may  be,  is  impreg- 
nated with  chlorides  or  sulphides  of  silver,  and  is  in  many 
cases  quite  rich."* 

The  deposits  of  silver-ore  in  sandstone  at  Silver  Reef,  Utah, 
are  mainly  due  to  the  reducing  action  of  wood  and  plant 
remains,  more  or  less  perfectly  altered  to  lignite,  and  are 
treated  in  more  detail  under  that  head.f 

VIE.  THE  OCCURRENCE  OF  CARBON  COMBINED  WITH  HYDROGEN. 

Bituminous  Coal. 

Blende  and  galena  have  been  deposited  in  coal  in  the  outly- 
ing basins  of  the  Coal  Measures,  scattered  along  the  broad, 
northern  marginal  belt  of  the  Ozark  Uplift. 

Near  the  reservoir  at  Sedalia,  Mo.,  a  basin  in  the  Second 
Magnesian  Limestone  carries  a  little  coal  of  fair  quality,  in 
which  dark  brown  crystalline  blende  occurs  in  small  irregular 
bunches  and  in  sheets  filling  both  the  vertical  and  horizontal 
seams  and  joints.  The  greater  part  of  the  blende  is  in 
sheets,  J  to  1J  in.  thick,  made  up  of  agglomerated  imperfect 
crystals,  compressed  or  flattened  between  the  layers  of  the  coal. 
Some  specimens  show  blende  in  thin  parallel  seams,  not  thicker 
than  a  sheet  of  paper  and  -fa  to  -fa  in.  apart,  distributed  regu- 
larly through  the  coal.  About  2  tons  of  blende  were  mined  at 
this  locality. 

In  Morgan  and  Moniteau  counties,  Mo.,  in  a  number  of 
places,  blende  and  galena  are  found  in  similar  deposits  of  coal. 
At  Martin's  coal -bank,  near  Versailles,  Mo.,  the  coal  has  evi- 
dently been  disturbed  since  its  deposition,  and  vertical  seams  in 
the  coal,  J  in.  to  1  in.  in  width,  are  filled  with  sheets  of  crystal- 
line blende  and  galena  in  a  gangue  of  calcite  and  white  tallow- 
clay.  The  strike  of  the  lines  of  disturbance  of  the  coal,  pro- 
longed 500  to  1000  feet  southerly,  crosses  an  extensive  tract  of 
old  surface-workings  in  the  Second  Magnesian  Limestone. 
The  ground  is  thickly  covered  by  shallow  pits,  dug  in  search 
of  lead-ore.  These  deposits  of  lead  were  apparently  formed 

*  Ibid.,  pp.  117,  118.  f  See  pp.  322-327. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  321 

through  the  agency  of  the  same  system  of  fissures  that  intro- 
duced the  ore  in  the  coal. 

Blende  and  galena  were  formerly  mined  at  Simpson's  coal- 
bank,  in  Moniteau  county.  The  coal  is  a  hard  cannel,  filling  a 
basin  in  the  Second  Magnesian  Limestone ;  the  ores  occur  in 
seams,  seldom  more  than  an  inch  in  thickness,  in  the  joints  of 
the  coal.  The  ore  incidentally  obtained  in  mining  the  coal 
afforded  an  occasional  shipment  to  the  smelters. 

Vanadium  is  found  in  a  lignite  coal  in  the  province  of  Men- 
doza,  Argentine  Republic.  The  ashes  of  this  coal  carry  van- 
adic  acid,  V205.  It  also  occurs  in  anthracite  mined  near  Yauli, 
Peru.* 

Gold  has  been  repeatedly  reported  in  the  ash  of  the  Creta- 
ceous coals  of  the  West.  H.  M.  Chance  records  that  the  coal 
of  the  Cambria  Coal  Co.  near  Newcastle,  Wyoming,  is  said, 
by  the  chemist  of  the  company,  to  carry  gold.f  Mr.  H.  Rives 
Ellis,  of  Salt  Lake  City,  informs  the  writer  that  he  obtained  an 
average  of  60  to  80  cents  gold  per  ton  of  ash  from  the  Pleasant 
Valley,  Utah,  and  Kemmerer,  Wyoming,  coals.  In  this  con- 
nection, the  paper  by  G.  A.  Koenig  and  M.  StockderJ  is  of 
interest,  although  the  coal  described  appears  to  be  more  nearly 
an  infusible  hydrocarbon,  such  as  might  result  from  the  par- 
tial oxygenation  of  albertite. 

Mr.  Henry  Sewell  describes  the  occurrence  of  antimonial 
silver-ores,  in  association  with  strata  carrying  beds  of  bitu- 
minous coal,  in  the  mineral  caves  of  Huallanca,  Peru,  located 
at  an  elevation  of  14,700  ft.  above  the  sea.  These  silver-mines 
are  situated  in  a  coal-formation,  upturned  on  edge  by  an  out- 
burst of  porphyry,  the  upheaval  forming  immense  backbones, 
with  the  stratification  standing  almost  perpendicular.  A  bed 
of  coal  is  mined  for  blacksmithing  purposes  within  a  distance 
of  150  yards  of  the  ore-bearing  beds.  The  ore  is  tetrahedrite, 
with  about  800  ounces  of  silver  per  ton,  and  occurs  lining  cav- 

*  2lst  Annual  Report  of  U.  S.  Geol.  Sur.,  1899-1900,  Part  VI. ;  Mineral  Re- 
sources of  the  U.  S.,  p.  315. 

f  "The  Discovery  of  New  Gold  Districts,"  by  H.  M.  Chance,  Trans.,  xxix., 
227. 

J  "On  the  Occurrence  of  Lustrous  Coal  with  Native  Silver  in  a  Vein  in  Por- 
phyry, in  Ouray  County,  Colo.,"  Trans.,  ix.,  650.  See,  also,  "Modes  of  Oc- 
currence of  Pyrite  in  Bituminous  Coal,"  by  Amos  T.  Brown,  Trans.,  xvi., 
539-546. 

21 


322  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

erns,  in  beds  of  sandstone.  Some  of  these  caverns  are  25  to  30 
ft.  long  and  of  nearly  equal  height,  their  inner  surfaces  covered 
with  a  coating  2  to  3  in.  thick  of  crystallized  silver-ores,  mostly 
tetrahedrite.  Silver-ores  also  occur  in  the  shale  beds  adjacent 
to  the  sandstone.* 

Lignite. 

At  Silver  Reef,  Utah,  silver  has  been  deposited  in  lignitic- 
sandstones,  determined  by  dewberry  to  be  of  Triassic  age.f 
The  mines  since  1885  have  only  been  worked  by  leasers  in  a 
small  way.  During  the  height  of  production  in  1877-79,  the 
total  output  was  2,122,471  ounces  of  silver.J  The  ore-bearing 
beds  were  30  to  40  ft.  in  thickness,  of  which  usually  only  16 
ft.  was  pay-ore.  The  ore  occurred  in  flat  shoots  that  were,  in 
some  places,  300  ft.  wide,  and  extended  400  to  500  ft.  deep  on 
the  dip  of  the  formation.  The  ore  was  richest  near  the  out- 
crop, and,  as  it  was  followed  in  depth,  gradually  got  poor.  Near 
the  surface  the  silver  was  in  the  form  of  chloride,  associated  in 
places  with  the  blue  and  green  carbonates  of  copper  in  very 
small  quantity.  As  the  ore  was  followed  in  depth,  the  chloride 
gave  place  to  silver-sulphide,  and  scales  of  native  silver  came 
in,  especially  in  the  branches  of  trees  and  distributed  in  the 
plant-shales.  No  other  ores  were  found,  and  the  gangue-min- 
erals  usually  occurring  in  ore-deposits,  as  quartz,  calcite,  barite, 
etc.,  were  absent.  When,  following  the  inclination  of  the 
strata,  the  workings  attained  a  vertical  depth  of  400  to  500  ft., 
the  ore  changed,  becoming  low-grade  and  difficult  to  amal- 
gamate in  pans ;  the  ore-shoots  at  the  same  time  contracted, 
becoming  narrow,  and  only  2  or  3  ft.  in  height.  Exploration 
was  continued  for  several  years,  but  finally  all  search  in  depth 
for  pay-ore  was  abandoned.  § 

*  "  The  Silver  Caves  of  Peru,"  by  Henry  Sewell,  Eng.  and  Min.  Jour.,  vol. 
xxiv. ,  p.  292.  Abstract  taken  from  the  London  Mining  Journal. 

t  "Report  on  the  Properties  of  the  Stormont  Silver-Mining  Company  at  Silver 
Reef,  Utah,"  by  J.  S.  Newberry,  Eng.  and  Min.  Jour.,  vol.  xxx.,  p.  269.  See, 
also,  "The  Silver  Eeef  Sandstones,"  by  J.  S.  Newberry,  Eng.  and  Min.  Jour., 
vol.  xxxi.,  p.  4. 

J  Eng.  and  Min.  Jour.,  vol.  xxix.,  p.  26. 

$  "Silver  Reef  District,  Southern  Utah"  (author  unknown),  Eng.  and  Min. 
Jour.,  vol.  xxix.,  pp.  25-26,  45-46,  59-60,  79-80,  and  96. 

"The  Silver  Sandstone  District  of  Utah,"  by  C.  M.  Rolker,  Trans.,  ix.,  21. 

"The  Peculiar  Features  of  the  Bassick  Mine;"  Discussion  by  R.  P.  Roth  well, 
Trans.,  xi.,  117-119.  Genesis  of  Ore-Deposits,  pp.  130,  131. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  323 

Many  writers  report  that  traces  of  silver  and  copper  occur  in 
the  extension  of  these  same  sandstone  reefs,  which  can  be 
traced  by  their  outcrop  for  a  distance  of  10  to  20  miles  to  the 
southwest.  An  unknown  author,  in  the  early  development  of 
the  district  (May,  1877),  thus  describes  the  peculiar  occurrence 
of  the  ore :  "  The  formation  is  a  beautifully  stratified  red  and 
white  sandstone,  but  greatly  broken  up  and  eroded.  Where 
the  strata  have  been  undisturbed  they  rise  to  a  height  of  per- 
haps a  thousand  feet  above  the  adjacent  valley,  in  table-moun- 
tains, alternately  banded  in  red  and  white,  and  plainly  showing 
the  former  height  of  the  whole  country.  The  numerous  ex- 
tinct volcanoes  and  the  vast  quantities  of  volcanic  rock  found 
throughout  southern  Utah,  and  particularly  this  section,  point 
to  at  least  one  agent,  and,  no  doubt,  a  powerful  one,  which 
served  to  produce  the  numerous  foldings  and  contortions  of 
the  strata,  while  the  great  sandy  deserts,  covered  with  sage  and 
cactus,  bear  abundant  evidence  to  the  erosion.  On  the  north- 
ern side  of  what  was  once  a  vast  basin,  lying  between  several 
ranges  of  high  mountains  of  old  rock,  where  the  erosion  of  an 
anticlinal  has  left  ridges  of  reefs  cropping  out  at  various  an- 
gles, are  situated  the  mines.  .  .  .  The  sandstone  consists  of 
red  and  white  deposits,  carrying  some  lime  as  a  cementing  ma- 
terial, with  occasional  layers  of  clayey  or  shaly  rock,  and  con- 
siderable carbon  scattered  throughout.  This  carbon,  which  is 
evidently  from  the  decomposition  of  drift  material,  of  which 
the  impression  in  the  rock  and  even  the  plant  itself  is  yet  dis- 
tinct, occurs  in  important  layers  in  places.  .  .  .  Petrifactions, 
even  of  the  size  of  large  trees,  are  not  uncommon,  some  of 
which  form  a  valuable  ore.  The  white  sandstone,  which  ap- 
pears to  be  of  a  somewhat  finer  texture  than  the  red,  seems, 
so  far,  to  have  carried  the  ore.  .  .  .  These  veins,  as  they 
are  there  called,  are  entirely  conformable  with  the  strata,  and 
in  no  case  do  they  cut  across  the  adjacent  layers  of  rock. 
They  appear  to  be  richest  where  there  is  the  most  carbon, 
which  evidently  has  acted  as  a  reagent  to  precipitate  the  silver 
from  solution  and  to  deposit  it,  sometimes  as  flakes  of  metallic 
silver,  in  its  midst.  In  some  cases  the  form  of  the  plant,  of 
apparently  a  reedy  nature,  is  yet  distinct,  in  which  the  cells  are 
yet  visible,  but  to  a  great  extent  filled  with  valuable  ore.  Other 
beds  carry  considerable  copper  in  the  form  of  blue  or  green 


324  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

carbonate,  and  also  iron  in  nodules  which  run  very  high  in  sil- 
ver. ...  A  light  sandstone,  containing  streaks  or  fine  layers 
of  a  dark  material,  which  elsewhere  would  not  attract  atten- 
tion, is  there  found,  sometimes,  to  run  from  $50  to  $100  a  ton ; 
while  the  darker  rock,  containing  considerable  carbon,  copper, 
or  iron-nodules,  will  at  times  run  into  the  hundreds,  or  even 
thousands."* 

Mr.  Watson  M.  Nesbit,  who  was  connected  with  mining  oper- 
ations at  Silver  Reef  from  1878  to  1888,  gives  the  author  the  fol- 
lowing statement  of  the  manner  of  occurrence  of  the  ore :  In  the 
Barbee  and  Walker  mine,  water  was  struck  at  a  depth  of  about 
500  ft.  vertically.  Near  that  point  the  ore  changed  in  appear- 
ance and  character,  and  gave  great  trouble  in  amalgamation, 
the  extraction  being  very  low.  The  ore  was  treated  hot,  in 
pans;  a  thick  scum  rose  on  the  pans,  like  heavy  petroleum  oil, 
and  had  to  be  removed  from  time  to  time  during  the  amalgama- 
tion. From  a  charge  of  1|  tons  of  ore,  as  much  as  a  gallon  of 
this  oily  material  would  be  obtained.  The  ore  at  water-level, 
if  carefully  stoped,  averaged  12  to  16  oz.  of  silver  per  ton ; 
but  only  a  part  of  the  silver  could  be  saved  in  pans.  A  very 
little  pyrite  appeared  at  water-level — the  first  seen  in  the  mines. 
About  100  to  200  ft.  above  water-level,  on  the  slope  of  the  beds, 
the  ore  was  in  places  very  rich ;  and  small  bunches  of  lignite 
coal,  4  to  10  in.  across,  were  found  imbedded  in  the  soft  sand- 
stone, with  native  silver  deposited  in  thin  scales  on  the  joints 
of  the  coal.  Most  of  the  ore  at  this  depth  was  silver-sulphide. 
At  one  place  a  tree-trunk,  18  in.  in  diameter,  was  found ;  the 
heart-wood  was  silicified  and  very  hard,  and  carried  8  to  10  oz. 
of  silver  per  ton.  The  sap-wood  and  bark,  3  to  6  in.  in  thick- 
ness, were  altered  to  soft,  crumbling  lignite,  full  of  silver-sul- 
phide ;  it  assayed  5000  oz.  of  silver  per  ton.  The  ores  from 
the  Silver  Reef  mines  never  showed  any  gold  by  assay ;  but  in 
leaching  the  ore  by  the  Russell  process,  the  silver-sulphides 
produced  contained  a  trace  of  gold. 

Review  of  the  Phenomena  at  Silver  Reef. — Light  is  thrown  on 
the  change  in  the  mineral  character  of  the  ore  at  water-level, 
and  on  the  difficulty  experienced  in  amalgamation,  by  the  dis- 

*  "The  Silver  Sandstones  of  Utah,"  by  C.  F.  A.,  Salt  Lake  City,  Eng.  and 
Min.  Jour.,  vol.  xxiii.,  p.  317. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  325 

covery  announced  by  dewberry*  that  the  ores  carried  selenium, 
— the  average  of  four  analyses  giving  selenium,  0.23  per  cent., 
and  silver,  0.26  per  cent.  The  selenium  in  one  specimen 
amounted  to  90  ounces  per  ton. 

Whether  the  silver  was  deposited  at  the  same  time  the  sedi- 
ments were  laid  down,  or  was  introduced  by  solutions  upflow- 
ing  through  faul ting-fissures  in  a  later  geological  age,  has  been 
a  much  debated  question.  Without  dwelling  upon  this  point, 
— for,  in  either  event,  the  primary  deposition  of  the  ore  was 
due  to  the  hydrogen  and  carbon  of  the  plant-remains  enclosed 
in  the  sandstones, — certain  peculiar  features  of  the  occurrence 
deserve  notice.  The  structure  at  Silver  Reef  may  be  stated  as 
a  broad  anticlinal  arch,  broken  up  by  faults  coursing  northerly 
and  southerly,  rudely  parallel  to  the  axis  of  the  fold.  A  basin, 
nearly  3  miles  across,  occupied  by  the  valley  of  the  Virgin  river, 
was  eroded  through  the  crest  of  the  arch,  leaving  the  two  cliffs 
facing  one  another,  the  strata  dipping  away  from  the  basin  on 
the  two  sides.  The  total  area  of  the  several  ore-producing 
belts  of  sandstone-outcrop,  left  by  erosion,  covered  less  than 
500  acres. 

Silver  Reef  conforms  to  the  general  law  of  areal  distribution 
of  mining-districts,  namely,  that  "  Ore-deposits  have  been  formed 
only  in  local  areas  of  disturbance.  Between  and  surrounding  such 
areas  of  mineralization  extend  broad,  barren  tracts  of  undisturbed 
strata"-\  and  also  conforms  to  the  law  of  mineral  occurrence, 
namely,  that  "  All  workable  deposits  of  ore  occur  in  direct  associa- 
tion with  faulting-fissures  traversing  the  strata,  and  with  zones  or  beds 
of  crushed  and  brecciated  rock,  produced  by  movements  of  disturbance. 
The  undisturbed  rocks  are  everywhere  barren  of  ore."{  The  de- 
scriptions apply  to  a  mineral  area  which,  prior  to  the  recent 
erosion  of  the  basin,  may  have  possibly  covered  four  or  five 
square  miles,  with  pay-ore  found  in  no  place  outside  this  special 
area. 

A  writer  notes  that  only  the  fractured,  jointed  and  perme- 
able portions  of  the  bed  are  rich ;  where  undisturbed  and 
massive,  the  sandstone  is  barren.  Also  that  vertical  fault- 

*  "The  Silver  Eeef  Sandstones,"  by  J.  S.  Newberry,  Eng.  and  Min.  Jour.,  vol. 
xxxi.,  p.  5. 

f  "Lead-  and  Zinc-Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney, 
Trans.,  xxii.,  192.  J  Ibid.,  p.  184. 


326  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

planes  frequently  bound  the  ore.*  These  are  conditions  that  are 
found  in  impregnated  beds  of  zinc-  and  lead-ores  in  Southwest 
Missouri  and  Northern  Arkansas,  and  also  in  the  flat  deposits 
of  gold,  associated  with  tellurium,  in  the  Cambrian  sandstone 
near  Deadwood,  South  Dakota. 

Selenium  usually  occurs  with  minerals  believed  to  have  been 
formed  by  highly-heated  vapors  and  solutions  and  in  direct 
association  with  igneous  disturbances.  Its  presence  at  Silver 
Reef  seems  to  favor  the  theory  of  the  deposition  of  the  silver 
through  the  fissures.  It  appears  that  secondary  enrichment 
has  taken  place  on  an  extensive  scale,  and  that  the  silver  was 
deposited  originally  in  the  sandstone  in  combination  with  sele- 
nium and  probably  with  sulphur  by  the  reducing  action  of  the 
lignitic  matter.  Afterwards,  these  primary  ore-bodies  were  en- 
riched by  the  secondary  precipitation  of  silver-sulphides,  by  the 
agency  of  descending  surface-waters,  aided  greatly  by  the  pro- 
gressive erosion  of  the  basin.  In  this  migration  of  the  ore — 
the  outcrop  of  the  sandstone  gradually  disintegrating  and  wear- 
ing away  from  exposure  to  weather — to  the  deposits  of  silver- 
sulphides,  re-formed  at  deeper  levels  on  the  dip  of  the  same 
beds,  the  reducing  agent  has  been  the  organic  material  distrib- 
uted through  the  ore-horizon.  Later,  these  reinforced  ores 
were,  near  the  outcrop,  altered  to  silver-chloride,  cerargyrite, 
the  trace  of  copper  occurring  with  the  silver  forming  the  car- 
bonates, azurite  and  malachite.  When  the  mine-workings 
passed  below  this  zone  of  enrichment  there  were  found  only 
small  bodies  of  ore,  that  had  remained  unaltered  since  the  first 
deposition  of  silver  in  the  beds. 

Similar  occurrences  have  been  described  of  copper-ores  re- 
placing the  wood  of  trunks  and  branches  of  trees,  and  encrust- 
ing the  leaves  and  stems  of  fossil-plants,  in  the  Triassic  sand- 
stones of  New  Mexico, f  and  in  the  Permian  sandstones  of 
Russia.  J 

E.  J.   Schmitz  writes   of  the   occurrence   of  copper-ores   as 

*  " Silver  Keef  District,  Southern  Utah,"  by  K.  P.  Kothwell  or  Thomas 
Couch  (?),  Eng.  and  Min.  Jour.,  vol.  xxix.,  pp.  25-26. 

f  "The  Origin  of  Copper-  and  Silver-Ores  in  Triassic  Sand-Kock,"  by  F.  M.  F. 
Cazin,  Eng.  and  Min.  Jour.,  vol.  xxx.,  p.  381.  "The  Silver  Keef  Sandstones," 
by  J.  S.  Newberry,  Eng.  and  Min.  Jour.,  vol.  xxxi.,  pp.  4-5. 

J  Trans.,  ix.,  p.  33. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  327 

pseudomorphic  replacement  of  wood  and  branches  of  trees  in 
bituminous  clay-slate  in  the  Permian  of  Texas.*  In  the  dis- 
cussion of  this  paper,  Mr.  Henry  Louis  describes  deposits 
somewhat  analogous  in  the  Permian  of  Nova  Scotia,  at  New 
Annan,  where  the  ore  occurs  in  nodules  of  chalcopyrite,  chalco- 
cite,  and  iron-py rites, f  associated  with  plant-remains  converted 
into  anthracite. 

Posepny  also  describes  remarkable  specimens  of  tree-trunks 
altered  to  galena  from  the  Vesuvius  mine,  Freihung,  Bavaria.  J 

Bituminous  Shales. 

Rich  deposits  of  blende,  formed  in  great  part  by  the  second- 
ary enrichment  of  smaller,  or  less  mineralized,  primary  ore- 
bodies,  are  found  near  the  surface  in  the  Joplin,  Mo.,  district, 
in  the  vicinity  of  Carthage,  Lehigh,  Central  City  and  Reding's 
Mill.  At  these  localities  the  ore  occurs  in  two  ways :  in  the 
beds  of  soft,  decomposed  carbonaceous  shales  in  the  Coal  Meas- 
ures, occupying  shallow  basins  in  the  Subcarboniferous  lime- 
stone of  the  region ;  or,  more  commonly,  in  horizontal  chan- 
nels eroded  in  the  underlying  limestone  and  filled  with  soft, 
dark  mud,  intermixed  with  bituminous  matter,  derived  from 
these  same  shales,  crushed  by  faulting  movements  and  washed 
into  the  openings  by  surface-waters.  Without  regard  to  the 
character  of  the  enclosing  formation,  these  forms  of  ore-deposit 
are  known  to  the  miners  as  "  mud-runs."  These  occurrences 
are  seldom  far  from  the  surface ;  the  deepest  "  run "  of  this 
character  observed,  near  Reding's  Mill,  was  at  a  depth  of  90  ft. 
At  Lehigh,  similar  deposits  were  found  in  the  bottom-lands 
along  the  stream,  within  a  few  feet  of  the  surface,  where  the 
permanent  water-level  came  near  to  the  top  of  the  ground. 

The  ore  occurs  in  minute  crystals,  thickly  disseminated 
through  the  soft,  shaly  gangue,  or  enveloped  in  semi-fluid 
black  mud.  In  some  of  the  deposits  the  crystals  of  blende  are 
agglomerated,  forming  irregular  masses  and  sheets  of  pure  ore. 
The  crystals  are  of  uniform  size,  usually  from  y1^  to  J-  of  an  in. 

*  "Copper-Ores  in  the  Permian  of  Texas,"  by  E.  J.  Schinitz,  Trans.,  xxvi., 
101. 

t  "  Copper-Ores  in  the  Permian  of  Texas ;"  Discussion  by  Henry  Louis,  Trans., 
xxvi.,  1051,  1052. 

J  Genesis  of  Ore-Deposits,  pp.  129,  130. 


328  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

in  diameter,  transparent,  resin-yellow  in  color,  with  a  sh,ade  of 
red,  resembling  in  appearance  the  small  garnets  found  in  some 
placer  gold-bearing  gravels.  The  small  size  of  the  crystals  is 
probably  due  to  the  concentration  of  the  solutions  from  which 
they  were  deposited,  and  to  their  rapid  formation.  In  some 
instances  blende  forms  crystals  in  these  shaly  beds  from  J  in. 
to  more  than  an  inch  in  diameter,  presumably  from  a  slower 
and  more  prolonged  growth.  In  all  the  deposits  of  this  type, 
the  reducing  agent  has  been  bituminous  matter  acting  upon 
surface-waters,  which  carried  in  solution  the  sulphates«of  the 
metals  leached  from  ore-bodies  at  higher  levels,  that  were  un- 
dergoing oxidation.  The  following  equation  shows  the  char- 
acter of  the  change : 

ZnS04  +  2CH  +  H20  +  0  =  ZnS  +  2H2C03. 

It  has  been  observed  that  these  shallow  mud-runs  usually 
occupy  synclinal  basins  or  troughs,  and  that  surface-erosion  has 
often  removed  a  considerable  depth  of  the  ore-bearing  forma- 
tions from  the  immediate  vicinity;  the  deposits  being  located 
where  they  have  received  the  drainage  from  surrounding  min- 
eral-areas. 

At  the  Britton  mine,  Central  City,  the  ore  occurs  at  a  depth 
40  to  50  ft.  from  the  surface,  in  a  broad,  flat,  compound-run, 
75  to  150  ft.  wide  and  6  to  12  ft.  high,  developed  on  its  course 
for  a  length  of  550  ft,  northerly  and  southerly.*  The  ore  is 
granular,  crystallized  blende  in  a  stratum  of  soft,  black  mud 
and  broken  chert.  The  particles  of  blende  are  less  than  ^  in. 
in  diameter,  deep  garnet-red  in '  color,  and,  although  thickly 
distributed  in  the  mud,  are  not  agglomerated.  A  number  of 
similar  deposits  are  developed  in  the  vicinity. 

Ore-deposits  of  this  character  are  easily  mined  with  pick 
and  shovel ;  powder  is  only  used  to  break  up  an  occasional 
boulder  in  the  ore-body.  The  ore  requires  very  little  crushing 
and  readily  concentrates,  yielding  from  12  to  20  per  cent,  of 
clean  blende.  The  product  is  very  pure,  assaying  from  62  to 
64  per  cent,  of  metallic  zinc. 

Reding's  mine,  about  4  miles  southeast  of  Joplin,  is  situated 

*  For  a  definition  of  these  forms  of  ore-deposits,  see  "  The  Lead-  and  Zinc- 
Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney,  Trans.,  xxii.,  189,  190. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  329 

in  a  shallow  basin  in  a  low  range  of  hills,  bordering  the  north 
side  of  the  valley  of  Shoal  creek.  At  the  time  of  the  exami- 
nation, this  mud-run  was  opened  75  ft.  in  length,  north  and 
south,  with  a  width  of  36  ft,  and  a  height  of  12  to  18  ft.  The 
ore  occurs  in  dark-brown  mud,  in  finely  disseminated  crystals, 
and  in  crystallized  masses  and  sheets  of  galena  and  blende. 
Beautiful  specimens  of  galena  are  found  in  very  perfect  cubical 
crystals,  1  to  2  in.  on  a  side.  The  upper  part  of  the  run  is 
mostly  crystallized  galena,  while  the  lower  part  is  blende,  with 
a  smaller  proportion  of  galena.  Boulders  of  flint  and  black 
clay-shales  are  found  in  the  ore,  together  with  much  coarsely 
crystalline  rotten  dolomite. 

This  ore-deposit  is  remarkable  for  its  extreme  richness.  To 
the  date  of  my  examination,  the  yield  of  the  mine,  estimated 
upon  all  material  extracted,  had  been  15  to  20  per  cent,  of  clean 
ore.  When  first  formed,  it  was  evidently  a  small  run  of  blende 
and  galena  in  dolomite ;  subsequently,  surface-waters  eroded  a 
cavern-like  channel  following  the  course  of  the  run.  Material 
washed  from  the  surface  formations  of  broken  and  crushed 
bituminous  shale  filled  this  channel  and  enveloped  the  ore-body. 
Finally,  the  ore  primarily  deposited  was  greatly  reinforced  by 
secondary  deposition,  both  galena  and  blende  being  crystallized 
in  the  fluid  mud  by  the  reducing  action  of  the  hydrocarbon. 

A  small  basin  of  coal-shales,  near  Belleville,  Jasper  county, 
Mo.,  carried  beautifully  preserved  fossil-plants.  The  outer 
surface  of  the  mass  of  shales,  for  a  depth  of  about  a  foot,  con- 
tained scattered  crystals  of  blende,  from  J  to  f  in.  in  diameter, 
mingled  with  a  few  crystals  of  galena  and  pyrite.  The  central 
portion  did  not  carry  any  mineral,  the  mass  having  been  min- 
eralized from  the  outside,  toward  the  interior,  as  far  only  as 
the  mineral-bearing  waters  could  penetrate  the  dense  plastic 
clay.  The  crystals,  in  their  growth,  have  distorted  otherwise 
perfect  fossil-plants,  crowding  parts  of  the  fern-fronds  to  one 
side ;  giving  evidence  that  the  deposition  of  the  minerals  was 
of  later  date  than  the  preservation  of  the  plant-remains.  These 
plants  were  determined  by  David  White  to  belong  to  a  hori- 
zon near  the  middle,  or  the  upper  part,  of  the  Lower  Coal- 
Measures.* 

*  "  Flora  of  the  Outlying  Carboniferous  Basins  of  Southwestern  Missouri," 
Bulletin  of  U.  S.  Geol.  Sur.,  No.  98. 


330  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

On  the  Mine  La  Motte  grant,  in  Southeast  Missouri,  deposits 
of  disseminated  galena  in  black  shale  of  Cambrian  age  outcrop 
at  the  surface,  and  were  worked  for  lead  during  the  early 
period  of  mining  in  that  region.  The  galena  occurs  in  crystal- 
line nodules,  from  J  to  J  in.  in  diameter,  thickly  distributed  in 
bands  through  the  shale.  This  shale-bed  appears  to  be  a  local 
formation.  The  ore-deposits  closely  resemble  in  mode  of  occur- 
rence those  of  disseminated  lead  in  the  Cambrian  limestone  in 
the  belt  extending  from  Mine  La  Motte,  through  the  Flat  River 
district,  to  Bonne  Terre. 

The  secondary  formation  of  metallic  sulphides  is  now  taking 
place  in  the  Missouri  mines ;  blende  and  galena,  oxidizing  to 
sulphates  in  the  ore-deposits  near  the  surface,  are  carried  in 
solution  by  the  subaerial  waters  to  the  deeper  horizons,  and 
there  regenerated  by  the  deoxidizing  action  of  bituminous 
matter.  The  subject  is  too  extensive  to  admit  of  discussion 
here,  and  must  be  left  for  a  future  paper. 

A  single  instance,  however,  may  be  cited  of  the  reproduction 
of  blende  from  mine-waters.  An  old  tunnel,  driven  through 
bituminous  shale  on  the  Banker's  Tract,  near  Joplin,  became 
filled  with  water  draining  from  adjoining  mines  on  which 
work  had  been  suspended.  The  tunnel  remained  closed  and 
submerged  for  ten  or  twelve  years,  until  the  mines  were  un- 
watered  in  1898.  When  reopened,  the  surface  of  the  shales, 
011  the  roof  and  sides  of  the  tunnel,  was  found  to  be  thickly 
encrusted  with  minute  crystals  of  blende,  one-  or  two-hun- 
dredths  of  an  inch  in  diameter.  In  places,  the  blende  was  de- 
posited on  the  pick-marks  made  when  the  tunnel  was  run. 

The  paper  of  T.  A.  Rickard,  on  "  The  Enterprise  Mine,  Rico, 
Colorado,"*  shows  the  existence  of  a  strongly-marked  resem- 
blance between  the  occurrence  of  the  flat  ore-deposits  at  Rico, 
carrying  silver  and  gold,  and  the  ore-formation  of  Southwest 
Missouri,  where  galena  and  blende  occur  in  simple  runs,  and 
also  in  compound  runs,  formed  in  like  manner,  in  the  favorable 
beds,  by  mineral-depositing  solutions  introduced  through  ver- 
tical fissures  from  an  unknown  source  in  depth,  and  where 
bituminous  matter,  contained  in  the  ore-bearing  strata,  has 
likewise  been  the  precipitating  agent  in  the  deposition  of 
the  ore. 

*  Trans.,  xxvi.,  906-980. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  331 

Experiments  made  in  the  laboratory,  to  determine  the  re- 
ducing action  of  the  black  shale  associated  with  the  ore-bodies, 
are  described  by  Rickard,  as  follows : 

"  A  piece  of  the  Rico  shale  was  put  into  a  weak  solution  of 
sulphate  of  silver  (Ag2S04)  containing  some  free  acid  intended 
to  neutralize  the  lime  (CaC03)  in  the  shale.  The  precipitation 
of  metallic  silver  became  visible  in  three  days.  The  parallel 
experiment  with  gold  was  more  interesting.  A  piece  of  ore 
(assaying  1147  oz.  of  gold  per  ton)  obtained  from  .  .  .  . 
Cripple  Creek,  was  taken,  and  its  gold  was  extracted  by  a  solu- 
tion containing  ferric  sulphate  (Fe2O3,3S03),  common  salt  (NaCl) 
and  a  little  free  acid  (H2S04).  This  Cripple  Creek  ore  car- 
ried the  black  oxide  of  manganese  (Mn02)  in  visible  quan- 
tity, and  thus  the  chlorine  used  to  form  the  gold-solution  was 
liberated  in  a  manner  simulating  natural  conditions.  Of  the 
gold,  .  .  .  .  99.91  per  cent,  was  extracted  and  subse- 
quently precipitated  on  the  Rico  shale  by  inserting  the  latter 
in  the  solution  thus  formed.  The  gilding  of  the  black  shale 
by  the  deposit  of  gold  became  visible  within  four  hours."* 

W.  Nicholas  has  made  a  series  of  similar  experiments  in  the 
precipitation  of  gold  by  black  carbonaceous  shales  from  the 
Victorian  quartz-reefs,  f 

The  peculiar  vein-formation  known  as  the  "  Indicator  "  is  an 
example  of  the  localization  of  rich  deposits  of  free  gold,  due  to 
the  reducing  action  of  carbonaceous  shales.  Rickard  defines 
the  Indicator  as  "  a  very  thin  thread  of  black  slate,  which  is 
remarkable  on  account  of  its  extraordinary  persistence,  and 
also  because  the  quartz  seams  which  cross  it  are  notably  en- 
riched at  the  point  of  intersection."!  It  is  also  referred  to  by 
Dr.  Don.§  The  Indicator  is  the  most  important  member  of  a 
series  of  thin  seams  of  black  shale,  more  or  less  impregnated 
with  pyrite  and  arsenopyrite,  traversing  the  slate  and  sandstone 
formation  of  the  district. 

Different  views  have  been  expressed  as  to  whether  the  car- 

*  Ibid.,  pp.  978,  979. 

t  "The  Origin  of  the  Gold-Bearing  Quartz  of  the  Bendigo  Keefs,"  by  T.  A. 
Rickard  ;  Discussion,  Trans. ,  xxii. ,  762-763. 

"  The  Origin  of  Gold  in  Certain  Victorian  Quartz-Keefs,"  by  William  Nicholas, 
Eng.  and  Min.  Jour.,  vol.  xxxvi.,  pp.  367,  368. 

J  "The  Indicator  Vein,  Ballarat,  Australia,"  Trans.,  xxx.,  1010. 

$  "  The  Genesis  of  Certain  Auriferous  Lodes,"    This  volume,  p.  162. 


332  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

bon  or  the  pyrite  in  the  Indicator  seam  was  the  reducing  agent 
in  the  formation  of  the  rich  bunches  of  gold-ore.  But  pyrite 
was  deposited  in  the  black  shale  by  the  reducing  action  of  the 
organic  matter ;  so  that,  in  any  event,  it  was  the  presence  of 
carbon  compounds  which,  directly  or  indirectly,  caused  the 
local  accumulation  of  the  gold. 

Owing  to  the  far  more  powerful  action  of  the  hydrocarbons, 
reduction  by  pyrite  contained  in  carbonaceous  shales  must  al- 
ways be  subordinate,  even  where  local  conditions,  such  as  the 
presence  of  free  oxygen  and  oxidized  metallic  salts,  admit  of 
the  pyrite  being  decomposed.  Any  ferrous  sulphate  produced, 
at  once  re-forms  pyrite,  giving  up  its  oxygen  to  the  carbon.  In 
the  depths  of  the  strata,  below  water-level,  wherever  any  form 
of  carbon  is  in  excess,  it  absolutely  protects  the  pyrite  by  con- 
suming all  the  free  oxygen.* 

Many  instances  might  be  cited  to  illustrate  the  influence  of 
the  organic  matter  contained  in  bituminous  shales  upon  the 
formation  of  ore-deposits. 

A  stratum  of  black  shale  in  the  Mono  silver-mine,  Dry 
Canon,  Utah,  formed  the  hanging-wall  of  the  rich  ore-shoot, 
from  which  large  masses  of  horn-silver  and  high-grade  sulphide- 
ores  were  mined,  carrying  from  500  to  3000  oz.  of  silver  per 
ton.  It  is  reported  that  a  carload  of  ore  from  this  mine  yielded 
over  $55,000. 

Emmons  says :  "  Most  famous,  in  view  of  the  enormous 
values  taken  from  them,  are  the  rich  silver-bodies  of  the  Mollie 
Gibson  and  Smuggler  mines  of  Aspen,  Colo. ;  but,  in  their  case, 
there  is  sufficient  organic  matter  present  to  explain  the  reduc- 
tion of  the  oxidized  solutions  to  sulphides.  They  occur  along 
a  vertical  fault,  formed  since  the  original  mineralization  of  the 
district,  and  consist  of  great  masses  of  polybasite  and  pink 
barite,  which,  in  places,  have  been  further  reduced  to  native- 
silver.  On  one  wall  of  the  ore-body  is  the  limestone,  of  which 
it  is  a  replacement,  and  on  the  other  a  black  bituminous 

shale."t 

Bickard,  discussing  this  subject,  writes :  "  The  idea  of  the 

*  This  subject  is  discussed  in  more  detail,  under  the  sub-head,  Protective  Ac- 
tion of  Carbon  and  of  Hydrocarbons,  Ante,  p.  311. 

f  "The  Secondary  Enrichment  of  Ore-Deposits,"  Trans.,  xxx.,  195.  See,  also, 
Genesis  of  Ore-Deposits,  pp.  450,  451, 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  333 

precipitation  of  the  ore  through  the  agency  of  carbonaceous 
matter  has  been  advanced  in  connection  with  ore-deposits  in 
other  regions.  I  may  quote,  as  instances,  the  black  Silurian 
slates  of  Bendigo,  Victoria;  the  Devonian  slates  of  Gympie, 
Queensland ;  the  Jurassic  slates  of  the  c  Mother  Lode  '  region 
in  Calaveras  and  Amador  counties,  California;  the  black  shale 
enclosing  the  gold-specimen  ores  of  Farncomb  Hill,  Brecken- 
ridge,  Summit  county,  Colorado  ;  .  .  .  and  the  celebrated  Indi- 
cator series  of  Ballarat,  Victoria."* 

In  this  connection,  reference  is  made  to  the  well-known  oc- 
currence of  copper-ores  at  Mansfeld,  Prussia,  in  beds  of  bitu- 
minous slate  and  bituminous  limestone.  Certain  of  the  lower 
limestone  beds  are  fetid.  These  copper-bearing  formations 
extend  over  a  large  district,  f  The  ore  contains  so  much  bitu- 
minous matter  that  only  a  little  brushwood  is  required  in 
roasting  the  ores  in  piles. 

Limestones  Containing  Organic  Matter. 

In  mining-regions  where  the  ores  occur  in  limestone,  it  is 
observed  that  in  most  instances  the  largest  and  most  produc- 
tive mines  are  in  belts  or  zones  of  crystalline  limestones  which 
are  either  exceptionally  pure  lime-carbonates  or,  more  fre- 
quently, dolomites  with  only  a  small  amount  of  insoluble  mat- 
ter. Such  formations,  peculiarly  favorable  for  ore,  are  rocks 
easily  crushed  by  movements  of  disturbance,  readily  permeated 
by  circulating-waters,  and,  from  their  -chemical  composition, 
rapidly  attacked  by  solutions  carrying  carbonic  acid.  Where 
situated  at  the  surface,  they  are  cavern-forming  limestones. 
Further,  it  is  noted  that  both  the  magnesian  limestones  and  the 
pure  lime-carbonates  usually  contain  some  form  of  organic 
matter  which,  though  small  in  amount,  appears  to  have 
strongly  influenced  the  deposition  of  the  minerals  in  the  strata. 

Otherwise  stated,  ore-deposits  in  limestone,  irrespective  of 
the  nature  of  the  minerals  constituting  the  ores,  conform  to 
the  general  law  of  selective  deposition,  namely,  that  "  Some 
geological  formations  appear  to  be  everywhere  barren  of  ore  ;  others 
occasionally  carry  small  deposits,  workable  where  the  conditions  are 

*  "The  Enterprise  Mine,  Kico,  Colorado,"  Trans.,  xxvi.,  978. 
t  Von  Cotta,  Treatise  on  Ore-Deposits,  Prime's  Translation,  p.  164. 


334  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

exceptionally  favorable  ;  but  in  each  mining  region  certain  strata  are 
ore-bearing  in  a  degree  exceeding  all  other  formations  combined."* 

Among  the  causes  that  have  induced  the  concentration  and 
deposition  of  the  ores  in  special  formations,  prominence  may 
rightly  be  given  to  the  deoxidizing  action  of  the  bitumen,  bi- 
tuminous coal,  lignite,  or  other  form  of  carbonaceous  matter 
disseminated  in  the  rock. 

In  Southeastern  Missouri,  the  lead-ore  now  mined  is  mostly 
from  deposits  of  disseminated  galena  in  the  dark-colored  mag- 
nesian  limestone,  rich  in  bituminous  matter,  of  the  Cambrian 
formation  at  Bonne  Terre  and  the  Flat  Eiver  mines.  Prac- 
tically all  the  zinc-ore,  and  the  greater  proportion  of  the  lead, 
produced  in  the  Joplin  region,  in  the  southwest  part  of  the 
State,  is  yielded  by  the  Cherokee  limestone,  the  upper  division 
of  the  Subcarboniferous.f  The  Cherokee  is  a  soft,  crystalline, 
pure  lime-carbonate,  carrying  bitumen.  Its  average  composi- 
tion, from  a  number  of  analyses,  is  as  follows  : 

Lime, 55.00 

Magnesia, .        .         .        .  0.23 

Alumina,       ....         ......  0.10 

Protoxide  of  Iron,         .......         .  0.05 

Protoxide  of  Manganese, 0.02 

Bitumen  and  insoluble,         .         .         .         .         .         .         .  1.00 

Carbonic  acid, 43.60 


100.00 

In  the  Upper  Mississippi  lead-region  the  productive  forma- 
tion has  been  the  Galena  limestone,  the  upper  member  of  the 
Trenton.  It  is  a  soft,  crystalline  dolomite ;  bituminous  matter 
is  present  in  relatively  small  amount,  yet  apparently  more  than 
sufficient  to  effect  the  precipitation  of  the  metals  and  preserve 
the  ores  from  oxidation  below  water-level.  The  deposits  of 
blende  in  the  mines  near  Mineral  Point  and  Shullsburg,  Wis- 
consin, occur  in  the  underlying  "  Blue  "  limestone  of  the  Tren- 
ton, and  the  ores  are  concentrated  about  the  intersection  of  the 
mineral-bearing  fissures  with  thin  strata  of  brown  shale,  sat- 
urated with  petroleum, — the  "  Oil-rock"  of  the  miners.! 

*  "  The  Lead-  and  Zinc-Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney, 
'Tram.,  xxii.,  187-188. 

t  "  The  Lead-  and  Zinc-Deposits  of  the  Mississippi  Valley,"  by  W.  P.  Jenney, 
Trans.  t  xxii.,  188. 

%  William  P.  Blake,  Discussion  of  "The  Lead-  and  Zinc-Deposits  of  the  Mis- 
sissippi Valley,"  Trans.,  xxii.,  631. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  335 

A  summary  review  of  the  occurrence  of  zinc-  and  lead-ores 
in  the  Mississippi  valley  shows  that  the  formation  of  the  de- 
posits has  been  due  to  solutions  of  normal  temperature ;  and 
that  the  chief  agent  in  the  primary  deposition,  and  in  the  sec- 
ondary enrichment  of  the  ores,  has  been  the  bituminous  sub- 
stances contained  in  the  strata  in  which  the  deposits  are  found. 
The  larger  part  of  the  minerals  constituting  the  ores  has  been 
deposited  either  by  crystallization  or  by  crystalline  growth  in 
the  lime-rock  or  dolomite  of  the  walls,  or  has  impregnated  the 
beds  of  specially  favored  geological  formations. 

In  the  limestone-area  at  Tintic  district,  Utah,  the  productive 
mines  occur  in  two  distinct  belts  in  the  Carboniferous  forma- 
tion ;  one,  extending  through  the  central  part  of  the  district, 
of  dark-colored,  magnesian  limestones ;  the  other,  traversing 
Godiva  mountain,  on  the  eastern  border  of  the  lime-area,  formed 
by  beds  of  gray  limestone  with  only  a  trace  of  magnesia. 

On  the  central  belt  are  situated  the  Gemini,  Bullion-Beck, 
Eureka  Hill  and  Centennial  Eureka  mines;  and  farther  south, 
also  in  magnesian  limestones,  are  located  the  Grand  Central 
and  the  Mammoth.  A  number  of  these  mines  have  been 
worked  continuously  since  the  early  development  of  the  district 
in  1870-71.  All  have  reached  a  depth  of  1000  to  1750  ft.; 
the  Mammoth  is  now  2100  ft.  deep. 

It  is  not  necessary  to  discuss  the  occurrence  of  the  ore,  be- 
yond its  relation  to  the  magnesian  limestones  in  which  the  de- 
posits are  found.  Locally,  these  limestones  vary  somewhat  in 
character ;  they  are  hard,  crystalline,  bluish-gray  to  bluish-black 
dolomites,  the  color  being  due  to  organic  matter.  In  certain 
places  the  beds  are  filled  with  nodules  and  thin  bands  of  hard, 
black  chert.  The  average  composition,  from  7  analyses,  of  the 
limestones  in  the  vicinity  of  the  Bullion-Beck  mine  is  (the 
organic  matter  and  loss  being  estimated  by  difference) : 

Calcium  carbonate,         .         .        .         .         .        .  .     48.76 

Magnesium  carbonate, 35.43 

Ferrous  carbonate,          ........       2.61 

Silica, 9.67 

Alumina, 3.00 

Organic  matter  and  loss,         .         .         .         .         .         .         .0.53 


100.00 

In  a  number  of  analyses  the  silica  varied  from  6.75  per  cent. 


336  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

to  13  per  cent.,  and  the  total  insoluble  matter  from  16  per  cent, 
to  18  per  cent. 

The  amount  of  silica  and  insoluble  matter  is  remarkable, 
for  there  is  every  evidence  in  the  mines  that  these  dolomitic 
limestones  are  rapidly  decomposed  and  eroded  by  carbonated 
waters.  The  explanation  of  this  marked  solubility  of  the 
dolomite,  notwithstanding  the  large  proportion  of  impurities, 
is  probably  to  be  sought  in  the  structure  of  the  rock.  In 
the  upper  levels  of  the  Bullion-Beck  and  the  Eureka  Hill 
mines,  where  the  subterraneous  erosion  by  surface-waters  has 
been  greatest,  large  masses  of  residual  dolomite  sand,  which 
have  resulted  from  the  disintegration  of  the  fissured  and  shat- 
tered beds,  occur,  filling  cavern-spaces  or  chambers  in  the  lime- 
stone. Beneath  the  heavy  wash  of  boulders  filling  the  gulch, 
the  limestone  beds,  for  a  depth  of  near  100  ft.,  without  change 
in  the  stratification,  are  decomposed  and  altered  in  situ  into  soft, 
sandy  dolomite,  stained  with  iron  and  manganese  oxides. 
Analyses  showed  that  this  decomposed  rock  had  substantially 
the  same  composition  as  the  loose  deposits  of  sand;  being 
dolomite,  with  the  residual  silica,  clay,  oxidized  iron  and  man- 
ganese contained  in  the  original  formation.  Surface-waters, 
carrying  carbonic  acid,  appear  first  to  attack  the  calcareous 
cement  between  the  crystalline  grains  of  dolomite,  at  the  same 
time  oxidizing  the  carbonates  of  manganese  and  iron  present, 
and  in  this  way  rapidly  disintegrate  the  rock. 

Many  caverns,  mostly  of  small  size  and  usually  more  recent 
in  formation  than  the  ore-bodies,  occur  in  the  limestone.  It  is 
noted  that  they  are  generally  located  along  the  course  of  the 
vertical  faulting-fissures,  which  have  been  the  channels  fol- 
lowed by  the  solutions  depositing  the  ore,  the  shattering  and 
brecciation  of  the  beds,  due  to  the  faulting  movement,  in- 
creasing the  action  of  surface-waters  in  the  erosion  of  the 
rock. 

In  a  few  instances  the  ore  actually  fills  pre-existing  caverns. 
The  largest  of  these  caverns  in  the  Bullion-Beck  mine,  formed 
before  the  minerals  were  introduced  in  the  primary  deposition, 
was  filled  with  argentiferous  galena,  in  great  part  deposited  by 
crystallization.  The  rock-floor  of  the  cavern  was  covered  by  a 
horizontal  stratum  of  chert  nodules,  overlain  by  sand-beds,  10 
to  15  ft.  in  thickness,  with  disseminated  pyrite  and  galena,  the 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  337 

massive  crystalline  lead-ore  resting  on  the  sedimentary  beds. 
The  flat-beds  covering  the  clay  floor  were  unquestionably  formed 
from  the  residual  sand  and  chert  contained  in  the  rock,  dis- 
solved away  by  the  circulating-waters  in  making  the  cavern. 
Suchf  occurrences  of  ore  deposited  by  crystallization  are  rare 
in  these  mines ;  practically  all  the  quartz,  and  nearly  all  the 
lead-  and  copper-ores,  are  formed  by  replacement. 

The  limestones  are  much  purer  in  the  Grand  Central  and 
Mammoth  mines.  An  average  of  6  analyses  gave  (ferrous  car- 
bonate, alumina  and  organic  matter  not  determined) : 

Calcium  carbonate, 55.38 

Magnesium  carbonate,    .         .         .         .         .         .         .         .42.84 

Silica, 0.65 

Undetermined  and  loss, .1.13 


100.00 

This  is  a  bluish-gray,  brown,  or  bluish-black,  crystalline  dolo- 
mite, free  from  chert.  The  weathered  outcrop  of  certain  beds 
shows  the  rock  to  be  made  up  of  the  broken  and  water-worn 
joints  of  minute  crinoid  stems,  one-  to  three-hundredths  of  an 
inch  in  diameter,  with  fragments  of  shells  and  an  occasional 
small  coral.  The  stratification  is  generally  preserved ;  in  some 
places  the  rock  is  cross-sheeted  by  movements  of  disturbance, 
and  locally  the  beds  have  been  brecciated  and  recemented  by 
their  own  attrition  material  into  a  massive  rock,  with  but  traces 
of  bedded  structure. 

This  limestone,  even  where  not  mineralized,  is  easily  distin- 
guished by  the  appearance  and  fracture  of  the  rock, — being 
dark-colored  and  crystalline,  with  spots  and  small  vugs  of  cal- 
cite  and  stains  of  iron  and  manganese  oxides  on  the  joints.  It 
is  often  sonorous,  giving  a  clear  metallic  ring  when  struck  with 
a  pick.  It  crumbles  under  a  blow  into  small,  ragged,  rough 
fragments,  having  the  fracture  of  loaf  sugar. 

The  beds  are  thin, brittle, easily  shattered  and  crushed  by  fault- 
ing-movements.  On  account  of  the  absence  of  clay  in  the  rock, 
the  breccias  and  attrition-material  produced  are  permeable  to 
circulating-waters;  even  small  fissures  and  fractures  in  the  lime 
keep  open.  Caves  of  considerable  size  are  not  infrequently 
encountered  in  the  formation,  but  appear  to  have  been  formed 
subsequent  to  the  ore.  It  is  noteworthy  that  deposits  of  loose 

22 


338  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

dolomite-sands  are  seldom  formed  in  this  pure  dolomite;  neither 
is  the  rock  usually  altered  in  place  to  iron-stained  rotten  dolo- 
mite. The  action  of  surface-waters  is  to  dissolve  the  rock  com- 
pletely, and  not  to  disintegrate  the  rock  by  attacking  the  calca- 
reous cement  between  the  grains. 

The  ore-bodies  afford  evidence  that  this  limestone,  especially 
where  fissured  and  fractured,  is  easily  replaced  by  silica  and  by 
the  other  gangue-minerals,  ankerite,  siderite,  barite  and  calcite. 
Not  only  has  the  limestone  been  metasomatically  replaced  by 
primary  sulphide-ores,  carrying  lead,  copper,  iron,  arsenic, 
silver  and  gold,  but  the  complex  products  of  their  oxidation 
and  redeposition  have,  also,  more  or  less  perfectly  replaced  the 
rock.  It  is  observed  that  the  darker  and  coarsely  crystalline 
lime-beds  are  highly  favorable  for  ore, — beds  made  up  of  com- 
minuted fossil-remains,  crinoid  stems,  broken  corals  and  shells. 

Eliminating  the  highly  impure  sediments,  which  seldom 
carry  workable  deposits,  the  structure  of  the  rock  appears  to 
be  far  more  important  than  the  chemical  composition  in  de- 
termining whether  certain  strata  are  ore-bearing  or  barren. 
Analyses  of  the  magnesian  limestones  over  a  broad  belt  show 
that  they  vary  but  little  in  composition.  The  beds  which  have 
been  found  to  be  unfavorable  for  ore  are  usually  dense,  finely 
crystalline  and  impermeable ;  the  rock  generally  breaking 
under  a  blow  of  a  hammer  with  a  "  dead  "  sound,  and  a  smooth, 
splintery  fracture,  like  the  fracture  of  quartzite.  Organic  mat- 
ter is  not  at  all  prominent  in  this  limestone,  although  it  gives 
the  color  to  the  rock. 

The  principal  ore-bearing  formation  in  Godiva  mountain  is  a 
stratum,  200  to  400  ft.  in  thickness,  of  massive,  gray,  very 
coarsely  crystalline  limestone.  It  is  a  pure  lime-carbonate, 
carrying  some  undetermined  form  of  bituminous  material, 
which  gives  to  the  rock,  when  broken,  a  sulphurous,  fetid 
odor.  On  dissolving  the  limestone  in  acid,  the  bitumen  sepa- 
rates in  clots.  An  analysis  of  this  limestone  gave  (the  organic 
matter  and  loss  being  estimated  by  difference) : 

Calcium  carbonate,         .         .         .         .         .         .....     98.75 

Alumina  and  iron-oxides,       .         .         .         .         .         .         .0.40 

Silica,    .        -.       " 0.20 

Magnesia,       ........  trace. 

Organic  matter  and  loss, 0. 65 

100.00 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  339 

The  weathered  outcrop  of  the  gray  limestone  is,  in  many 
places,  bluish-black  from  the  concentration  of  the  bitumen  in 
the  surface  of  the  rock.  The  beds  are  formed  of  water-worn 
grains  and  broken  fragments  of  small  shells.  A  coral  (zaphren- 
tis),  1  to  2J  in.  long,  is  its  characteristic  fossil.  It  exceeds  in 
chemical  solubility  all  other  ore-bearing  limestones  in  this  sec- 
tion of  the  district.  The  perfect  manner  in  which  great  masses 
of  the  rock  are  replaced  by  the  ore  is  evidence  of  this. 

The  gray-limestone  formation  extends  northerly  and  south- 
erly through  the  whole  length  of  Godiva  mountain,  bounded 
on  either  side  by  limestones  more  or  less  magnesian  in  charac- 
ter. Many  of  these  magnesian  limestones,  interbedded  in  the 
series,  are  highly  impure  sediments,  with  25  to  35  per  cent,  of 
silica,  5  to  10  per  cent,  of  iron  and  alumina,  6  to  12  per  cent, 
of  magnesia,  and  20  to  30  per  cent,  of  lime.  These  formations 
have  been  found  unfavorable  for  ore. 

On  this  gray-lime  belt  are  located  the  Uncle  Sam,  May-Day 
and  Yankee  Consolidated  mines, — properties  developed  since 
1897.  The  deepest  workings  have  attained  a  depth  of  800  ft. 
The  Uncle  Sam  mine  has  been  noted  for  its  large  output  of 
high-grade  lead-ore,  carrying  silver,  in  a  gangue  mainly,  com- 
posed of  lime-carbonate. 

Quartz-ores  prevail  in  the  other  mines  of  the  belt,  with  lead, 
silver,  and  usually  a  small  amount  of  gold. 

The  ores  have  been  introduced  in  the  strata  through  belts  of 
nearly  vertical  faulting-fissures.  Along  the  course  of  these 
fissures  the  ore-bodies  have  formed  in  the  limestone.  In  some 
places  the  ore-deposits  take  on  the  form  of  fissure-veins,  the 
ore  being  confined  within  the  walls  of  the  fissure  and  deposited 
in  a  more  or  less  tabular  sheet,  pitching  like  the  ore-shoots  in 
quartz-veins  in  the  metamorphic  rocks.  More  commonly  the 
faulting  movements  forming  the  fissures  have  so  fractured  the 
beds  that  the  mineral  deposits  are  not  limited  by  the  fissure- 
walls  and  extend  irregularly  into  the  limestone.  The  largest 
ore-bodies  have  formed  in  spaces  of  multiple  fissuring,  where 
the  belt  of  master-fissures  cuts  through  lime-beds,  broken  and 
rifted  in  different  directions  by  the  complex  intersection  of 
sheeted  belts,  due  to  cross-fissures  and  to  diagonal  fissures. 

The  ores  of  primary  formation  are  mostly  deposited  by  re- 
placement of  the  limestone.  Quartz  occurs  in  many  varied 


340  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

forms, — from  massive  limestone,  more  or  less  completely  altered 
to  quartz,  with  little  change  in  structure,  to  the  white,  crystal- 
line mineral,  grading  insensibly  into  soft,  crumbling,  pulveru- 
lent quartz,  in  appearance  resembling  granulated  sugar. 

In  certain  places  in  these  mines  the  limestone  appears  to 
have  been  sheeted  and  broken  into  large,  thin  and  sharp  frag- 
ments before  it  was  replaced  by  the  ore ;  the  sharp  edges  of 
the  pieces  of  limestone  were  not  rounded  in  the  conversion ; 
there  has  not  been  any  solution  of  the  rock  without  the  per- 
fect pseudomorphic  replacement  of  its  structure  by  the  min- 
erals. 

This  has  occurred  not  only  in  the  replacement  of  the  lime- 
stone by  quartz,  but  also  in  its  replacement  by  massive  argentif- 
erous galena,  as  fine-grained  in  its  crystalline  structure  as 
steel.  The  galena  reproduces  the  shape  of  the  original  lime- 
stone fragments,  so  that  they  are  fossilized  by  lead-sulphide,  as 
wood  is  petrified  by  the  infiltration  of  silica,  only  less  per- 
fectly. 

The  largest  body  of  galena  of  this  character  occurred  in  the 
Uncle  Sam  mine.  The  ore-body,  50  ft.  long,  13  to  20  ft.  wide, 
and  50  to  60  ft.  high,  was  formed  entirely  of  pure  lead-sulphide, 
with  no  other  minerals  except  calcite  and  the  lime  wall-rock. 
The  ore  averaged  75  per  cent,  of  lead  and  50  oz.  of  silver  per 
ton.  In  this  ore-body  the  massive  limestone,  prior  to  its  min- 
eralization, had  been  fractured  vertically  in  large,  sheeted  frag- 
ments, some  of  which  would  measure  10  to  15  ft.  long  and  10 
to  25  ft.  high,  but  only  6  to  15  in.  thick.  Even  the  largest 
masses  of  rock  were  altered  throughout  to  steel-galena.  Nu- 
merous vertical  open  seams  and  fractures,  from  the  thickness 
of  a  knife-blade  to  2  in.  in  width,  separated  these  irregular 
sheets  of  ore  one  from  another.  A  vertical  fracture,  12  to  18 
in.  wide,  passed  through  the  ore-body ;  it  was  more  recent  in 
formation  than  the  primary  ore  and  was  filled  writh  coarsely 
crystalline  galena,  with  cleavage  faces  2  to  3  inches  across,  de- 
posited by  crystallization. 

In  general,  in  the  mines  on  Godiva  mountain,  fine-grained 
galena,  replacing  the  limestone,  is  of  primary  origin,  while 
coarsely  crystalline  galena  is  usually  secondary ;  although  some 
of  the  lead-ore  deposited  by  crystallization  (or  crustification) 
appears  to  be  primary. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  341 

Review  of  the  Phenomena  of  the  Deposition  of  Ores  in  Limestone* 
— A  study  should  be  made  of  the  structure  of  the  ore-bearing 
limestones,  with  the  special  object  of  determining  the  causes 
that  have  made  certain  strata  favorable  for  ore,  while  other 
beds  in  the  same  geological  formation,  having  an  almost  iden- 
tical chemical  composition,  and  so  situated  that  they  are  tra- 
versed by  the  same  fissures,  through  which  the  mineral-depos- 
iting waters  have  been  introduced,  have  remained  barren.  In 
many  instances  the  productive  and  the  barren  strata  are  inter- 
bedded  and  so  situated  that  the  ore-bearing  fissures  cut  through 
all  the  beds  alike,  without  any  change  in  this  selective  deposi- 
tion of  the  ores. 

Analyses  of  these  ore-producing  limestones  are  needed  to 
determine  the  amount  and  character  of  the  carbonaceous  sub- 
stances present,  and  also  the  minute  traces  of  other  elements, 
some  of  which  may  be  found  to  have  had  an  influence  on  the 
formation  of  the  deposits.  That  such  an  influence  may  have 
been  exerted  seems  probable,  when  we  consider  the  enormous 
masses  of  the  highly  soluble  limestones  that  have  been  dis- 
solved or  replaced  in  the  creation  of  the  ore-bodies.  It  has 
been  shown,  for  example,  that  the  small  percentage  of  bitu- 
men or  other  hydrocarbon  contained  in  the  rock,  and  set  free 
by  its  dissolution,  has  strongly  aided  in  the  deposition  of  the 
ore.  , 

Prof.  Church,  discussing  the  deposition  of  ores  in  limestone, 
says:  "  The  operation  of  solutions  whose  composition  we  do 
not  know  can  be  judged  only  by  their  effects.  When  metaso- 
matic  replacement  takes  place  in  limestone,  it  is  generally  as- 
sumed that  lime-carbonate  goes  into  solution,  while  its  place  is 
taken  by  the  ore-substances, — that  is  to  say,  that  the  action  is 
molecular  substitution,  and  not  atomic;  but  it  is  conceivable 
that  the  change  should  begin  by  an  interchange  of  acidic  ele- 
ments— that  Si02  should  drive  out  CO2.  Subsequent  changes 
might  remove  the  lime-silicate  by  another  process  of  substitu- 
tion, since  it  is  more  soluble  than  silica;*  but  the  point  is  that 
C02  would  be  liberated,  and,  though  the  original  ore-solution 
were  free  from  C02,  it  would  immediately  become  charged 

*  In  the  Tintic  mines,  lime-silicate  does  not  appear  to  have  been  formed  ;  the 
silica  directly  replacing  the  lime-carbonate,  or  the  carbonate  of  lime  and  magne- 
sia, as  the  case  may  be. 


342  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

with  that  agent  and  exert  the  well-known  dissolving  power  of 
carbonic  acid  solutions.  In  this  way  a  solution  which  would 
have  but  feeble  power  in  other  rocks  may  in  limestone  set  up 
a  chain  of  reactions  that  would  intensify  its  effects.  .  .  .  Lime- 
stone contains  the  elements  for  self-destruction,  since  the 
breaking-up  of  one  lime-carbonate  molecule  may  cause  the 
solution  of  another;  and  as  this  cannot  be  said  of  any  other 
rock,  we  reach  a  possible  explanation  of  the  comparative  fre- 
quency of  ore-bodies  in  limestone.  The  dolomites  would,  of 
course,  present  similar  reactions."  Prof.  Church  continues, 
respecting  "  The  selection  of  a  favored  stratum  for  ore-deposi- 
tion. In  some  situations  the*  solutions,  before  reaching  the 
stratum  of  actual  ore-deposition,  must  have  passed  several 
strata  suitable  for  their  action,  if  they  had  possessed  from  the 
beginning  the  power  of  solution  which  they  showed  ultimately. 
.  .  .  Ore-solutions  exhibit  a  selective  power  which  is  extraordi- 
nary in  a  water  fully  supplied  with  dissolving  qualities,  but 
quite  explicable  in  a  solution  which  lacks  this  power."* 

Many  contributory  causes  have  in  all  probability  co-operated 
in  the  deposition  of  the  ore,  such  as  decrease  of  pressure  and 
reduction  in  the  temperature  of  the  solutions,  the  mingling  of 
mineral-bearing  waters  of  different  chemical  composition  enter- 
ing the  limestone  formation  through  distinct  fissured  belts,  etc.; 
but  the  important  factor  appears  to  have  been  the  great  solu- 
bility of  these  limestones  and  dolomites  in  the  waters  which 
brought  in  the  minerals,  joined  with  the  chemical  activity  of 
the  contained  hydrocarbons  released  in  the  dissolution  of  the 
rock. 

In  the  solution  of  the  limestone,  the  incidental  liberation  of 
large  volumes  of  carbonic  acid,  ever  dissolving  more  and  more 
of  the  rock,  set  free  a  constantly  renewed  supply  of  car- 
bonaceous matter,  whose  function  was  to  remove  all  free  oxy- 
gen and  reduce  the  sulphates  in  the  waters  to  sulphides.  At 
the  same  time,  the  calcium-  and  magnesium-carbonates,  when 
dissolved,  neutralized  the  acids  and  destroyed  the  chemical 
equilibrium,  so  that  the  mineral-saturated  waters  could  no 
longer  hold  the  metals  in  solution,  after  the  addition  of  the 
elements  derived  from  the  limestone.  The  combined  action  of 

*  Genesis  of  Ore-Deposits,  pp.  196,  197.     Trans.,  vol.  xxiii.,  595,  596. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  343 

the  carbon,  hydrogen,  lime  and  magnesia  contained  in  the 
rock  was  to  deoxidize  the  solutions  and  bring  them  to  the 
"  critical-point,"  when  deposition  of  the  ores  rapidly  took 
place.  - 

In  conclusion :  The  ores  of  primary  formation  in  the  Tintic 
mines  have  been,  in  most  of  the  occurrences,  deposited  from 
highly  heated  solutions  by  the  metasomatic  replacement  of 
the  limestone;  only  in  relatively  subordinate  amount  have 
the  metallic  sulphides  been  formed  by  crystalline  growth  in 
the  rock,  or  by  crystallization  in  the  interspaces  of  the  ore- 
bodies. 

In  the  instance  cited,  in  the  Uncle  Sam  mine,*  in  the  large 
body  of  steel-galena,  without  quartz,  replacing  the  fractured 
lime  strata,  the  deposition  seems  to  have  been  from  solutions 
either  free  from  silica,  or  more  probably  of  so  low  a  tempera- 
ture that  the  chemical  reaction  in  the  substitution  of  quartz  for 
the  lime-carbonate  could  not  take  place. 

In  Tintic,  the  limestones,  when  unaltered,  retain  the  included 
carbonaceous  matter  deposited  with  the  sediments.  In  the  ore- 
bodies,  all  forms  of  the  hydrocarbons  have  been  destroyed, 
either  in  the  primary  formation  of  the  minerals  or  in  the  sub- 
sequent oxidation;  the  deepest  mines  in  the  district  (1700 
and  2100  ft.,  vertical  depth)  not  having  reached  ground-water 
level. 

Whatever  may  have  been  the  role  of  the  volatile  hydrocar- 
bons in  the  original  creation  of  the  deposits,  no  evidence  has 
been  found  of  their  ever  having  been  present.  Tintic  district 
has  been  a  center  of  intense  volcanic  activity,  and  it  seems 
almost  inevitable  that,  with  the  presence  of  notable  quantities 
of  bituminous  matter  in  the  rocks,  volatile  hydrocarbons  would 
have  been  formed. 

Many  examples  might  be  given  of  limestones,  especially  of 
magnesian  limestones,  which  carry  more  or  less  organic  matter 
and  constitute  the  favored  geological  formations  in  the  selective 
deposition  of  the  ore.  The  zinc-  and  lead-deposits  of  Missouri 
and  the  lead-  and  copper-ores  of  Tintic  District,  Utah,  carrying 
silver  and  gold,  were  chosen,  owing  to  the  author's  more  de- 
tailed acquaintance  with  the  ore-deposits  of  those  regions. 

*  See  ante,  p.  340. 


344  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

Petroleum. 

The  occurrence  of  petroleum  in  the  Redington  quicksilver- 
mine,  New  Idria,  California,  is  reported  by  Luther  Wagoner.* 
He  says :  "  Mineral-oil  occurs  in  considerable  quantity,  a  barrel 
of  forty  gallons  being  collected  in  one  drift.  It  was  used  for 
lubrication  of  the  machinery." 

Prof.  Egleston,  writing  of  the  quicksilver-mines  in  northern 
California,  says  :  "  At  the  Rattlesnake  mine,  near  Pine  Flat, 
where  large  quantities  of  metallic  mercury  are  found,  the  rock 
contains  so  much  petroleum  that  it  has  been  necessary  to  make 
special  arrangements  to  burn  the  carbides  of  hydrogen,  since 
the  distillation  of  the  petroleum  causes  an  extra  quantity  of 
poor  soot  to  be  formed  in  the  condensation-chambers."f 

At  the  zinc-  and  lead-mines  near  Shullsburg,  Wisconsin,  thin 
partings  or  beds  of  brown  shale,  highly  charged  with  petro- 
leum, are  found  in  the  Trenton  limestone.  Prof.  Blake,  dis- 
cussing the  peculiar  occurrence  of  this  shale,  known  as  the  "  oil- 
rock,"  says  :  "  We  find  that  this  petroleum-shale,  this  horizon 
of  hydrocarbons,  is  to-day  the  chief  lower  horizon  of  deposi- 
tion of  the  lead-  and  zinc-ores.  Certainly,  if  this  shale  did  not 
influence  or  determine  the  original  primary  accumulation  of 
the  ores,  it  appears  to  have  exerted  a  very  important  influence 
upon  the  secondary  or  later  deposition,  from  solutions  perco- 
lating downwards."  J 

In  the  mines  at  Silver  Reef,  Utah,  an  oily  substance,  sup- 
posed to  be  petroleum,  is  reported  to  have  occurred  in  the  re- 
fractory ores  at  water-level.  § 

Rudolf  Keck  notes  the  association  of  organic  matter  with 
ore-deposits.  He  says  :  "  Organic  matter  occurs  in  the  state  of 
asphaltum  in  the  cinnabar  mines  in  the  Bavarian  Palatinate ; 
in  that  of  petroleum,  in  the  mines  of  California,  Nevada  and 
Hungary  ;  in  that  of  anthracite  and  graphite,  in  mines  in  Tran- 
sylvania, Portugal,  Derbyshire,  Calcutta,  Saxony,  Baden,  etc."|| 

*  "The  Geology  of  the  Quicksilver- Mines  of  California,"  by  Luther  Wagoner, 
Eng.  and  Min.  Jour. ,  vol.  xxxiv. ,  p.  334. 

f  "  Notes  on  the  Treatment  of  Mercury  in  North  California,"  by  T.  Egleston, 
Trans.,  in.,  273. 

J  William  P.  Blake,  Discussion  of  the  "Lead-  and  Zinc-Deposits  of  the  Missis- 
sippi Valley,"  Trans.,  xxii.,  631.  %  See  ante,  pp.  322-327. 

||  "  The  Genesis  of  Ore-Deposits,"  by  Kudolf  Keck,  Eng.  and  Min.  Jour.,  vol. 
xxxv.,  p.  3. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.       .  345 

Bitumen. 

The  occurrence  of  bitumen,  and  its  influence  in  the  forma- 
tion of  the  zinc-  and  lead-deposits  in  the  Cherokee  limestone, 
in  Southwest  Missouri,  has  already  been  discussed.* 

Becker  notes  the  existence  of  bitumen  in  the  Manhattan, 
Knoxville,  Phoenix,  Oathill,  Manzanita,  Great  Western  and 
Great  Eastern  quicksilver-mines,  and  also  at  Sulphur  Bank, 
California.  At  the  Phoenix  mine,  a  peculiar  non-oxygenated 
hydrocarbon  (napalite),  with  90  per  cent,  of  carbon  and  10  per 
cent,  of  hydrogen,  occurs  quite  abundantly. f 

Luther  Wagoner,  in  an  article  on  the  geology  of  the  quick- 
silver-mines of  California,  says :  "  Oil  (petroleum),  more  or  less 
oxidized,  is  observed  in  all  mines  of  quicksilver  on  this  coast, 
and  in  general  is  found  as  bitumen  or  a  thick  tar."J 

Prof.  Christy  thus  describes  the  occurrence  of  bitumen  at 
New  Almaden,  Cal. :  "  The  ore  at  New  Almaden  is  cinnabar. 
Native  quicksilver  occurs  also;  but,  as  a  rule,  in  small  quanti- 
ties only.  Pyrite  occasionally  accompanies  the  ore.  Bitumen 
is  quite  common,  sometimes  as  a  fragile,  black,  lustrous  solid, 
resembling  soft  bituminous  coal,  but  melting  easily,  like  tar ;  at 
other  times  it  occurs  in  the  vugs  of  the  gangue,  in  a  liquid 
state,  like  coal-tar.  I  have  found  lumps  of  apparently  pure 
cinnabar  from  the  New  Almaden  to  give  a  voluminous  residue 
of  pulverulent  charcoal,  when  subjected  to  sublimation  out  of 
contact  with  the  air.  This  would  seem  to  show  that  the  bi- 
tuminous substance  is  intimately  associated  with  the  cinna- 
bar.'^ 

Marsh-Gas  (CH4). 

In  the  quicksilver-mines  of  California  marsh-gas  was  discov- 
ered by  Becker.  In  the  Phoenix  mine,  on  the  150-  and  300-ft. 
levels,  inflammable  gas,  mainly  composed  of  marsh-gas,  issues 
from  cracks  in  the  rock.||  At  Sulphur  Bank,  California,  79 

*  See  ante,  pp.  305,  306. 

t  "  Geology  of  the  Quicksilver-Deposits  of  the  Pacific  Slope,"  by  Geo.  F, 
Becker,  U.  S.  Geol.  Surv.,  Monograph  xiii.,  pp.  371,  372. 

J  "The  Geology  of  the  Quicksilver-Mines  of  California,"  by  Luther  Wagoner, 
Eng.  and  Min.  Jour.,  vol.  xxxiv.,  p.  334. 

$  "  Quicksilver- Reduction  at  New  Almaden,"  by  Samuel  B.  Christy,  Trans., 
xiii.,  547-548. 

||  ''Geology  of  the  Quicksilver- Deposits  of  the  Pacific  Slope,"  by  George  F. 
Becker,  p.  373. 


346  •    THE    CHEMISTRY    OF    ORE-DEPOSITION. 

parts  of  marsh-gas  were  found  in  1000  parts  of  the  gases  es- 
caping with  the  ore-depositing  waters.* 

Flows  of  gas  under  heavy  pressure  were  struck  in  the  deeper 
levels  of  the  Silver-Islet  mine,  Lake  Superior.  Subsequently, 
in  extending  the  levels,  vugs  and  cavities  in  the  vein  were 
found,  lined  with  crystals  of  galena  and  calcite,  in  which  the 
gas  had  probably  been  stored.  In  sinking  the  shaft,  gas  was 
also  encountered  in  the  slate,  and  it  appears  to  have  per- 
vaded the  country-rock  below  the  8th  level  (440  ft.,  vertical 
depth).  The  gas  was  associated  with  small  flows  of  strong, 
acrid  mineral-water,  carrying  much  calcium  chloride.  It 
burned  with  a  purple,  blue,  or  yellowish  flame,  and  was  sup- 
posed to  be  light  carburetted  hydrogen,  but  it  was  never 
analyzed,  f 

Small  quantities  of  hydrocarbon-gas  are  stated  by  Mr.  B. 
Tibbey  to  have  been  struck  in  following  the  vein  on  the  300-ft. 
level  of  the  Illinois  mine,  Walkerville,  Butte  City,  Montana. 
The  gas  burned  with  a  bright-yellow  flame,  like  ordinary  il- 
luminating gas.  This  occurrence  is  remarkable,  as  the  vein 
occurs  in  granite. 

Review  of  the  Action  of  Volatile  Hydrocarbons. — In  the  Joplin, 
Mo.,  mines,  the  greater  part  of  the  bitumen  set  free  by  the  ex- 
tensive subterraneous  erosion  of  the  lime  strata  is  still  pre- 
served in  the  ore-bodies  below  water-level,  owing  to  the  primary 
deposition  having  been  effected  by  mineral-solutions  of  normal 
temperature.  The  same  is  also  true  of  the  petroleum  occurring 
with  the  zinc-ore  in  the  oil-rock  in  the  Trenton  limestone  in 
Wisconsin,  to  which  reference  has  been  made.  But  in  many 
ore-deposits  in  other  mining-regions  the  heat  accompanying 
the  deposition  has  been  so  great,  and  the  chemical  activities  so 
intense,  that  every  trace  of  volatile  hydrocarbons  has  been  de- 
stroyed. 

Petroleum  contained  in  the  strata  may  be  decomposed  by 
(1)  destructive  distillation,  due  to  the  earth-temperatures  or  to 
the  heat  of  the  ascending  mineral-solutions;  (2)  by  oxidation, 
the  carbon  and  hydrogen  forming  carbon-dioxide  and  water; 
and  (3)  by  the  action  of  sulphur,  which  dehydrogenizes  the  oil. 

*  Ibid.,  p.  258. 

f  "  The  Silver-Islet  Mine  and  Its  Present  Development,"  by  Francis  A.  Lowe, 
Eng.  and  Min.  Jour.,  vol.  xxxiv.,  pp.  320-323.  See  also  ante,  p.  313. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  347 

Petroleum  and  similar  hydrocarbons,  when  heated  and  sub- 
jected to  the  action  of  sulphur  at  temperatures  (in  the  case  of 
the  heavier  oils)  far  below  that  at  which  distillation  occurs,  are 
rapidly  decomposed,  with  formation  of  sulphuretted  hydrogen 
and  of  oils  with  a  greater  proportion  of  carbon  than  the  original 
oil ;  or,  if  the  sulphur  be  in  excess,  carbon  is  in  some  instances 
deposited. 

The  role  of  the  volatile  hydrocarbons  in  the  primary  forma- 
tion of  mineral-deposits,  especially  where  the  deposition  is  due 
to  igneous  disturbances,  has  not  received  the  attention  it  de- 
serves. Investigation  is  needed  of  the  action  that  marsh-gas 
and  other  hydrocarbon-gases  exert  in  the  deposition  of  ores; 
particularly  in  the  formation  of  deposits  of  cinnabar,  which  are 
frequently  associated  with  bituminous  shale,  bitumen  and  vola- 
tile hydrocarbons. 

Marsh-gas  has  a  theoretic  reducing  power  one-half  that  of 
hydrogen  and  fifty  per  cent,  greater  than  that  of  pure  carbon. 
In  the  formation  of  ore-deposits,  directly  induced  by  igneous 
action,  temperatures  must  inevitably  occur  in  the  depths  of  the 
strata,  such  that  gaseous  hydrocarbons  would  act  with  great 
energy  in  the  deoxidation  and  precipitation  of  the  metals. 
Under  like  conditions,  petroleum,  and  the  volatile  carbon  com- 
pounds with  high  boiling-points,  would  exert  a  reducing  power 
but  little  inferior,  and,  from  the  high  specific  gravity  of  their 
vapor,  would  displace  steam  and  all  other  gases  of  less  relative 
weight. 

VIII.  THE  RELATIVE  REDUCING  POWER  OF  MINERALS. 

Calculation  of  the  Theoretic  Reducing  Powers  of  Various  Organic  and 
Inorganic  Mineral  Substances  usually  Occurring  in  Association 
with  Ore-Deposits,  Based  upon  the  Weight  of  Oxygen  Consumed. 

The  quantitative  value,  or  amount  of  work  accomplished  in 
the  formation  of  ore-deposits  by  the  various  reducing  sub- 
stances, is  measured  by  the  weight  of  oxygen  with  which  they 
unite.  This  work  of  deoxidation  may  be  termed  the  "duty" 
of  the  reducing  agent. 

In  calculating  this  duty  for  the  more  common  organic  and 
inorganic  minerals  which  occur  in  ore-bodies  or  in  strata 
in  which  ores  were  formed,  or  into  which  they  were  intro- 


348  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

duced  by  the  waters,  either  in  the  original  deposition  or  in  the 
secondary  enrichment  of  the  deposits,  it  has  been  found  more 
convenient  to  make  the  values  relative,  assuming  hydrogen,  the 
most  powerful  deoxidizing  agent,  to  have  a  value  of  100. 
Let  R  represent  the  relative  reducing  power,  or  duty,  of  any 

mineral  substance. 
Q  be  the  weight  of  oxygen  consumed  by  one  part  of  the 

mineral. 
S  be  the  weight  of  the  mineral  required  to  unite  with  one 

part  of  oxygen. 
P  be  the  weight  of  hydrogen  which  combines  with  100 

parts  of  oxygen. 

The  value  of  Q  may  be  determined  in  each  case  from  the 
chemical  reactions  which  take  place. 
Thus,  for  hydrogen, 

2H  +  0  =  H20, 
2  +  16=18, 

whence,  by  proportion,  the  weight  of  oxygen  consumed  by  I 
part  of  hydrogen  is  determined. 

2  :  16  ::  1  :  Q=  8.00. 

R  has  been  assumed  for  hydrogen  as  100. 
In  the  case  of  carbon,  the  reaction  is 


12  -t-  32  =  44, 

whence,  12  :  32  :  :  1  :  Q  =  2.6666. 

The  relative  power,  or  duty,  of  carbon  compared  with  hydro- 
gen is 

8  :  2.6666  :  :  100  :  .£=33.33. 

For  oxygen  the  value  of  P  is  determined  from  the  weight  of 
hydrogen  that  unites  with  one  atom  of  oxygen  : 

0-f  2H  =  H20, 
16  :  2  ::  100  :  P=  12.5. 

P  is  a  constant  and  always  a  minus  quantity;  the  oxygen 
combined  with  a  mineral  substance  diminishing  its  reducing, 
power. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  349 

,  Q  and  S  are  determinable  by  the  following  formulas  : 


_,       =  -,       -. 

8  100'  §' 

whence,  by  substitution, 

«-  "l         1      _12.5  1  r>_12.5 

=    ~~  --       r= 


100 

From  the  above  it  is  seen  that  in  assuming,  for  convenience, 
the  value  of  R  for  hydrogen  as  100,  it  was  equivalent  to  multi- 
plying the  corresponding  value  of  Q  (=  8)  by  12.5.  Conse- 
quently the  several  values  of  R,  being  calculated  for  equal 
weights  of  the  mineral  substances,  are  in  each  instance  the 
weight  of  oxygen  which  is  consumed  by  12.5  parts  of  the 
reducing  agent.  Thus,  12.5  parts  of  carbon  consume  33.33 
parts  of  oxygen,  etc. 

The  "  duty  "  of  any  compound  substance  is  the  sum  of  the 
reducing  powers  of  the  elements  of  which  it  is  composed. 
Thus,  for  the  hydrocarbons  : 

Let  a  =  the  percentage  of  carbon, 
b  =    "  "  "  hydrogen, 

c  =    "  "  "  oxygen. 

Then  R  =  (33.33  a  +  100  b)  —  12.5  c. 

By  a  formula  of  this  kind  R  can  be  calculated  directly  from 
the  percentage-composition  of  any  substance.  Even  in  the  com- 
plex metallic  sulphides,  arsenides,  etc.,  R  may  be  calculated 
from  the  composition  by  substituting  in  the  formula  the  value 
of  R  for  sulphur,  arsenic,  etc. 

For  carbon-monoxide  the  value  of  R  may  be  calculated  from 
the  percentage-composition:  carbon,  42.86;  oxygen,  57.14. 

0.4286  X  33.33  =  14.28 
Less  0.5714  x  12.5    =    7.14 

7.14  =  JR. 
Or  from  the  equations  and  proportions  : 

CO  +  O  =  CO,, 

28+16  =  44. 

28  :  16  ::  1  :  §=0.5714, 

8  :  0.5714  ::100  :  ^  =  7.14. 


350  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

Marsh- Gas, CH4. — Marsh-gas  (methane) belongs  to  the  paraffin 
series  of  volatile  hydrocarbons ;  its  composition  is 

Carbon,  .        .     •   ..       .        .        .        .        .       '.        .        .      75.00 

Hydrogen,      .        .        .        .        .        .        .        .        .        .      25.00 


100.00 

By  oxidation,  marsh-gas  forms  carbonic  acid  and  water,  thus: 


16  :  64  ::       1  :  Q=    4.00. 
8  :     4::  100  :  R=  50.00. 
Or,  calculated  from  the  composition, 


33.33  X  0.75  =  25.00. 
100.00  X  0.25  =  25.00. 


Petroleum.  —  American  petroleum  is  in  great  part  a  mixture 
of  hydrocarbon  oils  of  the  paraffin  series,  represented  by  the 
formula  CnH2n4.2.  The  heavier  oils  average,  approximately, 
carbon,  85  per  cent.;  hydrogen,  15  per  cent;  corresponding 
very  nearly  to  the  formula,  C]6H34.  Assuming  that  the  carbon 
is  completely  oxidized  to  carbonic  acid,  and  the  excess  of  hydro- 
gen to  water  : 


from  which  R  =  43.36. 

Ititumen.  —  With  bitumen  is  included  mineral-tar,  maltha,  and 
the  solid  oxygenated  hydrocarbons,  such  as  grahamite.  Their 
composition,  while  variable,  usually  falls  within  the  limits  of  the 
analyses  No.  1  and  No.  2  : 

No.  1.  No.  2.  No.  3. 

Carbon,      .  ,      ..-       .        .        .    80.00  .        89.00  81.00 

Hydrogen,.         ....     14.00  11.00  10.00 

Oxygen,     .         .        .         .        .,    6.00  0.00  9.00 

100.00  100.00  100.00 

The  value  of  R  for  analysis  No.  1  =  39.92,  and  for  analysis 
No.  2  —  40.67.  Analysis  No.  3,  of  grahamite  (gilsonite),  with 
but  10  per  cent,  of  hydrogen,  gives  a  value  for  R  of  35.88.  In 
the  above  analyses  it  is  probable  that  some  nitrogen  and  sul- 
phur are  included  with  the  oxygen,  so  that  the  deduction  made 
for  oxygen  is  slightly  too  great. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  351 

Bituminous  Coal. — The  average  composition  of  bituminous 
coal  may  be  stated  as  falling  within  the  limits  of  the  analyses 
1  and  2: 

No.  1.  No.  2. 

Carbon, 81.00  88.00 

Hydrogen, 4.00  7.00 

Oxygen, 15.00  5.00 


100.00  100.00 

The  duty  calculated  from  the  composition  in  the  above  anal- 
yses is.  for  coal  No.  1,  jR  =  29.13;  and  for  coal  No.  2,  R  = 
35.71. 

Lignite.  —  The  composition  of  lignite  is  extremely  variable  and 
is  much  affected  by  the  amount  of  decomposition  it  has  under- 
gone. Assuming  that  the  analyses  given  below  represent  the 
ordinary  limits  of  composition,  the  value  of  H  for  lignite  "No.  1 
is  19.50,  and  for  No.  2,  28.83. 

No.  1.  No.  2. 

Carbon,      .        .        .        *        .        .        .60.00  73.00 

Hydrogen,         ...        „        .        .       4.00  7.00 

Oxygen,     *        .         .        .        .     .   f         .     36.00  20.00 

100.00  100.00 

Native  Humus  Acid.  —  Dana  gives  the  composition  of  humus 
acid  from  Bohemian  brown-coal  as  C^H^O^,  which  corresponds- 

to: 

Carbon,.  .  •.  .        ,.        .        .        .        .        .         .  55.31 

Hydrogen,  .  .  -  .         .        .                 ..       .        .        .  4.61 

Oxygen,  .  .  ........  40.08 

loo.oa 

998  :      1440  :  :       1  :  Q  =    1.4428. 
8  :  1.4428  :  :  100  :  It  =  18.04. 

Or,  calculated  from  the  composition, 

0.5531  X    33.33  =  18.44 

0.0461x100.00=    4.61 

23J05 

Less  0.4008  X    12.5    =    5.01 


Sulphur.  —  Sulphur  in  ore-deposits  may  oxidize  under  cer- 
tain conditions  to  sulphurous  acid,  but  usually  sulphuric  acid 
is  formed. 


352  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

S  -f  02  =  S02;  whence,  R  =  12.50 

,R  =  18.75 

S  -f-  03  =  S03;  whence  J  Q  =  1.50 

Is  =  0.667. 

Combined  sulphur  may,  for  convenience  in  calculating  the 
duty  of  sulphides,  be  regarded  as  oxidizing  to  S04 ;  as  if  all  the 
oxygen  combined  with  the  sulphur  and  none  with  the  base, 
giving  the  values  E  =  25.00 ;  Q  =  2.00 ;  £  =  0.50. 

Sulphuretted  Hydrogen. — The  complete  oxidation  of  sulphu- 
retted hydrogen  forms  sulphuric  acid,  H2S  -(-  O4  =  H2S04,  from 
which  H  ==  23.53.  When  oxygen  is  deficient,  water  is  formed, 
with  separation  of  sulphur.  The  reaction  then  is : 

H2S  '+0  =  84-  H20 ;  whence,  R  =  5.88. 

Pyrite  and  Marcasite. — Three  distinct  reactions  may  occur  in 
the  oxidation  of  pyrite  and  marcasite  (FeS2)  : 

(1)  With  liberation  of  sulphur,  and  formation  of  ferrous-sul- 
phate— 

FeS2  -f  04  =  S  -f  FeS04 ;  whence,  R  =  6.67 ;  Q  =  0.533 ; 

S  =  1.876. 

(2)  With  formation  of  ferrous  sulphate  and  free  sulphuric 
acid,  one  atom  of  sulphur  may  be  -regarded  as  oxidizing  to 
S03,  the  other  to  S04— 

FeS2  -|-  07  -f  H20  =  FeS04  -f  H2S04;  whence,  JR  =  11.67; 
§  =  0.933;  £=1.072. 

(3)  When  the  oxidation  of  pyrite  takes  place  with  excess  of 
air,  ferrous  sulphate  is  first  formed,  and  by  a  complicated  series 
of  reactions,  with  further  absorption  of  oxygen,  the  final  result 
is  the  formation  of  limonite  and  sulphuric  acid.     The  equation 
may  be  written : 

4FeS2  +  030  -f  11H20  ==  2Fe203,3H20  +  8H2S04, 

Giving  R  =  12.50 ;  Q  =  1.00 ;  S  =  1.00. 

In  the  substitution  of  blende  and  galena  for  pyrite  in  secondary 
deposition,  the  reactions  corresponding  to  equation  (1)  may  be 
expressed : 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  353 

FeS2  +  ZnSO4  =  ZnS  -f-  FeS04  -f-  S. 
FeS2  -f  PbS04  =  PbS  +  FeS04  +  S. 

Pyrite  also  deoxidizes  sulphuric  acid,  with  the  formation  of 
sulphuretted  hydrogen  and  sulphur  : 

FeS2  -f  H2S04  =  H2S  +  S  +  FeS04. 

The  reduction  of  zinc-  and  lead-sulphate  and  lead-carbonate 
by  pyrite  is  shown  by  the  following  equations,  corresponding  to 
•equation  (2) : 

FeS2  -f  ZnS04  +  H20  +  0,  =  ZnS  +  FeS04  +  H,S04. 
FeS2  -f  PbS04  +  H20  +  0,  =  PbS  -f  FeS04  +  H2S04. 
FeS2  +  PbC03  +  H20  +  03  =  PbS  -f  FeS04  -f  H2CO3. 

In  the  presence  of  an  excess  of  air,  reactions,  corresponding 
to  equation  (3),  take  place  in  the  reduction  of  these  soluble 
salts  of  zinc  and  lead,  as  follows : 

4FeS2  +  ZnS04  +  11H20  +  026  =  ZnS  +  2Fe203,3H20  +  8H2S04. 
4FeS2  +  PbS04  +  11H20  +  O26  =  PbS  -f  2Fe203,3H20  +  8H2S04. 
4FeS2-f  PbCO,  +  11H20  -f  026  =PbS  +  2Fe203,3H2O  +  H2C03 

-f  7H2S04. 

Arsenic  and  Antimony. — The  values  of  R  for  arsenic  and  anti- 
mony are  obtained  from  the  following  equations  : 

2 As  +  O6  =  As205;  whence,  R  =  6.67. 

2Sb  -f  O3  =  Sb203 ;  whence,  R  =  2.50. 

Arsenopyrite. — The  composition  of  arsenopyrite,  FeAsS,  is  as 
follows : 

Iron,      .         .        .        .        .        .        ....        .        .     34.30 

Arsenic, .      '..      .         .     46.00 

Sulphur,         .         .        .        ...        ....        .     19.70 

100.00 

The  value  of  R  may  be  calculated  either  from  the  reaction, 
the  arsenic  oxidizing  to  As2OB,  or  from  the  composition,  as 
follows : 

2FeAsS  +  013  =  As205  +  2FeS04. 

23 


354  THE    CHEMISTRY    OF    ORE-DEPOSITION. 


326  :          208  ::  1      :  Q  = 
8  :       0.638  :  :  100  :  E  =  7.98. 

0.197X25        =4.92 
0.46    X    6.67=3.06 


Enargite.  —  For  enargite,  CusAsS4,  or  3Cu2S,  As2S5,  the  com- 
position and  the  computations  are  as  follows  : 

Copper,  .        .        .        .        .        .        .     48.3 

Arsenic,          .         .         .         .         .         .         .         .         .         .19.1 

Sulphur,         .         .        .        .        .      .  i"  .     .        .        .         .     32.6 


100.0 

3Cu2S,  As2S5  +  2H2O  +  035  =  As2O5  +  6CuSO4  +  2H2S04. 

One-fourth  of  the  sulphur,  or  8.15  per  cent.,  is  oxidized  to 
S03,  and  the  remainder  (24.45  per  cent.)  to  S04. 

786.4:        560  ::  1       :  Q  =  0.7121. 
8     :  0.7121  ::  100  :  .ft  =8.90. 

0.0815  X  18.75  =  1.53 
0.2445  X  25.00  =6.11 
0.191  X  6.67  =  1.27 

8^91=  £. 

Stibnite. — For  stibnite,  Sb2S3,  the  composition  and  the  compu- 
tations are  as  follows  : 

Antimony,     .         .         .         .         .  •;    V        .        .         .         .71.4 
Sulphur,        .  .      .         .        ..        .,       .        ,        .        .         .     28.6 

100.0 

Dana  gives  the  product  of  the  oxidation  of  stibnite  as  valen- 
tinite,  Sb203. 

Sb2S3  +  012+  3H20  =^Sb8Os  +  3H2S04. 
336  :  192  ::  1       :  Q=  0.5714. 

8  :       0.5714::  100  :  ^  =  7.15. 
Or,  calculated  from  the  composition, 

0.286  X  18.75=5.36 
0.714  x     2.50=  1.78 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  355 

Pyrrhotite. — Similarly  for  pyrrhotite,  FenS12 : 

FenS12  +  047  +H20  =  llFeS04  +  H2S04, 

Giving  R  =  9.40 ;    §=0.752. 

Ferrous  Sulphate. — The  reactions  in  the  case  of  ferrous  sul- 
phate, FeS04,  are  as  follows  : 

In  the  oxidation  of  pyrite  and  marcasite,  a  mixture  of  ferrous 
sulphate  and  free  sulphuric  acid  is  first  formed.  Weed*  gives 
the  products  of  the  further  absorption  of  oxygen  as 

H2S04,Fe(OH)3  and  Fe2(S04)3. 
The  reaction  that  takes  place  may  be  written : 

6FeS04  +  2H2S04  +  4H20  +  03  =  2(H2S04,  Fe(OH)3)  + 
2(Fe2(S04)3)  +  H20. 

Six  parts  of  ferrous  sulphate  absorb  3  parts  of  oxygen ;  or, 
by  reduction,  2  parts  of  ferrous  sulphate  absorb  1  part  of 
oxygen. 

304  :  16  ::       1  :  §=0.05263. 

8  :     0.05263  ::  100:  E=  0.66. 
£=19.1. 

Summary. 

The  following  table  of  comparative  reducing  powers  gives 
the  quantitative  value,  or  gross  amount,  of  the  work  done  by 
each  of  the  deoxidizing  agents.  It  is  necessary,  however,  to 
supplement  these  theoretic  results  by  observations  in  the  field, 
especially  of  ore-deposits  undergoing  decomposition  and  re- 
formation ;  and  also  by  experimental  research  in  the  labora- 
tory, in  order  to  estimate  accurately  in  each  particular  instance 
the  chemical  energy,  or  velocity  with  which  the  action  takes 
place. 

Fortunately,  with  respect  to  the  greater  number  of  the  more 
important  reducing  substances  commonly  occurring  in  ore- 
deposits,  the  gravimetric  power,  or  duty,  and  the  chemical 

*  "The  Enrichment  of  Gold-  and  Silver- Veins,"  by  Walter  H.  Weed,  Genesis 
of  Ore-Deposits,  p.  478  ;  Trans.,  xxx.,  429,  430. 


356  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

energy  run  nearly  parallel ;  so  that  one  may  be  taken  as  the 
measure  of  the  other. 

The  results  of  these  calculations  confirm  the  observations 
made  in  the  zinc-  and  lead-mines  of  the  Joplin,  Mo.,  region,  in 
the  investigation  of  the  secondary  formation  of  the  ores,  of 
the  relative  order  of  the  reducing  powers  of  the  principal  de- 
oxidizing agents,  viz. :  1,  bitumen  ;  2,  bituminous  coal  and  car- 
bonaceous shales ;  3,  marcasite  and  pyrite  ;  4,  blende ;  5,  ga- 
lena. 

Ferrous  sulphate  appears  to  be  exceptional ;  notwithstanding 
the  extreme  low  duty  (0.66),  and  notwithstanding  that,  inform- 
ing ferric  sulphate,  19.1  parts  of  the  salt  combine  with  only 
one  part  of  oxygen,  yet  in  the  zone  of  oxidation,  where  the 
chemical  activities  have  full  play  in  the  breaking-up  of  an  ore- 
body,  it  fulfils  a  special  mission,  at  once  oxidizing  and  reduc- 
ing. Its  chemical  energy  is  such  that  it  reduces  cuprous  oxide 
to  the  metallic  state ;  a  change  which  none  of  the  other  deoxi- 
dizing agents  usually  found  in  ore-bodies  are  able  to  accom- 
plish.* Further,  its  field  of  operation  is  the  zone  of  oxidation 
and  that  border-land  where  the  zone  of  oxidation  merges  into 
the  zone  of  reduction. 

This  low  quantitative-value  is  in  many  instances  more  than 
offset  by  the  large  amount  of  ferrous  and  ferric  sulphates  con- 
tinuously supplied  by  the  progressive  oxidation  of  the  pyrite 
in  the  ore-deposits.  The  mine-waters  lixiviating  the  decom- 
posing ore,  although  the  volume  of  the  flow  may  be  consider- 
able, are  frequently  strongly  acid  from  the  free  sulphuric  acid 
and  iron  sulphates  held  in  solution. 

In  conclusion,  the  hydrocarbons,  combining  the  highest 
quantitative  deoxidizing  power  with  an  intense  chemical  activ- 
ity, are  the  most  powerful  of  all  reducing  agents.  The  action 
of  the  solid  oxygenated  hydrocarbons,  bitumen,  bituminous 
coal,  and  the  lignitic  matter  finely  disseminated  in  shales,  is 
greatly  accelerated  by  the  facility  with  which  these  carbon- 
compounds,  when  in  powder,  are  carried  by  the  circulating 
waters  into  every  part  of  the  ore-bodies. 

*  "  Enrichment  of  Gold-  and  Silver- Veins,"  by  Walter  H.  Weed,  Trans.,  xxx., 
431 ;  Genesis  of  Ore-Deposits,  p.  480. 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  357 

TABLE. 

THE  RELATIVE  REDUCING  POWER,  It,  OR  DUTY,  OF  EQUAL 
WEIGHTS  OF  THE  ORGANIC  AND  INORGANIC  MINERAL  SUB- 
STANCES USUALLY  OCCURRING  IN  THE  ORE-BODIES,  OR  IN 
THE  WALL-ROCK,  OR  INTRODUCED  WITH  THE  CIRCULATING 
WATERS;  HYDROGEN  BEING  ASSUMED  AS  100. 

Hydrogen   (occurs   combined   with   carbon),  oxi-         It. 

dized  to  H,O, •  .  •  100.00 

Marsh-gas,  CH4  (carbon  75  per  cent.,  hydrogen  25 

per  cent),  oxidized  to  H2CO3+H20,          .         .       50.00 
Petroleum,  CnH2n+2  (carbon  85  per  cent,  hydro- 
gen 15  per  cent),     .         .         .         .         .         .       43.36 

Bitumen  (carbon  89  per  cent.,  hydrogen  11  per 

cent,  oxygen  0  per  cent),         .         •         *         •       40.67 
Bitumen  (carbon  80  per  cent,  hydrogen  14  per 

cent.,  oxygen  6  per  cent),         ...         .       39.92 

Bitumen  (grahamite)  (carbon  81  per  cent.,  hydro- 
gen 10  per  cent,  oxygen  9  per  cent),       *         .       35.88 
Bituminous  Coal  (carbon  88  per  cent,  hydrogen 

7  per  cent,  oxygen  5  per  cent.),  .  .  .  35.71 
Bituminous  Coal  (carbon  81  per  cent,  hydrogen 

4  per  cent.,  oxygen  15  per  cent),  .  .  .  29.13 
Carbon  (graphite,  etc.),  oxidized  to  C02,  ,  .  33.33 
Carbon,  oxidized  to  CO,  .  .  ,  .  .  .  16.67 
Lignite  (carbon  73  per  cent,  hydrogen  7  per  cent., 

oxygen  20  per  cent), 28.83 

Lignite   (carbon    60   per    cent.,    hydrogen   4   per 

cent,  oxygen  36  per  cent),      ...        .         .        ,.       19.50 

Native    Humus    Acid,    C46H46O25   (carbon    55    per 
cent,  hydrogen    5    per   cent,   oxygen  40  per 
cent),      .         .  , ......       .         .         .       18.04 

Sulphur  (combined),  oxidized  to  S04,    .         .         .       25.00 
Sulphur,  oxidized  to  S03,      .         .  .      .         .         .       18.75 

Sulphur,  oxidized  to  S02,  .  .  '.--  .  .  12.50 
Sulphuretted  Hydrogen,  H2S,  oxidized  to  H2S04>  .  23.53 
Sulphuretted  Hydrogen,  H2S,  oxidized  to  H20-f  S,  .  5.88 

(oxidation  of  Fe  to\ 
2Fe203,3H20;  andS         12.50 
to  SO,  / 


358  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

Pyrite  and  Marcasite,  oxidation  to  FeS04,  .  .  11.67 

Pi/rite  and  Marcasite,  oxidation  to  FeS04  and  S,  .  6.67 

Pyrrhotite,  FenSw,  oxidized  to  FeS04  and  H2S04,  9.40 
Enargite,  Cu3AsS4,  oxidized  to  As20_,  CuS04  and 

HJ304,  .  .  .  .  °  .  .  .  8.90 
Chalcopyrite)  CuFeS2,  oxidized  to  CuS04  and 

FeS04, !  8.72 

Covellite,  CuS,  oxidized  to  CuS04,  •  .  .-  .  8.39 

Blende,  ZnS,  oxidized  to  ZnS04,  .  .  .  8.25 
Arsenopyrite,  FeAsS,  oxidized  to  As205  and 

FeS04,  .  7.98 

Calcium  Disulphide,  CaS2,  oxidized  to  CaS04  and  S,  •  7.69 

Stibnite,  Sb2S3,  oxidized  to  Sb203  and  H2S04,  .  7.15 

Carbon  Monoxide,  CO,  oxidized  to  C02,  .  .  7.14 
Bvrnite,  Cu3FeS3,  oxidized  to  Cu2S04,  CuS04  and 

FeS04,     .......         ;  7.01 

Arsenic,  oxidized  to  As205,  .  -.  .  •  .  .  .  6.67 
Tetrahedrite,  4Cu2S.Sb2S3,  oxidized  to  Cu2S04, 

CuS04  and  Sb203,  .  '.  .  .  .  6.39 

Iron,  oxidized  to  Fe203,  .->  <  .  •  .  5.36 

Iron,  oxidized  to  Fe304,  '\  .  .  ,.  .  4.76 

Iron,  oxidized  to  FeO,  .  .  .  .  .  3.58 

Chakocite,  Cu2S,  oxidized  to  Cu2S04,  .  ....  5.04 

Galena,  PbS,  oxidized  to  TbS04, .  .  •  .  v  3.35 

Tellurium,  oxidized  to  Te02,  '  .  .  .  •  . .;  .  3.20 

Copper,  oxidized  to  CuO,  .  .  .  .  ,„  3.15 

Copper,  oxidized  to  Cu20,  .  .  .  .  .  1.58 

Antimony,  oxidized  to  Sb203,  .  .  .-  .  2.50 

Rhodochrosite,  MnC03,  oxidized  to  Mn02,  -.  .  1.75 

Siderite,  FeC03,  oxidized  to  Fe203,  .  .  .  0.86 

Ferrous  Sulphate,  FeS04,  oxidized  to  Fe2(S04)3,  .  0.66 
Magnetite,  Fe304,  oxidized  to  Fe203,  .  .  .  .  0.46 


THE  CHEMISTRY  OF  ORE-DEPOSITION.  359 

DISCUSSION. 

( Trans.,  xxxiii.,  1065.) 

JOHN  A.  CHURCH,  New  York,  N.  Y. :  Professor  Jenney  has 
performed  a  notable  service  in  presenting  this  summary  of  the 
steadily  increasing  body  of  observation  on  the  presence  of  carbon 
in  rocks  of  all  kinds  and  its  probable  influence  upon  ore-deposi- 
tion, and  in  formulating  a  mode  of  comparing  directly  the  relative 
resistance  of  minerals  to  oxidation,  as  well  as  their  reducing- 
power,  and  the  protective  action  which  minerals  having  higher 
reducing-powers  exert  in  preventing  the  oxidation  of  associated 
minerals  which  possess  relatively  lower  affinities  for  oxygen. 

I  have  had  an  opportunity  of  observing  a  vein  which  falls 
within  the  scope  of  his  interesting  discussion.  The  vein  at  Ku 
Shau  Tzu,  Mongolia,  lies  directly  across  a  contact  of  limestone 
and  overlying  bituminous  shales.  Probably  it  occupies  a  com- 
pression-fissure. The  shale  has  been  reduced  to  such  a  condi- 
tion of  non-coherence  that  much  of  it  can  be  crushed  in  the 
hand,  producing  a  handful  of  angular  fragments  resembling 
beech-nuts  in  shape  and  size. 

In  the  limestone  the  metals  are  principally  in  argentiferous 
galena  with  some  pyrite  and  blende;  but  the  latter  two  are 
very  subordinate  in  quantity  to  the  galena.  In  short,  it  is  an 
every-day  lead-vein  in  limestone,  with  siliceous  limestone 
gangue.  It  is  one  of  those  veins  in  which  the  ore  is  not  con- 
tinuous, but  consists  of  a  band  in  the  country-rock  in  which 
seams  of  lead  sulphide  begin  at  one  wall  and  cross  in  a  bent 
form,  increasing  in  thickness,  to  the  other  wall,  where  they 
thin  out  and  end.  This  may  indicate  torsional  stress,  but  the 
shape  of  the  lenses  points  to  some  other  action.  They  often 
ran  nearly  parallel  to  the  hanging-wall  for  a  considerable  dis- 
tance and  crossed  the  vein  on  a  moderate  angle,  but  turned 
sharply  along  the  vein  on  approaching  the  foot-wall.  The  inter- 
mediate rock  contains  nodules,  bunches  and  specks  of  ore,  and 
the  lenses  vary  exceedingly  in  size,  shape  and  position  in  the 
vein. 

In  the  bituminous  shale  the  deposition  of  ore  is  not  at  all 
like  that  in  the  limestone.  The  minerals  in  the  shale  are  tetra- 
hedrite  and  native  silver,  the  latter  occurring  in  fine  scales  and 
sheets  of  pure  metal,  weighing  from  50  to  possibly  100  oz. 
I  cannot  speak  of  these  larger  sheets  from  much  acquaintance, 


360  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

for  all  but  one  of  them  were  stolen  by  the  miners,  but  the 
metallic  silver  in  scales  and  sheets  was  an  important  part  of 
the  ore. 

It  is  necessary  to  exclude  the  notion  of  secondary  deposition 
at  Ku  Shau  Tzu,  because  the  influence  of  the  shale  with  its 
superabundant  store  of  powerful  reducing-agent  should  have 
gathered  to  itself  every  metal  taken  into  solution  by  descending 
surface-waters.  Whether  that  was  the  case  immediately  at  the 
surface  I  do  not  know,  as  the  mine  was  an  old  one  when  I  first 
saw  it.  The  absence  of  galena,  blende  and  pyrite  from  the 
shale,  at  depths  of  300  and  400  ft,  indicates  that  secondary  de- 
position, if  present  at  any  time,  did  not  reach  so  far;  and  this 
was  to  be  expected  from  the  reducing-power  of  the  shale  at  the 
surface. 

I  considered  that  the  conditions  indicated  deposition  from  a 
solution  rising  through  the  limestone  first  and  afterward 
through  the  shale  which  once  covered  the  lime-rock,  though 
now  it  is  tilted  and  partially  eroded.  The  limestone  precipi- 
tated what  it  could,  and  the  abundant  store  of  carbon  in  the 
shale  perhaps  took  the  last  traces  of  metal.  But  this  explana- 
tion is  not  without  its  difficulties  when  applied  to  the  lime- 
stone, however  confident  we  may  be  of  the  reducing-powers 
of  the  shale. 

The  feeble  reducing-power  to  which  galena  yields — only 
3.35  per  cent,  of  II,  according  to  Prof.  Jenney — explains  its 
presence  in  the  limestone  well  enough,  but  why  should  this 
rock  precipitate  also  blende  (8.25  per  cent.)  and  pyrite  (11.67 
per  cent.),  while  it  left  tetrahedrite  (6.39  per  cent.)  to  the 
shale  ?  The  reduction  of  metallic  silver  in  the  shale  is,  of 
course,  not  surprising. 

There  must  have  been  some  other  selective  agency  than  mere 
position  or  the  chemical  energy  of  carbon  at  work  to  produce 
these  effects.  The  same  considerations  lead  us  to  doubt  that 
there  was  an  interchange  of  elements  between  different  parts  of 
the  ascending  column  of  mineral  solution,  by  which  the  com- 
plete precipitation  of  any  mineral  in  one  rock,  the  shale,  for 
instance,  would  so  dilute  the  mother-liquor  there  that  this  min- 
eral would  pass  by  diffusion  from  the  solution  going  through 
the  limestone  to  that  in  the  shale.  Such  action  is  familiar  in 
chemical  work.  When  a  drop  of  reagent  causes  partial  precip- 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  361 

itation,  the  remainder  of  the  dissolved  substance  is  diffused  im- 
mediately through  the  whole  body  of  liquid.  This  could  not 
have  taken  place  at  Ku  Shau  Tzu  without  producing  more 
abundant  deposition  in  one  of  the  rocks  than  in  the  other,  ac- 
cording to  its  precipitating  energy,  and  the  phenomenon  there 
is  not  quantitative,  but  selective,  concentration.  The  quantity 
of  mineral  was  greatest  in  the  limestone. 

It  is  conceivable  that  the  deposition  of  ore  in  the  shale  would 
liberate  carbon,  which,  going  into  solution,  might  reach  the 
limestone  and  there  act  upon  the  advancing  ore-solution,  thus 
giving  the  shale  a  large  radius  of  action,  and  making  it  con- 
tribute to  deposition  in  the  neighboring  rock. 

This  question  of  interchange  of  elements  between  solutions, 
or  diffusion,  is  of  great  interest  and  importance,  and  though  it 
is  riot  germane  to  the  subject  of  Prof.  Jenney's  paper,  I  may 
be  permitted  to  point  out  that  some  observations  indicate  that 
there  is  no  horizontal  diffusion  or  exchange  of  dissolved  sub- 
stances between  the  two  halves  or  ends  of  the  moving  column 
of  solution,  which  we  may  consider  conveniently  to  have  the 
same  length  as  the  vein.  There  is  evidence  that  the  solution 
from  which  an  ore  of  general  average  composition  is  deposited 
may  produce  ore-bodies  that  vary  in  their  different  parts  in  a 
manner  important  to  the  miner  if  not  to  Nature. 

In  the  well-known  case  of  the  Crown  Point-Belcher  bonanza, 
one-half  of  the  ore-body  contained  more  gold  in  proportion  to 
silver  than  the  other  half,  and  the  difference  was  not  fortuitous, 
but  persisted  through  the  whole  extent  of  the  bonanza.  The 
country-rock  was  eruptive,  the  mass  of  the  deposit  was  silica, 
the  total  length  was  only  500  ft.,  and  it  is  difficult  to  see  how 
there  could  have  been  selective  deposition  from  a  uniform  solu- 
tion. Granting  that  the  difference  began  at  the  point  where 
the  solution  was  formed,  this  difference  in  the  two  halves  of  the 
current  must  have  been  preserved  throughout  its  wander- 
ings,— a  proof  that  there  were  no  exchanges  between  the  two 
halves. 

Of  course,  if  lateral  secretion  in  its  first  and  most  restricted 
sense  were  true,  and  the  ore  were  derived  from  the  immediate 
walls  of  the  vein,  an  explanation  might  be  found.  This  ex- 
tremely limited  conception  is,  I  believe,  entirely  abandoned; 
and  the  persistent  difference  of  the  Crown  Point-Belcher  solu- 


362  THE    CHEMISTRY    OF    ORE-DEPOSITION. 

tion  along  adjacent  vertical  and,  perhaps,  horizontal  lines  of 
travel,  possibly  to  great  distances,  is  an  unexplained  phenom- 
enon. Other  cases  are  known  in  which  the  facts  indicate  that 
there  was  no  exchange  of  elements  between  the  parts  of  the 
common  solution  from  which  the  respective  ends  of  the  ore- 
body  were  formed. 

It  is  not  probable  that  the  north  and  south  ends  of  the  Crown 
Point-Belcher  ore-body  differ  in  date,  for  the  mass  was  decidedly 
lenticular,  very  thick  in  the  middle  and  thinning  out  in  all 
directions.  The  natural  conclusion  is  that  the  action,  being  a 
replacement  of  country-rock,  began  in  the  central  portion  of  the 
mass,  and  the  greater  thickness  there  is  the  effect  of  longer 
action.  This  is  equivalent  to  saying  that  the  action  was  contin- 
uous over  the  whole  of  the  steadily  increasing  vein-area,  and 
that  ore  was  forming  in  the  center  while  it  was  forming  at 
both  ends. 

Occurrences  of  this  kind  have  an  obvious  bearing  upon  the 
views  which  Prof.  Van  Hise  has  expressed  upon  the  movement 
of  waters  in  the  rocks.  A  natural  explanation  of  the  Crown 
Point-Belcher  case  is  that  the  thin-leaved  porphyry  of  the  Corn- 
stock  offered  a  means  of  ready  flow  which  operated  as  a  chan- 
nel, to  which  waters  from  widely  different  sources  of  origin 
were  directed ;  but  this  only  emphasizes  the  fact  that  the  two 
currents  maintained  their  individuality  through  long  wander- 
ings, and  even  when  joined  in  a  channel  of  limited  section.  It 
also  implies  that  gold  and  silver  can  be  picked  up  anywhere  in 
the  middle  of  the  earth,  a  conclusion  which  cannot  be  admitted; 
for  it  is  probable  that  the  solution  of  metals  is  as  selective  and 
phenomenal  as  is  their  deposition. 

Differential  deposition,  as  in  this  case,  necessarily  brings  up 
the  question  of  electro-chemical  action ;  but  which  way  would 
it  work,  for  or  against  differentiation  ?  My  impression  is  that 
it  would  act  for  uniformity,  and  there  is  no  evidence  that  elec- 
trical action  in  the  rocks  is  strong  enough  to  move  a  metal  or 
salt  through  500  ft.  of  minute  channels. 

Prof.  Jenney's  description  of  the  ore-deposition  in  the  Tintic 
limestones  may  be  accepted  as  accurate  for  the  galena  of  the 
celebrated  "  Emma  "  mine,  in  Little  Cottonwood  Canyon,  Utah. 
I  well  remember  a  large  mass  of  galena  there,  almost  pure  in 
the  center,  and  surrounded  by  a  thick  mass  consisting  of  de- 


THE    CHEMISTRY    OF    ORE-DEPOSITION.  363 

•composed  limestone  fragments  in  galena,  graduating  to  enclo- 
sures of  galena  in  limestone  as  the  distance  from  the  center 
increased,  and  ending  with  scattered,  small  impregnations  of 
galena  in  the  nearly  unaltered  limestone  walls.  The  angular 
shape  of  the  inclusions  mentioned  by  Prof.  Jenney  was  note- 
worthy there  also. 

Every  mining  engineer  will  recall  from  his  own  experience 
occurrences  which  sustain  the  general  position  which  Prof. 
Jenney  takes  in  reference  to  the  presence  of  carbon  in  the 
rocks  of  mining  districts.  One  of  the  problems  at  Tombstone 
which  the  new  owners  are  attacking  with  such  faith  is  the 
future  of  the  Contention  vein,  where  it  passes  through  the 
Lucky  Cuss  limestone,  wThich  is  strongly  fetid  for  100  or  200  ft. 
in  thickness.  It  may  be  years  before  it  is  reached,  but  it  pre- 
sents the  elements  for  active  chemical  exchanges.  When  I 
was  a  superintendent  in  Tombstone,  two  of  my  men,  who  were 
mining  manganese  in  the  higher  strata  of  this  limestone,  nearly 
lost  their  lives  by  an  effusion  of  C02  into  a  shallow,  open  pit 
where  they  were  working.  The  gas  accumulated  during  the 
night  and  surprised  them  in  the  morning.  These  facts  may 
indicate  the  influence  of  carbon  in  that  mining  district. 

At  the  New  Almaden  quicksilver-mine  there  is  an  enormous 
discharge  of  carbon  dioxide,  which  bubbles  and  hisses  through 
the  water  in  the  bottom,  and  twice,  at  least,  has  so  filled  the 
large  chambers  of  the  old  mine  as  to  drive  the  whole  mining- 
force  from  its  work. 

The  Mining  and  Scientific  Press,  San  Francisco,  of  May  2, 
1903,  has  the  following  interesting  note  upon  the  occurrence  of 
carbon  dioxide : 

"  Metal  mines,  as  well  as  coal  mines,  produce  carbonic  acid  gas,  though  more 
rarely  the  inflammable  '  fire  damp.'  In  some  instances  the  carbonic  acid  gas 
has  been  so  abundant  that  the  mining  work  has  had  to  be  abandoned.  This  was 
the  case  in  a  long  drift  from  a  deep  shaft  at  the  New  Almaden,  Cal.,  quicksilver- 
mine.  Subsequently,  an  air-tight  bulkhead  was  built  in  the  drift,  and  pipes  placed 
connecting  an  air-compressor  at  the  surface  with  the  bulkheaded  drift.  The  in- 
take of  the  compressor  was  attached  to  the  pipe  leading  into  the  mine,  the  carbon 
dioxide  was  drawn  from  the  mine  and  by  means  of  special  machinery  compressed 
into  steel  cylinders  under  a  pressure  of  1,200  Ib.  per  sq.  in.,  in  which  form  it 
was  sold  for  the  carbonating  liquids.  The  Abbott  quicksih7er-mine  in  Lake 
county,  Cal.,  makes  a  large  amount  of  '  firegis'  similar  to  the  'fire  damp'  of 
coal  mines.  The  occurrence  of  fire  damp  in  metal  mines  is  unusual.  In  the 
case  of  the  Abbott  mine  its  presence  is  supposed  to  be  due  to  the  bituminous 
matter  in  the  surrounding  rocks." 


364  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 


No.  13. 
Ore-Deposits  Near  Igneous  Contacts. 

BY   WALTER   HARVEY  WEED,    WASHINGTON,    D.    C. 

(New  Haven  Meeting,  October,  1902.     Trans.,  xxxiii.,  715.) 

CONTENTS. 

PAGE 

INTRODUCTION, 364 

WHY  ORE-DEPOSITS  ARE  COMMON  ABOUT  IGNEOUS  CONTACTS,        .        .        .  365 
OUTLINE  OF  A  GENETIC  CLASSIFICATION  OF  ORE-DEPOSITS,        .        .        .  366 

Ores  of  Igneous  Origin, 366 

Igneous-Emanation  Deposits, 368- 

Fumarolic  Deposits,    .  368 

Gas-Aqueous  Deposits, 368 

Deposited  by  Meteoric  Waters, 369 

CONTACT  METAMORPHIC  DEPOSITS, 369 

Classes  of  Deposits, 370 

Contact  Zones, 371 

Character  of  Gangue, .        .         .        .  371 

Character  of  Ore-Deposit, 372 

Literature, 373 

Geographic  Distribution, 373 

Copper- Deposits — Cananea  Type, 374 

British  Columbia — Boundary  District, 374 

Mexico, 376 

Germany, 378 

Gold-Deposits, 380 

Bannack  Type, 381 

Elkhorn, 382 

Similkameen, .        .        .        .  383 

CHANGES  IN  ROCKS  DUE  TO  CONTACT  METAMORPHISM,    .        .        .        .        .  384 
Changes  in  Mass,  Volume,  and  Mineral  Composition,       ....  385 

GENESIS  OF  CONTACT  METAMORPHIC  DEPOSITS, 387 

Cause  of  Contact  Metamorphism, 387 

PERMANENCE  IN  DEPTH,    .        .        .        . 393. 

MINERAL  VEINS  NEAR  IGNEOUS  CONTACTS, 394 

CONCLUSIONS,      .        .        *•-.'•    ...._;  ;       v 395- 

INTRODUCTION. 

THIS  paper  deals  with  certain  ore-deposits  whose  structural 
features  or  mineral  contents  (or  both)  result,  directly  or  indi- 
rectly, from  igneous  intrusions  and  their  after-effects.  It  is 
largely  a  discussion  of  contact  metamorphic  ore-deposits  based 
upon  the  physical  changes  in  rocks  due  to  contact  action.  It 
involves  a  classification  of  ore-deposits  only  so  far  as  is  abso- 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  365 

lutely  necessary  for  brevity  of  discussion.  A  genetic  classifica- 
tion of  ore-deposits  is  admitted  to  be  the  rational  and  only  cor- 
rect classification  from  a  scientific  point  of  view.  To  the 
practical  miner,  such  a  classification  may  be  of  utility  if  the 
correct  discrimination  of  the  nature  and  genesis  of  a  deposit 
enables  him  to  more  nearly  determine  the  probable  extent  and 
value  of  the  deposit,  and  to  exploit  it  intelligently.  It  is  be- 
lieved that  the  facts  set  forth  in  this  paper  and  the  explanation 
of  them  admit  of  such  a  practical  use. 

WHY  ORE-DEPOSITS  ARE  COMMON  ABOUT  IGNEOUS  CONTACTS. 

As  is  well  known,  the  granitic  rocks  which  adjoin  contact 
areas  are  parts  of  great  masses  of  igneous  magma  which  did 
not  reach  the  surface,  but  cooled  slowly  underground  and  con- 
solidated into  coarse-grained  rocks.  Subsequent  uplift  and 
denudation  have  exposed  both  the  great  bodies  of  igneous  rock, 
and  the  sediments  baked  and  altered  by  them,  in  consequence 
of  the  heat  and  vapors  given  off  by  the  cooling  magma. 

Igneous  contacts  are  ore-bearing  because,  (a)  differentiation 
of  the  cooling  magma  tends  to  segregate  the  highly  basic  and 
metal-bearing  portion  at  the  border  of  the  cooling  mass ;  (b) 
pneumatolytic  processes  are  most  active  about  the  borders  of 
igneous  masses ;  (c)  the  force  of  the  intrusion  may  have  shat- 
tered the  adjacent  rocks,  forming  cracks  and  fissures  that  be- 
come channels  for  circulating  waters;  (d)  the  shrinkage  of  the 
intrusive  magma  due  to  progressive  cooling  after  solidification, 
and  the  shrinkage  of  the  metamorphic  zone  itself,  would  result 
in  the  formation  of  fissures ;  and  (e)  as  will  be  shown  later,  the 
porosity  induced  in  certain  sedimentary  rocks  by  contact  meta- 
morphism  (which  maybe  compared  to  the  burning  of  clay  into 
brick)  has  furnished  channels  for  circulating  waters  and  gases, 
so  that  ore-deposition  has  resulted.  The  origin  and  character 
of  the  latter  class  of  deposits  is  the  only  strictly  novel  feature 
of  the  paper.  The  deposits  formed  near  igneous  contacts  by 
the  operation  of  these  causes  have  widely  different  characters. 
To  discuss  them  a  systematic  arrangement  is  necessary,  and 
the  following  provisional  genetic  classification  has  been  pro- 
posed.* 

*  Compare  Eng.  Min.  Jour.,  vol.  Ixxv.,  No.  7,  p.  256,  Feb.  14,  1903. 


366  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

OUTLINE  OF  A  GENETIC  CLASSIFICATION  OF  ORE-DEPOSITS. 

I.  Igneous  (magmatic  segregations). 

A.  Siliceous. 

B.  Basic. 

II.  Igneous-emanation  deposits  (deposited  by  highly  heated 
vapors  and  gases  in  part  above  the  critical 
point,  e.g.,  365°  and  200  atm.  for  H2O). 

A.  Contact-metamorphic  deposits. 

B.  Veins  (closely  allied  to  magmatic  veins  and  to 

division  IV.). 

III.  Fumarolic  deposits  (metallic  oxides,  etc.,  in  clefts  in  lavas ; 

of  no  commercial  importance). 

IV.  Gas-aqueous    (pneumato-hydato-genetic)    deposits.      Igne- 

ous, gaseous  and  aqueous  emanations,  alone  or 
mingled  with  ground-waters. 

A.  Filling-deposits. 

B.  Replacement-deposits. 
V.  Deposited  by  meteoric  waters. 

A.  Underground. 

B.  Surficial. 

In  this  classification  I  have  attempted  to  group  the  geological 
processes  forming  ore-deposits  in  such  a  way  as  to  show  genetic 
relations,  it  being  understood  that  opinions  will  differ  as  to  the 
class  to  which  a  particular  deposit  is  to  be  assigned. 

Major  subdivisions  are  based  upon  magmatic  segregations  at 
one  end  and  cold  aqueous  deposits  at  the  other,  with  interme- 
diate groups  due  to  the  emanations  from  igneous  rock,  the 
eruptive  after-actions  of  Vogt,  to  which  the  term  pneuma- 
tolytic  has  commonly  been  given ;  fumarolic,  when  these  ema- 
nations issue  at  low  temperature  and  pressure;  gas-aqueous,  in 
which  the  emanations  from  igneous  rocks-,  with  their  burden  of 
metals,  mingle  with  ground-water ;  aqueous,  in  which  meteoric 
waters  alone  are  active,  both  chemically  and  mechanically. 

Ores  of  Igneous  Origin. 

The  igneous  deposits  are  divided  into  basic  and  siliceous,  the 
former  including  the  deposits  of  iron,  copper,  etc.,  found  at 
igneous  borders  and  as  dikes,  the  latter  the  ore-bearing  peg- 
matites, with  quartz-veins  as  extreme  examples. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  367 

The  existence  of  certain  ore-deposits  of  an  igneous  origin 
seems  to  be  fully  proven  and  generally  accepted.  It  is  well 
known  that  the  igneous  magmas  differentiate  into  siliceous  and 
basic  portions,*  the  resulting  rocks  being  the  siliceous  aplites 
(alaskites)  and  highly  basic  rocks  of  various  kinds.  Where  ex- 
treme differentiation  has  taken  place,  the  basic  residual  por- 
tion contains  so  much  iron  or  copper  solidified  as  to  form 
workable  ore-deposits,  constituting  the  subdivision  B  of  the 
table.  The  same  extreme  segregation  would  produce  the  sili- 
ceous magma  commonly  seen  as  acid  granites  or  aplites,  which 
frequently  pass  into  pegmatites,  and  the  latter,  in  turn,  into 
quartz-veins.  These  facts  are  well  known,  f 

Some  of  these  observers,  however,  believe  that  pegmatites 
and  allied  quartz- veins  are  due  to  igneous  emanations  of  watery 
vapor,  and  are  not  direct  segregations.  Whatever  may  be  the 
result  of  further  study  concerning  the  origin  of  these  interest- 
ing veins,  there  is  no  doubt  that  in  part,  at  least,  they  are  of 
pneumatolytic  origin.  There  is,  however,  abundant  evidence 
to  show  that  acid  rocks  are  commonly  associated  with  gold- 
deposits.  Richard  Beck,  in  his  book  on  ore-deposits,  describes 
the  occurrence  of  intrusive  bodies  of  granite  near  Lake  Schart- 
ash  which  carry  gold ;  and  various  observers  have  described 
dikes  of  similar  acidic  granite  at  Berezovsk  containing  quartz 
filling  contraction-cracks,  and  consequently  a  normal  constit- 
uent of  the  rock,  which  are  mined  for  their  gold  values.  In  a 
treatise  entitled  "  Criaderos  Minerales  de  Mexico,"  Aguilera 
has  given  very  many  examples  of  the  association  of  ores  with 
extremely  siliceous  rocks.  J 

In  a  general  way,  the  laws  of  segregation  outlined  by  Pirs- 
son  indicate  that  we  should  expect  the  siliceous  segregation  in 
the  center  of  the  igneous  mass  and  the  basic  ones  at  the  bor- 
ders, while  the  basic  dikes  would  traverse  the  igneous  contacts, 
cutting  both  the  igneous  rock  and  the  adjacent  altered  sedi- 
mentary rocks. 

*  Weed  and  Pirsson,  "Shonkin  Sag  Laccolith,"  Amer.  Jour.  Sci.,  July,  1901. 

f  Kemp,  "Role  of  the  Igneous  Rocks  in  the  Formation  of  Veins,"  Trans., 
xxxi.,  p.  182;  also,  Genesis  of  Ore-Deposits,  p.  693.  Van  Hise,  Trans.,  xxxi.,  p. 
287.  Lindgren,  "  Character  and  Genesis  of  Certain  Contact-Deposits,"  Trans., 
xxxi.,  p.  243;  also,  Genesis  of  Ore-Deposits,  p.  733.  A.  W.  Howitt,  Roy.  Soc.  Vic., 
Oct.  14,  1886. 

|  "  Distribucion  Geografica  y  Geologico  de  los  Criaderos  Minerales  de  Mexico,"' 
Jose*  G.  Aguilera,  Acad.  Sci.  Off.  Secretario  Fomento,  Mexico,  1901. 


368  ORB-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

Igneous- Emanation  Deposits. 

Under  this  title  I  have  grouped  contact-metamorphic  depos- 
its and  pneumatolytic  veins.  The  contact-metamorphic  de- 
posits have  been  shown  by  Vogt,  Lindgren,  Beck  and  others 
to  be  formed  under  conditions  which  preclude  either  the  pres- 
ence of  ordinary  ground-water  or  steam  at  low  temperature  and 
pressure. 

Pneumatolytic  veins,  of  which  the  Cornwall  tin-veins  are 
classic  examples,  are  admitted  by  most  competent  observers 
to  be  formed  by  igneous  emanations  proceeding  from  the  still 
hot  granite  rocks.*  The  group  includes  part  of  those  em- 
braced in  Vogt's  "  Ore-Deposits  Formed  by  Eruptive  After- 
Actions." 

The  contact-metamorphic  deposits  are  treated  at  consider- 
able length  in  the  succeeding  pages. 

Fumarolie  Deposits. 

Under  this  group  I  have  classed  deposits  of  ferric  chloride, 
cuprous  oxide,  and  other  metallic  minerals  formed  in  clefts  of 
volcanic  craters.  Deposits  of  this  kind  have  been  observed 
by  G-eikie  and  many  other  geologists,  and  the  evidence  concern- 
ing them  is  summarized  in  discussing  the  origin  of  contact- 
metamorphic  deposits.  They  are  assigned  to  a  separate  class 
because  they  are  formed  at  the  surface  of  the  earth  under  con- 
ditions which  do  not  and  cannot  prevail  in  depth. 

Gas- Aqueous  Deposits. 

This  group  is  formed  to  include  those  ore-deposits  formed  by 
hot  waters  containing  metallic  salts  and  other  substances  de- 
rived wholly  or  in  part  from  igneous  emanations.  This  class  of 
deposits  corresponds  closely  to  Vogt's  igneo-aqueous  or  eruptive- 
after-action  group, f  but  it  is  as  well  to  emphasize  the  distinction 
to  be  made  between  hot  waters  carrying  only  the  substances 
dissolved  out  of  the  rocks  traversed  by  them  and  those  charged 
with  substances  undoubtedly  derived  from  igneous  emanations. 
The  evidence  concerning  these  deposits  has  been  very  ably 
summed  up  by  Suess  in  his  recent  paper.  J  Professor  Suess 

*  Zeitschf.  Kryst.  u  Min.,  vol.  xvi.,  1890.  |  Trans.,  xxxi.,  p.  125  et  seq. 

1  "  Ueber  Heisse  Quellen,"  Gesd.  Deutsch.  Naturforscher  und  Arzte,  1902. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  369 

expresses  his  belief  in  the  inability  of  ordinary  circulating 
waters  to  derive  the  unusual  substances,  such  as  boron,  fluo- 
rine, chlorine,  etc.,  from  ordinary  igneous  and  sedimentary 
rocks.  In  fact,  Professor  Suess  goes  further,  and  says,  the 
water  of  the  famous  hot  springs  of  the  Carlsbad  region  is 
original  or  primitive  water  derived  from  the  underlying  igne- 
ous hearths  and  containing  little,  if  any,  meteoric  water.  On 
the  other  hand,  there  seems  to  be  no  question  but  that  in  many 
instances  circulating  meteoric  waters  intercept  the  uprising 
primitive  waters,  and  the  solutions  thus  formed  deposit  ores. 
In  such  cases  the  meteoric  waters  are  the  vehicle  and  not  the 
agent.  This  has  been  concisely  stated  by  Lindgren  as  fol- 
lows : 

"  Where  fissures  traverse  the  cooling  magmas,  and  the  rocks  surrounding 
them,  it  is  natural  that  these  mineralizing  agents  [emanations]  carrying  their 
load  of  heavy  metals  should  ascend,  at  first  under  pneumatolytic  conditions, 
above  the  critical  temperature.  Beaching  the  zone  of  circulating  atmospheric 
waters,  it  is  natural  that  they  should  mix  with  these,  which  probably  greatly 
predominated  in  quantity.  To  this  combination  of  agencies,  found  in  the  ascend- 
ing waters  of  such  regions  of  igneous  intrusion,  the  formation  of  most  metallif- 
erous veins  is  probably  due."* 

Deposited  by  Meteoric  Waters. 

Under  "  Underground  Deposits  "  I  have  grouped  the  de- 
posits formed  by  circulating  ground-waters  in  one  class;  those 
of  residual  origin,  being  leached  veins,  in  an  entirely  separate 
class;  as  surficial  deposits  I  would  include  chemical  deposits 
of  various  kinds,  and  mechanical  deposits,  such  as  sedimentary 
rocks,  placers,  etc. 

Believing,  with  Professor  Kemp,  that  the  greatest  number  of 
copper  and  precious-metal  deposits  of  the  world  are  near  igne- 
ous rocks  with  which  they  are  genetically  connected,  I  hold, 
with  Vogt,  that  normal  terrestrial  water-circulation  has  had  a 
minor  part  in  the  primary  origin  of  the  deposits  in  question, 
though  it  may  have  produced  later  concentration  from  contact 
portions  of  the  magmas  rich  in  metals  or  from  low-grade  de- 
posits of  direct  contact-metamorphic  origin. 

CONTACT  METAMORPHIC  DEPOSITS. 

Under  the  title  of  contact  metamorphic  deposits  I  include 
all  ore-deposits  which  result  from  the  metamorphic  action  of 

*  Genesis  of  Ore-Deposits,  p.  612  ;  also,  Trans.,  xxx.,  p.  692. 
24 


370  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

intrusive  igneous  rocks  upon  the  sedimentary  rocks  which  they 
penetrate.  Such  deposits  occur  only  in  the  zones  of  altered 
sediments  about  igneous  intrusions;  they  are  genetically  con- 
nected with  such  intrusions,  and  are,  therefore,  fittingly  desig- 
nated as  ore-deposits  of  contact  metamorphic  origin.  The 
following  subdivisions  are  proposed  : 

Deposited  by  Igneous  Emanations. 
(All  classes  omitted  save  the  one  under  discussion.) 
Contact  Metamorphic  Deposits. 

Characterized  by  gangue  consisting  essentially  of  gar- 
net, epidote,  actinolite,  calcite,  and  other  lime-alumina 
silicates. 

(a)  Deposits  confined  to  contact  : 

1.  Magnetite  deposits. 

2.  Chalcopyrite  deposits,  Kristiania  type. 

3.  Gold-ores,  Bannack  type. 

(b)  Deposits  impregnating  and  replacing  beds  of  contact 

zone  : 

1.  Chalcopyrite  deposits — (a)  Pyrrhotite  ores,  (b)  mag- 

netite ores,  Cananea  type. 

2.  Gold  tellurium  ores,  Elkhorn  type. 

3.  Arsenopyrite  ores,  Similkameen  type. 

In  the  present  paper  I  shall  particularly  describe  certain  ore- 
deposits  occurring  in  sedimentary  rocks  altered  by  contact  met- 
amorphism,  and  endeavor  to  show  that  thermal  metamorphism 
effects  certain  physical  changes  in  the  sedimentary  rocks  of 
the  contact-zone  favorable  to  ore-deposition,  either  because  the 
vapors  and  gases  of  the  cooling  magma  penetrate  the  altered 
rocks  and  deposit  metallic  sulphides  or  by  reason  of  a  later 
impregnation,  by  circulating  waters,  of  particular  strata,  made 
porous  by  thermal  metamorphism.  They,  therefore,  embrace  both 
the  "  contact  "-deposits  of  the  Kristiania  type  and  the  types 
herein  described,  and  which  have  been  called  bed-impregna- 
tions by  Dalmer*  and  "  Strikes  "  by  Beck.f  These  embrace  the 
Cananea  type  and  the  types  of  gold-deposits,  heretofore  un- 
known, which  structurally  and  genetically  resemble  the  first 
types  mentioned,  but  differ  in  mineral  contents. 

*  "Problems  in  the  Geology  of  Ore-Deposits,"  Genesis  of  Ore-Deposits,  p.  650; 
also,  Trans.,  xxxi.,  p.  139. 

f  Kichard  Beck,  Lehre  von  den  Erzlagerstatlen,  1901,  p.  485. 


-    ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  371 

As  the  admirable  treatise  of  Lindgren*  presents  a  discussion 
of  contact  metamorphism  in  describing  the  genesis  of  depos- 
its of  the  Kristiania  type,  much  concerning  this  subject  may 
be  profitably  omitted  from  the  present  paper,  though  it  is 
necessary  for  a  clear  understanding  of  the  subject  to  give  an 
outline  of  the  principal  facts. 

Contact  Zones. 

In  many  mining  districts  there  occur  great  masses  of  gran- 
itic rocks,  surrounded  by  sedimentary  strata  which,  near  the 
contact,  exhibit  marked  alteration,  the  intensity  of  which  dimin- 
ishes as  the  distance  from  the  igneous  rock  increases  until  the 
alteration  fades  out  and  the  rocks  are  of  normal  character. 
Such  areas  are  known  as  contact  metamorphic  zones,  which 
often  form  a  halo  about  igneous  centers;  for  example,  about 
the  "  stocks  "  of  granitic  rocks  of  the  Crazy  Mountains,  Mon- 
tana, or  the  batholitic  masses  of  the  Black  Hills,  Dakota.  In 
other  cases  great  areas  of  granitic  rock,  such,  for  example,  as 
the  great  mass  of  granite  called  the  Butte  batholith,  of  Mon- 
tana, which  is  60  miles  long  and  40  miles  broad,  are  bordered 
by  a  zone  of  rocks  altered  by  contact  metamorphism  which 
may  be  a  mile  or  more  wide,  as,  for  instance,  near  Helena, 
Montana.  Such  contact  zones  are  often  the  seat  of  mineral 
deposits  of  great  economic  value,  as  is  illustrated  by  the  Drum- 
lummon  and  other  mines  at  Marysville,  Montana ;  several  mines 
at  Granite  and  Philipsburg,  Montana;  the  Whitlatch-Union 
and  other  mines,  once  productive,  at  Helena ;  the  copper-mines 
at  Clifton  and  Morenci,  Arizona;  those  at  Cananea,  Sonora, 
and  many  other  localities  in  Mexico.  I  exclude  the  common 
contact-deposits  of  the  text-books,  in  which  it  appears  probable 
that  the  igneous  rock  has,  by  its  presence,  localized  and  de- 
flected circulating  waters  and  thus  determined  the  site  of  ore- 
deposition. 

Character  of  Gangue. 

Contact  metamorphic  deposits  of  whatever  type  are  distin- 
guished by  a  gangue  consisting  essentially  of  garnet,  calcite, 
epidote,  actinolite,  with  or  without  accessory  wollastonite,  vesu- 

*  "Metasomatic  Processes  in  Fissure- Veins,"  Genesis  of  Ore-Deposits,  p.  498; 
also,  Trans.,  xxx.,  578. 


372  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

vianite,  flue-rite,  etc.,  and  other  minerals  characteristic  of  con- 
tact metamorphic  zones.  As  will  be  shown  later,  the  gangue 
is  normally  a  rock  formed  by  the  alteration  of  an  impure  lime- 
stone. Other  rocks  characteristic  of  contact  action,  such  as 
hornrels,  marble,  quartzite,  adinole,  etc.,  are  often  present,  but 
the  ore-deposit  is  practically  confined  to  the  rocks  resulting 
from  the  alteration  of  impure  limestones,  for  reasons  explained 
later. 

Character  of  Ore-Deposit. 

The  Kristiania  type  of  contact-deposit  has  already  been  de- 
scribed by  Lindgren.*  Specular  iron  and  -magnetite  are  com- 
mon in  true  "  contact  "-deposits,  but  they  occur  only  rarely  in 
the  deposits  separated  from  the  contact.  The  ore-minerals  pre- 
sent considerable  variety,  and  according  to  their  metallic  con- 
tents may  be  grouped  as  copper-ores  and  as  gold-ores.  A  more 
complete  classification  would  be,  however, 

(1)  Chalcopyrite  deposits  :  (a)  pyrrhotitic  type,  (b)  magnetic. 

(2)  Telluride  deposits. 

(3)  Arsenopyrite  deposits. 

The  first  class  includes  the  chalcopyrite  ore-bodies  carrying 
accessory  galena  at  Cananea,  Mexico.  The  subtypes  are  dis- 
tinguished at  Boundary,  British  Columbia.  In  the  pyrrhotite 
type  that  mineral  predominates,  but  the  copper  values  are  in 
chalcopyrite  and  accessory  pyrite,  while  in  the  magnetite  type 
this  mineral  replaces  pyrrhotite.  The  second  class  is  charac- 
terized by  the  presence  of  telluride  of  gold.  In  the  Elkhorn 
example  the  ore-mineral  is  an  auriferous  tetradymite  with  as- 
sociated bismuthinite.  At  Bannack,  Mont.,  there  is  free  gold, 
with  much  more  abundant  sylvanite.  In  the  third  class  arsen- 
opyrite  occurs,  carrying  very  high  values  in  gold,  together  with 
free  gold.  The  only  known  example  of  this  class  is  the  Nickel 
Plate  mine,  near  Lake  Okanagan,  British  Columbia. 

The  characteristic  feature  is  the  gangue  of  earthy  silicate 
minerals  in  which  the  ore-minerals  are  disseminated.  In  most 
cases  the  ore-minerals  and  the  sulphides  are  of  simultaneous 
origin  (or  nearly  so).  The  deposits  are  the  direct  result  of  the 
deposition  of  ore  by  the  vapors  and  gases  of  the  cooling  magma 

*  "  Character  and  Genesis  of  Certain  Contact- Deposits,"  Genesis  of  Ore-Deposits, 
p.  716;  also,  Trans.,  xxxi.,  226. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  373 

(possibly,  in  part,  the  gases  given  off  by  the  alteration  of  the 

sediments). 

Literature. 

Geologists  have  long  recognized  the  peculiar  characters  of 
ore-deposits  in  the  contact  metamorphic  zone  about  igneous 
intrusions,  nor  would  it  be  possible  for  a  careful  observer  to 
fail  to  note  the  successful  mines  and  the  multitude  of  unsuc- 
cessful prospect-pits  which  commonly  mark  such  areas.  It  is 
unnecessary  to  go  into  detail  on  this  subject,  as  it  has  been  cov- 
ered by  Lindgren  in  the  paper  cited.*  It  is  evident  that  Kemp,f 
although  grouping  contact  metamorphic  deposits  as  contact-de- 
posits, recognized  their  individual  character,  as  shown  by  the 
examples  given  under  that  head  in  his  classification,  though  he 
gives  no  details  of  occurrence  nor  shows  their  difference  from 
those  of  the  Kristiania  type. 

Despite  this  very  general  recognition  of  such  deposits,  no  dis- 
crimination was  attempted  until  Yon  Groddeck  defined  contact- 
deposits  of  the  Kristiania  type,  showing  that  they  formed  a 
distinct  and  separate  class  of  ore-deposits,  differing  in  occur- 
rence and  genesis  from  all  other  types.  The  contact  meta- 
morphic deposits  discussed  herein  resemble  those  of  this  class, 
though  excluded  from  it  by  definition, J  as  they  are  not  contact- 
deposits,  though  quite  as  truly  a  result  of  contact  meta- 
morphism.  There  is  a  marked  correspondence  between  the  two 
types  as  regards  mineral  association  and  genesis ;  but  the  struc- 
tural differences  are  so  important,  and  have  so  marked  a  bear- 
ing, not  alone  on  the  theory  of  their  genesis  but,  also,  in  the 
working  of  the  deposits  and  a  determination  of  their  value  as 
mines,  that  they  merit  a  full  discussion. 

Geographic  Distribution. 

Ore-deposits  in  the  zone  of  contact  metamorphism  are  quite 
common,  though  in  the  past  the  more  noted  mines  have  been 
fissure-veins  whose  contents  may  or  may  not  have  been  derived 
from  contact  metamorphic  deposits.  As  great,  massive,  igne- 

*  "  Character  and  Genesis  of  Certain  Contact-Deposits,"  Genesis  of  Ore-Deposits, 
p.  716;  also,  Trans.,  xxxi.,  226. 

f  Ore-Deposits  of  the  United  States,  3d  ed.,  1902,  p.  58. 

J  Lindgren,  Genesis  of  Ore-Deposits,  p.  717,  under  heading  Position  ;  also, 
Trans.,  xxxi.,  227. 


374  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

cms  intrusions  are  most  commonly  found  in  regions  where  pe- 
riods of  great  volcanic  activity  have  been  followed  by  uplift 
and  profound  erosion,  it  is  in  mountainous  districts  that  most 
contact  metamorphic  deposits  occur. 

No  attempt  will  be  made  to  discuss  or  describe  contact-de- 
posits of  the  Kristiania  type.  The  Jimenez  copper-mine,  Chi- 
huahua, Mexico,*  is  a  typical  example  of  this  class,  and  the 
Indian  Queen  mine  at  Birch  Creek,  in  Beaverhead  county, 
Montana,  is  another  example,  in  which  later  fracturing  and  en- 
richment have  taken  place. 

Examples  of  the  Cananea  type  of  contact  metamorphic  de- 
posits are  less  common,  though  the  two  noted  herein  are  now 
rated  among  the  most  productive  mines. 

Copper-Deposits — Cananea  Type. 

British  Columbia. — The  ore-deposits  of  the  Boundary  district 
of  British  Columbia  have  been  described  by  Mr.  S.  F.  Emmons 
as  also  of  contact  metamorphic  origin.  The  deposits  are  on 
Boundary  Creek,  near  Greenwood,  and  comprise  the  workable 
ore-bodies  of  several  producing  mines.  The  ores  carry  2  to  5 
per  cent,  copper  and  a  few  dwts.  of  gold  per  ton ;  but  as  they 
occur  in  very  large  bodies  and  are  metallurgically  docile,  they 
are  profitably  exploited.  The  ore-bodies  occur  in  belts  of  met- 
amorphosed limestones,  2  miles  or  more  wide,  that  are  ad- 
jacent to  a  mass  of  light-gray,  coarsely  crystalline,  granitic 
diorite. 

The  ores  consist  of  sulphides  of  iron  and  copper,  associated 
with  considerable  magnetic  oxide  of  iron,  of  contempora- 
neous formation.  These  minerals  occur  in  a  gangue  of  al- 
tered limestone  consisting  of  amphibole,  garnet,  vesuvianite, 
zoisite,  etc.  Microscopic  study  shows  that  these  are  the  re- 
sult of  metasomatic  replacement,  during  which  a  granular  lime- 
stone has  been  converted  into  an  amphibolitic  rock  with  the 
simultaneous  development  of  sulphides  and  magnetite.  From 
Barrell's  studiesf  I  regard  it  as  probable  that  the  action  has 
been  the  alteration  of  an  impure  limestone  by  normal  contact 

*  Weed,  Trans.,  xxxii.,  396,  "Notes  on  Certain  Mines  in  the  States  of  Chihua- 
hua, Sinaloa  and  Sonora,  Mexico." 

f  Am.  Journ.  Sci.,  vol.  xiii.,  April,  1902,  p.  279  et  seq. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 


375 


metamorphism.  This  is  also  the  view  held  by  Dr.  A.  R. 
Ledoux.* 

According  to  Emmons,f  the  ore-bodies  are  irregular  in  oc- 
currence, and  graduate  insensibly  in  every  direction,  inward  as 
well  as  outward,  from  ore  into  low-grade  rock,  the  fracture- 
planes  or  walls  failing  to  definitely  enclose  the  ore-shoots  or 
define  their  direction.  In  this  respect  they  resemble  the  south- 
ernmost ore-bodies  at  Cananea,  but  differ  from  the  Cananea 
type,  in  which  relatively  thin  beds  of  impure  limestone  alter- 
nate with  less  congenial  varieties  of  this  rock,  so  that  the  ore- 
strata  are  fairly  sharply  defined.  The  Greenwood  deposits  are 
cut  by  dikes,  which  may  be  regarded  as  the  final  result  of  igne- 
ous action.  As  I  stated  in  discussing  the  genesis  of  this  class  of 
ore-bodies,  the  process  of  metamorphism  is  complete  before  the 
magma  solidifies ;  and  if  the  sulphides  were  introduced  during 
metamorphism  they  would  be  cut  by  the  aplite  and  lamprophyric 
dikes  that  represent  the  final  fissuring  of  the  outer  mass  of 
chilled  magma  and  filling  of  fissures  from  the  molten  interior. 

A  later  and  more  detailed  account  of  the  ore-deposits  of  this 
district  by  BrockJ  gives  further  details,  and,  in  part,  confirms 
these  observations  of  Emmons,  though  presenting  very  im- 
portant additions.  The  ore-deposits  are  notable  for  their  great 
size,  the  Mother  lode  ore-body  being  140  feet  thick  and  devel- 
.oped  for  1180  feet  in  length  and  500  feet  in  depth;  the  Knob- 
Ironsides  lode  is  much  larger,  being  800  feet  wide,  proven  for 
800  feet  in  depth,  and  several  thousand  feet  in  outcrop.  Brock 
distinguishes  two  types,  a  pyritic,  characterized  by  pyrrhotite, 
with  chalcopyrite  and  iron  pyrites,  and  a  magnetitic  type,  with 
magnetite  and  copper  pyrites.  Though  segregated  in  places, 
the  chalcopyrite  is  remarkably  evenly  distributed  through  the  de- 
posits. "  Rarely  do  magnetite  and  pyrrhotite  occur  in  the  same 
deposit." §  Specular  iron  is  found  sparingly  in  a  half-dozen 
properties.  Occasionally  marcasite,  and  sometimes  arseno- 
pyrite,  galena,  zinc-blende  and  molybdenite,  are  present.  Te- 
trahedrite  occurs  in  one  mine  and  bismuthinite  in  another. 

*  "  Production  of  Copper  in  the  Boundary  District,"  Canadian  Min.  InsL,  vol. 
v.,  p.  172. 

f  Genesis  of  Ore- Deposits,  p.  757. 

J  Canadian  Mining  Institute,  vol.  v.,  p.  365,  March,  1902. 

$  Brock,  Canadian  Min.  InsL,  vol.  v.,  p.  368. 


376 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 


The  description  of  the  gangue  shows  red  and  green  garnet 
and  epidote  to  be  abundant  in  and  near  the  veins,  "  and  the 
progress  of  their  formation  may  be  observed  in  many  points 
in  all  stages,  not  only  when  limestone  but  also  when  greenstone 
and  granite  form  the  country- rock,"*  thus  apparently  contra- 
dicting the  hypothesis  that  such  contact  minerals  result  only 
from  the  metamorphism  of  impure  limestones.  At  the  Mother 
lode  the  marmorized  limestones  contain  the  above-mentioned 
minerals,  but  the  mass  of  the  rock  consists  of  felty  actinolite. 
The  gold  values  are  commonly  in  the  chalcopyrite.  Magnetite 
and  pyrrhotite,  when  occurring  alone,  are  commonly  almost 
barren,  the  Winnipeg  pyrrhotite  being  an  exception.  There 
is  a  lack  of  veins  and  stringers  enriching  the  main  ore-body, 
but  there  appears  to  be  an  enrichment  of  the  ore  where  dikes 
cross  it.  The  ores  are  very  low-grade,  a  representative  ore 
carrying  copper  1.95  per  cent,  iron  14  per  cent,  lime  17  per 
cent,  silica  39  per  cent,  with  0.119  ozs.  gold  per  ton  and  0.44 
ozs.  silver. 

Brock  considers  the  ore-bodies  to  be  composite  veins  "  formed 
by  mineralizing  solution  traversing  the  country-rock,  princi- 
pally along  fissures  or  zones  of  fissures  in  which  they  deposit 
the  economic  minerals  and  from  which  they  replace  with  their 
mineral  contents,  particle  by  particle,  sometimes  completely, 
the  original  material  of  the  country-rock."  In  the  same  paper 
he  says,  however,  that  "  there  seems  to  be  strong  reason  for 
supposing  the  deposits  to  be  connected  with  eruptive  after- 
actions." 

Mexico. — The  Cananea  copper-deposits,  which,  during  the 
last  year  (1901),  have  been  so  vigorously  exploited  that  they 
have  produced  140,000,000  Ibs.  of  copper,  are  situated  in  the 
Cananea  mountains,  50  miles  southwest  of  Bisbee,  Arizona, 
and  30  miles  south  of  the  international  boundary-line.  This 
mountain  range  is  from  6  to  12  miles  wide  and  25  miles  long. 
It  rises  abruptly  from  flat  or  gently-inclined  prairies  to  a  height 
of  8000  feet  above  sea-level,  or  4500  feet  above  the  plain.  The 
range  extends  in  a  northwest  and  southeast  direction,  and  it  is 
bisected,  by  the  low  Puertecitos  Pass,  into  two  nearly  equal 
parts.  The  ore-deposits  occur  in  the  southern  portion  of  the 
range. 

*  Brock,  loc  cit.     This  author  examined  no  thin  sections,  however. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  377 

The  mountains  consist  of  the  dissected  and  denuded  remains 
of  an  old  volcano,  probably  of  late  Tertiary  age.  At  Puerteci- 
tos  Pass  there  is  a  central  core  of  normal  granite  surrounded 
by  massive  andesite  and  baked  and  altered  sedimentary  rocks. 
The  main  crest  of  the  mountains  southward  is  formed  of  mar- 
ble, hornstone,  quartzite  and  garnet-epidote  rocks,  resulting 
from  the  intense  alteration  of  impure  limestone  by  the  heat  of 
igneous  intrusions.  These  rocks  are  cut  by  large  intrusions  of 
quartz-porphyry  and  small  diabase  dikes.  The  entire  range  is 
flanked  by  foothills  and  mesas  formed  of  well-bedded  andesitic 
tuffs  dipping  away  from  the  range  at  angles  of  from  10°  to  30°, 
and  representing  the  fragmental  products  of  the  old  volcano, 
which  once  formed  its  cone. 

The  ores  consist  of  chalcopyrite,  together  with  copper  glance, 
pyrite,  zinc-blende,  and  a  little  galena.  They  occur  in  deposits 
which  are,  in  part,  beds  of  altered  limestone  tilted  at  steep 
angles  and  richly  impregnated  with  metallic  sulphides,  and,  in 
part,  deposits  formed  in  fractures  along  and  across  the  quartz- 
porphyry  and  quartzite  without  any  very  definite  relation  to 
the  igneous  contact. 

Near  the  Ronquillo  smelter  of  the  Greene  Consolidated 
Copper  Company  the  ore-bodies  of  the  group  of  mines  em- 
bracing the  Capote,  Yeta  Grande,  Cobre  Grande  and  Oversight 
properties  occur  mainly  along  these  fractures.  .  The  outcrops 
are  great  ridges  of  iron  gossan,  traceable  for  Ions:  distances, 
and  the  ore-bodies  are  very  large,  one  in  the  Capote  being  165 
feet  by  125  feet,  and  oval  in  cross-section.  These  "  veins  "  con- 
form, however,  in  dip  and  strike,  to  the  ore-bodies  that  consist 
of  beds  of  altered  limestone. 

The  ore-deposits  continue  for  a  distance  of  about  8  miles 
along  the  central  portion  of  the  range,  and  north  of  the  Ron- 
quillo group  of  mines,  just  mentioned,  they  pass  into  metamor- 
phosed limestones  impregnated  with  copper.  In  the  exposures 
near  the  northerri  part  of  this  area  the  ore  is  seen  to  be  con- 
fined almost  entirely  to  the  garnet-epidote-diopside  rocks, 
which  occur  interbedded  with  hornstones,  marble,  etc. ;  and,  as 
will  be  shown  later,  this  accords  with  the  views  of  their  genesis 
presented  herein.  In  addition  to  the  ore-bodies  in  course  of 
exploitation,  there  are  many  beds  that  contain  much  galena  and 
zinc-blende. 


378  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

These  copper-ores  are  usually  very  low  in  gold-  and  silver- 
content  ;  but  there  are  certain  exceptions  to  this,  notably  the 
Alfreina  mine,  the  ores  of  which  carry  high  values  in  gold. 

The  development  work  at  most  of  the  northerly  properties  has 
not  yet  reached  the  sulphide  ores.  At  the  Puertecitos  mine  the 
working-tunnel  passes  through  a  bed  30  feet  wide  that  carries 
a  large  amount  of  chalcopyrite,  with  a  little  zinc  and  galena, 
the  ore  averaging  about  15  per  cent,  copper.  This  bed  is 
capped  by  a  white  marble,  which,  as  shown  elsewhere,  is  a  rela- 
tively impervious  rock.  The  ore  consists,  approximately,  of:* 

Per  cent. 

Chalcopyrite, 25 

Galena,      ...........       5 

Calcite,      .  .         ....        .         .35 

Actinolite, 20 

Quartz,      ...........     15 

The  chalcopyrite  and  galena  show  an  evident  association  with 
the  dull  green,  finely  fibrous  actinolite.  The  sulphides  occur 
in  grains  up  to  three-fourths  of  an  inch  across ;  they  are  not 
crystalline,  but  of  irregular  form  and  of  compound  structure 
(i.e.j  not  of  uniform  crystalline  orientation).  The  actinolite 
and  calcite  occur  in  patches,  but  the  quartz  is  idiomorphic,  and 
the  crystals  penetrate  both  the  minerals  just  mentioned.  The 
ore,  howrever,  appears  to  cover  and  enclose  the  quartz. 

Germany. — Richard  Beck  has  described  very  fully  a  deposit  of 
this  structural  type  in  his  recent  book,  and  I  therefore  insert  a 
translation  of  his  description  in  full  :f 

"  1.  The  ore-deposits  of  the  contact  area  of  the  granite  of  Berggiesshiibel, 
in  Saxony. 

"The  ore-deposits  of  Berggiesshiibel,  in  the  so-called  Elbe  Valley  moun- 
tains of  southeastern  Saxony,  represent  a  specially  well-studied  and  typical 
example  of  contact  metamorphic  ore-occurrences,  and  for  this  reason  will  be  here 
first  described,  and  in  some  detail,  although  they  have  long  since  lost  their  eco- 
nomic importance. 

"At  Berggiesshiibel,  in  the  moderately  uptilted  schist  rocks,  several  granite 
stocks  appear,  among  which  the  one  of  Markersbach  occupies  the  foremost  place 
by  its  size  and  by  the  extent  of  its  contact  phenomena.  Close  to  its  western  bor- 
der lies  the  mine  district  of  the  old  mining  town  of  Berggiesshiibel. 

"The  outcrops  of  the  various  beds  of  the  Phyllite  formation  and  the  lower 
Silurian  formation  are  there  distinctly  seen  terminating  at  the  border  of  the 

*  These  figures  are  based  upon  estimates  made  by  measurement  of  specimens 
and  thin  sections  of  the  ore. 

f  Lehre  von  den  Erzlagerstatten,  Leipzig,  1901,  p.  609. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  379 

granite,  and  various  exposures  and  other  evidences  prove  that  the  surface  of  the 
eruptive  stock  dips  at  a  low  angle  under  the  schists  thus  traversed.  The  sedi- 
mentary rocks  thus  adjoining  and,  in  part,  overlying  the  granite  have  been  sub- 
jected to  strong  contact  metamorphosis. 

"Turning  specially  to  the  Silurian  formation,  we  find  that  the  clay  slates 
were  changed  into  hornstone,  horn  schists  and  knot-schist,  while  the  diabase 
tuffs,— the  so-called  Schalsteine, — were  changed  into  various  kinds  of  hornblende 
schists,  especially  actinolite  schist,  also  banded  salite-hornblende  schist.  The 
limestone  layers,  however,  intercalated  in  the  clay  schists  and  especially  in  the 
tuffs,  were  turned  into  marble  beds,  or,  in  part,  into  salite-garnet  rock,  or,  finally, 
into  magnetic  iron  beds. 

"These  limestone  strata  may  be  followed  from  NW.  to  SE.  in  their  strike,  for 
long  distances,  in  many  good  exposures,  deep  limestone  quarries  and  natural 
outcrops,  from  Maxen  across  the  villages  of  Biensdorf  and  Gersdorf,  to  the  point 
where  they  enter  into  the  contact-area  of  the  granite.  Over  this  whole  distance, 
however,  these  limestones  are  devoid  of  ore,  except  a  few  quite  insignificant  beds 
of  red  and  brown  hematite,  which  occur  in  quite  limited  patches,  for  example,  at 
Nenntmannsdorf ,  at  the  boundary  between  limestones  and  schists. 

"In  the  contact-area,  however,  the  calcium  carbonate  has  been  partly  or  en- 
tirely displaced  from  these  beds,  and  replaced  by  secretions  from  immigrant  sili- 
cate and  ore-solutions,  such  a$  salite  and  garnet,  as  well  as  magnetite  and  various 
sulphide  ores.  The  distribution  of  the  marble,  calcium  silicates  and  ores  within 
the  beds  is  very  remarkable  and  diverse,  and  throws  a  bright  light  on  the  manner 
of  this  replacement  metamorphosis. 

"First  let  us  note  that  the  marble  still  shows  clearly  the  stratification  of  the 
originally  dense  Silurian  limestone  out  of  which  it  was  formed.  Even  the  altera- 
tion between  thin  limestone  beds  and  diabase  tuffs,  which  occurs  not  infrequently 
in  the  Silurian  at  that  place,  may  repeatedly  be  observed  in  the  contact-area 
between  marble  and  hornblende  schist,  except  that  the  limestone,  wherever  it 
formed  thin  streaks  and  layers,  has  for  the  most  part  been  changed  throughout 
into  a  light-green  pyroxene  rock. 

' '  In  the  larger  limestone  layers  in  the  contact-area  one  notices  not  infrequently 
a  structure  consisting  of  separate  marble  bands,  separated  by  layers  of  salite- 
garnet  rock,  and  also  a  thin-stratified  alteration  between  garnet-rock  and  mag- 
netic iron-ore.  More  usually,  however,  quite  irregular  nests  and  lumps  of 
magnetic  iron-ore  lie  in  the  midst  of  the  marble,  cutting  across  its  stratifica- 
tion. In  such  cases  they  frequently  penetrate  into  the  marble  with  jagged  or 
stringer-like  projections.  At  some  places,  as,  for  example,  in  the  limestone 
workings  near  the  Hermann  shaft,  even  irregularly  vein-shaped  masses  of  mag- 
netic iron-ore  were  observed  in  the  midst  of  the  limestone.  On  the  whole,  the 
ore  clings  especially  to  the  lower  boundary  of  the  marble  bed,  frequently  swell- 
ing up  from  there,  cutting  with  its  upper  boundary  across  the  strata  of  the 
marble  and  entirely  replacing  it  for  long  distances,  in  some  places  for  a  width  of 
5  m.  Finally,  the  ore-bodies  are  at  times  traversed  by  ramified  stringers  of  the 
garnet- rock,  forming  a  network  among  themselves.  It  thus  appears  that  the 
ore-mass  was  broken,  but  that  the  infiltration  of  the  solutions  furnishing  the 
garnet  continued  after  this  mechanical  disturbance.  That  phenomena  of  disrup- 
tion took  place  during  the  contact  metamorphosis,  at  the  time  of  the  transition 
of  the  dense  limestone  into  marble,  is  furthermore  indicated  by  the  frequent 
stringers  of  coarsely  foliated  calcspar,  which  traverse  the  blackish  marble  as 
white  bands.  They  seem  to  have  been  formed  during  the  process  itself,  as 
primary  stringers.  Occasionally  they  carry  some  garnet. 


380 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 


"  Other  ores  besides  magnetic  iron  take  part  in  the  composition  of  the  ore- 
beds  of  the  locality,  especially  copper  minerals,  such  as  chalcopyrite,  erubescite, 
copper  glance,  rarely  gray  copper-ore.  From  these  have  resulted  a  number  of 
secondary  copper-ores,  malachite,  etc.  Less  frequent  admixtures  are  iron  pyrites, 
arsenical  pyrites,"galena  and  zinc-blende. 

"  While  the  subsequent  introduction  of  all  these  ores  into  the  limestone  beds  of 
that  locality  is  beyond  question,  doubts  may  still  be  entertained  concerning  the 
origin  of  the  metalliferous  solutions.  Two  theories  may  be  advanced  in  regard 
to  this  point.  One  theory  is,  that  the  metallic  compounds  in  question  were  origi- 
nally finely  distributed  through  the  adjoining  rock,  especially  in  the  diabase 
tuffs,  and  were  only  later  concentrated  through  the  contact  metamorphosis,  through 
redeposition  in  the  limestone  by  means  of  mineralizing  agents  derived  from  the 
granite,  after  expulsion  of  the  carbonic  acid  of  the  calcium  carbonate.  The 
other  theory  is  that  these  metallic  compounds  were  directly  brought  up  with  the 
granite  from  great  depths,  and  were  infiltrated  into  the  adjoining  rock  in  solution 
in  the  over-heated  water  accompanying  the  eruption.  The  latter  theory  has  the 
greater  probability,  since  all  the  hornblende  schists  and  hornstones  are  rich  in 
iron  at  the  contact  also, — much  richer,  in  fact,  than  elsewhere,  aside  from  the 
contact. 

FIG.  1. 

'ese/er  Stolln 


Section  through  the  contact  zone  of  Rerggiesshiibel,  Saxony. 
G  =  Markersbach  granite  ;  ag  =  andalusite-mica  rock ;  h  =  hornblende  and 
pyroxene-schists ;  kn  =  spotted  schists  ;  e  =  ore-bodies  ;  k  =  crystalline  lime- 
stone ;  p  =  quartz-porphyry  ;  t  =  Sub-Turonian   and  Cenomanian. — R.  Beck, 
Erzlogerstatten,  p.  611. 

"This  is  rendered  still  more  probable  by  the  fact  that  in  the  same  district  ore- 
lodes  also  exist  in  the  granite,  which  are  characterized  by  copper-ores,  and,  in 
part,  traverse  the  ore-beds.  They  seem  to  represent  the  main  channels  of  supply 
for  the  metallic  solutions  emanating  from  the  granite. 

11  Finally,  besides  these  copper-lodes,  tin-bearing  stringers  are  also  known  to 
occur  in  the  metamorphic  limestone-beds  of  that  locality.  These  stringers  consist 
of  orthoclase,  fluorspar,  quartz  and  lithia-mica  distributed  in  zones.  Near  them 
A.  "VV.  Stelzneralso  discovered  tinstone,  together  with  chalcopyrite  and  pyrite,  as 
impregnations  of  certain  strata  of  the  beds,  consisting  mainly  of  chlorite. 

"The  Markersbach  granite  is  thus  seen  to  be  surrounded  by  an  aureole. of 
highly  diverse  metallic  compounds. 

"  The  iron-mining  industry  of  Berggiesshiibel,  formerly  of  some  importance,  is 
now  practically  extinct." 

Gold-Deposits. 

The  recognition  of  telluride  ores  in  contact-deposits  is,  I  be- 
lieve, new.  It  is  expressly  stated  by  Lindgren,  as  a  result  of 
his  review  of  the  literature  on  the  subject  and  his  own  experi- 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  381 

ence,  that  no  tellurides  occur  in  contact-deposits.*  I  have 
found  several  examples  of  this  interesting  type  of  deposit, 
which  is  clearly  entitled  to  rank  as  a  special  class  in  meta- 
morphic  deposits.  This  at  once  brings  up  the  question  of  per- 
manence in  depth  of  such  deposits,  discussed  elsewhere  in  this 
paper. 

Western  Montana  is  a  mountainous  region  in  which  there 
are  several  great  areas  of  granitic  rocks  breaking  up  through 
sedimentary  strata  and  earlier  igneous  rocks.  Along  the  lime- 
stone contacts  of  these  granitic  intrusions  (batholiths)  ore-de- 
posits are  often  encountered,  though  they  are  rarely  of  any 
great  economic  importance.  Most  commonly  they  are  of  the 
Kristiania  type,  examples  of  which  may  be  found  at  George- 
town, Cable,  and  other  localities  west  of  Anaconda;  in  the 
Highland  Range  south  of  Butte ;  in  the  Indian  Queen  mine,  on 
Birch  Creek,  in  Beaverhead  county ;  at  Elkhorn,  and  at  very 
many  localities  about  the  granitic  borders  mentioned.  There 
are,  however,  examples  of  contact  metamorphic  deposits  of  the 
Cananea  type  at  Elkhorn  and  Philipsburg. 

Bannack  Type. — The  placers  of  Grasshopper  Creek,  at  Ban- 
nack,  were  the  first  great  gold-placers  discovered  in  Montana. 
Attention  was  soon  attracted  by  the  ledges  on  the  slopes  above 
the  basin,  in  which  the  richest  gravels  occurred,  and  a  "  lode  " 
excitement,  almost  as  fierce  as  that  of  the  placer-days,  followed. 
Enormously  rich  ores  were  taken  out,  several  mills  were 
erected,  and  the  ground  was  burrowed  to  a  shallow  depth 
wherever  the  pockets  and  streaks  of  rich  ore  occurred.  Yet, 
despite  the  attractive  prospects  and  good  returns,  the  ore-depos- 
its have  never  been  explored  in  depth,  the  deepest  shaft  being 
about  300  feet  deep. 

The  ore-deposits  are. typical  contact  metamorphic  deposits. 
A  central  boss  of  diorite,  about  three-fourths  of  a  mile  in  di- 
ameter, is  surrounded  by  a  series  of  upturned  Paleozoic  lime- 
stones and  associated  shaly  rocks,  dipping  away  from  the 
granite  on  all  sides  at  angles  of  10°  to  45°.  This  dome  or  an- 
ticline has  been  eroded,  and  the  granite  now  forms  the  surface 
of  the  low  central  portion  of  a  basin,  whose  surrounding 
heights  are  formed  of  limestones  flanked  by  heavily-bedded 

*  "Character  and  Genesis  of  Certain  Contact-Deposits,"  Genesis  of  Ore-Deposits, 
p.  717,  under  heading  ''Constituent  Minerals;"  also,  Trans.,  xxxi.,  227. 


382  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

quartzites  of  Carboniferous  age.  The  diorite  intrusion,  though 
laccolithic  in  its  general  character,  has  a  very  uneven  contact, 
breaking  irregularly  through  the  limestones,  and  holding  in- 
cluded blocks  of  the  latter  within  its  mass,  while  tongues  of 
the  igneous  rock  project  out  and  penetrate  the  adjacent  sedi- 
mentary rock. 

The  limestones  are  highly  altered  about  the  contact;  but, 
owing  to  the  fact  that  the  diorite  comes  in  contact  with  lime- 
stones of  varying  composition,  the  resulting  rocks  differ  greatly 
in  mineral  constituents.  In  the  main,  these  contact  rocks  are 
either  impure  marbles  or  are  composed  of  brown  garnet,  epi- 
dote,  calcite,  and  other  common  contact  metamorphic  minerals. 
The  ore-deposits,  in  part,  follow  the  actual  contact  between  di- 
orite and  contact  rocks.  Where  limestones  prevailed,  the  ore- 
bodies  were  irregular ;  tongues  and  chambers  of  ore  extend  out 
into  the  limestone,  and  the  ore  (now  oxidized)  consists  of 
porous  iron-stained  quartz  the  cavities  of  which  show  the  crys- 
talline form  and  striations  of  coarsely  crystalline  gold-bearing 
pyrite.  Where  the  garnet  rocks  prevail  the  ores  do  not  follow 
the  contact,  except  in  a  general  way,  but  occur  in  the  more 
garnetiferous  bands  which  alternate  with  epidotic  rocks  and 
marbles  and  mark  the  alteration  of  beds  of  limestone  of  differ- 
ing composition.  The  ore-minerals  consist  of  telluride  of 
gold,  together  with  some  free  gold,  disseminated  and  rather 
abundant  specular  iron,  some  pyrite  and  less  chalcopyrite.  As 
usual,  the  telluride  ores  are  spotty,  occurring  in  rich  bunches, 
but  there  is  also  a  general  dissemination  through  the  rock,  and 
all  the  garnet-specular-iron  rock  contains  a  few  dollars  per  ton 
in  gold,  as  shown  by  a  large  number  of  assays. 

Elkhorn. — The  Elkhorn  district  is  situated  in  central  Mon- 
tana, about  half-way  between  Helena  and  Butte.  The  ore- 
deposits  occur  at  the  eastern  border  of  the  great  granite 
area  that  covers  the  greater  part  of  Jefferson  county.  At 
Elkhorn  this  granite  cuts  abruptly  across  the  ends  of  tilted 
sedimentary  beds  embracing  a  great  variety  of  rock  types 
of  different  geologic  ages.  The  granite  is  of  Tertiary  age, 
and  later  than  the  fragmental  andesitic  rocks  which  form 
the  neighboring  peaks  and  which  rest  upon  the  sediments. 
The  principal  ore-deposit,  that  of  the  Elkhorn  mine,  is  not  a 
contact  metamorphic  deposit,  but  a  "  saddle  "  deposit  formed  in 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  383 

the  axis  of  a  steeply  dipping  fold,  between  an  altered  shale 
(hornstone)  hanging-wall  and  a  crystalline  dolomite  crushed 
along  the  fold.  The  sedimentary  rocks  near  the  igneous  con- 
tacts are  highly  altered,  and  are  good  examples  of  contact 
metamorphic  rocks.  Iron  ore-deposits  on  Elkhorn  Peak  are 
contact-deposits  of  the  Kristiania  type,  and  there  are  several 
true  contact-deposits  of  pyrite  of  too  low-grade  to  work. 

A  half  mile  northwest  of  the  Elkhorn  mine,  on  the  western 
slope  of  a  steep  and  wooded  ridge  composed  of  altered  sedi- 
mentary rocks,  lies  the  Dolcoath  mine,  a  property  as  yet  in  the 
prospect  stage.  Shipments  of  sorted  ore  have  been  made,  and 
the  oxidized  ore  shows  native  gold  flecking  the  rock.  The 
ore  is  a  bed  of  garnet-diopside  rock  (altered  limestone)  15  to 
18  inches  thick,  dipping  at  55°  to  the  east  and  carrying  gold  in 
bismuth  sulphide  (bismuthinite)  and  bismuth  telluride  (tetra- 
dymite).  This  ore  stratum  is  conformable  with  the  adjacent 
beds,  but  differs  from  them  in  composition.  The  rocks  have 
been  studied  by  Dr  Barrell,*  who  determines  their  approxi- 
mate composition  to  be  as  follows  : . 


Ore  Stratum. 

Footwall. 

Hanging-Wall, 

.    45 

Diopside  

...   30 

Augite 

5 

.  40 

Garnet  

...   10 

Biotite 

25 

Calcite 

12 

Basic  feldspar 

60 

66 

Sulphides,  with  gold 

.     3 

Sulphides,  no  gold 

..     4 

100 

100 

100 

Samples  from  the  sacked  ore  of  the  upper  levels  yielded 
$156.00  per  ton  in  gold,  but  average  samples  from  the  bottom 
level,  made  during  an  expert  examination  of  the  property  by  a 
Butte  mining  engineer,  yielded  but  $4.50  per  ton  in  gold. 

Similkameen  Type  (British  Columbia). — The  Nickel  Plate  mine, 
which  promises  to  be  a  great  gold-producer,  is  situated  near 
the  Similkameen  river,  Osoyoos  mining  division,  west  of  Pen- 
ticton.f  The  ore  consists  of  a  gar net-calcite-epi dote  rock, 
whose  mineralogical  comppsition  and  geological  occurrence 
both  show  that  it  is  an  altered  impure  limestone.  The  ore- 
mineral  is  arsenical  pyrites,  disseminated  through  this  gangue 

*  Op.  cit.,  Am.  Jour.  Sri.,  April,  1902,  p.  295. 

f  Report  of  the  Minister  of  Mines  of  B.  C.  for  1900,  p.  883. 


384  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

rock  and  concentrated  in  the  high-grade  ores,  which  occur  in 
extraordinarily  rich  bands.  Mr.  H.  V.  Winchell  informs  me 
that  the  ore-body  is  of  contact  metamorphic  type.  The  speci- 
mens which  he  collected  show  the  arsenopyrite  to  be  confined, 
almost  exclusively,  to  the  garnetiferous  portion  of  the  ore,  the 
green  (epidotic  ?)  portion  being  very  low-grade. 

So  far  as  known,  arsenopyrite  has  never  before  been  founa 
in  contact-deposits.  It  has,  however,  been  observed  in  certain 
pegmatitic  veins  which  are  believed  by  some  observers  to  be  of 
pneumatolytic  origin.* 

CHANGES  IN  ROCKS  DUE  TO  CONTACT  METAMORPHISM. 

General  Effect. 

It  is  a  well-known  fact  that  certain  intruded  igneous  rocks 
have  exercised  a  profound  influence  upon  the  wall-rocks  con- 
fining and  adjoining  them,  while  other  types  of  igneous  mag- 
mas have  produced  only  a  slight  effect.  To  a  large  degree 
this  alteration,  or  contact  metamorphism,  is  due,  as  has  been 
shown  by  Id  dings, f  to  the  length  of  time  the  adjacent  rocks 
have  been  heated.  If  the  conduit  of  a  volcano  is  broken 
through  sedimentary  rocks,  and  this  conduit  serves  as  a  vent 
for  a  prolonged  period  of  time,  and  is  finally  filled  by  magma 
that  cools  as  a  coarse-grained  rock,  it  is  evident  that*  these  con- 
ditions favor  extreme  metamorphism  of  the  adjacent  material. 
If  a  small  sheet  or  dike  breaks  through  sedimentary  strata,  and 
is  promptly  chilled,  the  magma  exercises  but  little  apparent 
influence  upon  the  wall-rock.  It  is,  therefore,  largely  a  ques- 
tion of  physics.  The  great  intrusion  takes  a  long  time  to  cool ; 
the  magma  crystallizes  as  a  granular  rock,  and  the  adjacent 
rocks  are  heated  for  a  long  period.  It  is  partly,  therefore,  a 
question  of  the  mass  of  the  magma  cooling.  Professor  Kemp { 
has  succinctly  stated  the  known  facts  upon  this  subject  in  his 
recent  paper  upon  the  "  Role  of  Igneous  Rocks."  On  the  other 
hand,  although  the  result  of  such  long-continued  heating  of 

*  O.  A.  Derby,  "Notes  on  Brazilian  Gold-Ores,"  Trans.,  xxxiii.,  282. 
f  "  Electric  Peak  and  Sepulchre  Mountain,"  12th  Ann.  Rept.  U.  S.  Geol.  Survey, 
Pt.  I.,  pp.  569-664. 

J  Genesis  of  Ore-Deposits,  p.  692  ;  also,  Trans.,  xxxi.,  180. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  385 

wall-rocks  has  been  recognized  by  geologists  for  many  years, 
the  fact  that  different  rocks  show  varying  effects  has  been  com- 
monly imputed  to  the  nature  of  the  rock,  and  until  recently 
there  has  been  no  lucid  discussion  of  the  effect  of  contact  met- 
amorphism  upon  sedimentary  rocks.  Quite  recently  there  ap- 
peared a  paper  by  Prof.  Joseph  Barrell,  entitled  "  The  Physi- 
cal Effects  of  Contact  Metamorphism."*  In  this  paper  it  was 
shown  that  the  metamorphism  of  sedimentary  rocks  by  the 
heat  of  igneous  masses  is  accompanied  by  the  liberation  of 
enormous  volumes  of  gases,  with  attendant  shrinkage  of  vol- 
ume and  the  formation  of  vein-fissures  and  impregnation  de- 
posits. Several  writers,  particularly  Vogt,  Kemp,  and  Lindgren, 
have  recently  drawn  attention  to  the  metasomatic  and  impreg- 
nation effects  of  the  mineralizing  vapors  coming  from  the  cool- 
ing igneous  magma  and  carrying  dissolved  metallic  minerals 
along  favorable  channels  in  the  contact  zone.  In  addition  to 
this  eruptive  after-action  of  Vogt,  there  is  a  more  or  less  com- 
plete expulsion  of  carbon  dioxide  and  combined  water  from  the 
sedimentary  rocks,  accompanied  by  the  formation  of  new  min- 
erals and  the  induration  of  the  rocks.  As  is  well  known,  the 
alteration  of  pure  sedimentary  rocks  by  contact  metamorphism 
is  as  follows  :  Sandstone  to  quartzite  ;  clay-stone,  or  shale,  to 
hornstone  ;  limestone  to  marble;  but  as,  in  nature,  these  pure 
rocks  seldom  exist,  and  it  is  the  impure  limestones,  sandstones 
and  shales  which  are  most  common,  the  alteration  of  such  rocks 
produces  a  more  or  less  striking  metamorphism — the  material 
recrystallizing  as  garnet,  wollastonite,  epidote,  etc. 

Changes  in  Mass,  Volume,  and  Mineral  Composition. 

As  the  chemical  elements  remain  the  same  in  the  altered  as 
in  the  unaltered  rocks,  save  for  the  greater  or  less  expul- 
sion of  water  and  carbon  dioxide,  it  is  possible  to  tabulate 
the  mineralogic  changes.  This  has  been  done  by  Professor 
Barrell,  and  from  his  table  it  is  possible  to  work  out  not  only 
the  original  composition  of  the  unaltered  sediment,  but  the 
changes  in  mass  and  volume  which  have  taken  place  in  the 
process  of  metamorphism. 

The  greatest  changes  in  volume   are  due  to  escaping  gases 

*  Am.  'Jour.  Sci.,  vol.  xiii.,  April,  1902,  p.  279. 
25 


386  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

and  vapors.  His  conclusion  that  metasomatic  additions  dur- 
ing this  metamorphism  are  prevented  by  the  internal  pressure 
of  the  escaping  gases  is  not  regarded  as  correct  for  all  cases, 
though  it  is  based  upon  the  belief  that  by  the  time  the  pres- 
sure is  relieved  sufficiently  to  permit  the  ingress  of  heated 
waters  or  mineralizing  vapors  from  the  adjacent  magma  the 
rock  is  recrystallized ;  also,  as  a  result  of  the  hydrostatic  pres- 
sure of  the  still  liquid  magma,  it  is  usually  dense.  While  it 
may  be  true,  as  stated  by  Barrell,  that  metasomatic  infiltration 
of  the  metamorphic  strata  does  not  usually  take  place,  yet  in- 
stances have  come  within  the  observation  of  the  writer  where 
such  action  is  very  pronounced.  Differential  shrinkage  has 
given  the  strata  the  porosity  of  a  burned  brick,  and,  as  aptly 
noted  by  Barrel],  the  analogy  is  the  more  appropriate  since  in 
these  cases  the  action  is  one  of  thermal  metamorphism,  without 
sufficient  pressure  to  result  in  a  close  texture.  Two  instances 
are  given  by  Barrell,  both  in  the  Elkhorn  region  of  Mon- 
tana, one  already  quoted.  The  conditions  in  the  region  are 
particularly  favorable  for  a  study  of  the  varying  effects  of  the 
thermal  metamorphism  caused  by  the  intrusion  of  a  large 
igneous  mass  into  sediments  of  widely  varying  composition. 
The  granite  mass  cuts  across  tilted  strata  whose  inclination 
favors  alteration,  and  whose  wide  variety  of  composition  results 
in  striking  differences  in  the  porosity  of  the  altered  rock.  In- 
asmuch as  the  altered  sediments  are  on  top  of  the  granite, 
they  have  not  been  subjected  to  the  same  pressure  that  would 
have  changed  them  if  they  had  been  part  of  the  rock  enclos- 
ing the  intrusion.  Moreover,  the  pressure  would  be  trans- 
mitted by  the  denser  layers,  and  would  not  be  transverse  to 
the  borders. 

A  consideration  of  the  physical  conditions  involved  shows 
that  in  many  instances  the  porosity  induced  by  thermal  meta- 
morphism of  rocks  forming  the  side-walls  of  igneous  intru- 
sions is  probably  counteracted  by  the  hydrostatic  pressure  of 
the  magmas.  It  has  been  found  that  metamorphism  of  the 
sedimentary  rocks  would  be  practically  completed  before  solid- 
ification of  the  magma  begins,*  and  completed  while  the  mag- 
ma was  able  to  act  hydrostatically  and  transmit  lateral  pressure. 

*  Barrell,  op.  cit.,  p.  294. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  387 

Under  these  conditions  the  shrinkage  of  the  vertical  walls 
would  be  largely  lateral,  and  result  in  a  corresponding  lateral 
expansion  and  a  vertical  subsidence  of  the  magma.  Where, 
however,  as  is  so  commonly  the  case,  great  masses  of  granite 
are  capped  by  relatively  thin  layers  of  altered  sediments,  as, 
for  example,  in  the  region  about  Helena,  Montana,  the  sedi- 
ments above  the  magma,  though  subjected  to  pressure,  would 
transmit  this  pressure  along  the  heavier  and  more  competent 
beds ;  while  the  intervening,  weaker  members  would  retain  the 
porosity  due  to  recrystallization  and  escape  of  gases,  except,  of 
course,  at  the  immediate  contact  with  the  magma.  It  is  evi- 
dent that  in  such  cases  the  porosity  of  the  strata  near  the 
igneous  inclusion  favors  the  escape  of  pneumatolytic  gases 
along  and  through  the  porous  strata. 

GENESIS  OF  CONTACT  METAMORPHIC  DEPOSITS. 
Cause  of  Contact  Metamorphism. 

That  contact  metamorphism  is  due  to  intrusive  masses  of 
molten  magma  is  now  generally  accepted.  The  usual  theory 
advanced  is  that  the  heat  of  the  magma,  together  with  the 
watery  vapors  given  oft  by  it,  have  caused  the  metamorphism. 
This  is  the  explanation  advanced  by  both  Lindgren  and  Yogt. 
The  latter  has  quoted  the  Swedish  physicist,  Arrhenius,  as 
showing  that  the  physical  and  chemical  action  of  watery  vapors 
upon  a  magma  proves  such  vapors  to  be  competent  to  extract 
the  heavy  metals  from  the  magma.  Barrell,  however,  has 
shown  that  the  intrusion  of  magma  heats  the  adjacent  sedi- 
mentary rocks  to  very  high  temperatures,  generating  enormous 
volumes  of  gas  and  watery  vapor  by  changes  caused  in  the 
nature  of  the  sedimentary  rocks,  and,  moreover,  that  the  pro- 
cess of  recrystallization  is  complete  before  the  magma  cools. 
This  latter  conclusion,  reached  from  a  study  of  the  physico- 
chemical  actions  involved,  is  confirmed  by  the  field-evidence  at 
Elkhorn,  Mont.,  where  tongues  and  dikes  of  the  igneous  rock 
penetrate  the  contact  rocks,  and  accounts  for  similar  dikes  which 
at  Boundary  Creek,  B.  C.,  cut  the  contact  ore-bodies.  It  is, 
therefore,  not  necessary  to  assume  that  watery  vapor  from  the 
cooling  igneous  mass  has  played  the  only  part  in  the  metamor- 
phism. 

Whether  we  do  or  do  not  accept  this  statement  as  completely 


388  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

proven,  it  must  be  admitted  that  the  effect  of  the  igneous 
magma  upon  its  confining  walls  is  not  limited  to  this  first  met- 
amorphism  of  the  sedimentary  rock.  The  molten  magma  gives 
off  vapors, — pneumatolytic  vapors  they  have  been  called, — and 
that  these  escape  into  the  adjacent  rocks  we  have  abundant 
evidence.  As  some  geologists  appear  to  question  our  knowl- 
edge concerning  this  action,  it  may  be  well  to  summarize  the 
known  facts  concerning  the  gaseous  emanations  of  igneous 
rocks.  At  present  our  knowledge  of  these  is  derived  from  (1) 
analyses  of  the  gaseous  emanations  of  volcanoes  and  lava- 
flows;  (2)  analyses  of  the  gases  occluded  in  cold  rocks;  (3) 
analyses  of  the  sublimation-products  formed  by  fumaroles ;  and 
(4)  evidence  of  contact  metamorphism  of  included  masses  of 
sediments  entirely  surrounded  by  the  igneous  rock. 

Concerning  the  first  of  these  proofs,  there  is  considerable 
direct  positive  evidence  furnished  by  competent  observers  and 
chemists.  This  has  been  summarized  by  Geikie,*  who  states 
that  hydrochloric  acid  is  evolved  in  abundance  from  the  clefts  at 
Vesuvius ;  also  vast  quantities  of  free  hydrogen  or  combustible 
compounds  of  this  gas  are  given  off  from  Vesuvius,  and  were 
distinctly  recognized  by  Fouque  in  the  eruptions  of  Santorin.f 
These  gases,  when  studied  spectroscopically,  were  found  to 
contain  traces  of  chlorine,  soda  and  copper.  Analyses,  by 
Fouque,  of  the  gaseous  emanations  were  found  to  contain 
abundant  free  oxygen,  as  well  as  hydrogen,  and  one  analysis 

gave  the  results  in  column  I. : 

i.  ii. 

Carbon  dioxide,  .         .V.         .         .         .  0.22  15.38 

Oxygen,       ,       :.        ..  -•      .         ....  21.11  13.67 

Nitrogen,    .        ....         .        .         .  21.90  54.94 

Hydrogen, 56.70  8.12 

Marsh  gas  (methane),           .         .         .         .        .  .07  5.46 

Argon,         .         .         .         .         .         .         .        .      0.71 

In  column  II.  is  given  the  analysis  by  Moissan  of  the  gas 
collected  by  Lacroix  from  a  fumarole  on  the  Riviere  Blanche, 
Martinique,  whose  temperature  was  high  enough  to  melt  lead 
rapidly,  but  not  zinc  (i.e.,  about  400°  C.).  An  abundance  of 
sulphur  and  ammonium  chloride  was  deposited  about  it.J 

Fouque  infers  §  that  the  water  vapor  of  volcanic  vents  may 

*  Manual  of  Geology,  p.  188.  f  Santorin  et  ses  Eruptions,  p.  225. 

£  Comptes  Rendus,  cxxxv.    1085,  1902.  \  Santorin  et  ses  Eruptions,  p.  225. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  389 

exist  in  a  state  of  disassociation  from  the  molten  magma  when 
lavas  rise.  Fluorine  and  iodine  have  likewise  been  observed. 

In  a  recent  lecture,  Prof.  Eduard  Suess*  has  directed  atten- 
tion to  the  gaseous  emanations  of  volcanoes,  and  indicated 
their  part  in  the  formation  of  mineral  veins.  After  describing 
his  own  observations  at  Vesuvius,  he  says : 

"  Turning  now  to  the  gases  accompanying  the  eruptions. 
After  steam,  chlorine  and  gases  containing  sulphur  are  the 
most  important,  and  carbonic  acid  gas  comes  next.  Their  oc- 
currence follows  a  definite  law.  So  far  as  it  has  been  possible 
to  approach  them,  all  fumaroles  actually  within  vents  contain 
steam;  but  the  hottest  fumaroles  (over  500°  C.)  on  the  surface 
of  cooling  lava-streams,  where  approach  is  easier,  are  dry.  In 
the  emanations  from  these  high-temperature  fumaroles  are 
found  chlorine  compounds,  and  along  with  them  fluorine, 
boron  and  phosphorus, — substances  which  are  the  first  to  disap- 
pear as  the  temperature  of  the  fumarole  sinks.  Sulphur  per- 
sists longer,  often  combined  with  arsenic.  Carbonic  acid  is 
given  off  freely  till  a  much  later  stage,  sometimes  till  the  fuma- 
role is  comparatively  cool,  notwithstanding  that  it  is  observed 
in  the  hottest  dry  fumaroles.  Fumaroles  in  different  <  phases 
of  emanation  '  may  occur  quite  near  one  another.  The  steam 
of  the  volcano  cannot  be  derived  from  vadous  infiltration ;  for, 
if  it  is,  whence  the  carbonic  acid  ?  Both  must  come  from  the 
deeper  regions  of  the  earth ;  they  are  the  outward  sign  of  the 
process  of  giving  off  gases  which  began  when  the  earth  first 
solidified,  and  which  to-day,  although  restricted  to  certain 
points  and  lines,  has  not  yet  come  to  a  final  end.  It  is  in  this 
manner  that  the  oceans  and  the  whole  vadous  hydrosphere 
have  been  separated  from  the  solid  crust.  Volcanoes  are  not 
fed  by  infiltration  of  the  sea,  but  the  waters  of  the  sea  are  in- 
creased by  every  eruption." 

Concerning  the  analyses  of  the  gases  occluded  in  the  cold 
rocks,  the  evidence  is  not  so  satisfactory.  From  the  study  of 
microscopic  slides  it  is  well  known  that  gaseous  and  watery 
inclusions  occur  in  crystalline  rocks,  and  various  attempts  have 
been  made  by  chemists  to  estimate  the  quantity  of  included 
vapor  so  held.  Recently,  Dr.  M.  "W.  Travers,  in  a  paper  on 
the  "  Origin  of  Gases  Evolved  on  Heating  Mineral  Substances, 
Meteorites,  etc.,"  has  shown  "  that  in  the  majority  of  cases 

*  Geographical  Journal,  London,  vol.  xx. ,  p.  520,  November,  1902. 


390  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

where  a  mineral  substance  evolves  gas  under  the  influence  of 
heat,  the  gas  is  the  product  of  the  decomposition  or  interaction  of 
its  non-gaseous  constituents  at  the  moment  of  the  experiment."* 

Notwithstanding  this  fact,  however,  we  have  abundant  evi- 
dence, in  the  analyses  of  obsidian  and  pitchstone,  of  the  pres- 
ence of  a  considerable  proportion  of  water ;  and  it  is  well 
known  that  these  rocks  change  into  pumice  on  heating.  Also 
the  presence  of  fluorite  in  the  dense  and  almost  glassy  phono- 
lites  of  Montana  is  to  be  remarked  here.  The  Hawaiian 
Island  lavas,  though  highly  vesicular,  contain  practically  no 
water,  and  Whitman  Crossf  has  noted  the  absence  of  steam 
from  the  lava  cauldron  of  Kilauea,  although  there  was  an  abun- 
dance of  sulphurous  vapors  and  brown  vapors  of  an  unknown 
composition  given  off  from  clefts  immediately  adjacent  to  the 
lava  lake. 

Attention  might  also  be  directed  to  the  recent  work  of  Ar- 
mand  Gautier,J  in  which  he  shows  that  granite  and  other 
crystalline  rocks  evolve  large  quantities  of  vapors  when  heated. 

Third,  the  analyses  of  the  sublimation  products  found  about 
fumaroles  show  conclusively  that  metallic  salts,  as  well  as  non- 
metallic,  are  given  off  by  the  igneous  emanations,  or  result 
from  reactions  between  the  escaping  vapors  and  the  solids 
with  which  they  come  in  contact.  Besides  sulphur,  chlorides 
of  sodium,  potassium,  iron,  copper  and  lead  also  occur,  and 
specular  iron,  oxide  of  copper  and  iron  chloride  have  been  ob- 
served by  Geikie  and  Fouque.§ 

Fourth,  the  evidence  of  contact  metamorphism,  as  studied  in 
included  masses,  affords  direct  proof  of  the  action  of  pneuma- 
tolytic  vapors  when  the  original  composition  of  the  included 
mass  can  be  known  with  any  certainty.  Under  such  conditions 
one  can  exclude  the  reactions  indicated  in  the  case  of  the  con- 
fining walls  of  the  magma,  and  there  is  no  doubt  that  in  many 
cases  there  is  a  direct  migration  of  material,  particularly  sili- 
cates, also  fluorine  and  chlorine,  together  with  copper  sulphide 
and  iron  oxide,  into  the  included  masses.  Such  masses  have 
been  studied  by  Lindgren||  at  the  Seven  Devils  district  of 

*  Proc.  Royal  Soc.,  vol.  Ixiv.,  p.  142.     (Read  Nov.  24,  1898.) 
f  Verbal  communication. 

j  Zeit.  Prak.  Geol,  vol.  ix.,  p.  383, 1901.      |  Geikie,  Manual  of  Geology,  p.  188. 
||  ' '  Character  and  Genesis  of  Certain  Contact-Deposits,"  Genesis  of  Ore-Deposits, 
p.  722;  also,  Trans.,  xxxi.,  232. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  391 

Idaho,  and  by  Kemp  in  the  San  Jose  district,  and  Tamaulipas, 
Mexico. 

Inasmuch  as  included  fragments  of  pure  limestone  are 
changed  to  garnet-rock  and  impregnated  with  metallic  sul- 
phides, vesuvianite,  axinite,  etc.,  whose  constituents  are  not 
normal  to  any  of  the  original  rocks  surrounding  the  intrusion, 
the  evidence  is  satisfactory  that  there  was  a  migration  of  mate- 
rial in  the  form  of  vapor  from  the  igneous  magma  into  the  ad- 
jacent rocks. 

From  this  evidence  we  are  justified  in  assuming  that  there  is 
a  series  of  "  eruptive  after-effects,"  as  Yogt  has  called  them, 
which  start  at  the  moment  of  the  intrusion  and  continue  until 
the  rocks  have  completely  cooled,  and  which  grade  one  into 
the  other.  • 

On  the  other  hand,  if  the  resulting  metamorphic  rocks  are 
porous,  as  in  certain  cases  we  know  them  to  be,  the  vapors 
from  the  cooling  magma  will  be  "  blown  in  "  (to  use  Yogt's 
term),  and  ore-deposits  may  be  formed  in  this  way. 

Professor  Suess,  in  the  lecture  already  quoted,  has  called 
renewed  attention  to  the  fact  that  mineral  veins  are  to  be  re- 
garded as  the  result  of  waning  phases  of  volcanic  (igneous) 
phenomena.  "  Hot  springs  may  be  taken  as  the  latest  phase  of 
a  whole  series  which  led  up  to  the  present  deposits  of  ore."  His 
whole  paper  is  an  argument  against  the  theory  that  either  the  ma- 
jority of  ore-deposits  or  of  hot  springs  are  of  meteoric  derivation. 

That  gaseous  emanations  rising  through  fissures  toward  the 
earth's  surface  can  mingle  with  ordinary  meteoric  ground-water 
must  be  admitted,  and  it  is  believed  that  much  of  the  discus- 
sion between  those  who  advocate  the  deposition  of  ores  by  cir- 
culating ground-waters,  deriving  their  metallic  contents  from 
the  generally  cold  rocks  traversed  in  their  course  from  the 
earth's  surface  downward  and  back  again  to  the  surface,  has 
arisen  because  of  the  failure  to  recognize  that  in  this  mingling 
of  igneous  emanations  and  ground-waters  we  have  the  true 
explanation.  The  ground-waters  alone,  either  cold  or  heated, 
would  not  ordinarily  take  up  enough  material  from  the  rocks 
traversed  by  them  to  enable  the  waters  to  deposit  ores  in  veins. 
On  the  contrary,  it  is  the  gaseous  emanations  carried  by  the 
ground-waters  into  trunk-channels  that  deposit  ores  by  reaction 
with  other  currents,  wall-rock,  etc. 


392  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

Contact  metamorphic  deposits,  properly  so-called,  occur  as  a 
result  of  the  metamorphism  of  sedimentary  rocks  by  igneous 
intrusions.  The  definition  thus  excludes  all  deposits  formed 
along  ordinary  contacts,  due  solely  to  circulating  waters,  even 
where  such  waters  contain  substances  derived  from  igneous  em- 
anations dissolved  in  the  waters, — as,  for  example,  the  Mercur, 
Utah,  and  Judith  Mountain,  Montana,  deposits,  and  other  ore- 
bodies  of  similar  character.  When  the  ore-minerals  are  inter- 
grown  with  the  garnet-epidote  and  other  gangue  minerals,  the 
deposits  are  clearly  pneumatolytic.*  Another  class  is  the  result 
of  later  impregnation  by  igneous  emanations  penetrating  a 
porous  stratum,  the  stratum  itself  made  porous  as  a  result  of 
metamorphism.  A  third  class  are  the  result  of  the  precipita- 
tion of  copper  or  other  sulphides  from  ascending  alkaline  solu- 
tions, supposedly  hot  waters,  by  the  lean  sulphides  formed  by 
pneumatolytic  action  (deposits  of  the  second  class).  In  the 
first  class  the  ores  are  of  simultaneous  origin  with  the  gangue 
minerals  which  are  admittedly  due  to  contact  metamorphism. 
In  the  second  class,  ores  were  introduced  subsequent  to  the  met- 
amorphism of  the  rock  (Elkhorn  type).  The  third  is  probably 
difficult  to  distinguish  from  the  first,  but  is  believed  to  exist  at 
Cananea,  Mexico,  though  not  the  kind  designated  by  that  name. 

Barrell  has  calculated  the  changes  taking  place  in  two  ex- 
amples at  Elkhorn.  The  first  is  a  thin  band  of  hornstone  oc- 
curring in  marble  and  consisting  of  50  per  cent,  of  diopside, 
with  46  per  cent,  of  feldspar  and  2  per  cent,  each  of  quartz  and 
fluorite.  It  is  evident  that  the  crystallization  of  diopside  and 
feldspar  left  the  stratum  very  porous,  and  that  the  pores  were 
filled  by  quartz  and  fluorite  from  pneumatolytic  vapors. 

The  second  instance  given  by  him  is  the  ore-stratum  of  the 
Dolcoath  mine,  already  described.  This  is  a  typical  instance 
of  a  porous  layer. 

lt  It  is  seen  that  even  if  all  the  calcite  of  the  ore-bearing  stratum  be  regarded  as 
a  primary  mineral,  the  shrinkage  in  the  ore-stratum  has  been  somewhat  greater 
than  in  either  the  foot-  or  hanging-wall,  since  the  feldspars  and  biotite  are  min- 
erals which,  as  shown  by  the  alkalies  present,  were  formed  from  sediments  not 
fully  hydrated  or  carbonated.  Moreover,  a  microscopic  examination  of  the  ore- 
stratum  shows  parallel  sinuous  cracks  due  to  tension,  and  not  to  shear,  and  now 
filled  with  calcite.  Elsewhere  in  the  section  the  calcite  exists  as  a  sponge,  hold- 
ing garnet,  dicpside,  and  ore-grains  within  it,  and  its  secondary  nature  is  not  so 

*  I.e.,  formed  by  the  action  of  gases  or  vapors  at  high  temperatures  and  pres- 
sures reacting  upon  solid  materials. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  393 

clear.     The  ore  is  associated  with  the  calcite,  and  also  with  a  certain  coarser  crys- 
tallization of  the  diopside."* 

Professor  Barrell  calculates  the  shrinkage  of  the  ore-stratum 
at  40  per  cent.,  of  the  hanging-wall  at  15  per  cent.,  and  the 
footwall  at  25  per  cent.,  so  that  it  is  evident  that  we  have  here 
a  steeply  inclined  pervious  stratum  capped  by  a  relatively  dense 
impervious  bed,  and  offering  a  favorable  channel  for  uprising 
vapors,  given  off  by  the  cooling  magma  beneath,  or  for  circu- 
lating waters. 

The  source  of  the  metallic  mineral  deposited  in  these  contact- 
rocks,  if  not  positively  known,  is  commonly  assigned  to  the  sol- 
fataric  vapor  given  off  by  the  cooling  igneous  magmas.  There 
has  always  been  more  or  less  skepticism  concerning  the  source 
of  the  oxide  of  iron,  magnetite  and  specularite,  which  are  such 
common  and  characteristic  features  of  true  contact-deposits. 
Inasmuch  as  the  disassociation  of  the  interstitial  water  of  the 
sedimentary  rocks  by  the  intrusion  of  highly-heated  magma 
would  provide  a  sufficient  supply  of  oxygen,  the  occurrence  of 
such  ores,  produced  by  reaction  with  the  iron-compounds  pres- 
ent, would  be  explained,  while  the  fact  that  such  deposits  are 
almost  entirely  confined  to  the  immediate  vicinity  of  the  igne- 
ous contact  can  be  readily  understood. 

PERMANENCE  IN  DEPTH   OF  ORE-DEPOSITS  OF  THIS  CLASS. 

So  far  as  development  and  experience  show,  the  deposits 
of  the  Kristiania  type  occurring  at  actual  contacts  are  very 
bunchy,  and  cease  in  depth;  a  notable  example  being  the  Seven 
Devils,  Idaho,  deposits.  In  the  Cananea,  Mexico,  example, 
and  the  Boundary,  British  Columbia,  deposits,  the  copper-ore 
is  more  uniformly  distributed,  and  there  seems  no  theoretical 
reason  why  the  primary  sulphide-ore  should  not  continue  of 
unchanged  tenor  in  depth  down  to  the  igneous  contact.  In 
the  case  of  the  gold-ores,  both  tellurides  and  arsenopyrite,  so 
little  is  known  that  no  prognosis. can  be  made.  The  deepest 
workings  at  Bannack  are  but  300  feet  below  the  surface.  At 
Cripple  Creek,  where  the  deposits  are  not  of  contact-metamor- 
phic  origin,  though  they  are  considered  to  result  from  volcanic 
emanations,  the  values  decreased  with  depth.  However,  recent 
discoveries  indicate  workable  bodies  of  auriferous  gray  copper 
at  greater  depths.  The  Cornwall  tin-  and  copper-veins  are 

*  Op.  tit.,  pp.  295,  296. 


394  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

now  practically  worked  out.  At  the  Dolcoath  the  ore  is  low- 
grade  at  150  feet.  If  the  theory  of  genesis  be  true,  there  is  no 
reason  now  known  for  the  impoverishment  of  contact  meta- 
m orphic  deposits  in  depth. 

MINERAL  VEINS  NEAR  IGNEOUS  CONTACTS. 
In  addition  to  the  pneumatolytic  deposits  on  igneous  con- 
tacts and  those  in  altered  strata  near  the  contacts,  there  are 
many  productive  mines  working  true  veins  cutting  the  igneous 
rock  and  the  contact-rocks  above  them.  Such  vein-fissures  are 
caused  both  by  the  contraction  due  to  the  crystallization  and 
cooling  of  the  igneous  rock  and  by  the  shrinkage  of  the  meta- 
morphic  zone  above  the  igneous  rock.  Examples  of  this  type 
have  already  been  mentioned.  As  shown  by  Pirsson,*  the 
radial  fissures  which  form  so  remarkable  a  feature  of  certain 
igneous  centers  are  not  due  to  the  initial  expanding  force  of 
the  intruded  magma,  but  to  the  contraction-cracks.  The  vast 
amount  of  heat  given  off  by  the  cooling  magma  effects  a  con- 
siderable expansion  of  the  surrounding  rocks.  As  the  magma 
and  its  surrounding  shell  of  heated  sediments  cools  down  it 
must  contract,  and  this  contraction  will  result  in  a  cracking 
both  of  the  igneous  rock  and  the  contact-zone ;  and,  if  the 
rocks  of  the  contact-zone  are  homogeneous,  the  cracks  will  as- 
sume a  more  or  less  radial  position.  If  these  cracks  extend  to  a 
depth  sufficient  to  reach  still  molten  magma,  they  will  be  filled, 
and  dikes  will  be  formed ;  if  not,  the  cracks  become  channels 
for  pneumatolytic  vapors  and  later  circulating  waters,  and  thus 
pegmatite  veins  and  true  mineral  veins  may  be  formed,  and  may 
merge  into  one  another.  It  is  possible  that  the  (now  brecciated) 
Granite  Mountain  vein  at  Philipsburg,  and  the  very  pro- 
ductive veins  at  Marysville,  Montana,  may  have  originated  in 
this  manner.  But,  in  addition  to  radial  cracks,  the  shrinkage 
would  also  tend  to  produce  cracks  parallel  to  the  borders  of 
the  intrusion, f — a  phenomenon  observed  in  casting,  and  also  in 
the  cooling  of  lava-sheets, — as,  for  example,  those  of  Obsidian 
Cliff,  in  the  Yellowstone  Park  region,  a  discussion  of  which 
has  been  given  by  Iddings.J  As  circulating  solutions  travers- 

*  "Complementary  Hocks  and  Kadial  Dikes,"  Amer.  Jour.  Sci.,  vol.  1.,  1895, 
p.  116. 

f  For  ore-deposits  of  this  type,  see  Beck,  op.  cit.,  p.  182,  Fig.  119. 
J  7th  Ann.  Rept.,  U.  S.  Geol.  Surv.,  for  1885-6,  pp.  249-295. 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  395 

ing  contact-zones  would  course  through  the  more  basic  differ- 
entiated part  of  the  magma,  which  is  well  known  to  be  richer 
in  metals  than  the  normal  magma,  there  has  been  a  combina- 
tion of  conditions  favoring  ore-formation,  and  it  is  easy  to  see 
why  such  ore-deposits  occur  in  or  near  the  contacts  of  great 
igneous  masses. 

I  hold  that  the  metallic  contents  of  such  veins  are  not  gath- 
ered by  ordinary  meteoric  water,  as  maintained  by  Van  Hise. 
The  water-content  of  the  sedimentary  rocks  (ground-water) 
present  at  the  time  of  eruption  was  expelled  by  contact  meta- 
morphism.  The  ore-forming  solutions  were  in  part  of  direct 
igneous  origin;*  these  primitive  hot  vapors  and  waters  rise  and 
penetrate  the  zone  of  circulating  meteoric  waters,  heating  the 
latter  and  charging  them  with  both  metallic  salts  and  with  fluo- 
rine, chlorine,  boron  and  other  active  mineralizers.  The  result- 
ing mixture  of  plutonic  and  meteoric  waters  is  a  much  more 
energetic  solvent  than  normal  ground-water,  and  is  capable  of 
adding  metallic  salts  extracted  from  the  rocks  traversed  by  the 
waters  to  the  original  material  derived  from  the  igneous  emana- 
tions. 

CONCLUSIONS. 

Contact  metamorphic  ore-deposits  occur  about  the  margin  of 
intrusive  masses  of  granular  igneous  rock,  either  at  the  actual 
contact  or  in  the  zone  of  metamorphosed  sedimentaries.  The 
deposits  of  economic  value  occur  only  where  strata  or  blocks  of 
impure  limestone  have  been  crystallized  as  garnetiferous  or 
actinolite-calcite  rocks,  with  consequent  porosity.  The  ore- 
minerals  are  intimately  associated  with  these  aluminous  sili- 
cates, and  may  be  either  intergrown,  or  metasomatic  replace- 
ments, or  the  result  of  interstitial  filling  with  partial  replace- 
ment. The  conversion  to  garnet-epidote-calcite,  etc.,  rock  was 
complete  before  the  consolidation  of  the  igneous  rock.  The 
ore-minerals  were  introduced  in  gases  and  vapors — solfataric 
emanations — from  the  eruptive  masses  of  which  they  constitute 
pneumatolytic  after-actions,  or  by  hot  circulating  primitive 
waters  given  off  by  the  cooling  igneous  mass.  This  theory  of 
the  genesis  being  true,  the  deposits  should  extend  downward  in 
depth  to  the  granular  rock. 

*  I.e.,  primitive  or  igneogenous.  The  geyser  waters  of  Iceland,  New  Zealand 
and  the  Yellowstone  regions  are  probably  mainly  of  this  character,  as  maintained 
by  Suess. 


396  ORE-DEPOSITS  NEAR  IGNEOUS  CONTACTS. 

DISCUSSION. 

(Traits.,  xxxiii.,  1070.) 

W.  L.  AUSTIN,  New  York,  N.  Y. : — In  Mr.  Weed's  interest- 
ing paper,  frequent  reference  is  made  to  the  Cananea  copper- 
deposits,  which  are  said  to  have  been  so  vigorously  exploited 
that  they  produced  14,000,000  Ib.  of  copper  in  1901. 

The  ore-bodies  which  yielded  this  large  quantity  of  metal  are 
described  as  a  product  of  contact-metamorphism,  and  in  Mr. 
Weed's  genetic  classification  of  such  deposits,  they  receive  a 
place  under  the  sub-heading,  "Deposits  impregnating  and  re- 
placing beds  of  contact-zone."  They  are  considered  by  Mr. 
Weed  to  represent  a  special  type  under  this  head,  and  are  fur- 
ther classified  as :  "  1.  Chalcopyrite  deposits :  (a)  Pyrrhotite 
ores ;  (b)  Magnetite  ores,  Cananea  type." 

In  condensing  much  information  into  a  comparatively  small 
space,  the  presentation  of  a  subject  may  be  so  abbreviated  as  to 
detract  from  its  clearness.  The  situation  at  La  Cananea,  con- 
sidering its  importance  from  an  economic  as  well  as  scientific 
standpoint,  may  be  worthy  of  more  detailed  description.  As 
Mr.  Weed  rightly  remarks,  "  structural  differences  are  so  im- 
portant, and  have  so  marked  a  bearing,  not  alone  on  the  theory 
of  their  genesis,  but,  also,  in  the  working  of  the  deposits  and 
a  determination  of  their  value  as  mines,  that  they  merit  a  full 
discussion." 

It  is  my  present  purpose :  (1)  to  show  that  it  is  doubtful 
whether  the  copper  of  La  Cananea  is  mined,  except  to  a  limited 
extent,  from  contact-metamorphic  deposits;  (2)  to  emphasize 
the  importance  of  the  mineral-bearing  porphyry  in  connection 
with  the  genesis  of  the  Cananea  deposits ;  and  (3)  to  question 
the  correctness  of  Mr.  Weed's  opinion  that,  in  this  locality, 
"  the  deposits  should  extend  downward  in  depth  to  the  granu- 
lar rock." 

Contact-metamorphic  ore-deposits  are  very  common  in  the 
West  and  Southwest.  Among  the  better  known  of  those  in 
which  copper  is  the  principal  economic  mineral  are  those  of  the 
Seven  Devils  district,  Idaho;  Saline  Valley,  California;  the 
Planet  mine  on  Bill  Williams  Fork,  Marble  mountain,  in  the 
Santa  Catalina  mountains,  and  Clifton,  Arizona;  La  Cananea, 
and  the  Santo  Emo  deposits  on  the  Yaqui  river,  Sonora;  Teras- 
sas  Station,  Chihuahua ;  and  La  Jibosa  mine,  Velardena  copper- 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  397 

mine,  and  Sacrificio  mountain,  Durango.  There  are  many  others 
which  I  have  not  personally  visited,  but  concerning  which  I 
have  received  private  communications,  or  have  found  described 
in  current  technical  literature. 

These  may  all  be  classed  together  as  ore-deposits  occurring 
at  or  near  the  contact  of  igneous  rocks  with  limestone  beds,  and 
owing  their  existence  to  the  presence  of  the  eruptives. 

This  general  type  of  deposit  is  recognizable  at  first  sight; 
but  it  is  not  always  with  a  simple  contact  that  the  observer  has 
to  deal.  Associated  with  the  actual  contact  ore-bodies  are 
mineralized  eruptives,  fissure-veins  and  replacements  in  the 
limestone.  Mr.  Weed,  recognizing  the  variations  displayed 
by  deposits  of  this  description,  has  proposed  a  tentative  classifi- 
cation, which  might  be  further  discussed  to  advantage. 

By  reason  of  the  very  nature  of  the  genesis  of  these  de- 
posits, there  must  be  much  diversity  among  them.  In  fact, 
hardly  any  two  of  them  are  exactly  alike.  They  all  have  a 
certain  mutual  resemblance,  and  differ  radically  from  any 
other  class;  but,  unless  a  broad  significance  is  given  to  the 
term  contact-metamorphism,  it  will  scarcely  cover  them  all, 
and,  in  any  event,  there  will  be  almost  as  many  "  types  "  as  de- 
posits. 

The  selection  of  the  Cananea  deposits  as  typical  of  contact- 
metamorphism,  and  the  ascription  to  this  type  of  the  large  pro- 
duction of  copper  quoted  above,  seems  to  me  to  be  ill-advised ; 
and  the  statement  that  in  this  instance  the  primary  sulphide- 
ore  should  continue  of  unchanged  tenor  in  depth  down  to  a 
hypothetical  contact  with  granular  rock,  certainly  calls  for  fur- 
ther elucidation. 

There  are  numerous  contacts  between  the  limestone  and  the 
igneous  rocks  of  the  Cananea  district; — in  fact,  all  the  lime- 
stone patches  are  almost  surrounded  by  porphyritic  rocks  of 
one  kind  or  another; — but  neither  at  any  one  of  the  important 
mines,  nor  at  any  other  points  so  far  as  I  know,  has  a  contact 
between  the  limestone  and  a  granular  igneous  rock  been  ob- 
served. 

The  ore-deposits  of  La  Sierra  de  la  Cananea,  as  hitherto  de- 
veloped, are  scattered  through  the  mountains  along  a  N".  W.-S.E. 
belt  for  about  8  miles.  Puertocito  is  at  the  extreme  northern 
end  of  the  belt ;  the  Elisa  mine  at  about  the  middle ;  Capote 


398  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

basin  (with  the  Capote,  Oversight,  Yeta  Grande  and  Chivatera 
mines)  are  south  of  the  Elisa ;  and  at  the  southern  end  is  the 
Cobre  Grande  mine.  The  Elenita  deposits  are  really  a  part  or 
Puertocito.  At  various  points  between  these  main  ore-bodies 
are  smaller  ones. 

At  Puertocito  and  Elenita  there  are  masses  of  garnetiferous 
minerals  with  associated  copper  carbonates  and  silicates,  pyrite, 
chalcopyrite  and  bornite ;  at  the  Elisa  there  are  irregular  bodies 
of  chalcopyrite  along  a  fault-fissure  in  the  metamorphosed 
limestone ;  at  the  Oversight  and  Capote  mines  there  are  much 
larger  masses  of  feldspathic  porphyry  carrying  chalcocite,  which 
have  yielded  much  the  greater  part  of  the  copper  produced  in 
the  district.  The  deposits  of  Elenita  and  Puertocito  had  no 
part  in  the  large  copper-production  mentioned  in  Mr.  Weed's 
paper;  not  until  late  in  April,  1903,  was  any  ore  shipped  from 
this  part  of  the  belt. 

At  the  present  time  (April,  1903)  the  Oversight  mine  occu- 
pies the  place  of  honor  among  the  developed  properties,  having 
temporarily  exceeded  the  production  of  the  Capote,  which  was 
the  first  large  bonanza  found  in  the  district.  The  first-class  ore 
of  the  Oversight  is  a  soft,  white  feldspathic  porphyry,  heavily 
mineralized  with  chalcocite.  At  the  southern  end  of  the  mine, 
the  surface-indications  of  underlying  ore-bodies  are  so  slight 
that  one  not  very  familiar  with  the  characteristics  of  deposits 
of  this  class  would  hardly  have  ventured  to  predict  the  dis- 
coveries which  have  been  made  a  few  feet  below.  The  por- 
phyry shows  at  the  top  no  mineralization ;  no  gossan ;  no  "  cop- 
per stains."  The  solutions  which  effected  the  decomposition 
of  the  original  pyrite,  carried  the  iron  with  them  and  deposited 
it  elsewhere, — a  process  which  can  be  seen  in  operation  to-day 
in  other  parts  of  the  district.  In  such  cases,  silica  and  silicates 
are  usually  substituted  for  the  minerals  removed. 

Underneath  there  is  an  ore-body  of  irregular  shape,  already 
developed  for  several  hundred  feet  in  depth,  and  in  places  sev- 
eral hundred  feet  wide.  It  is  in  reality  a  southerly  continua- 
tion of  the  Capote  ore-zone — a  second  great  concentration  of 
chalcocite  in  the  porphyry.  Its  limits  as  here  stated  are  merely 
those  of  the  ore  rich  enough  to  be  shipped ;  in  fact,  the  chalco-  . 
cite-bearing  rock  merges  into  cupriferous  pyrite  bodies  of  very 
much  larger  dimensions,  but  of  lower  grade.  This  much  is 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  399 

known  :  but  what  is  the  extent  of  these  ore-bodies,  or  how  many 
more  of  them  there  may  be,  has  not  yet  been  ascertained.  Only 
the  first-class,  and  the  higher  grades  of  the  second-class  ore,  are 
at  present  taken  out;  lower-grade  material  is  left  standing. 

It  is  not  my  present  intention  to  discuss  the  extent  and  value 
of  the  Cananea  ore-bodies.  That  matter  has  been  briefly 
touched  upon,  only  in  order  to  bring  out  the  fact,  that  by  far 
the  greater  part  of  the  copper  produced  by  the  mines  of  La 
Cananea  has  come  from  masses  of  mineralized  porphyry,  and 
not  from  "  chalcopyrite  ore-bodies  carrying  accessory  galena,  . . . 
practically  confined  to  the  rocks  resulting  from  the  alteration  of 
impure  limestones."  A  statement  of  this  kind,  coming  from 
such  an  authority  as  Mr.  Weed,  might  possibly  cause  others  to 
feel  warranted  in  making  large  expenditures  upon  deposits  of 
the  class  indicated,  basing  their  hopes  on  the  supposition  that 
the  bonanzas  of  La  Cananea  were  found  in  contact-metamorphic 
deposits,  with  a  probability  of  their  extending  "  downward  in 
depth  to  the  granular  rock." 

Porphyry  is  by  far  the  predominating  rock  along  the  Cananea 
ore-belt.  I  use  the  term  "  porphyry  "  in  its  general  sense,  for 
there  are  several  varieties.  Possibly  all  varieties  have  had 
their  origin  in  the  same  eruptive  magma,  the  sub-species  being 
due  to  magmatic  differentiation,  or  to  the  incorporation  of  por- 
tions of  other  rocks  with  which  the  eruptives  came  into  con- 
tact. In  places  is  found  typical  quartz-porphyry ;  but  where 
the  ore-bodies  occur,  the  quartz  is  not  so  much  in  evidence. 
There  are  in  the  district  other  varieties  of  igneous  rocks,  such 
as  granite,  diorite,  diabase  and  andesite ;  but  these  are  mostly 
at  some  distance  from  the  ore-belt,  and  as  far  as  I  know  are 
not  mineralized  to  any  noticeable  degree.  The  porphyry,  how- 
ever, wherever  it  has  been  artificially  exposed  within  the  entire 
length  of  8  miles  here  in  question,  is  more  or  less  pyritic,  and 
in  places  the  sulphides  are  massed  so  as  to  form  ore-bodies. 
The  mineral  belt  has  been  extensively  prospected,  and  tunnels 
many  hundreds  of  feet  in  length  cross  its  trend  in  a  number  of 
places.  In  these  tunnels,  many  of  which  are  considerable  dis- 
tances away  from  the  producing  mines,  this  mineralized  por- 
phyry is  exposed;  and  at  such  points  its  character  can  be 
studied  to  advantage.  It  extends  from  the  mines  on  the  ex- 
treme north  to  those  on  the  extreme  south,  and  is  essentially 


400  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

the  mineral-bearer  of  the  district.  The  limestone  occurs  only 
in  spots.  Where  the  heavily  mineralized  porphyry  has  come 
into  contact  with  this  limestone,  there  are  the  usual  contact- 
metamorphic  phenomena;  hut  these  ore-bodies  are  of  subor- 
dinate commercial  importance ;  in  fact,  but  for  the  mineralized 
porphyry  the  history  of  La  Cananea  would  have  been  a  totally 
different  one. 

The  quartzites  do  not  contain  mineral  deposits,  except  where 
cupriferous  solutions  from  the  decomposing  porphyry  have 
found  cracks  and  fissures  in  which  to  deposit  their  burdens ; 
and  these  are  practically  a  negligible  quantity. 

Where  the  limestone  has  been  metamorphosed  by  contact 
with  the  porphyries,  it  has  become  one  of  the  most,  if  not  the 
most,  resistant  of  the  rocks  of  the  district.  Proof  of  this  state- 
ment is  furnished  by  the  garnetiferous  bluffs  which  constitute 
such  prominent  landmarks  at  the  Puertocito  end  of  the  belt. 
Not  in  this  district  only,  but  everywhere,  such  resistance  to 
weathering  is  characteristic  of  rocks  thus  metamorphosed;  for 
the  process  itself  is  largely  one  of  silicification. 

The  ore-bodies  which  have  made  La  Cananea  famous  are 
soft  porphyritic  masses,  partly  of  mineralized  porphyry,  partly 
of  dark-colored  plastic  clay  less  heavily  charged  with  copper- 
ore.  The  one  merges  insensibly  into  the  other,  and  much  of 
the  material  is  of  a  nondescript  character,  depending  on  the 
degree  of  decomposition  which  the  rock  has  undergone.  It 
bears  no  resemblance  to  metamorphosed  limestone,  although 
fragments  of  that  rock  are  found  in  it,  as  are  also  masses  of 
quartzite. 

It  is  common,  where  porphyritic  flows  have  broken  through 
limestone  beds,  to  find  included  masses  of  the  latter  caught  in, 
and  surrounded  by,  the  porphyry ;  and  the  Cananea  deposits  are 
no  exception. 

The  ore  is  so  soft  that  no  amount  of  timbering  can  hold  the 
workings  open ;  the  stopes  have  to  be  filled  as  soon  as  the  ore 
is  removed.  The  ground  swells  to  such  an  extent  that  on  the 
third  level  of  the  deep  Capote  workings  the  shaft  can  only  be 
kept  open  by  maintaining  a  passage-way  around  it.  In  the 
bottom  of  the  mine  the  tops,  sides  and  bottoms  of  the  drifts  are 
squeezed  together,  like  those  of  a  tunnel  run  into  a  bank  of 
plastic  clay.  One  peculiarity  of  the  low-grade  ore-bodies  is,  that 


ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS.  401 

although  the  rock  may  have  lost  its  pristine  character  and  may 
be  as  soft  as  stiff  putty,  the  pyrite  distributed  through  it  is  un- 
oxidized  and  bright,  even  on  its  surface. 

The  ore  from  the  Capote  and  Oversight  mines  comes  to  the 
concentrator  and  smelter  mostly  as  whitish-gray  clayey  "  fines/'* 
In  the  concentrator  the  Oversight  ore  in  particular  gives  trouble, 
because  it  "  thickens  "  the  water,  thereby  preventing  the  min- 
eral from  separating  out.  On  the  concentrating-tables,  garnets 
and  similar  minerals,  characteristic  of  contact-metamorphism, 
are  noticeably  inconspicuous.  At  Puertocito  the  mineralized 
porphyry  taken  from  one  of  the  shafts  "  slacks  "  in  the  air  to  a 
powder. 

That  white  feldspathic  porphyry,  similar  to,  if  not  identical 
with,  that  of  La  Sierra  de  la  Cananea,  may  be  itself  a  highly 
cupriferous  mineral-bearer,  is  evidenced  by  the  deposits  at  Ajo 
in  southern  Arizona,  not  far  northwest  of  La  Cananea.  Here 
masses  of  mineralized  porphyry  form  hills  within  a  basin  of 
other  eruptive  matter.  The  rock  is  pyritic  throughout,  and  in 
places  the  ore  is  identical  with  that  of  the  Capote  basin.  I 
noticed  no  sedimentary  rocks  at  Ajo.  The  ore-bodies  are  por- 
phyry, carrying  pyrite,  with  chalcocite,  and  other  cupriferous 
minerals. 

At  Clifton,  also,  notably  on  Metcalf  hill,  the  mineralized  por- 
phyry, constituting  the  ore-bodies  of  the  Arizona  Copper  Co., 
is  of  similar  nature,  if  not  the  same,  as  that  of  Ajo  and  La 
Cananea.  And  the  same  may  be  said  of  the  rock  in  which  lies 
the  large  pyritic  body  of  Iron  mountain,  in  California. 

For  the  reasons  above  given,  and  without  wishing  to  dispar- 
age the  statements  of  such  an  eminent  and  accomplished  geolo- 
gist as  Mr.  Weed,  I  question  the  propriety  of  describing  the 
large  copper-producing  ore-bodies  of  La  Cananea  as  a  type  of 
contact-metamorphic  deposits.  The  porphyries  have  certainly 
taken  a  more  important  part  in  the  genesis  of  these  cupriferous 
deposits  than  that  wrhich  he  has  assigned  to  them.  At  Puerto- 
cito, as  well  as  in  the  Capote  basin,  it  would  seem  to  be  more 
in  accord  with  the  facts  to  assume  that  the  pyritic  minerals 
brought  up  by  the  porphyry  became,  through  magmatic  differ- 
entiation, more  concentrated  in  certain  localities  than  in  others, 
and  that  these  heavily  mineralized  portions  were  very  suscep- 
tible to  attack  from  atmospheric  waters.  In  the  Capote  basin, 

26 


402  ORE-DEPOSITS    NEAR    IGNEOUS    CONTACTS. 

where  the  mineralization  was  the  greatest,  the  porphyry  yielded 
readily  to  decay,  the  result  being  the  formation  of  ferric  masses 
(gossan),  which  were  left  on  or  near  the  surface,  and  the  con- 

\O  / " 

centration  of  the  copper  below  in  the  form  of  chalcocite.  The 
gossan  found  on  the  top  of  the  ground  is  a  fairly  good  flux,  and 
is  used  as  such ;  but  it  becomes  more  and  more  siliceous  with 
depth,  until  it  rests  on  the  ore.  It  presents  an  irregular  bottom- 
limit,  penetrating  the  ore  in  places.  Immediately  under  the 
gossan  comes  the  chalcocite-bearing  porphyry.  At  the  junction 
of  the  two,  native  silver  is  sometimes  found.  The  workings  in 
this  portion  of  the  Capote  mine  were  very  hot ;  and  the  more 
it  was  attempted  to  ventilate  them,  the  hotter  they  became. 
Quartz-sand  also  (used  for  building-purposes)  was  found  in  this 
zone. 

The  subject  of  the  formation  of  chalcocite  ore-bodies  by  the 
oxidation  of  pyritic  minerals  and  subsequent  precipitation  of 
the  copper  sulphide  on  deeper-lying,  unaltered  ore,  has  been 
handled  in  such  a  masterly  manner  by  Mr.  H.  Y.  Winchell,  of 
Butte,*  that  it  would  be  superfluous  to  go  further  into  the 
matter  here. 

There  are  contact-metamorphic  deposits  at  La  Cananea ;  but 
they  were  of  comparatively  subordinate  importance  in  con- 
nection with  the  output  of  copper  in  1901,  and  they  are  still 
subordinate.  The  main  ore-deposits  are  concentrations  in  the 
porphyry  of  chalcocite  derived  from  cupriferous  pyrite,  which 
came  up  as  an  accessory  component  of  the  original  rock. 

A  correct  diagnosis  of  the  genesis  of  an  ore-deposit  is  of 
more  than  scientific  interest;  it  is  of  great  economic  impor- 
tance. A  better  appreciation  of  this  truism  by  those  in  respon- 
sible charge  of  mining  operations  would  result  in  the  saving  of 
vast  sums  of  money  which  are  uselessly  expended  at  the  pres- 
ent time. 

In  regard  to  the  occurrence  of  arsenopyrite  in,  or  close  to, 
contact-metamorphic  deposits,  the  case  of  Sacrificio  mountain, 
in  Durango,  might  be  cited  in  addition  to  those  mentioned  by 
Mr.  Weed.  These  deposits,  which  are  typically  contact-meta- 
morphic in  the  sense  given  the  term  by  Mr.  Weed — "  zones  of 
altered  sediments  about  igneous  intrusions  " — are  associated 
with  veins  of  arsenopyrite. 

*  Engineering  and  Mining  Journal,  vol.  Ixxv.,  p.  782. 


ORE-DEPOSITION    AND    VEIN-ENRICHMENT.  40S 

No.  14. 

Ore-Deposition  and  Vein-Enrichment  by  Ascending  Hot 

Waters. 

BY  WALTER   HARVEY   WEED,    WASHINGTON,    D.    C. 

(New  Haven  Meeting,  October,  1902.     Trans.,  xxxiii.,  747.) 

THE  enrichment  of  mineral-veins  as  a  result  of  the  migra- 
tion of  material  from  an  upper  oxidized  or  disintegrated  part 
of  a  vein  to  a  lower  level,  where  it  is  redeposited,  is  now,  I 
believe,  quite  generally  accepted  as  one  explanation  of  the 
occurrence  of  bonanzas  in  gold-  and  silver-veins,  as  well  as  that 
of  bodies  of  high-grade  ores  in  cupriferous  deposits.*  Yogt  has 
called  attentionf  to  the  fact  that  there  are  numerous  examples 
of  such  rich  shoots  which  are  "  of  exclusively  primary  char- 
acter, and  dependent  upon  the  laws  which  governed  the  origi- 
nal ore-deposition."  To  this  I  would  add  that  there  are  also 
other  examples  which  are  neither  of  primary  origin  nor  due  to 
descending  waters,  but  result  from  a  reopening  of  the  veins 
and  their  penetration  by  ascending  heated  waters  whose  metal- 
lic contents  are  deposited  by  reaction  with  the  primary  pyrite 
(and  possibly  other  minerals),  forming  "  secondary "  enrich- 
ments. 

My  studies  of  the  copper-veins  of  Butte,  Montana,  show: 
That  the  veins  there  are  of  several  ages  and  systems ;  that  the 
older  primary  quartz-pyrite  veins  were  reopened  by  later  move- 
ments, correlated  with  a  period  of  volcanic  activity ;  and  that 
they  were  penetrated  by  hot  alkaline  waters  carrying  copper 
and  arsenic  in  solution,  which  were  deposited  presumably  by 
reaction  with  the  pyrite  of  the  original  vein. 

The  enormous  development  of  the  Butte  deposits,  attendant 
upon  the  extraction  of  nearly  10,000  tons  of  ore  a  day,  has  re- 
vealed many  facts  concerning  the  nature  and  distribution  of  the 
ores.  Enargite,  the  copper  sulpharsenate,  formerly  a  relatively 
rare  mineral,  is  now  found  to  be  the  chief  ore  of  some  veins, 

*  Weed,  "  Enrichment  of  Mineral- Veins  by  Later  Metallic  Sulphides,"  Geol. 
Soc.  Am.  Buil.,  vol.  xi.,  pp.  179-206. 

f  "  Problems  in  the  Geology  of  Ore-Deposits,"  Genesis  of  Ore-Deposits,  p.  679 ; 
also,  Trans.,  xxxi.,  p.  168. 


404  ORE-DEPOSITION    AND    VEIN-ENRICHMENT. 

and  to  constitute  a  large  part  of  the  high-grade  ore  of  the  east- 
ern properties.  Its  distribution  is  peculiar,  and  its  significance 
can  only  be  understood  as  a  result  of  detailed  study,  but  sev- 
eral facts  stand  out  prominently,  viz. :  It  occurs  in  immense  ore- 
bodies,  connected  with  faults,  extending  from  the  oxidation  zone 
to  unknown  depths  in  some  veins.  But,  in  most  cases,  it  first 
appears  in  deep-level  workings.  This  ore  was  recently  found 
in  the  2000-ft.  and  2200-ft,  level  of  several  mines ;  it  is  clearly 
younger  than  the  pyritic  ores,  but  older  than  the  great  glance 
ore-bodies,  and  is  formed  in  small  quantity  in  later  fault-veins. 

In  the  discussion  of  the  genesis  of  the  Butte  deposits  with 
the  late  Clarence  King,  he  at  first  combated  the  principle  of 
secondary  enrichment,  and  adduced  the  presence  of  enargite  as 
a  conclusive  argument  against  it.  The  later  discovery  of 
masses  of  brecciated  enargite  cemented  by  glance  proves  the 
enargite  to  be  of  earlier  formation ;  and  though  the  pyrite  is 
the  only  possible  source  of  the  copper  and  arsenic  in  the  origi- 
nal vein,  numerous  assays  showed  almost  total  absence  of  arse- 
nic from  these  ores.  In  brief,  all  the  evidence  showed  that 
enargite,  though  not  a  "  primary  "  vein-mineral  of  the  original 
vein,  did  not  come  from  descending  solutions,  but  must  have 
come  from  below. 

The  bonanza-ore  of  Neihart,  Montana,  has  been  described  by 
me  as  an  example  of  secondary  enrichment  by  descending  waters. 
In  the  light  of  a  riper  experience  and  the  experimental  work  of 
Dr.  Stokes,  it  appears  possible  that  the  pearceite  (arsenical  poly- 
basite)  ores  result  from  uprising  alkaline  solutions,  though 
later  descending  solutions,  carrying  material  derived  from  the 
oxidation  of  the  ores,  have  to  some  extent  complicated  the 
situation.  At  any  rate,  it  is  difficult  to  account  for  the  large 
amounts  of  arsenic  necessary  for  the  formation  of  these  ores  by 
the  oxidation  of  very  large  amounts  of  primary  pyrite  almost 
devoid  of  this  element ;  and  it  is  known  that  arsenic  occurs 
elsewhere  in  hot-spring  waters,  as  at  La  Bourboule,  France,* 
and  in  the  Yellowstone  Park.f 

*  Hague,  ' '  Notes  on  the  Deposition  of  Scorodite, ' '  Am.  Jour.  Sci. ,  xxxiv. ,  3d 
ser.,  Sept.,  1887,  p.  171. 

f  Weed  and  Pirsson,  "  Sulphur,  Orpiment  and  Kealgar  in  the  Yellowstone 
Park,"  Am.  Jour.  Sci.,  xlii.,  p.  401,  1895. 

Gooch  and  Whitfield,  "  Waters  of  the  Yellowstone,"  Bull.  47,  U.  S.  Geol.  Surv.f 
p.  teetseq.,  1888. 


ORE-DEPOSITION    AND    VEIN-ENRICHMENT.  405 

Recent  experiments  made  in  the  U.  S.  Geological  Survey 
Laboratory,  by  Dr.  H.  IN".  Stokes,  show  that  metallic  sulphides 
are  reduced  and  precipitated  from  alkaline  solutions  of  the 
general  character  of  hot-spring  waters  by  pyrite.  The  metallic 
substances  may  be  assumed  to  be  present  as  oxides  of  zinc, 
copper,  lead,  etc.  The  reaction  with  the  alkaline  waters  alone 
is  represented  by  the  equation  : 


8  FeS2  +  15  Na2C03  =  4  Fe2O8  +  14  Na2S  +  ]STa2S2O3  +15  C02. 

In  the  presence  of  a  metallic  oxide  reacting  with  Na2S,  e.g., 
ZnO,  PbO,  etc.,  the  equilibrium  will  not  be  reached  short  of 
total  decomposition  of  FeS2,  and  we  get 

8  FeS,  +  14  ZnC03  +  Ha2CO,  =  14  ZnS  +  4  Fe203 

3+15  C02. 


These  are  the  only  products  present,  and  the  reaction  is  com- 
plete with  excess  of  ZnC03.  The  formation  of  Fe203  by  action 
of  a  metallic  salt  on  FeS2  and  the  formation  of  thiosulphate 
have  not  been  previously  known.  The  latter  was  proved  beyond 
question  by  qualitative  and  quantitative  methods,  and  there  is 
no  evidence  of  the  formation  of  sulphites.  Pyrite  and  mar- 
casite,  with  CuO  in  bicarbonate  solution,  react  as  follows  : 

2  FeS2  +  6  CuC03  +  2  KHC03  =  3  Cu2S  +  Fe2O3  + 
K2S04  +  8  C02  +  H20. 

Experiments  with  both  pyrite  and  marcasite  at  200°  C.  show 
that  the  theoretical  amount  of  sulphuric  acid  is  actually  formed. 

That  such  waters  actually  occur  in  nature  is  not  absolutely 
known.  The  Yellowstone  Park  waters  are,  however,  nearly 
of  this  character,  and  several  springs  at  the  Norris  Geyser 
Basin  are  actually  depositing  the  red  and  yellow  sulphide  of 
arsenic,  and  one  case  auriferous  pyrite.*  The  Boulder  hot 
springs,  where  mineral-veins  are  now  in  process  of  formation, 
in  which  small  amounts  of  copper,  gold  and  silver  are  de- 
posited, are  dilute  solutions  of  alkaline  waters.  f 

From  my  study  of  the  waters  and  veins  of  the  last-named 

*  Weed  and  Pirsson,  Am.  Jour.  Sci.,  xlii.,  p.  401,  1895. 

t  Weed,  "  Mineral  -Vein  Formation  at  Boulder  Hot  Springs,  Montana,"  21st 
Ann.  Sept.,  U.  S.  Geol.  Surv.,  Part  II.,  p.  233,  1900. 


406  ORE-DEPOSITION    AND    VEIN-ENRICHMENT. 

locality,  I  am  led  to  the  following  theory  of  primary  ore-depo- 
sition : 

Theory  of  Ore-Deposition  by  Thermal  Springs. 

Recent  researches  have  demonstrated  that  openings  cannot 
exist  in  the  rocks  which  compose  the  outer  crust  of  the  earth 
at  depths  of  30,000  feet  or  more,  and  that,  indeed,  under  cer- 
tain conditions,  they  cannot  exist  at  depths  very  much  less  than 
that.  Observations  made  upon  deeply  buried  rocks,  brought  to 
the  surface  by  uplift  and  erosion,  are  in  perfect  accord  with 
these  deductions,  and  prove  that  the  "  unknown  depths  "  from 
which  ore-deposits  in  waters  are  derived  cannot  exceed  these 
figures.  Assuming  this  to  be  true,  it  will  probably  be  admitted 
(since  heat  and  pressure  facilitate  solution),  that  hot  waters  cir- 
culating at  considerable  depths  will  dissolve  and  take  into  solu- 
tion the  various  materials  with  which  they  come  in  contact. 
The  capacity  of  hot  water  to  contain  such  substances  in  solu- 
tion will  depend  upon  heat  and  pressure.  The  water  will  take 
up  the  less  readily  soluble  salts  only  while  the  conditions 
are  favorable.  With  less  heat  and  pressure  the  solution  may 
become  saturated  for  any  one  substance,  and,  though  still  hold- 
ing it  in  solution,  be  incapable  of  taking  up  any  more  of  that 
substance.  In  this  unstable  condition  a  slightly  lessened  pres- 
sure and  heat  would  bring  about  precipitation. 

For  this  discussion  it  does  not  matter  whether  the  hot  waters 
are  of  igneous,  or  of  original  meteoric  origin,  since  they  are 
admittedly  hot  and  traverse  the  deep-seated  rock. 

In  an  ideal  hot  spring,  the  circulating  waters  slowly  traversing 
heated,  but  solid,  igneous  rocks,  out  of  which  they  dissolve  vari- 
ous substances,  flow  toward  the  point  of  easiest  escape,  which 
is  the  hot-spring  fissure.  For  convenience,  we  will  assume  this 
fissure  to  be  straight,  one  thousand  or  two  thousand  feet  deep, 
and  the  waters  to  move  upward  very  slowly.  In  its  lower  part, 
as  in  the  pores  of  the  adjacent  rocks,  heat  and  pressure  are 
very  great  and  the  waters  are  not  saturated,  even  for  the  most 
insoluble  substances,  and  no  minerals  are  deposited.  Nearer 
the  surface  diminished  heat  and  pressure  make  the  water  in- 
capable of  taking  more  of  the  less  soluble  materials  in  solution, 
forming  what  may  be  conveniently  called  the  zone  of  satura- 
tion. Some  salts,  like  alkaline  sulphates,  etc.,  are  extremely 
soluble,  and  the  point  of  saturation  is  scarcely  ever  reached  in 


ORE-DEPOSITION    AND    VEIN-ENRICHMENT.  407 

nature,  even  at  the  earth's  surface.  Others,  like  silica,  may  be 
present  in  such  amount  as  to  saturate  the  water,  but  the  solu- 
tion is  clear  until  cooling  and  relief  of  pressure  cause  super- 
saturation,  and  precipitation  occurs;  an  example  of  this  was 
seen  at  the  Opal  and  the  Coral  Springs  of  the  Norris  Geyser 
Basin,  in  the  Yellowstone  Park.  Still  higher  in  the  hypotheti- 
cal hot-spring  pipe,  diminished  heat  and  pressure  cause  the 
separation  of  the  less  soluble  constituents,  and  for  such  mate- 
rials this  part  of  the  tube  is  the  zone  of  precipitation.  It  is 
well  known  that  the  metallic  sulphides  are  soluble  in  alka- 
line solutions  under  heat  and  pressure,  but  examples  show- 
ing their  deposition  by  living  hot  springs  are  extremely  rare. 
The  more  soluble  substances  will  be  carried  farther  upward  be- 
fore precipitation,  and  one  might  even  suppose,  if  the  solubili- 
ties of  the  substances  were  sufficiently  unlike,  that  zones  would 
be  formed,  each  one  of  which  consisted  mainly  of  the  particu- 
lar substance  thrown  out  by  the  change  of  pressure.  This 
would  produce  an  orderly  distribution  of  the  ores  in  a  vertical 
direction.  This,  indeed,  has  been  observed  frequently.  Cham- 
berlin  records  it  for  the  lead-  and  zinc-deposits  of  Wisconsin, 
and  Rickard*  for  those  of  Colorado  and  elsewhere.  In  the 
writer's  own  experience  the  order  appears  to  be  galena  on 
top,  passing  into  highly  zinciferous  ores  below,  and  this  into 
low-grade  pyrite.f  It  is  a  common  experience  to  find  this  asso- 
ciation in  silver-lead  deposits  in  limestone.  This  would  account, 
also,  for  impoverishment  in  depth  and  the  passing  into  the 
ever-present  and  readily  deposited  silica. 

The  conditions  in  a  hot-spring  tube  are  admittedly  those 
postulated,  i.e.,  lessening  heat  and  pressure  as  the  surface  is 
approached;  the  assumptions  made  are  natural  ones.  This, 
then,  would  explain  why  hot  springs  do  not  deposit  metallic 
sulphides  at  the  earth's  surface.  Owing  to  their  relative  in- 
solubility these  are  deposited  (if  present  in  the  water)  at  depths 
below  the  surface.  The  Sulphur  Bank  quicksilver  mines  of 
California  are  examples.  At  the  surface  they  showed  only 

*  T.  A.  Rickard,  Trans.  Inst.  Min.  and  Metal,  London,  vol.  vi.,  1S?9,  p.  196. 

f  Weed  and  Pirsson,  "Castle  Mountain  Mining  District,  Montana,"  Bull. 
139,-  U.  S.  Geol.  Surv.,  1896.  Also  abstract  in  Jour.  GeoL,  vol.  v.,  p.  210,  1897. 

Weed,  "Geology  of  the  Little  Belt  Mountains,  Montana,"  2Qth  Ann.  Rept., 
U.  S.  GeoL  Surv.,  Pt.  III.,  pp.  271-461,  1901. 


408  ORE-DEPOSITION    AND    VEIN-ENRICHMENT. 

sulphur  and  no  quicksilver.  In  depth,  quicksilver-ores  ap- 
peared. Were  these  springs  to  die  out  and  degradation  to 
remove  the  upper  200  feet  of  the  ground,  quicksilver-veins 
would  be  exposed.  It  is  probable  that  somewhat  analogous 
conditions  may  exist  at  many  hot-spring  localities,  and  that  if 
we  could  expose  the  lower  part  of  the  conduit  we  should  find 
ore-deposits.  This  is  the  theory  which  the  writer  at  present 
holds  as  to  the  genesis  of  the  silver-gold-veins  of  Lump  Gulch 
and  other  mining  districts  of  Jefferson  county,  Montana,  and 
which  he  believes  is  a  rational  ascension  theory.  All  second- 
ary alterations  are  here  excluded,  these  remarks  applying  only 
to  the  primary  vein-filling.  It  is  lateral  secretion  only  in  the 
very  special  and  limited  application  of  that  term  to  the  leach- 
ing of  relatively  deep-seated  rocks,  and  the  gathering  of  such 
waters  in  a  hot-spring  conduit. 

•  The  close  resemblance  in  nature  and  occurrence  of  these 
Boulder  hot-spring  veins  to  the  jasper  reefs  of  Clancy,  Lump 
Gulch  and  many  other  mining  districts  in  the  granite  area  of 
Jefferson  county,  Montana,  has  already  been  stated.  It  may 
be  accepted  as  certain  that  they  also  owe  their  origin  to  hot 
springs,  and  that  the  ore-deposits  of  such  veins  were  formed 

by  hot  waters. 

Theory  of  Enrichment. 

Applying  these  conclusions  to  the  question  of  vein-enrich- 
ments, it  is  first  necessary  to  recall  that  bonanzas  and  rich 
ore-shoots  are  very  frequently  associated  with  brecciation  and 
recementation  of  the  vein-filling.  Where  the  evidence  pre- 
cludes "  secondary  "  enrichment  from  above,  the  possibility  of 
enrichment  by  a  new  or  renewed  supply  of  hot  water  coming 
up  the  newly-formed  fracture  must  be  considered.  The  suc- 
cessive reopening  of  veins  was  formerly  an  accepted  explana^ 
tion  of  an  orderly  sequence  of  mineral  crusts,  implying  a  re- 
peated uniform  reopening.  Such  exceptional  cases  may  occur, 
but  it  is  certain  that  many  veins  occupy  fissures  that  are  lines 
of  weakness  in  successive  periods  of  earth  movement.  Even 
in  the  deposits  still  forming  at  Boulder  Hot  Springs,  Montana, 
the  veins  have  been  fractured  and  the  fragments  cemented  by 
newly  deposited  silica.  At  Butte  and  Neihart  the  veins  have 
been  broken  by  post-mineral  fractures  with  later  deposition  of 
rich  ores.  The  evidence  at  Butte  (furnished  by  rock-walls,  de- 


ORE-DEPOSITION    AND    VEIN-ENRICHMENT.  409 

posited  ore  and  structural  conditions)  shows  that  the  primary 
quartz-pyrite  veins  were  broken  by  fissures  that  became  the 
conduit  for  ascending  hot  alkaline  waters.  Such  waters  would 
tend  to  deposit  any  burden  of  metallic  salts  in  zones  as  already 
outlined  ;  they  would  also  be  influenced  by  the  existence  of  the 
crushed  pyrite  of  earlier  deposition,  which  is  an  energetic  re- 
ducing-agent.* 

Dr.  H.  £N".  Stokes  has  continued  his  painstaking  experi- 
mental work  on  the  action  of  pyrite  and  marcasite,  and  the 
bearings  of  his  results  upon  the  chemistry  of  ore-deposition  are 
of  very  great  importance.  It  is  well  known  that  almost  all 
hot-spring  waters  contain  alkaline  carbonates  in  solution.  In 
an  unpublished  abstract  of  his  report,  which  I  have  his  per- 
mission to  quote,  he  says  : 

"  Behavior  of  Pyrite  with  Carbonate  or  Bicarbonate  Solution. 

"  The  reaction  is  as  follows  in  case  of  either  pyrite  or  marcasite  and  Na^CC^  or 
KHCO3,  at  100°  or  190°  : 

"  8  FeS2  +  15  Na2C03  =  4  Fe2O3  +  14  Na,S  -f  Na^A  +  15  CO2. 

"The  reaction  is  reversible,  as  far  as  the  sulphide  is  concerned,  and  is  more 
complicated  than  represented,  because  some  alkaline  polysulphide  is  formed. 
Being  reversible,  it  is  not  possible  to  prove  satisfactorily  the  presence  of  Fe2O3 
in  the  solid  residue,  but  the  solution  was  shown  to  contain  Na2S,  Na2Sx  and 
Na2S203. 

"If,  however,  the  sulphide  be  removed  as  fast  as  formed,  the  reaction  pro- 
ceeds to  an  end,  giving,  finally,  only  Fe2O3,  while  the  thiosulphate  accumulates  in 
the  solution.  This  can  be  accomplished  in  several  ways  : 

11  (a)  A  circulating  alkaline  solution,  carrying  away  the  sulphur  as  sulphide 
and  thiosulphate,  would  leave  the  pyrite  or  marcasite  ultimately  as  Fe2O3  or  its 
hydrate.  This  can  hardly  be  effected  in  the  laboratory  on  account  of  experi- 
mental difficulties. 

"  (b)  The  addition  of  a  metallic  salt  capable  of  precipitating  the  sulphide  as 
fast  as  formed  allows  the  reaction  to  proceed  to  an  end.  This  is  what  occurs  in 
the  above  reaction  with  lead  and  zinc  : 


"  8  FeS2  -f-  14  PbCO3  +  Na^COs  =  14  PbS  +  4  Fe2O3  +  Na2S2O3  +  15  CO2, 

and  also  with  copper  and  silver  (modified  by  the  further  conversion  of  thiosul- 
phate into  sulphide  and  sulphate)  : 

"  8  FeS2  +  14  Ag2CO3  -f  Na-jCOg  =  14  Ag2S  +  4Fe2O3  +  Na,2SO4  +  15  CO2. 


"  (c)  Since  CO2  partially  decomposes  soluble  sulphides,  we  actually  have  a  por- 
tion of  free  H2S,  which  may  be  volatilized,  thus  enabling  the  reaction  tp  proceed 
to  an  end.  By  heating  FeS2  with  KHCO3-solution  in  a  sealed  vessel  filled  with 
CO2,  and  so  arranged  that  the  volatilized  H2S  is  continually  taken  up  by  an  ab- 

*  H.  N.  Stokes,  "Pyrite  and  Marcasite,"  Bull  186,  U.  S.  Geol.  Surv. 


410  ORE-DEPOSITION    AND    VEIN-ENRICHMENT. 

sorbent,  it  was  found  possible  to  convert  FeS2  completely  into  hematite,  without 
direct  contact  with  metallic  salts  and  in  absence  of  oxygen.  The  same  experi- 
ment was  made  with  artificial  amorphous  Fe2S3,  which  can  be  converted  into 
Fe2O3  by  long  boiling  with  water,  H2S  escaping. 

"  It  would  seem  from  the  above  : 

"1.  That  the  conversion  of  FeS2  into  Fe2O3  is  not  a  necessary  proof  of  the 
action  of  oxidizing  (descending)  waters,  but  may  be  due  to  any  alkaline  solution 
free  from  oxygen. 

"2.  The  circulating  solutions  which  have  acted  on  FeS2  may  carry  away 
alkaline  sulphide,  and  cause  the  deposition  of  other  sulphides,  as  of  copper,  zinc, 
lead,  silver,  at  another  place. ' ' 

These  reactions  apply  to  enrichment  produced  by  ascending 
alkaline  waters,  such  as  those  characteristic  of  the  Yellowstone 
Park,  Boulder  Hot  Springs,  and  many  of  the  hot  springs  of  the 
Rocky  Mountain  region. 

If  the  hot  ascending  waters  were  acid,  a  different  set  of  re- 
actions, determined  by  Dr.  Stokes'  work,  explain  the  solution 
of  gold,  silver  and  copper  from  minerals  of  the  original  vein- 
filling,  and  their  deposition  at  a  higher  level  on  cooling.*  The 
reaction  is  possible  with  a  neutral  solution,  but  not  an  alka- 
line one. 

Conclusions. 

1.  Ascending  hot-spring  waters,  if  metalliferous,  may  deposit 
different  ores  with  an  orderly  vertical  distribution.     Existing 
veins   now  mined   often    show  this    arrangement  of  metallic 
sulphide. 

2.  Ascending  hot  alkaline  waters  coming  up  through  crushed 
and  reopened  veins  containing  pyrite  (or  marcasite)  react  with 
this  sulphide,  and  zinc,  lead,  copper  or  silver,  if  present,  is 
thrown  down  as  sulphide. 

3.  Ascending  hot  acid  waters  may  leach  the  lower  levels  of 
reopened  veins  and  deposit  gold,  silver  and  copper  upon  cool- 
ing at  higher  levels. 

*  The  full  results  of  this  very  important  experimental  work  of  Dr.  Stokes 
will  soon  be  published.  See,  also,  by  him,  "Pyrite  and  Marcasite,"  Bull  186, 
U.  S.  Geol.  Surv. 


BASALTIC    ZONES    AS    GUIDES'  TO    ORE-DEPOSITS.  411 

No.  15. 


Basaltic  Zones  as  Guides  to  Ore-Deposits  in  the  Cripple 
Creek  District,  Colorado. 

BY  E.    A.    STEVENS,*  VICTOR,    COLO. 
(New  York  and  Philadelphia  Meeting,  February  and  May,  1902,     Trans.,  xxxiii.,  686.) 

IT  has  been  ascertained  in  recent  years  that  certain  rock- 
types,  geological  formations  and  structural  conditions  may  be 
used  as  fairly  reliable  guides,  when  prospecting  in  recognized 
mineral  belts  or  mining  districts,  with  a  reasonable  certainty 
of  discovering  "pay-ore;"  and  that  such  is  considered  as  a 
practically  established  conclusion  may  be  inferred  from  a  peru- 
sal of  the  recent  reports  of  the  IT.  S.  Geological  Survey  and  the 
literature  of  the  several  scientific  societies  discussing  mining, 
geology,  and  kindred  subjects. 

Cripple  Creek  is  no  exception  to  this  conclusion,  and  the 
rock-type  or  association,  rather  than  the  structural  condition,  is 
the  most  infallible  guide. f 

These  guides  consist  of  four,  possibly  five,  dike-rocks,  three 
of  which  are  extremely  basic,  while  the  fourth  is  an  acid  rock 
of  an  entirely  dissimilar  character.  The  basic  rocks  are  neph- 
eline-basalt,  limburgite,  feldspar-basalt  and  tephrite.  There  are 
grounds,  however,  for  believing  that  the  two  latter  are  subdi- 
visions of  one  type,  and  therefore  will  be  described  under  one 
head.  The  acid  rock  is  quartz-porphyry. 

Nepheline-basalt  is  a  rock  encountered  in  but  few  localities 
elsewhere  on  this  continent,  and  occurs  in  narrow  dikes  cut- 
ting various  formations.  When  typical, J  it  is  composed  of 

*  Died  January  31,  1902.  The  manuscript  of  this  paper  was  received  only  a 
few  days  before  his  untimely  death. 

f  The  writer  will  not  deny  that  in  a  very  few  instances  there  is  apparently  a 
relation  existing  between  a  late,  extremely  basic  andesite  and  ore-deposition,  but 
is  very  confident  that  sufficient  development  will  demonstrate,  as  in  similar  cases 
heretofore,  that  these  deposits  are  more  closely  allied  to  basaltic  dikes  or  zones. 

J  The  nepheline-basalt  of  this  district  is  not  a  typical  rock  ;  for  instance,  the 
dike  extending  northward  from  Battle  mountain,  along  the  east  side  of  Arequa 
gulch,  contains  glass,  much  megascopic  biotite  and  plagioclase,  and  is  remarkably 
poor  in  nepheline.  This  condition  confirms  the  opinion  of  the  writer,  expressed 
in  a  previous  paper  (Trans.,  xxx.,  763),  that  much  of  the  so-called  nepheline- 
basalt  is  limburgite. 


412  BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS. 

nepheline,  augite  and  olivine,  with  hornblende,  mica,  and, 
rarely,  plagioclase,  as  accessories.  In  this  district,  however,  it 
may  contain  all  of  the  above,  with  the  addition  of  magnetite. 

Limburgite,  which  was  positively  identified  in  this  district 
quite  recently,  is  a  rock  closely  allied  to  nepheline-basalt,  both 
structurally  and  chemically.  It  is  composed  of  a  glassy 
ground-mass,  containing  large  and  small  augites,  magnetite, 
abundant  megascopic  olivines,  and  some  mica,  shading  locally 
into  a  variety,  verite.  It  also  here  contains  the  rare  accesso- 
ries, plagioclase  and,  occasionally,  nepheline. 

The  last  of  the  basic  rocks,  usually  referred  to  as  feldspar- 
basalt,  is  probably  tephrite,*  as  nepheline,  which  is  present 
microscopically,  is  too  abundant  locally  to  be  considered  as 
other  than  an  essential  constituent.  This  rock  is  composed  of 
plagioclase,  augite,  and  some  nepheline.  The  accessories  here 
are  biotite,  magnetite,  apatite,  titanite,  an  undetermined  min- 
eral which  is  probably  sanidine,  and,  rarely,  olivine. 

The  one  dike  of  quartz-porphyry,  with  its  few  branches,  is 
unique  in  its  occurrence.  It  was  casually  referred  to  by  Dr. 
Cross  in  Part  II.,  Sixteenth  Annual  Report,  U.  S.  Geological 
Survey,  and  has  otherwise  escaped  observation.  (See  Fig.  4.) 
It  has  a  very  compact,  bluish-black  ground-mass,  composed  of 
orthoclase,  much  plagioclase,  quartz,  and  some  augite  or  other 
dark  silicate.  The  structure  is  distinctly  tabular-jointed.  Scat- 
tered through  the  ground-mass  are  a  few  double-terminated, 
greasy  quartz-crystals,  and  an  occasional  phenocryst  of  ortho- 
clase or  sanidine.  Physiographically,  it,  like  the  tephrite,  re- 
sembles the  nepheline-basalt  and  limburgite.  These  rocks,  as 
dikes,  comprise  the  later  intrusions ;  nepheline-basalt  and  lim- 
burgite were  contemporaneous,  and  probably  the  last  extruded. 

These  dikes  cut  all  the  earlier  formations  of  the  district. 
The  latter,  with  the  exception  of  granite,  schist  and  diabase, 
are  generally  classed,  by  the  miners,  as  "  porphyry;"  they 
really  consist  of  andesitic  and  phonolitic  tuff  and  breccia,  mas- 
sive and  dike  andesite,  phonolite,  trachytic-phonolite,  nepheline- 
syenite,  and,  in  two  instances,  trachyte.  Owing  to  the  early 

*  No  nepheline  is  present  in  the  dike  of  the  Seavey  shaft  on  Block  7  of  State 
land  ;  but  in  the  same  dike,  where  exposed  by  the  40-f t.  shaft  of  the  ' '  Little 
Daisy"  mine,  the  higher  power  of  the  microscope  reveals  many  crystals  in 
each  slide. 


BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS.  413 

decomposition  of  the  basalt  and  limburgite  upon  exposure  to 
the  atmosphere,  these  dikes,  with  one  exception  of  limburgite, 
form  no  outcrops ;  nor  have  they,  except  on  very  rare  occasions, 
been  found  in  a  sufficiently  fresh  condition  for  determination. 
The  same  is  also  true  of  the  tephrite.  The  two  former,  when 
fresh,  are  very  compact,  of  a  greenish-black  color,  showing  only 
phenocrysts  of  olivine,  except  the  verite,  which  contains  many 
crystals  of  biotite  an  inch  or  more  in  diameter.  The  tephrite 
exhibits  a  compact  ground-mass,  containing  megascopic  pheno- 
crysts of  augite  and  plagioclase. 

The  structure  of  each  basaltic  rock,  when  fresh,  is  jointed, 
and  the  fracture,  when  broken  transversely  between  joints,  is 
conchoidal.  The  first  stage  of  decomposition  is  a  zeolitization 
along  the  joint-planes,  which  is  soon  followed  by  devitrification, 
and,  subsequently,  a  breaking  down  of  the  entire  mass,  finally 
resulting  in  serpentine. 

The  practical  importance  of  the  presence  of  these  rocks  can- 
not be  overestimated.  It  is  not  intended  to  convey  the  idea 
that  at  every  point  at  which  one  of  these  dike-rocks  may  be 
exposed,  ore  is,  or  will  be,  found  in  paying  quantities.  It  is  a 
well-established  fact  that  the  ore  occurs  at  varying  intervals 
along  the  veins  in  the  form  of  "  shoots  "  or  "  chimneys,"  often 
separated  by  thousands  of  feet  of  barren  vein-matter.  The 
assertion  is  sometimes  made  that  there  is  not  a  profitable  mine 
in  the  district  that  does  not  show  either  the  presence  of  one  or 
more  of  these  dike-rocks  or  a  certain  direct  relation  existing 
between  them  and  the  ore.  This  relation  may  be  explained 
thus :  The  fissures  to  which  the  dikes  belong  are  approximately 
parallel  and  occur  in  systems,  and  one  or  more  of  the  fissures 
may  contain  the  dike  or  dikes,  which  are  very  erratic ;  and  it 
has  frequently  been  observed  that  the  dike-bearing  fissures 
may  be  devoid  of  filling  for  hundreds  of  feet  in  depth  and 
thousands  of  feet  in  length.  These  fissured  zones  often,  al- 
though not  always,  extend  entirely  across  the  district,*  and  are 

*  The  Beacon  hill  mines  are  on  a  direct  line  with  some  of  the  limburgite  dikes 
that  cut  Gold  hill  in  a  northerly  and  southerly  direction,  and  are  unquestiona- 
bly on  the  same  zones.  The  writer  has  traced  one  fissure,  which  contains  the 
western  branch  of  the  basaltic  mass  at  the  Dolly  Varden  mine,  southward 
through  Raven,  Guyot  and  Beacon  hills,  and  has  observed  ore  along  it  at  no 
less  than  ten  different  points.  A  like  condition  prevails  regarding  the  position 
of  the  mines  on  the  north  slope  of  Bull  and  the  east  slope  of  Ironclad  hills,  with 
reference  to  the  basaltic  zones  to  the  southward. 


FIG.  1. 


Showing  the  Structure  of  the  Ore-Zone, 
a,  Fissured  zone.     6,  Basalt,     c,  Ore-shoots,     c/,  Cross-fissures. 


BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS.  415 

from  100  to  1200  ft.  wide.  The  zone  comprises  hundreds  of 
fissures  (many  of  which  are  often  detected  only  by  the  aid  of  a 
powerful  microscope),  separated  at  times  by  microscopic  bands, 
and  at  others  by  many  feet,  of  country-rock.  The  veins  and 
their  ore-deposits  may  occur  either  in  the  dike-bearing  fissure, 
including  the  dike,  or  any  other  fissure  or  fissures  of  the  zone. 
(See  Fig.  1.) 

It  may  be  inferred  from  an  examination  of  this  figure  that 
the  ore-deposits  should  be  more  properly  assigned  to  the  cross- 
veins,  as  the  greater  number  of  the  "  shoots  "  or  "  chimneys  " 
occur  at  the  points  where  these  intersect  the  main  veins. 
This  condition  will  be  briefly  explained  for  the  benefit  of  those 
who  are  not  familiar  with  the  local  characteristics  of  ore-depos- 
its. It  will  be  readily  understood  that  at  these  points  of  inter- 
section the  channels  for  water  would  be  more  open,  and  the 
solutions  containing  the  minerals  wrould  meet  with  much  less 
obstruction  to  circulation  than  if  there  was  but  one  system  of 
fissures  or  fractures,  and  would,  consequently,  spread  over 
areas  and  follow  lines  of  least  resistance.  Comparatively 
speaking,  our  studies  and  observations  are  but  superficial,  and 
we  may  not  judge  of  the  conditions  farther  down  in  the  earth 
(where  is  presumed  to  be  the  ultimate  source  or  turning-point 
of  the  mineral-bearing  solutions) ;  we  can  observe  them  only  as 
they  approach  the  surface.  There  are  instances  where  veins 
crossing  the  main  fractures  at  a  high  angle  contain  the  only 
known  shoots,  which  reach  the  surface  hundreds  of  feet  away 
from  the  points  of  intersection.  But  in  sinking  upon  or  devel- 
oping these  "  shoots  "  in  depth,  it  is  found  that  they  gradually, 
though  persistently,  approach  the  point  of  crossing  with  the 
main  system  in  their  downward  course ;  and  in  many  instances 
they  have  been  found  to  pass  through  the  intersection,  return 
to  it,  and  then  follow  the  main  system  to  as  great  a  depth  as  de- 
veloped. (See  Fig.  2.) 

These  are  the  zones,  therefore,  that  must  be  discovered  be- 
fore permanent  mines  can  be  opened  up ;  but,  as  usual,  the 
difficulty  lies  in  distinguishing  those  which  are  likely  to  prove 
productive. 

Dikes  of  considerable  thickness  maintain  their  individuality 
through  the  various  stages  of  decomposition  and  alteration,  in- 
dependent of  their  environment,  while  the  very  thin  dikes  pass 


416 


BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS. 


into  the  hydrous  silicates  of  magnesium  or  aluminum,  forming 
the  ordinary  so-called  "  talc  "  of  our  veins, — under  which  con- 
dition, from  a  practical  standpoint,  identification  becomes  im- 
possible. Another  obstacle  to  the  determination  is  the  extreme 


FIG.  2. 


W 


Section  on  line  A-A,  Fig.  1. 
a,  Fissured  zone.     6,  Basalt,     c,  Ore -shoots,     d,  Cross-fissures. 

secondary  silicification  to  which  not  only  the  dikes  themselves, 
but  the  entire  area  of  eruptive  rocks  have  been  subjected.* 

*  It  has  recently  been  stated  that  the  proximity  of  the  veins,  while  conducting 
exploration-work  in  this  district,  may  be  recognized  by  an  increased  silicification, 
which  reaches  its  maximum  at  and  through  the  veins.  A  very  casual  examina- 
tion of  the  surface  of  this  region  will  suggest  the  untenability  of  this  position. 
The  veins  of  this  district  have  eroded  away  proportionately  to  the  enclosing 
breccia  and  granite  ;  no  more  nor  no  less.  If  they  were  silicified  to  an  extreme 
or  even  an  unusual  degree,  comparatively,  they  would  form  sharply-defined  ridges 
against  the  breccia  or  granite  background  ;  while,  if  silicified  to  a  less  degree, 
gulches,  hollows  or  depressions  would  mark  their  apices. 


BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS.  417 

Moreover,  it  is  not  always  possible,  with  limited  development, 
to  determine  to  what  extent  the  intrusions  may  he  apophyses, 
which  many  of  the  so-called  dikes  of  these  basaltic  rocks  have 
proven  to  be.  Under  such  conditions  the  accompanying  ore- 
deposits,  if  any,  correspond  in  amount  to  the  dike-matter,  as 
will  be  instanced  later  on.  This  district  has  been  subjected  to 
many  disturbances,  both  orogenic  and  volcanic,  as  is  indicated 
by  the  many  faults,  fractures  and  displacements  in  and  sur- 
rounding the  locality,  and  the  variety  of  ejectamenta  thrown 
out  by  the  volcano.  The  disturbances  may  have  been  confined 
to  one  period,  but  that  period  must  have  been  divided  by  long 
intervals  of  time. 

Each  movement  had  its  own  system  of  fissures,  often  inter- 
secting the  preceding  system  at  a  low  angle,  and  its  distinct 
type  of  lava  to  fill  those  fissures. 

It  is  proper  at  this  time  to  state  that  the  pre-Tertiary  fissures, 
most  noticeable  in  the  southern  portion  of  the  district,  have  no 
observable  connection  with  the  Cripple  Creek  volcano,  and, 
when  filled  with  dike-rock,  the  filling  is  of  diabase. 

For  reasons  which  have  already  been  given,  it  is  known  that 
the  rocks  referred  to  as  guides  represent  the  latest  lava  ex- 
truded by  the  volcano. 

It  is  also  positively  known  that  ore-deposition  occurred  sub- 
sequent to  the  latest  eruption  or  intrusions,  as  mineralization 
has  occurred  through  and  along  the  latest  dikes  where  they  are 
intersected,  crossed  or  followed  by  the  fissures  which  form  the 
veins.  And  it  is  a  significant  fact  that  these  later  fissures, 
while  occurring  almost  independently  of  the  dikes,  seem  to  be- 
long to  the  same  general  fissured  zones,  and  doubtless  repre- 
sent shrinkage-cracks,  probably  along  lines  of  weakness  re- 
sulting from  the  contraction  of  the  mass  upon  cooling,  imme- 
diately following  the  intrusion  of  the  dikes.  These  cracks  were 
further  enlarged,  individualized  and  intensified  by  faulting- 
movements,  which  unquestionably  are  responsible  for  transpor- 
tation, localization,  and  probably,  to  some  extent,  deposition  of 
the  ore. 

It  has  been  argued  by  some  that  the  later  dikes  cut  the 
veins,  and  that  at  the  points  of  intersection  for  the  full  width  of 
the  dikes  no  ore  could  be  found.  This  opinion,  it  is  believed, 
is  formed  from  a  lack  of  careful  investigation  and  study,  and 

27 


418  BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS. 

an  improper  appreciation  of  circumstances  and  surroundings. 
Existing  conditions  do  not  warrant  such  a  belief  or  confirm 
such  an  opinion. 

The  most  prominent  instance  upon  which  this  argument  is 
based  has  been  thoroughly  investigated  by  the  writer,  physio- 
graphically,  chemically  and  microscopically.  It  was  thereby 
positively  determined  that  the  rock  in  question  is  not  a  Terti- 
ary basalt,  but  an  ancient  diabase.  Several  years  ago  (owing 
to  its  extreme  decomposition  and  alteration  and  the  position 
which  it  occupies,  being  near  the  contact  between  the  breccia 
and  granite)  it  was  mistaken  for  andesite.  It  is  also  inferred, 
from  such  investigation,  that  the  rock  was  so  highly  altered 
long  prior  to  the  circulation  of  the  ore-bearing  solutions  that 
none  of  the  necessary  reagents  for  precipitation  had  been  re- 
tained; nor  could  it,  in  its  condition,  maintain  the  temperature 
presumed  to  be  necessarily  attendant  upon  ore-deposition. 

It  is  not  to  be  expected  that  the  fissures  would  maintain 
their  individuality  through  a  decomposed,  crumbling  forma- 
tion, although  considerable  silicification  might  characterize  the 
mass  locally. 

It  has  further  been  urged,  in  support  of  this  theory,  that  the 
deposits,  admitting  that  such  occur,  through  and  along  dikes, 
are  "  secondary  enrichments  "  from  decomposition  and  leach- 
ing of  the  ores  from  the  lateral  points  where  the  veins  have 
been  cut  off  by,  and  adjoin,  the  dikes;  but  no  explanation  is 
offered  by  its  exponents  as  to  why  the  fissures  extend  uninter- 
ruptedly through  the  dikes,-  where  in  a  sufficiently  preserved 
condition  to  support  them. 

The  latter  argument  is  not  logical,  as  the  deposits  occurring 
in  the  dikes  are  composed  of  sulphides  and  tellurides,  corre- 
sponding in  every  particular  with  the  veins  before  entering  or 
crossing  them.  And  even  if  these  fissures  and  veins,  contain- 
ing ores  consisting  of  the  original  minerals,  did  not  extend 
through  the  dikes,  the  explanation  would  be  that  the  dikes 
were  still  in  a  plastic  state  when  the  fissures  were  formed,  all 
evidence  of  which  would  then  become  obliterated  when  the 
lava  solidified.  There  are  instances,  to  be  sure,  where  the 
original  gold-bearing  minerals  to  be  seen  in  the  dikes  have  be- 
come much  more  oxidized  than  in  the  enclosing  country-rock; 
but  this  condition  should  be  expected  in  all  basic  rocks,  owing 


to  their  many  easily-destructible 
constituents.  In  the  quartz-por- 
phyry, however,  the  sulphides  and 
tellurides  show  the  effects  of  oxida- 
tion much  less  than  in  the  enclosing 
breccia  and  phonolite,  although  this 
dike  is  characterized  by  both  augite 
or  pyroxene  and  plagioclase. 

The  following  mines,  with  which 
the  writer  is  familiar,  having  been 
connected  with  them  professionally 
or  otherwise,  will  be  cited  as  ex- 
amples in  support  of  the  arguments 
advanced  in  this  paper : 

1.  In  various  "  workings  "  of  the 
Portland,    Independence,     Strong, 
Dillon,    Monument    and     Granite 
mines,  upon  Battle  mountain,  there 
is  a  zone  containing  several  distinct 
nepheline-basalt  dikes,  all  having  a 
general    northerly    and    southerly 
course,  and  many  short,  lenticular* 
masses  or  "  plugs  "  of  the  same  ba- 
salt, often  wholly  altered  or  heavily 
mineralized,  forming  locally  good 
ore.     This  zone  is  about  1200  ft. 
wide. 

2.  The  May  Belle  Tunnel,  Gold 
Coin,  Ajax,  Dead  Pine,  Triumph, 
Coriolanus    and    Carbonate    Queen 
mines,  upon    the    same    mountain, 
are  penetrated  or  crossed  by  dikes 
of  limburgite,  or  the  fissured  zone 
to  which  the    dikes  belong.     This 
zone  is  about  600  ft.  wide,  and  a 
broken,  erratic  dike  of  limburgite 
extends  along  it,  having  a  N.  and 
S.  course.     Near  the  southern  ex- 
tremity of  the  zone  one  of  the  fis- 
sures is  filled  with  verite  for  a  dis- 

*  Inclination  with  dip  of  veins,  in  all  cases 
herein  cited. 


3. 


a 
Showing    the   .Relation    between 

Limburgite  and  the  Ore-Zone. 

a,  Fissured  zone.    6,  Limburgite. 

c,  Ore- shoots. 


.420  BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS. 

tance  of  several  hundred  feet.  Near  the  center  of  the  zone, 
transversely,  occurs  a  small  vent  or  crater,  filled  with  limbur- 
gite.  (See  Fig.  3.)  The  dike  splits  near  the  Ajax  mine,  the 
branches  separating,  and  the  principal  one  veers  slightly  to 
the  northwestward,  passing  through  Eclipse  ground  near  Arequa 
gulch,  and  into  the  Moose  mine  on  Raven  hill. 

3.  The  Thompson,  Elkton,  Raven  and  Tornado  mines,  located 
upon  Raven  hill,  have  their  workings  in  and  along  nepheline- 
basalt  dikes,  the  entire  thickness  of  which,  at  times,  comprises 
the  ore-bodies. 

4.  The  Pointer,  Midget,  National  and  Moon- Anchor  mines, 
all  upon  Gold  Hill,  save  the  National,  are  situated  upon  a  nar- 
row-fissured zone,  having  a  NNE.  course.      One  strong  'dike  of 
limburgite   which    enters    them    is   traceable    for    a   half-mile 
through  the  granite  to  the  southward.     Near  the  contact  (be- 
tween the  granite  and  breccia)  the  dike  is  scattered  by  a  quartz- 
porphyry  dike,  which  it  then  follows.     A  few  hundred  feet  to 
the  northeast  of  this  point  it  again  becomes  well-defined  and 
passes  to  the  northward.     In  the  northern  portion  of  this  zone 
occur  several  parallel  dikes  of  limburgite. 

It  has  very  recently  been  discovered  by  the  writer  that  the 
ore-deposit  worked  through  the  National  mine  is  associated 
with  one  of  the  late  igneous  eruptives.  This  mine  is  located 
on  a  narrow  easterly  and  westerly  fissure-system  in  the  granite, 
some  500  feet  west  of  the  westernmost  fissure  of  the  north-south 
zone.  The  condition  of  the  few  lens-shaped  masses  of  basaltic 
rock  (which  is  limburgite),  conforming  to  the  fissure-cavities, 
stamps  this  occurrence  as  an  apophysis.  This  supposition  is 
also  borne  out  by  the  fact  that  the  ore-body  was  very  limited. 

5.  The  Red  Spruce,  Accident,  Mint,  Union  Belle,  Hillside, 
Moonlight  and  Anchoria-Leland  mines,  on  Gold  Hill,  are  pene- 
trated by,  or  have  their  ore-bodies  composed  of,  or  associated 
with,  quartz-porphyry  and  limburgite.*     The  quartz-porphyry 

*  The  dike  of  limburgite  following  the  NE.-SW.  fissured  zone,  represented  as 
coming  in  at  the  southwest  corner  of  Fig.  4,  reaches  across,  diagonally,  from 
another  N.-S.  fissured  zone  to  the  west.  It  does  not  cross  the  westernmost  zone, 
however,  but  turns  southward  and  follows  it  for  some  distance  before  "pinch- 
ing." This  N.-S.  zone  passes  through  the  Gold  Bond  property,  the  El  Keno 
mine, — famous  for  having  produced  the  first  calaverite-bearing  ore  of  the  district, 
— and  its  influence  is  next  observed  in  the  Dead  Shot  and  Mary  Nevin  properties 
to  the  southward. 


BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS. 


421 


dike  occupies  one  or  more  fissures  of  a  zone  having  a  course 
approximately  northeast.  This  dike  is  much  brecciated,  and 
not  as  well  defined  as  the  basaltic  dikes.  It  was  contempora- 
neous with  a  movement  of  the  country  which  had  not  entirely 

FIG.  4. 


Gr 


Limburgite  Dike  in  El  Reno  Mine. 
6r,  Breccia.    Gr,  Granite.     Qp,  Quartz-porphyry.    6,  Ore-shoots.     Ib,  Limburgite. 

subsided  until  the  dike  had  cooled;  therefore,  its  continuity  is 
broken  in  many  places  between  the  contact,  where  it  has  its 
westerly  termination,  and  the  point  where  it  is  intersected  by 
the  limburgite,  described  in  case  4.  A  portion  of  the  limbur- 
gite  deviates  from  its  regular  course  at  this  point,  and  subordi- 


422  BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS. 

nate  amounts  are  observed  at  various  intervals  accompanying 
the  quartz-porphyry  as  far  as  explored.  This  is  the  narrowest 
zone  of  the  several  described,  not  exceeding  100  feet  in  width 
at  any  point. 

The  Red  Spruce  and  Accident  mines,  in  this  connection,  de- 
serve especial  mention,  as  they  differ  considerably  from  any 
other  mines  in  the  district.  They  are  both  situated  on  the 
true  contact*  between  the  breccia  and  granite.  There  are 
small,  detached  bodies  of  phonolite,  trachyte,  limburgite  and 
quartz-porphyry  present  in  their  workings,  The  first  two  are. 
of  limited,  the  third  of  general,  and  the  last  of  special,  eco- 
nomic importance.  The  limburgite  which  appears  in  the  Acci- 
dent shaft  at  a  depth  of  240  feet  crosses  the  contact  at  an 
approximately  right  angle,  piercing  the  granite  to  the  west- 
ward. This  is  an  apophysis,  and  its  individual  influence  is  not 
remarkable.  The  quartz-porphyry  follows  the  contact,  at 
times,  then  deviates  to  the  westward,  into  the  breccia,  fol- 
lowing fissures  parallel  to  the  contact  for  50  or  more  feet,  and 
then  again  breaks  across  the  formation  to  the  contact.-  A 
branch  of  this  dike  extends  northward  under  conditions  as 
described,  while  the  main  dike  passes  to  the  northeast  into  the 
Mint,  Union  Belle  and  Hillside  mines.  The  chief  ore-bodies 
of  the  Accident  and  Red  Spruce  mines  contain  lead,  silver 
and  gray  copperf  (all  characteristic  of  quartz-porphyry),  some 
gold-bearing  pyrite,  also  calaverite  and  sylvanite. 

6.  The  Zenobia,  Pharmacist,  Burns,  Orphan  Belle,  Isabella, 
Block  8  of  State  land,  Free  Coinage,  Lucky  Guss,  Deadwood, 
Delmonico,  Vindicator,  Christmas  and  Golden  Cycle  mines, 
situated  upon  Bull  Hill,  are  crossed  by  or  associated  with 
tephrite  or  feldspar-basalt. 

*  A  line  drawn  from  the  northeast  shoulder  of  the  contact,  near  the  center  of 
Fig.  4,  northwestward,  along  the  easterly  side  of  the  detached  granite  mass, 
would  represent  the  position  of  the  contact  as  described  in  all  literature  and 
shown  on  all  maps  of  the  district  so  far  published.  This  is  for  the  reason  that 
all  of  the  maps  are  copies,  with  a  few  omissions  or  additions,  of  the  "  Special 
Cripple  Creek  Sheet"  issued  by  the  U.  S.  Geological  Survey.  Dr.  Cross,  who 
was  in  charge  of  the  field-work  of  the  Survey,  attempted  to  represent  approxi- 
mately, only,  the  position  of  the  contact  at  this  and  other  points. 

f  The  superintendent  of  the  Accident  mine  informs  me  that  he  found  a  "kid- 
ney" of  gray  copper-ore  in  a  "split"  in  the  dike  (quartz-porphyry),  containing 
about  1000  pounds,  which  sampled  5000  ounces  silver  and  50  ounces  gold  per 
ton. 


BASALTIC    ZONES    AS    GUIDES    TO    ORE-DEPOSITS.  423 

7.  An  examination  of  the  Victor  mine  disclosed  lenticular 
masses  of  a  basaltic  rock  accompanying  the  vein,  too  highly 
mineralized  for  accurate  classification. 

8.  The  same  condition  was  observed  in  the  Doctor-Jack  Pot 
workings  on  Raven  Hill ;  and  much  of  the  breccia,  heretofore 
€lassed  as  "  andesitic,"  contains  fragments  of  basalt  or  limbur- 
gite. 

It  will  be  observed,  therefore,  that  the  mines  which  have 
produced  90  per  cent,  of  the  gold  of  this  district,  which  has 
amounted  to  more  than  $115,000,000  during  the  past  ten  years, 
are  penetrated  or  crossed  by,  or  closely  associated  with,  the 
various  basaltic  rocks  and  the  dike  of  quartz-porphyry ;  and  for 
these  very  important  reasons  I  infer,  and  it  appears  to  be  both 
logical  and  proper  to  state,  that  the  rock-types  and  association 
above  described  are  the  true  and  only  guides  to  point  out  the 
probable  course  to  pursue  in  order  to  open  a  "  pay  mine "  in 
the  Cripple  Creek  district. 


424  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 


No.  16. 


The  Geological  Features  of  the  Gold-Production  of  North 

America.* 

BY   WALDEMAR  LINDGREN,    WASHINGTON,    D.    C. 

(New  Haven  Meeting,  October,  1902.    Trans.,  xxxiii.,  790.    Part  III.  omitted  in  this 
republication.) 

CONTENTS. 

PAGE 

I.  INTRODUCTION,        .        .        .        .        •.        . '       .         .     •    .         .        .     424 

II.  GEOLOGICAL  FEATURES  :        .        .        .        ...        •        •        .     427 

The  Gold- Bearing  Fissure- Veins,     .......  .427 

.Contact-Metamorphic  Deposits,        .        ...        .         .  .  432 

Classification  According  to  Age,      .         .         .         .                 .  .  433 

Introduction, .-   ...    ,  .  433 

Pre-Cambrian  Deposits,     .                  .        ...         .         .  .  434 

Cretaceous  Veins  of  the  Pacific  Coast,       .         .        .        .  .  435 

Late  Cretaceous  or  Early  Tertiary  Deposits  (Central  Belt;,  .  436 

Tertiary  Deposits,            £. 438 

Conclusions,     .         .         ......         .         .         .  .  442 

I.  INTRODUCTION. 

THE  precious  metals,  gold  and  silver,  are  the  basis  of  the 
monetary  systems  of  the  world.  It  is,  therefore,  natural  and  in- 
evitable that  widespread  interest  should  be  manifested  in  their 
production  and  in  the  various  classes  of  deposits  in  which  they 
are  contained. 

At  times  a  great  scarcity  of  the  precious  metals  has  pre- 
vailed; at  other  times  the  production  has  seemed  so  abnor- 
mally large  that  fears  have  been  entertained  regarding  their 
ultimate  retention  as  standards  of  value.  Since  most  nations 
have  adopted  the  gold  standard,  and  the  remaining  ones  appear 
likely  to  do  the  same  in  the  near  future,  the  question  of  avail- 
able supply  of  gold  for  the  present  and  future  very  naturally 
arises.  This  necessarily  involves  a  consideration  of  the  char- 
acteristics of  the  gold-deposits. 

After  the  absorption  of  the  gold  treasures  of  the  New  World 
by  the  conquistador es,  the  gold-placers  of  Brazil  and  Russia 

*  Published  with  the  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  425 

next  filled  the  world's  need ;  later,  when  these  sources  of  the 
precious  metal  began  to  be  exhausted,  came  the  great  discov- 
eries of  California  and  Australia,  which  for  a  time  caused 
doubts  to  arise  as  to  the  wisdom  of  maintaining  this  metal  as 
a  standard  of  value;  but  from  the  maximum  of  output  ob- 
tained during  the  early  years  a  steady  decline  began.  The  un- 
certainties as  to  the  amount  of  gold  available  for  the  future 
were  emphatically  expressed  by  eminent  geologists  and  mining 
engineers. 

After  an  admirable  discussion  of  the  gold-resources  of  the 
world,  Prof.  Edward  Suess,  of  Vienna,  in  his  book,  The  Future 
of  Gold,1  came  to  the  conclusion  that  there  was  scarcely  any 
hope  of  further  considerable  discoveries,  and  that  the  output 
would  gradually  decrease,  so  that  the  metal  would  no  longer  be 
able  to  maintain  its  present  economic  position. 

About  the  same  time,  in  1880,  Alexander  Del  Mar  published 
his  History  of  the  Precious  Metals,  and  arrived,  in  the  main,  at 
similar  conclusions.  He  believed  that  not  only  physical  devas- 
tation, but  moral  and  political  decay,  follows  as  the  result  of 
gold-mining,  and  that  the  total  supply  of  both  metals,  and  par- 
ticularly of  gold,  will  continue  to  diminish  both  in  the  mines 
of  the  Pacific  coast  and  in  those  of  other  countries.  It  seemed 
to  him  "  but  too  evident  that  the  future  supply  of  these  metals 
will  not  only  fail  to  keep  pace  with  the  growth  of  population 
and  commerce,  but  they  will  absolutely  diminish." 

There  seemed,  indeed,  to  be  good  reason  for  such  conclu- 
sions, for  the  gold-supply  of  the  world  was  steadily  diminish- 
ing and  no  new  sources  seemed  in  sight.  But  these  years 
proved  to  be  the  turning-point,  and  the  production  again  began 
to  increase,  at  first,  however,  very  slowly.  In  1892,  S.  F. 
Emmons,  in  a  most  valuable  review  of  the  gold-  and  silver-pro- 
duction, came  to  the  conclusion  that  a  further  advance  in  the 
output  of  gold  was  probable ;  that  the  annual  production  of  the 
United  States  would  soon  "  increase  to  $40,000,000,  and  per- 
haps beyond;"  and  that  the  gold-production  of  the  world  would 
"increase  to  $150,000,000  within  a  few  years,  and  perhaps  to 
$200,000,000  before  the  close  of  the  decade." 2  These  predic- 
tions have  been  greatly  exceeded  by  the  results  of  the  work  of 

1  Die  Zukunft  des  Gotdes  (1877). 

2  Mineral  Resources  of  the  United  States  for  1892,  pp.  90  to  93  (1893). 


426  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

the  last  few  years.  The  treasures  of  South  Africa  and  West 
Australia  were  found;  in  Alaska  and  British  Columbia  new 
deposits  of  wonderful  extent  were  opened;  and  even  in  such 
presumably  well-prospected  regions  as  Colorado,  California, 
Arizona,  Montana,  and  Mexico,  new  finds  were  constantly 
reported,  and  the  production  rose  steadily  and  rapidly. 

About  1880  the  world's  annual  production  of  gold  was  ap- 
proximately $100,000,000;  that  of  the  United  States  about 
$33,000,000.  In  1900  the  gold-production  of  the  world  had 
increased  to  nearly  $300,000,000,  and  that  of  the  United  States 
to  $79,000,000.  While  it  is  true  that  it  is  easier  to  criticise 
than  to  predict,  it  may  be  pointed  out  that  two  principal  errors 
vitiated  the  conclusions  of  Professor  Suess  and  Mr.  Del  Mar : 
In  the  first  place,  the  lands  of  the  world  were  deemed  to  be  so 
well  prospected  that  no  further  discoveries  were  probable ;  the 
second  error  lies  in  the  failure  to  anticipate  the  possibility  of 
new  processes  for  gold-extraction  and  the  utilization  of  vast 
reserves  of  low-grade  ore-bodies. 

The  figures  of  the  gold-production  during  the  last  decade 
may  indeed  cause  hesitation  in  further  predictions  as  to  the 
available  amount  of  gold.  As  to  ultimate  results,  it  would 
seem  as  if  we  should  be  justified  in  concluding,  with  Professor 
Suess,  that  the  gold-supply  of  the  world  will  gradually  decrease 
if  no  further  important  improvements  are  made  in  the  pro- 
cesses for  the  extraction  of  this  metal ;  but  regarding  events 
so  far  distant  no  predictions  may  safely  be  made.  Regarding 
the  immediate  future,  it  seems  likely  that  the  present  produc- 
tion of  the  world  will  be  sustained,  and  possibly  increased. 

The  purpose  of  this  paper  is  briefly  to  consider  the  product 
of  each  State  in  North  America,  emphasizing  especially  the 
derivation  of  the  gold  from  its  various  classes  of  deposits,  so 
as  to  arrive,  if  possible,  at  an  approximate  conclusion  as  to  the 
relative  importance  of  the  different  kinds  of  deposits,  and 
finally  to  indicate  the  probable  outlook  in  each  State  for  the 
immediate  future.  These  calculations  have  been  made  possible 
by  the  aid  of  the  reports  of  the  United  States  Mint  on  the 
production  of  the  precious  metals,  the  character  of  which  has 
steadily  improved,  and  which  afford  a  vast  amount  of  important 
data  for  the  student ;  and,  further,  by  the  reports  of  the  official 
geological  surveys  in  regard  to  the  economic  geology  of  the 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  427 

States.  Much  is  still  lacking,  more  especially  in  the  knowledge 
of  the  age  of  many  deposits,  and  this  paper  must,  therefore,  be 
considered  only  as  an  imperfect  first  attempt  to  collect  data 
which  are  at  the  disposition  of  many,  but  the  arrangement  of 
which  has  not  yet,  for  some  reason,  been  undertaken. 

II.  GEOLOGICAL  FEATURES. 
The  Gold-Bearing  Fissure-  Veins. 

Practically  all  the  gold-output  of  North  America  is  derived 
from  fissure-veins  or  from  deposits  which  possess  close  relation- 
ship to  fissure- veins.  Gold-bearing  fissure-veins  are  in  most 
cases  accompanied  by  placers,  which  are  only  the  result  of 
nature's  crushing,  concentrating,  and  refining;  and  these 
placers  may  be  of  different  ages  according  to  the  date  of  forma- 
tion of  the  vein.  Most  of  them  are  naturally  of  Pleistocene 
(recent)  or  Tertiary  age.  For  the  present  purpose  the  placers 
will  not  be  considered  separately,  but  as  belonging  to  the  fissure- 
veins  from  which  they  were  derived. 

The  deposits  in  fissure-veins  are  believed  to  have  been  formed 
chiefly  by  ascending  hot  waters.  The  general  trend  of  the  tes- 
timony indicates  that  the  gold  is  brought  up  from  lower  levels 
rather  than  derived  from  rocks  near  the  surface. 

Gold-bearing  fissure-veins  or-  equivalent  deposits  occur  in 
practically  all  kinds  of  rocks  known  on  the  continent ;  it  is 
apparently  not  possible  to  establish  wide-reaching  genetic  con- 
clusions on  the  basis  of  the  petrographical  character  of  the 
wall-rock.3 

The  influence  of  locality  is  much  stronger.  Gold-bearing 
veins  cluster  in  certain  localities.  A  critical  examination  will 
reveal  the  fact  that  many  vein-systems  are  massed  about  the 
contacts  of  intrusive  masses,  which  consolidated  far  below  the 
original  surface  of  the  earth  at  the  time  of  the  igneous  activity, 
and  which  have  been  exposed  by  subsequent  erosion.  Most 
commonly,  perhaps,  these  intrusive  rocks  are  diorite,  monzonite, 
quatftz-monzonite,  granodiorite,  or  their  porphyries,  more  rarely 
typical  granites.  Under  favorable  conditions  it  can  often  be 
proved,  and  in  other  cases  established  with  probability,  that 

3  This  point  has  recently  been  emphasized  by  W.  H.  Weed  in  his  paper,  The 
Influence  of  Country-Rock  on  Mineral  Veins,  Trans.  t  xxxi.,  634  (1901)  ;  p.  216, 
this  volume. 


428  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

the  upper  part  ot  the  vein  has  been  removed  by  the  same  ero- 
sion which  laid  bare  the  intruded  rock-masses.  In  other  words, 
the  top  of  the  vein  has  been  removed,  the  root  remains.  It 
seems  plausible  that  in  these  cases  the  igneous  intrusion  was 
one,  perhaps  the  principal,  of  the  genetic  causes.  Dynamic 
action  producing  fissures  in  and  about  the  intrusives  is  another 
genetic  cause.  The  age  of  these  veins  must  in  general  be  con- 
siderable, for  the  great  erosion  involved  has  usually  required  a 
long  time-interval. 

Another  large  class  of  vein-systems  cut  the  recent  or  com- 
paratively recent  lavas,  which  cover  the  surface  of  the  older, 
eroded  rocks  in  the  form  of  successive  volcanic  flows.  Fre- 
quently the  age  of  these  lavas  may  be  established  with  accuracy. 
From  available  data  we  may  be  enabled  to  determine  the  ap- 
proximate level  of  the  surface  of  the  earth  at  the  time  the 
last  flow  was  erupted;  and,  in  the  case  of  veins  cutting  this 
series,  we  are  enabled  to  say  with  certainty  that  a  given  part  of 
the  vein  was  near  the  original  surface  of  the  earth  existing  at 
the  time  of  vein-deposition.  This  given  part  may,  then,  be 
said  to  be  the  top  or  the  true  apex  of  the  vein. 

It  is  true  that  there  are  very  many  cases  in  which  we  cannot 
determine  with  certainty,  or  even  with  probability,  at  what 
vertical  distance  from  the  part  of  the.  vein  under  discussion  the 
original  surface  of  the  earth,  at  the  time  of  vein-formation,  was 
located.  But  this  does  not  diminish  the  force  of  the  argument 
in  the  two  principal  divisions  discussed.  There  are  certainly 
few  gold-bearing  districts  on  the  continent  which  do  not  occur 
either  near  or  in  intrusive  masses,  or  in  or  near  volcanic  flows. 
In  districts  of  igneous  activity  the  effusion  of  surface-lavas  is 
generally  accompanied  by  the  intrusion  of  bodies  of  magma  far 
below  the  surface,  which,  owing  to  physical  conditions,  consoli- 
dated as  granular  or  coarsely-porphyritic  rocks.  This  has  actu- 
ally been  shown  in  many  volcanic  districts  which  have  been 
deeply  and  rapidly  dissected  by  erosion.  In  rare  cases  we  may 
even  trace  the  vein  from  the  top  in  the  effusive  lavas  down  to 
the  root  in  intrusive  rocks.  It  may,  therefore,  be  concluded 
as  most  probable  that  the  two  classes  of  veins  described  above 
are  really  of  the  same  kind :  that  the  roots  reached  up  through 
once  overlying,  now  eroded,  lavas,  and  that  the  tops  generally 
may  be  traced  through  the  lavas  to  the  vicinity  of  the  intruded 
masses. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  429 

The  question  whether  any  difference  exists  in  mineral  com- 
position and  metasomatic  alteration  between  the  tops  and  the 
roots  of  veins  is  a  most  important  one,  but  it  cannot  be  defi- 
nitely answered  in  the  present  state  of  our  knowledge.  There 
are  arguments  pro  and  con.  Professor  De  Launay  answers  the 
query  in  the  affirmative,  and  many  of  his  arguments  have  great 
force.  This  much  is  certain :  that  in  many  cases  of  gold-quartz 
veins  differences  of  up  to  4,000  ft.  in  elevation  have  little  in- 
fluence on  the  minerals  and  vein-matter,  while  in  some  cases, 
and  chiefly  with  smelting-ores  rich  in  silver,  distinct  changes  in 
mineral  composition  appear  in  depth,  which  would  seem  to  be 
independent  of  secondary  alteration  or  enrichment. 

Fissure-veins  carrying  gold  have  certainly  been  formed  at 
various  times  in  the  geological  history  of  the  continent.  Cam- 
brian conglomerates  bear  witness  to  pre-Cambrian  gold-veins, 
and  very  recent  thermal  deposits  at  Steamboat  Springs,  Nev. 
(according  to  Becker),  and  at  Boulder,'  Mont,  (according  to 
Weed),  prove  that  gold  is  deposited  by  thermal  waters  to-day. 
But  the  process  has  evidently  not  been  a  continuous  one. 
Cambrian,  Silurian,  Devonian,  and  Carboniferous  gold-deposits 
are  not  definitely  known  to  exist  in  North  America.  Continu- 
ous sedimentation,  absence  of  dynamic  movements,  and  rela- 
tively slight  igneous  activity  characterized  these  periods.4 

The  great  eruptions  of  the  Cordilleran  belt  of  North  Amer- 
ica began  during  the  Triassic  period  of  the  Mesozoic  age,  and 
igneous  activity  has  continued  almost  without  interruption 
from  that  date  to  recent  time.  Each  eruption  has  probably 
been  accompanied  by  more  or  less  extensive  deposition  of  gold 
in  fractures  near  the  igneous  focus.  On  the  Pacific  coast  the 
eruptions  began  at  an  earlier  date  than  in  the  region  of  the 
Rocky  mountains;  and,  likewise,  many  of  the  gold-deposits  of 
the  Pacific  coast  antedate  those  of  the  Rocky  mountains.  In 
the  latter  province  the  igneous  rocks  began  to  break  out  at  the 
close  of  the  Cretaceous  period,  and  have  continued  at  least  up 
to  the  beginning  of  the  Pleistocene.  Certain  periods  of  depo- 
sition, however,  stand  out  prominently,  and  we  may  with  good 
reason  separate  the  distinctly  Cretaceous  or  late  Mesozoic  gold- 

4  Igneous  rocks  of  Palaeozoic  age  are  found  at  various  places  along  the  Sierra 
Nevada,  British  Columbia,  and  Alaska.  If  Palaeozoic  gold-deposits  are  found  on 
this  continent,  it  will  probably  be  along  this  line. 


430  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

belt  of  the  Sierra  Nevada  and  the  Pacific  coast  in  general  from 
the  Tertiary,  mostly  post-Miocene,  veins  so  extensively  devel- 
oped in  Mexico,  Nevada,  and  Colorado.  The  former  are  gen- 
etically connected  with  great  intrusions  of  granitic  and  dioritic 
rocks,  the  latter  with  big  flows  of  surface-lavas  which  erosion 
has  not,  as  yet,  removed.  But  both  in  the  Great  Basin  and  in 
the  Rocky  mountains  there  are  also  many  deposits  of  late  Ore. 
taceous  or  early  Tertiary  age  genetically  connected  with  intru- 
sions of  granitic  rocks  and,  very  commonly,  porphyries.  In 
very  many  cases  the  age  of  these  deposits  is  doubtful.  If  ero- 
sion has  been  exceptionally  active  in  the  particular  district  in 
which  they  occur,  they  may  well,  though  occurring  in  connec- 
tion with  deep-seated  intrusions,  be  of  Tertiary  age.  To  this 
class  of  doubtful  age  belong,  for  instance,  many  of  the  gold- 
veins  of  Montana.  Miocene  and  later  igneous  rocks  are  often 
lacking  in  this  region,  so  that  an  accurate  determination  of 
age  becomes  very  difficult. 

Still  another  complication  to  be  borne  in  mind  consists  in 
possible,  though  probably  rarely  occurring,  re-opening  of  veins 
and  superimposition  of  deposits  of  two  or  several  epochs.  All 
this  being  admitted,  there  still  exists,  in  my  opinion,  sufficient 
reason  for  attempting  a  division  of  the  deposits  according  to 
age.  It  is  readily  acknowledged  that  this  first  attempt  is  im- 
perfect, and  that  future  researches  will  probably  bring  many 
changes  in  the  divisions  here  tentatively  set  forth. 

The  next  question  is,  whether  there  is  any  notable  difference, 
in  mineral  constituents  and  metasomatic  alteration,  between 
deposits  of  various  periods.  The  mineral  vein  is  the  result  of 
two  variable  factors :  the  composition  of  the  mineral  waters 
and  the  conditions  at  the  time  of  deposition.  Is  there  any 
definite  gradual  change  in  both  or  either  of  those  factors  by 
which  the  older  deposits  can  be  distinguished  from  the  younger  ? 

The  question  of  depth  below  the  original  surface  has  already 
been  touched  upon,  and  in  considering  the  present  problem  it 
is  necessary  to  deal  with  those  parts  of  deposits  of  various  ages 
which  were  formed  at  the  same  distance  from  the  original  sur- 
face. A  definite  answer  is  difficult  because  the  older  deposits 
are  usually  more  deeply  eroded  than  the  recent  ones.  A  priori,. 
however,  there  seems  no  reason  why  a  difference  should  exist 
for  mineral  waters  of  as  many  different  kinds  of  composition 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  431 

as  are  seen  to-day  have  probably  always  reached  the  surface, 
and  the  conditions  of  deposition  at  corresponding  levels  and 
under  corresponding  circumstances  have  probably  always  been 
about  the  same. 

Looking  over  the  field,  it  is  undeniable  that  within  many 
belts  of  gold-deposits  of  contemporaneous  origin  the  veins  are 
very  similar  in  mineral  composition  and  metasomatic  develop- 
ment. The  Appalachian  belt  of  gold-quartz  veins  contains 
deposits  of  striking  similarity  from  one  end  to  the  other.  The 
Mesozoic  gold-quartz  veins  of  the  Pacific  coast  are  practically 
identical  in  character  from  Lower  California  to  Alaska,  and, 
moreover,  closely  related  in  character  to  the  far  older  Appala- 
chian belt.  Where  the  wall-rocks  were  easily  altered,  they 
contain  abundant  calcite  and  other  carbonates,  besides  much 
sericite.  This  points,  without  doubt,  to  a  remarkable  constancy 
throughout  the  whole  province  in  the  composition  of  the  min- 
eral waters  which  formed  the  veins.  They  were  manifestly 
distinguished  by  an  abundance  of  alkaline  carbonates.  On  the 
other  hand,  scarcely  one  of  the  veins,  which  in  so  many  part& 
of  the  Cordilleran  region  cut  volcanic  flows  of  Tertiary  age, 
can  be  classed  as  identical  with  the  Pacific  coast  type  of  gold- 
quartz  veins.  While  it  is  perhaps  not  permissible  to  say  that 
they  represent  one  type,  yet  most  of  them  have  certain  com- 
mon, peculiar  features,  constituting  a  relationship.  They  fre- 
quently contain  both  gold  and  silver;  the  gold  is  finely  divided, 
and  rarely  accumulates  below  the  veins  in  such  rich  placers  as 
are  found  associated  with  the  Pacific  coast  type  of  gold-quartz 
veins ;  the  metasomatic  alteration  is  generally  propylitic ;  that 
is,  accompanied  by  the  formation  of  chlorite,  epidote,  and,  near 
the  veins,  of  sericite  and  kaolin,  while  the  extensive  carbonatiza- 
tion  found  near  the  California  gold-quartz  veins  is  usually 
absent.  The  mineral  waters  accompanying  the  Tertiary  erup- 
tion certainly  differed  on  the  whole,  and  notably  from  those  of 
other  eruptive  periods,  and  were  apparently  lacking  in  alkaline 
carbonates.  Professor  Suess  recognized  this  type  long  ago, 
basing  his  conclusions  largely  on  von  Richthofen's  work.  Pro- 
fessor Vogt  has  more  recently  insisted  on  its  importance. 
There  are  several  types  of  these  Tertiary  veins,  and  it  is  per- 
haps not  advisable,  as  I  have  done  in  a  preliminary  note  on 
this  subject,  to  retain  the  name  propylitic  for  the  whole  group,, 
as  some  of  them  do  not  show  this  alteration  in  typical  form. 


432  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

In  conclusion,  it  may  be  said  that  gold-veins  of  the  same 
age  and  province  usually  have  the  same  characteristics.  Belts 
of  different  age  may  differ  greatly  in  general  features.  This  is 
probably  due  to  varying  composition  of  the  mineral  waters  fol- 
lowing different  periods  of  eruption. 

Possibly,  as  suggested  above  (p.  430),  the  depth  below  the  orig- 
inal surface  may  have  something  to  do  with  this  question,  as 
the  older  veins  are  usually  deeply  truncated  by  erosion,  and  a 
gradual  change  in  the  character  of  the  thermal  waters  may  have 
taken  place  during  the  upward  passage  of  the  solutions.  More 
likely,  however,  the  principal  cause  is  a  radical  difference  in  the 
composition  of  the  waters  throughout  the  province. 

In  comparing  different  veins  with  a  view  to  the  elucidation 
of  this  problem  only  those  having  country-rock  of  similar  gen- 
eral character  should  be  selected,  for  it  is  well  known  that  the 
composition  of  the  wall-rock  may  have  great  influence  on  the 
metasomatic  processes,  and  hence  on  the  composition  of  the 
vein. 

Contact- Metamorphic  Deposits. 

The  preceding  remarks  apply  exclusively  to  fissure-veins  and 
the  closely-related  irregular  deposits  in  which  the  gold  was 
deposited  by  heated  waters,  which,  as  a  rule,  probably  came  up 
from  below. 

There  is  another  source  of  gold  in  the  so-called  contact-met- 
amorphic  deposits  formed  at  or  near  the  contacts  of  intrusive 
granitic  or  porphyritic  rocks.  The  characteristic  mineral  asso- 
ciations (ordinarily  garnet,  epidote,  vesuvianite,  ilvaite,  magne- 
tite, specular  hematite,  and  sulphides)  of  these  deposits  are 
such  that  they  are  probably  best  explained  as  the  products  of 
the  action  of  water  above  the  critical  temperature.  This  water 
is  believed  to  have  been  given  off  from  the  hot  magma,  and  to 
have  been  accompanied  by  metallic  compounds,  sulphur,  etc., 
also  probably  above  their  critical  temperatures.  Under  these 
conditions — that  is,  a  temperature  of  not  less  than  -f-  365°  G., 
and  a  pressure  of  not  less  than  200  atmospheres — water  can 
only  exist  as  a  perfect  gas.  Minerals  formed  under  such  con- 
ditions are  known  as  of  pneumatolytic  origin. 

When  the  temperature  sinks  below  this  limit  the  water,  if 
under  sufficient  pressure,  remains  an  ordinary  fluid,  and  the 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  433 

deposits  formed  by  it  appear  to  undergo  a  change.  To  such 
conditions  the  deposits  of  ordinary  fissure-veins  should  proba- 
bly be  attributed. 

.Finally,  under  conditions  of  high  temperature  and  slight 
pressure  very  near  the  surface,  water,  as  well  as  other  com- 
pounds, may  be  converted  into  a  vapor,  and  such  deposits  as 
may  be  formed  by  this  action  are  said  to  be  due  to  sublimation. 
Escaping  gases  from  heated  rocks  near  the  surface  in  volcanic 
districts  are  called  fumaroles.  The  name  of  fumaroles  or  fu- 
marolic  action  is  sometimes  applied  to  contact-metamorphic 
deposits,  but  this  usage  appears  to  me  to  be  incorrect. 

Contact-metamorphic  deposits  occur  in  the  United  States,  as 
well  as  in  British  Columbia  and  Mexico.  Ordinarily,  copper 
sulphides  and  magnetite  are  the  principal  ore-minerals,  but  they 
may  carry  a  small  quantity  of  gold.  A  certain  small  amount 
of  gold  has  been  derived  from  these  deposits  in  the  United 
States  and  British  Columbia;  just  how  much  is  very  difficult 
to  decide.  In  Mexico  contact-metamorphic  deposits  are  more 
common,  and  sometimes  contain  much  gold.  It  is  probable  that 
more  than  $1,000,000  has  been  obtained  from  this  source  in 
Mexico;  but  here,  again,  exact  figures  are  unobtainable. 

Classification  According  to  Age. 

Introduction. — In  stating  the  production  of  gold  in  the  various 
States,  it  is  necessary  to  adopt  some  unit  for  its  measurement. 
The  one  selected  is  $1,000,000 ;  this  unit  will  be  indicated  by 
M2$.5  In  this  manner  the  results  will  be  much  more  clearly 
presented  than  by  long  series  of  figures.  The  most  scientific 
way  to  express  the  product  is  doubtless  in  kilograms ;  but  for 
the  present  purposes  the  adopted  unit  seems  much  more  tangi- 
ble and  more  easily  understood. 

From  the  Atlantic  to  the  Pacific  ocean,  the  mountains  of 
North  America  contain  gold,  although  the  largest  treasures 
are  stored  in  the  great  ranges  of  the  Cordilleran  region.  From 
the  time  of  discovery  up  to  1900  the  United  States  has  pro- 
duced about  M2$2,529,  Mexico  at  least  M2$200,  and  possibly 
twice  as  much,  and  British  North  America  M2$140,  making  a 
grand  total  of  M2$2,869.  This  great  product  is  divided  among 

6  For  example,  M2$1.0  =  $1,000,000.      M2$2.25  =  $2,250,000.      M2$0.5  = 
$500,000,  etc. 

28 


434  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

primary  veins  of  pre-Cambrian,  Mesozoic,  and  Tertiary  age. 
To  separate  the  last  two  groups  is  in  many  cases  a  difficult 
matter. 

Pre-Cambrian  Deposits. — Gold  was  discovered  in  veins  of  the 
older  rocks  of  the  Appalachian  Mountain  region  about  100 
years  ago,  in  Georgia,  the  Carolinas,  Tennessee,  Maryland,. 
Virginia,  and  even  farther  north.  Poorer  deposits  of  the  same 
kind  have  been  found  up  to  the  Canadian  line,  and  north  of 
this  richer  gold-veins  occur  again  in  Quebec,  Ontario,  and 
Nova  Scotia.  Again,  farther  westward  in  the  United  States,. 
in  Michigan,  probably  pre-Cambrian  gold-quartz  veins  occur 
on  a  smaller  scale.  Still  farther  west  they  are  developed  in 
the  Black  hills  of  South  Dakota,  and  also  in  Wyoming.  The 
last  two  are  the  only  localities  in  the  Cordilleran  region  in 
which  pre-Cambrian  deposits  have  been  recognized. 

The  primary  deposits  in  the  above-mentioned  districts  are 
chiefly  gold-quartz  veins  with  free  gold  and  auriferous  sul- 
phides. The  veins  were  probably  to  a  large  extent  formed 
before  the  Cambrian  period,  and  are  thus  the  most  ancient 
deposits  of  the  continent.  Among  the  evidence  pointing  di- 
rectly or  indirectly  to  this  conclusion,  the  following  have  es- 
pecial weight :  The  Triassic  sandstones  of  the  Atlantic  coast 
contain  placer-gold;  no  important  gold-deposits  are  found  in  the 
Palaeozoic  rocks  of  the  Appalachian  region ;  Carboniferous  con- 
glomerates in  Nova  Scotia  are  said  to  contain  water- worn  gold 
of  older  veins ;  in  the  Black  hills  the  Cambrian  conglomerates 
yield  placers  of  the  precious  metal.  During  the  19th  century 
the  Southern  States  produced  M2$47.0,  Nova  Scotia  and  adja- 
cent provinces  M2$l 7.0;  during  the  last  ten  years  the  South- 
ern States  have  yielded  M2$0.3  and  the  eastern  Canadian  prov- 
inces from  M2$0.5  to  M2f  1.0  per  annum.  The  deposits  are  not 
rich  according  to  our  standards  for  the  Cordilleran  region, 
but  the  yield  is  steady,  and  can  probably  be  relied  upon  for 
many  years  to  come. 

Economically,  the  most  important  pre-Cambrian  deposits  are 
found  in  the  Black  hills.  The  old  pre-Cambrian  schists  here 
contain  fissure-veins  and  seam-belts  of  free-milling  gold-ores 
covered  by  Cambrian  sandstones  containing  placer-gold.  These 
deposits  are  worked  on  a  large  scale ;  they  have  yielded,  since 
discovery  in  1876,  about  M2f  74.0,  and  produce  annually  M2$ B 
or  M*f  4. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  435 

Altogether,  then,  the  pre-Cambrian  deposits  have  given  us, 
since  discovery,  M2f  138.0.  In  most  cases  extensive  erosion  has 
taken  place  since  these  veins  were  formed,  and  the  surface  of 
the  land  at  the  time  of  their  formation  must  in  some  cases,  at 
least,  have  been  thousands  of  feet  above  the  level  at  which  they 
are  worked  at  present.  They  are  the  "  roots  "  rather  than  the 
"  tops  "  of  veins. 

Cretaceous  Veins  of  the  Pacific  Coast. — The  most  important 
gold-belt  in  North  America  extends  along  the  Pacific  coast. 
It  is  throughout  characterized  by  quartzose  ores  with  free 
gold  and  auriferous  sulphides.  A  great  erosion  has  taken 
place  since  the  veins  were  formed;  and  here,  too,  as  in  the 
pre-Cambrian  deposits,  we  have  to  deal  with  the  lower  parts  of 
veins,  the  upper  parts  having  generally  been  removed,  in  many 
places  to  the  extent  of  thousands  of  feet. 

Beginning  in  Lower  California,  Mexico,  100  miles  or  more 
south  of  the  boundary-line,  this  great  belt  continues  through 
San  Diego,  Los  Angeles,  and  Kern  counties ;  through  the  cen- 
tral part  of  California,  where  it  is  developed  in  great  strength ; 
then  on  to  northern  California,  southwestern  and  northeastern 
Oregon,  and  Idaho.  In  the  latter  States  it  is  modified  by  the 
appearance  of  many  silver-gold  deposits  and  veins  carrying 
auriferous  sulphides  without  free  gold.  Covered  for  a  distance 
by  the  lava-flows  of  the  Cascades,  it  again  appears  in  southern 
British  Columbia — on  Vancouver  Island,  among  other  places. 
Strong  development  is  again  attained  in  the  Cariboo  district,  in 
central  British  Columbia,  and  it  continues  through  the  Omi- 
neca,  Cassiar,  and  Atlin  districts  to  the  Klondike  region. 
Thence,  bending  westward,  it  follows  the  Yukon  to  the  western 
end  of  the  continent  at  Nome,  on  the  Seward  Peninsula. 

The  Cretaceous  age  of  this  belt  is  clearly  established  in  Cal- 
ifornia. In  Oregon  and  Idaho,  a  late  Mesozoic  age  is  extremely 
probable.  In  British  Columbia  and  Alaska,  the  evidence  is  not 
so  positive,  and  the  deposits  may  possibly,  in  part,  be  older. 

/Throughout  this  immense  stretch  of  country  the  veins  are 
accompanied  by  a  great  development  of  placers.  Placers  are, 
indeed,  characteristic  of  this  class  of  gold-veins,  and  by  far  the 
larger  part  of  the  yellow  metal  has  been  obtained  from  them. 
At  many  places  in  California,  as  well  as  in  Oregon  and  Alaska, 
the  veins  from  which  these  placers  were  derived  have  been  very 


436  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

disappointing,  the  fact  being  that  the  primary  deposits  are  often 
scattered  in  many  little  seams  rather  than  concentrated  in  great 
veins. 

California  alone  has  yielded  M2$l,380.0  from  this  belt;  Ore- 
gon M2$54.0;  British  Columbia  and  Northwest  Territory 
M2$123.0;  Alaska  M2$30.0.  The  total  is  over  M2$l,700.0. 
During  1900  the  belt  probably  yielded  M2$54.0,  of  which  one- 
half  came  from  British  Columbia  and  the  Yukon.  This  repre- 
sents a  great  increase  compared  with  the  figures  of  ten  years 
ago,  and  it  is  doubtful  whether  this  increase  will  be  maintained. 
At  least  M2$27.0  was  obtained  from  the  placers  on  the  Yukon 
and  in  Alaska.  If  no  further  great  discoveries  are  made  in 
this  region,  our  knowledge  of  placers  forces  us  to  the  belief 
that  this  last  figure  will  gradually  decrease.  Quartz-mining 
will  to  some  degree  compensate  for  this;  but  the  quartz-mines 
have  usually,  in  the  older  districts,  yielded  less  than  the  cor- 
responding placers.  California's  output  will  doubtless  be  main- 
tained at  about  the  present  figure  for  many  years. 

Late  Cretaceous  or  Early  Tertiary  Deposits  (Central  Belt}. — Be- 
sides the  Pacific  gold-belt,  there  is  a  broad  zone  in  the  central 
and  eastern  part  of  the  Cordilleran  region  which  contains  an 
abundance  of  gold-deposits  of  varying  character.  Many  of 
these  seem  to  have  been  formed  a  little  later  than  the  Califor- 
nia gold-quartz  veins,  perhaps  largely  at  the  very  close  of  the 
Cretaceous,  or  possibly  at  the  very  beginning  of  the  Tertiary 
period. 

This  broad  zone  begins  in  Mexico,  where  the  Pacific  States 
of  Sonora  and  Sinaloa  contain  many  gold-veins  in  pre-Creta- 
ceous  sediments,  granites,  and  crystalline  schists.  According 
to  Professor  Durable,  many  of  the  Sonoran  deposits  occur  in 
Triassic  rocks,  and  are  considered  by  him  to  be  of  the  same 
age  as  the  California  veins.  Similar  veins  in  old  rocks  con- 
tinue through  the  southwestern  part  of  Arizona,  but  their 
age  is  not  definitely  known.  Many  of  them  are  important 
producers. 

Although  undoubted  Tertiary  deposits  prevail  in  Nevada, 
those  of  an  older  period  are  probably  not  absent.  A  few  of 
them  are  free-milling  gold-quartz  veins,  but  in  the  majority  the 
ores  consist  chiefly  of  sulphides  alone,  and  the  value  of  the 
silver  exceeds  that  of  the  gold. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  437 

In  Utah  the  principal  gold-mines  are  those  of  the  Mercur 
district,  in  which  ores  suited  to  the  cyanide  process  occur  in 
limestone  close  to  intrusive  sheets  of  porphyry.  These  yielded 
over  M2$2.0  in  1900.  Most  of  the  remaining  amount  credited 
to  Utah  is  derived  from  gold-bearing  silver-ores  of  the  smelting 
class,  which  are  found  in  veins  and  irregular  deposits  in  sedi- 
mentary rocks  close  to  bodies  of  intrusive  (Cretaceous?)  por- 
phyries. The  future  of  the  gold-production  is  here  very  closely 
connected  with  the  vicissitudes  of  the  silver-  and  copper- 
markets. 

In  Colorado  the  most  important  Cretaceous  gold-deposits  are 
those  of  Leadville.  Here,  again,  the  ores  occur  in  Palaeozoic 
sediments  and  porphyry;  and  the  gold-production,  small  until 
a  few  years  ago,  reached  M2f  2.7  in  1900. 

In  Idaho  and  Montana  late  Mesozoic  and  early  Tertiary  veins 
are  developed  on  a  large  scale.  We  note  here  the  interesting 
fact  of  a  junction  with  the  Pacific  belt,  through  northeastern 
Oregon  and  central  Idaho,  into  Montana.  Going  eastward,  the 
free-milling  and  quartzose  character  is  partly  maintained,  but 
silver  becomes  more  prominent  in  the  ores,  and  auriferous 
sulphide  ores  often  replace  the  native  gold.  Central  Idaho 
formerly  contained  many  rich  placer-camps,  which  have  yielded 
their  millions.  As  in  Oregon  and  in  Montana,  the  first  years 
of  mining  were  largely  devoted  to  working  this  form  of  deposit. 
Bannack,  Alder  Gulch,  Helena,  and  Confederate  Gulch  are 
well-known  names  of  celebrated  placer-camps  in  Montana.  The 
great  producing  quartz-mines  are  not,  however,  those  from 
which  the  placers  have  been  derived.  They  contain  much 
silver,  and  pan-amalgamation  is  the  most  common  process. 

After  the  exhaustion  of  the  placers,  silver-ores  of  the  smelt- 
ing class,  containing  galena  and  other  sulphides,  together  with 
a  little  gold,  were  also  extensively  mined.  This  industry  has 
declined  during  recent  years;  but,  as  a  partial  compensation,  at 
least  M2$1.0  per  annum  is  obtained  as  a  by-product  from  the 
smelting  of  the  copper-ores  of  Butte. 

The  majority  of  gold-bearing  veins  in  Idaho  and  Montana 
are  genetically  connected  with  the  intrusion  of  very  large 
bodies  of  granitic  rocks  during  the  Cretaceous  period.  This 
explains  the  fact  of  relationship  with  the  Pacific  gold-belt,  for 
there,  too,  the  veins  stand  in  undoubted  causal  connection  with 
the  great  Mesozoic  granitic  "  batholiths,"  as  the  large  intrusive 


438  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

bodies  are  called.  As  far  as  we  know,  these  batholiths  are 
either  absent  or  only  developed  on  a  small  scale  in  Nevada, 
Utah,  and  Arizona. 

In  the  southern  part  of  British  Columbia  are  a  number  of 
veins  which  contain  copper-gold  ores,  and  to  less  extent  milling- 
ores,  and  which  are  believed  to  belong  to  the  late  Mesozoic 
period.  They  are  chiefly  found  in  diorites  and  allied  intrusive 
rocks. 

Looking  at  this  central  Mesozoic  gold-belt  as  a  whole,  it  is 
believed  that,  north  of  Mexico,  it  has  produced  at  least 
M2$286.0  since  discovery,  and  during  1900  its  tribute  to  the 
total  of  North  America  was  about  M2f  14.0. 

In  this  chain  of  deposits  the  gold-production  is  closely  asso- 
ciated with  the  silver  and  copper  industry,  for  sulphide  ores 
prevail  over  those  containing  native  gold.  No  wonderful  in- 
crease of  production  may  be  expected,  but  rather  a  steady 
maintenance,  and  possibly  a  gradual  growth  if  there  is  no  seri- 
ous decline  in  the  values  of  copper  and  silver.  Placer-mining, 
with  its  dwindling  tendency,  is  still  represented  in  Montana  and 
Idaho ;  in  the  other  States  of  this  belt  it  plays  a  comparatively 
insignificant  part. 

Tertiary  Deposits. — A  fourth  and  last  class  of  gold-produc- 
ing veins  are  of  Tertiary,  mostly  post-Miocene,  age.  They  are 
usually  found  in  regions  of  intense  volcanic  activity  cutting 
across  heavy  andesite-flows,  more  rarely  rhyolite  and  basalt. 
In  many  cases  these  veins  may  be  seen  to  continue  down  into 
the  underlying  floor,  upon  which  the  volcanic  flows  were 
poured  out,  and  which  may  be  of  igneous  or  sedimentary  char- 
acter. -Sometimes,  indeed,  an  active  erosion  has  removed 
much  of  the  volcanic  flows,  and  the  veins  crop  directly  in 
older  rocks. 

The  majority  of  these  veins  in  Tertiary  lavas  have  certain 
common  and  persistent  characteristics  and  form  a  fairly  well- 
defined  class,  usually  called  propylitic  veins,  alluding  to  the 
peculiar  alteration  of  adjoining  rocks  which  seems  to  charac- 
terize them.  The  ores  are  nearly  always  quartzose,  and  some- 
times contain  silver  alone ;  more  rarely  gold  alone ;  but  most 
commonly  both  gold  and  silver  in  about  equal  quantities  by 
value. 

They  are  often  characterized  by  great  richness,  the  word 
"  bonanza "  being  employed  to  represent  their  big  ore-shoots. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  439 

While  some  of  these  veins  yield  steady  and  reliable  products? 
many  of  them  burst  out  in  sudden  blazes  of  glory  like  shooting- 
stars,  only  to  be  extinguished  with  equal  suddenness.  The 
gold  is  nearly  always  in  such  peculiarly  fine  distribution  that 
extensive  and  rich  placers  are  rarely  formed  from  them ;  con- 
trasting, in  this  respect,  with  conditions  in  the  Pacific  gold- 
belt.  Many  of  them,  in  districts  of  great  erosion,  show  that 
the  values  continue  in  depth ;  but  the  ore  is  perhaps  less  rich 
than  in  those  parts  formed  nearer  to  the  original  surface.  In 
this  class  we  evidently  have  to  do  with  the  part  of  the  vein 
which  was  not  far  from  the  original  surface  at  the  time  of  ore- 
deposition.  In  some  cases  the  ores  can  be  proved  to  have  been 
formed  but  a  few  hundred  feet  from  this  surface.  Instead  of 
roots  of  veins,  as  in  the  Pacific  and  Appalachian  belts,  the  pro- 
pylitic  veins  ordinarily  represent  the  uppermost  part  of  the 
area  of  deposition  along  the  fissure.  Not  all  of  the  distinctly 
Tertiary  veins  possess,  however,  the  character  of  typical  propy- 
litic  veins.  Many  deviate  considerably,  but  few,  if  any,  show 
the  typical  development  of  gold-quartz  veins  of  the  Pacific 
coast. 

This  belt  of  Tertiary  veins  is  most  extensively  developed  in 
Mexico.  The  central  plateau  contains  the  great  silver-veins  of 
this  class,  which  always  contain  a  small  amount  of  gold,  and 
from  which  the  greater  part  of  Mexico's  gold-output  has  been 
derived.  But  along  the  western  slope  of  the  Sierra  Madre  in 
Chihuahua,  Zacatecas,  and  Sinaloa,  heavy  andesite-flows  contain 
gold-silver  veins  of  great  importance,  and  are,  together  with  the 
veins  of  the  older  belt  in  Sonora,  largely  responsible  for  the 
greatly-increased  gold- production  of  Mexico. 

Entering  the  United  States,  Tertiary  veins  are  found  in  Ari- 
zona and  New  Mexico.  In  Arizona,  probably  both  Cretaceous 
and  Tertiary  veins  occur,  and  in  the  present  state  of  our  knowl 
edge  their  separation  is  sometimes  difficult.  The  Common- 
wealth mine,  in  Cochise  county,  is  a  prominent  representative  of 
the  younger  veins ;  it  breaks  through  rhyolite,  and  is  at  present 
one  of  the  largest  producers  of  the  Territory.  One-third  of  the 
value  is  in  gold,  and  the  rest  in  silver. 

In  New  Mexico  are  several  districts  containing  these  veins — 
chiefly,  it  is  said,  in  andesitic  rock ;  but  the  output  of  this  Ter- 
ritory has  not  as  yet  reached  the  million-dollar  mark. 

The  development  of  Tertiary  veins  continues  northward  into 


440  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

Nevada  and  California.  San  Bernardino  county,  in  California, 
contains  silver-deposits  in  rhyolite,  and  probably  also  Tertiary 
gold-veins.  Veins  of  similar  kind  Continue  along  the  eastern 
foot  of  the  Sierra  Nevada  as  far  north  as  Alpine  county,  and 
become  most  productive  in  Mono  county ;  the  mines  at  Bodie, 
in  andesite,  produced  in  nine  years  M2$12.0  in  gold,  besides 
much  silver. 

Northward  from  this  point  few  Tertiary  veins  are  found, 
though  intense  volcanic  activity  prevailed  in  the  northern 
Sierra  Nevada  and  the  Cascades  during  the  Tertiary.  At  one 
or  two  places  in  Oregon,  chiefly  in  the  Bohemia  district  in  the 
Cascade  mountains,  the  volcanic  rocks  contain  gold-veins,  but 
they  have  not  as  yet  yielded  much.  Continuing  northward  into 
Washington,  the  Monte  Cristo  veins,  in  andesite  and  diorite, 
represent  this  type,  but  are  not  credited  with  extraordinary 
production. 

No. veins  of  this  class  are  thus  far  known  in  British  Co- 
lumbia or  the  Northwest  Territory,  but  on  the  southern  coast 
of  Alaska  we  meet  sporadic  cases  again.  The  Apollo  mine, 
on  Unga  Island,  breaks  through  andesite,  and  has  produced 
gold  for  the  last  few  years  to  a  maximum  annual  amount 
of  about  $400,000.  The  Alaskan  peninsula  also  shows  evi- 
dence of  more  recent  Tertiary  mineralization. 

Returning  southward  to  Nevada,  this  class  of  gold-deposits 
is  abundantly  represented.  The  Comstock  vein,  Tuscarora, 
Eureka,  Tonopah,  the  De  Lamar  veins,  are  known  or  believed 
to  be  of  propylitic  character,  and,  with  the  exception  of  the 
latter,  occur  in  volcanic  rocks.  The  Comstock  easily  leads, 
with  an  estimated  production  of  over  M2f  148.0  in  gold,  and  the 
other  districts  have  contributed  heavily  to  the  total  output,  al- 
though all  also  contain  much  silver  in  their  ores.  The  produc- 
tion of  Nevada  has  fluctuated  greatly,  and  after  long  decline 
is  again  increasing. 

A  line  of  Tertiary  veins  continues  northward  from  Nevada 
into  Idaho.  In  the  southern  part  of  that  State  they  are  repre- 
sented by  the  Owyhee  gold-silver  mines,  which  since  their  dis- 
covery have  yielded  M2fl2.0  in  gold;  and  farther  north  by  the 
bonanzas  of  Rocky  Bar,  Atlanta,  and  Custer,  which,  probably, 
should  be  referred  to  this  type.  Still  farther  north  is  the 
Thunder  Mountain  district,  which,  if  reports  are  reliable,  con- 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  441 

tains  gold  in  rhyolite.     No  Tertiary  primary  gold-deposits  have 
been  reported  north  of  this  point. 

Veins  of  this  class  occur  in  Utah — for  instance,  at  the  Horn- 
Silver  mine  and  atTintic;  but  these  deposits  carry  very  little  gold. 

Returning  now  to  New  Mexico,  a  belt  of  these  veins  continues 
northward  into  Colorado  and  reaches  a  development  not  known 
elsewhere,  except  in  Mexico.  The  total  output  of  Colorado  is 
probably  about  M2$250.0.  In  1900  the  output  was  M2$28.8. 
Excepting  the  Leadville  deposits,  the  principal  gold-producing 
districts  are  of  Tertiary  age.  Oldest  among  them  as  to  discovery 
are  the  veins  of  Gilpin,  Boulder,  and  Clear  Creek  counties,  which 
crop  in  Archaean  rocks  and  are  accompanied  by  andesite  dikes. 
These  districts  have  been  remarkably  steady  producers  since 
1859,  and  contribute  annually  about  M2f  3.0.  They  promise  to 
continue  their  production  for  a  long  time.  Another  important 
locality  is  the  San  Juan  district,  in  southwestern  Colorado, 
where  strong  quartz  veins  cut  heavy  andesitic  flows.  The  yield 
has  increased  greatly  since  1890,  and  in  1900  reached  M2$4. 
It  promises  well  for  the  future ;  and  some  of  the  mines,  like  the 
Camp  Bird,  have  proved  veritable  bonanzas.  The  output  will 
probably  continue  to  increase  for  some  years.  An  interesting 
feature  of  the  San  Juan  region  is  that  in  some  districts  which 
have  suffered  great  erosion  the  veins  are  found  to  continue  into 
bodies  of  intrusive  diorites  and  porphyries  of  later  age  than 
the  andesites,  thus  offering  a  comparison  of  conditions  near  the 
original  surface  and  at  a  considerable  distance  below  it. 

Finally,  there  is  the  great  Cripple  Creek  district,  which  has 
yielded  M2$77.3  during  the  period  1892  to  1900  inclusive,  and 
in  1900  produced  M2$18.  A  network  of  veins  occur  in  ande- 
site, phonolite,  and  underlying  granite,  and  have  thus  far 
chiefly  carried  telluride  ores.  What  may  be  expected  of  this 
district  in  the  future  is  a  most  important  question,  and  one  not 
easy  to  answer. 

North  of  Colorado  the  propylitic  deposits  are  almost  absent, 
though  they  appear  in  sporadic  form  in  Montana. 

Roughly  calculated,  about  M2$564.0  has  been  contributed  by 
the  propylitic  veins  to  the  total  gold-output  of  the  United 
States,  to  which  should  probably  be  added  at  least  M2f  160.0 
from  Mexico.  For  1900  we  may  estimate  M2$36.0  as  the  out- 
put of  these  veins  in  the  United  States,  and  perhaps  M2f  7.0 
in  Mexico. 


442  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

Conclusions. 

Summing  up  the  data  obtained,  we  should  estimate  as  fol- 
lows : 

Source  of  Production  of  Gold  in  North  America. 

Total  M«S.  1900  M2$. 

Pre-Cambrian,         .         .         .         .        .        ,         .139.0  5.0 

Cretaceous  (Pacific), 1,719.0  54.0 

Cretaceous  and  early  Tertiary  (Central),          .         .       287.0  14.0 

Tertiary  (largely  propylitic),  .        .         .        .       724.0  43.0 

2,869.0       116.0 

The  great  increase  in  the  gold-production  of  the  continent 
during  the  last  ten  years  has  been  due,/rsf,  to  important  dis- 
coveries of  new  districts  in  almost  every  producing  State ; 
second,  to  the  increased  activity  in  many  old  gold-districts  and 
mines  ;  third,  to  the  late  great  development  of  copper-smelting, 
by  which  much  gold  has  been  obtained  as  a  by-product -,  fourth, 
to  the  introduction  of  the  cyanide  process,  rendering  many 
classes  of  low-grade  ores  and  tailings  available;  and,  fifth,  to 
the  introduction  of  hydraulic  elevators  and  dredgers,  giving  a 
new  lease  of  life  to  many  old  and  decaying  placer-camps. 

Many  considerations  suggest  that  the  increase  will  probably 
not  continue  in  the  same  ratio  for  the  next  few  years,  providing 
that  no  great  discoveries  are  made  of  new  placers  in  the  far 
north  or  of  vein-systems  like  that  of  Cripple  Creek.  The 
greater  part  of  the  increase  has  been  derived  from  the  Northern 
placers  and  from  Cripple  Creek;  in  1900  the  gold  derived 
from  these  sources  amounted  to  M2$46.0.  Subtract  this  from 
a  total  for  North  America  of  M*$116.0,  and  only  M2$70.0  re- 
mains. The  placer-fields  now  known  in  Alaska  and  Northwest 
Territory  will  in  all  probability  gradually  decrease  their  out- 
put during  the  next  few  years.  Many  reserves  of  old  mill- 
tailings  and  dredging-grounds  to  which  new  processes  have 
been  applied  are  being  rapidly  exhausted.  Some  districts  pro- 
ducing gold  from  copper-ores  and  others  working  bonanzas  of 
the  Tertiary  veins  will  not  improbably  lessen  their  output. 
Against  this  stand  always  the  possibility  of  new  discoveries  and 
the  introduction  of  improved  processes.  Tentatively  striking 
a  balance,  a  small  decrease  of  the  gold-production  of  North 
America  would  seem  more  likely,  for  the  next  few  years,  than 
an  increase. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 


443 


TABLE  I. — Gold-Production  of  North  America. 

Unit:  M2$=  $1,000,000. 


Divisions. 

Total  from 
Discovery 

1877-1900,  incl. 

MS$. 

United  States. 

to  1900,  incl. 
MS$. 

3H$. 

1900. 

1901. 

1902.  « 

Alaska 

30.7 

30.7 

8.2 

6.9 

7.8 

Arizona 

42.1 

33.6 

4.2 

4.1 

4.2 

California 

1,380.0(?) 

351.1 

15.8 

16.9 

17.1 

Colorado  . 

251.  1(?) 

204.3 

28.8 

27.7 

27.5 

Idaho 

112.8 

42.8 

1.7 

1.9 

2.1 

Montana 

203.  5(?) 

83.6 

4.7 

4.7 

4.1 

Nevada          .     ... 

250.0(?) 

99.7 

2.0 

3.0 

3.5 

New  Mexico  

17.6 

13.3 

0.8 

0.7 

0.7 

Oregon  

54.5 

29.7 

1.7 

1.8 

1.9 

South  Dakota  

90.0 

89.4 

6.2 

6.5 

7.4 

Utah  

27.0 

24.1 

4.0 

3.7 

3.7 

Washington  

21.4(?) 

8.9 

0.7 

0.6 

0.4 

Wyoming  

1.0(7) 

1.0 

0.1 

Appalachian  States  

47.0 

8.0 

0.3 

0.2 

0.3 

(Mainly  Georgia   and 
the  Carolines.  ) 

2,528.7 

1,020.2 

79.2 

78.7 

80.7 

British  North  America. 

Nova  Scotia 

13.7 

9.7 

0.6 

0.5 

Quebec           

2.0(?) 

0.2 

Ontario  

1.2(?) 

1.1 

0.3 

0.2 

British  Columbia  

70.7 

21.1 

4.7 

5.3 

N.  W.  Territory  

52.6 

52.6 

22.3 

18.0 

14.6 

140.2 

84.7 

27.9 

24.0 

Mexico  

200.  0(?) 

66.5 

9.0 

10.3 

Total 

2  868.9 

1  171  4 

116.1 

113.0 

a  Preliminary  estimate  by  the  Director  of  the  Mint. 

NOTE  TO  TABLE  I. — This  table  has  been  compiled  chiefly  from  the  Mint  Reports 
of  the  United  States.  Regarding  the  United  States,  accurate  statistics  date  from 
1877 ;  the  first  column,  showing  the  total  production  of  each  State,  is  to  a  great 
extent  based  on  estimates  of  the  output  of  early  placer-mining,  by  J.  Ross  Browne, 
R.  W.  Raymond,  and  the  Mint  Bureau.  The  figures  given  for  California,  Ne- 
vada, Montana,  Washington,  Oregon,  and  Colorado  are  especially  uncertain.  The 
total  (M2$2,528.7)  exceeds  the  estimate  of  the  Mint  Bureau  by  nearly  M2$150.0, 
though  the  two  calculations  are  probably  based  on  the  same  evidence.  If  the 
results  of  the  Mint  Bureau  are  accepted  as  correct,  the  figures  given  jn  the  first 
column  are  too  high  ;  but  how  and  where  the  correction  should  be  applied  is  very 
difficult  to  say.  In  most  States,  however,  the  figures  in  the  first  column  will  be 
considered  too  low,  locally-current  estimates  being  much  higher. 

The  figures  for  British  North  America  are  probably  fairly  correct,  but  those 
from  Mexico  are  admittedly  only  estimates  by  the  Mint  Bureau  or  by  other 
statisticians. 


444 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 


TABLE  II. —  Tentative  Distribution  of  Gold-Production  of  North 
America  According  to  Age  of  Primary  Deposits. 

Unit:  M2f  =  $1,000, 000. 


Divisions. 
United  States. 

Distribution  of  Total  Production. 
From  Discovery  to  1900,  inclusive. 

MS$. 

Distribution  of  Produc- 
tion of  1900. 
M*, 

i* 

£ 

Mesozoic  (Paci- 
fic Coast  Belt). 

IS  $§  • 

«3I 

fill 

Tertiary  (Most- 
ly Post  -Mio- 
cene). 

Pre-Cambrian. 

Mesozoic  (Paci- 
fic Coast  Belt). 

i  ^i 

o'S  o> 

3Sa~ 
£s«l 

Jill 

Tertiary  (Most- 
ly Post  -  Mio- 
cene). 

Alaska 

29.7 
22.1 
1,350.0 

1.0 

7  8 

0.4 
2.2 
1.0 
26J 
1.0 

2.0 
0.4 

2.4 
? 

6.5 

Arizona 

20.0 

2.0 
2.7 

4.7 

? 

0.4 

California  

34.6 

30.0 
217.1 
22.8 
3.5? 
230.0 
10.0? 

...... 

14.8 

Idaho 

90.0 



0.7 

Montana 

200.0  ? 
20.0 
7.6? 

Nevada  . 

New  Mexico 

Oregon  .  . 

54.0 

0.5? 

1.7 

South  Dakota  
Utah  

74.0 

""25.6"' 

16.0 
2.0? 
11.4 

3.8 

4.0 

Washington   .  . 

10.0 

b.i 

0.3 

0.2 

Wyoming.  . 

1.0 

Appalachian  States 
(Mainly      Georgia 
and  the  Carolinas.  ) 

47.0 

122.0 

1,555.8 

286.6 

564.3 

4.2 

25.2 

13.8 

36.0 

British  N.  America 

Nova  Scotia 

13  7 

0.6 
0.3 

4.7 
22.3 

Quebec 

2.0? 
1.2? 

Ontario  

British  Columbia 

70.7 
52.6 

N.  W.  Territory 

16.9 

123.3 

0.9 

27.0 

Mexico. 

40.0? 



160.0? 



2.0? 

7.0? 

Total  

138.9 

1,719.1 

•286.6 

724.3 

5.1 

54.2 

13.8 

43.0 

NOTE  TO  TABLE  II. — It  should  be  expressly  stated  that  this  table  is  only  a  first 
tentative  estimate,  as  in  very  many  cases  the  data  for  exact  subdivision  are  not 
available.  The  distribution  for  1900  is,  of  course,  probably  more  nearly  correct 
than  the  segregation  of  the  total  product  attempted  in  the  first  part  of  the  table. 


THE  GOLD-PRODUCTION  OF   NORTH  AMERICA.  445 

DISCUSSION. 

(Trans.,  xxxiii.,  1077.) 

WILLET  G.  MILLER,  Toronto,  Canada:  With  regard  to  Mr. 
Lindgren's  impression  that  the  gold-supply  of  the  world  will 
gradually  decrease  if  no  further  important  improvements  are 
made  in  the  processes  of  gold-extraction,  it  seems  to  me  that 
no  very  important  improvements  are  needed  to  keep  up  the 
present  production  for  many  years  to  come.  In  many  regions 
there  are  large  deposits  of  auriferous  material  which  can  be 
worked  if  present  conditions  are  slightly  changed.  In  the  ter- 
ritory occupied  by  the  Archaean  protaxis  of  the  Province  of 
Ontario,  for  instance,  there  are  gold-deposits  of  large  size  which 
apparently  could  be  worked  at  a  profit  if  the  cost  of  production 
were  slightly  decreased.  Many  of  these  deposits  average  ap- 
proximately from  $1  to  $1.50  per  ton,  and  consist  of  quartz 
veins,  shattered,  impregnated  masses  of  granite  and  other  rocks, 
and  placer-deposits. 

In  the  Rainy  River  district,  in  Western  Ontario,  gold  occurs 
in  a  mass  of  rock  which  is  thus  described  in  the  government 
reports  of  the  Province :  "  It  consists  of  a  mixture  of  altered 
granite,  quartz,  and  chlorite,  with  streaks  of  green  schist.  It 
has  been  traced  3  or  4  miles,  and  has  a  general  direction  of 
northeast  and  southwest.  The  boundaries  are  rather  indefinite, 
but  as  near  as  can  be  ascertained  it  is  462  ft.  wide  at  the 
widest  known  place.  On  the  location  we  are  dealing  with  it 
varies  in  width  from  100  to  200  ft.  One  hundred  feet  is  its 
width  at  the  narrowest  place,  as  far  as  known."6  Judging  from 
careful  tests  which  have  been  made,  much  of  this  rock-matter 
contains  $1.50  value  per  ton  in  free-milling  gold.  It  has  not 
been  found  possible,  however,  to  work  it  at  a  profit. 

Gold  has  been  found  in  the  Vermilion  River  placers,  north 
of  Sudbury,  in  a  territory  covering  many  square  miles.7  The 
metal  occurs  free,  usually  in  a  state  of  very  fine  division,  and 
inclosed  in  pebbles  of  quartz.  Fire-assays  show  that  the  sand 
and  gravel  frequently  carry  a  value  of  more  than  $2  per  ton. 
Much  of  the  material,  while  lower  in  value,  averages  from  12 
to  15  cents  per  cubic  yard.  While  the  existence  of  these  placers 

6  Seventh  Report  of  the  Ontario  Bureau  of  Mines,  pp.  65,  130  and  131  (1897). 

7  Idem,  pp.  256  to  259  ;  Tenth  Report,  pp.  151  to  159  (1901). 


446  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

has  been  known  for  some  years,  success  has  not  been  achieved 
in  treating  them.  It  would  seem,  however,  that  a  compara- 
tively slight  improvement  in  the  present  methods  of  treatment 
should  bring  about  the  profitable  working  of  them. 

A  year  or  two  ago  similar  placers  were  discovered  on  Savant 
lake,  which  is  about  150  miles  northwest  of  Port  Arthur  and 
500  miles  from  the  last-mentioned  area.  In  panning  these 
sands  and  gravel  I  obtained  a  very  few  colors.  Fire-assays, 
however,  show  that  much  of  the  material,  which  consists  of 
coarse  sand,  gravel,  and  boulders,  averages  about  $1  per  ton  in 
gold.8  Some  of  the  metal  contained  in  the  fragments  of  rock 
probably  could  not  be  extracted  by  free-milling  processes. 
Similar  deposits,  which  have  not  been  examined  as  to  their  gold- 
content,  cover  a  large  territory  in  this  little-explored  region, 
and  it  would  appear  that  the  metal  is  present  in  most  of  this 
gravel.9  In  the  vicinity  of  Savant  lake  the  thickness  of  the 
sand-  and  gravel-deposits  is  at  some  points  over  100  ft.  The 
deposits  are  of  glacial  origin,  and  the  average  of  the  gold- 
content  of  the  gravel  from  the  tops  of  the  higher  hills  is  similar 
to  that  found  at  lower  levels. 

The  rocks  over  a  great  part  of  the  Archaean  area  of  Canada 
are  similar  in  character,  and  there  is  reason  to  believe  that  gold- 
deposits  carrying  values  like  those  mentioned  occur  widely  ex- 
tended over  this  vast,  imperfectly-explored  region.  It  may  be 
many  years,  probably  not  till  the  production  of  the  richer  de- 
posits of  other  parts  of  the  world  begins  to  decline,  before  these 
deposits  are  worked.  Since  the  gold-values  which  they  carry,, 
however,  are  so  close  to  those  of  deposits  which  even  now  are 
being  profitably  worked,  it  is  within  the  range  of  probability 
that  the  Canadian  protaxis  will,  in  the  years  to  come,  be  the 
scene  of  a  great  gold  industry.  Low-grade  deposits  in  other 
parts  of  the  world  also  will  then  add  their  quota,  and  the  day 
of  a  great  decline  in  gold-production,  a  time  of  "  not  only 
physical  devastation,  but  moral  and  political  decay,"  thus  seems 
far  distant. 

8  Twelfth  Report  of  the  Ontario  Bureau  of  Mines  pp.  89,  90  (1903). 

9  Summary  Report  of  the  Geological  Survey  of  Canada,  pp.  92  to  93  (1901). 


THE   GOLD-PRODUCTION    OF     NORTH    AMERICA.  447 

"W*.  L.  AUSTIN,  New  York,  N.  Y. :  In  Mr.  Lindgren's  instruc- 
tive paper  the  statement  is  made  in  the  reference  to  the  pre- 
Cambrian  gold-quartz  veins  of  South  Dakota  and  Wyoming,, 
that  these  two  "  are  the  only  localities  in  the  Cordilleran 
region  in  which  pre-Cambrian  deposits  have  been  recognized." 
Further  along  in  the  paper  [Part  III.,  not  reprinted  here]  it  is 
stated  that  "  gold-deposits  of  Archaean  age  are  not  known  in 
Colorado.  As  far  as  the  age  has  been  determined,  the  deposits 
are  divided  into  a  smaller  Mesozoic  and  a  much  greater  Ter- 
tiary and  probably  chiefly  post-Miocene  group." 

Mr.  Lindgren  has  apparently  overlooked  an  extensive  aurif- 
erous deposit  described  by  Messrs.  E.  C.  and  P.  H.  van  Diest 
in  a  paper  read  before  the  Colorado  Scientific  Society  in  1894. 
As  the  article  referred  to  is  not  readily  accessible,  and  as  the 
said  deposit  is  of  considerable  extent — the  beds  cropping  out 
3  miles  in  one  direction,  and  1  mile  in  another — a  few  extracts 
from  the  van  Diest  paper  may  be  considered  pertinent  in  dis- 
cussing "  The  Geological  Features  of  the  Gold-Production  of 
North  America."  Furthermore,  this  matter  has  commercial 
importance,  for  these  beds  may  become  at  an  early  day  a  not- 
inconsiderable  source  of  the  precious  metal. 

The  van  Diests  refer  tp  this  deposit  as  Cambrian;  but  it  is 
thought  that  no  serious  attempt  has  been  yet  made  to  fix  the 
age  other  than  approximately.  It  is  apparently  lower  than  the 
Silurian,  and  in  some  respects  resembles  the  pre-Cambrian 
deposits  of  the  Black  hills. 

Quoting  from  the  van  Diest  paper  :  "  The  district  examined 
is  on  the  Blto  Seco.  This  little  stream  unites  with  the  Rio  de 
la  Culebra  near  San  Luis — the  county  seat  of  Costilla  county — 
a  region  nearly  in  the  center  of  the  lower  neck  of  the  Pliocene 
lakes,  named  by  Endlich  the  Coronados  lakes.  Leaving  San 
Luis,  the  Rlto  flows  for  about  6  miles  in  a  northerly  direction 
through  scattered  debris,  when  the  lake  beds  forming  the  foot 
hills  are  reached.  Here  the  road  takes  an  easterly  direction, 
winding  its  way  for  afrout  3  miles  through  a  wide  and  shallow 
canyon  which  has  been  eroded  from  the  lake  beds.  According 
to  Hayden  the  lake  beds  at  this  point  should  lie  against  the 
Upper  Carboniferous.  No  dark-red  sandstones,  such  as  were 
observed  in  coming  over  Veta  Pass,  could  be  seen  anywhere, 
but  we  found  instead,  on  the  north  side  of  the  Rito  for  a  dis- 


448  THE    GOLD-PRODUCTION    OF    NORTH    AMERICA. 

tance  of  a  quarter  of  a  mile,  some  quartzite  beds  forming 
steep  cliffs,  while  further  along  the  stream  flows  over  light- 
colored  limestones  and  finally  over  granite. 

"  Directly  north  of  the  creek  a  thin  bed  of  conglomerate  ap- 
pears. It  is  composed  of  light-bluish  and  greenish  quartz  pebbles 
cemented  by  oxides  of  iron  and  manganese.  Resting  on  this 
bed  follow  layers  of  quartzites  whose  total  thickness  is  estimated 
at  160  ft.  These  quartzites  are  saccharoidal  in  appearance,  of 
pure  white  color  when  freshly  broken,  but  stained  by  a  film  of 
iron  oxide  where  they  have  been  exposed  to  the  influence  of 
the  weather.  The  quartzites  are  succeeded  by  a  thin  bed  of 
argillaceous  shale,  and  the  whole  section  is  topped  by  layers  of 
light-grey  siliceous  limestones  for  about  200  ft.,  where  a  quartzy 
parting  separates  them  from  others  of  somewhat  darker  color. 
.  .  .  Although  no  fossils  have  been  found  as  yet  in  the  de- 
scribed beds,  it  is  clear  from  a  stratigraphic  point  of  view  that 
the  limestones  are  of  Silurian  and  the  quartzites  of  Cambrian 
age.10  An  igneous  dike  about  30  ft.  in  width  runs  through  the 
limestone  beds  in  a  northerly  and  southerly  direction.  It  is 
of  a  dark  purplish-brown  color,  very  compact  and  fine  grained. 
In  appearance  it  resembles  more  the  older  basalt  occurring 
between  the  lake  beds,  and  is  distinctly  different  from  the 
younger  basaltic  overflow  which  caps  the  beds  south  and  west 
of  the  Bito  Seco.  The  dike  had  had  no  disturbing  influence 
whatever  on  the  limestone  beds,  as  is  shown  by  the  cuts  run 
into  the  limestone  on  either  side  of  the  dike.  Northerly  and 
higher  up  on  the  mountain  a  light-colored  porphyry  was  ob- 
served, but  owing  to  lack  of  time  there  was  no  opportunity 
afforded  to  determine  what  the  extent  of  this  eruptive  mass 
might  be,  and  what  connection,  if  any,  it  might  have  with  the 
dike,  nor  could  wre  determine  if,  in  an  easterly  direction,  other 
quartzites  and  limestones  rest  on  the  granite.  .  .  :• 

"  Close  inspection  of  the  rusty  faces  of  the  quartzite  cliff' 
has  lately  revealed  that  three  distinct  layers  of  auriferous  iron 
pyrite  occur  between  the  quartzite  beds,*the  lowrer  one  measur- 
ing about  12  ft.  in  thickness,  the  next  about  14  ft.,  and  the 
upper  one  8  ft.  At  the  time  of  our  visit  a  drift  had  been  run 

10  As  Cambrian  conglomerates  bear  witness  to  prc-Cambrian  gold-veins,  then 
these  deposits  must  be  pre-Cambrian  in  the  same  sense  as  those  of  the  Black  hills. 


THE    GOLD-PRODUCTION    OF    NORTH    AMERICA.  449 

in  the  middle  seam  for  a  distance  of  40  ft.  The  breast  and 
sides  of  this  drift  stood  in  almost  solid  pyrite.  This  pyritic 
ore  as  broken  down  assays  from  $5  to  $15  in  gold  per  ton. 
So  far  no  copper-,  zinc-,  or  other  sulphides  have  been  ob- 
served with  the  deposit.  The  field,  although  but  little  em- 
ployed, seems  to  be  of  promise,  and  it  is  to  be  hoped  that 
development  work  will  be  uninterruptedly  prosecuted."  u 

Since  the  above  was  written  these  quartzite-beds  have  been 
exploited  somewhat  further;  and  it  is  now  thought  that  the 
beds  are  more  nearly  an  arkose  than  quartzite.  This  deposit 
is  so  little  known  that  it  is  not  surprising  it  should  have 
escaped  Mr.  Lindgren's.  notice. 

11  Proceedings  of  the  Colorado  Scientific  Society,  vol.  v.,  pp.  76  to  80. 


29 


450  OSMOSIS    AS    A    FACTOR    IN    ORE-FORMATION. 

No.  17. 

Osmosis  as   a   Factor  in    Ore-Formation. 

BY  HALBERT  POWERS   GILLETTE,  NEW  YORK,  N.  Y. 
(New  York  Meeting,  October,  1903.     Trans.,  xxxiv.,  710.) 

FROM  the  known  laws  of  physical  chemistry  I  believe  it  can 
be  shown  that  progressive  mass  movement  of  water  solutions 
in  channels  has  seldom  been  the  means  of  ore-concentration  in 
veins.  It  is  my  purpose  in  this  paper  to  show  that  the  force 
known  as  "osmosis  "  has  been  the  principal  factor  in  ore-forma- 
tion. Convection-currents  have  doubtless  supplemented  osmo- 
sis, and  the  two  working  together  have  been  the  agencies  that 
have  gathered  the  scattered  particles  of  rare  minerals  into  the 
larger  masses  which  are  called  ore. 

Osmosis  is  commonly  thought  of  as  a  vague,  feeble  force 
that  causes  slow  diffusion  of  dissolving  matter  through  the 
solvent.  That  it  is  a  measurable  force,  often  of  great  intensity,, 
few  know,  except  those  who  are  familiar  with  the  laws  of  mod- 
ern physical  chemistry.  Therefore,  I  may  be  pardoned  for  go- 
ing briefly  into  the  elementary  mathematics  of  osmotic  pressure 
and  of  convection-currents. 

The  velocity  of  water  moving  through  any  channel  is  given 
by  the  Chezy  formula  : 

(1)  v  =  c  i/rs,  in  which  r  is  the  hydraulic  mean  radius ;  sr 
the  slope  of  the  channel  in  which  gravity  is  the  sole  propulsive 
force ;  and  c,  the  coefficient  of  roughness  of  the  sides  of  the 
channel. 

From  this  formula  it  is  evident  that  the  smaller  the  channel, 
the  smaller  the  velocity  of  water  under  a  constant  head.  In 
rock-crevices,  therefore,  where  the  head  is  constant,  water 
moves  much  more  slowly  than  in  large  fissures,  and  in  moving 
through  sand  or  porous  rock  it  is  to  an  even  greater  degree  re- 
tarded. Hence,  if  a  mass  of  water-saturated  sand  be  heated, 
the  finer  the  sand-grains,  the  more  slowly  will  the  temperature 
rise  at  parts  remote  from  the  source  of  heat.  Conversely,  cool- 
ing is  retarded  the  smaller  the  interstices  or  channels  through 
which  the  convection-currents  move.  The  importance  of  this 


OSMOSIS    AS    A    FACTOR    IN    ORE-FORMATION.  451 

fact  \vill  appear  later.  Osmosis  is  the  force  which  drives  a  so- 
lute through  a  solution.  When  a  substance  dissolves  it  behaves 
in  many  respects  exactly  as  if  it  were  vaporized.  In  fact,  it  has 
been  proved  by  Van't  Hoff  that  "  The  osmotic  pressure  of  a 
substance  in  solution  is  the  same  pressure  which  that  substance 
would  exert  were  it  in  gaseous  form  at  the  same  temperature 
and  occupying  the  same  volume."  l 
Expressed  mathematically  the  law  is  : 


in  which,  p  =  osmotic  pressure  in  pounds  per  square  inch. 
R  —  the  gas  constant  =  1,206  Ib.  per  sq.  in. 
T  =  absolute  temperature  =  t°  (Centigrade)  4-  273. 
V=  volume  of  the  solvent  containing  one  molecu- 


lar weight  of  the  solute. 


in  which,  M  =  sum  of  the  atomic  weights  of  the  atoms  in  a 

molecule  of  the  substance. 
r  =  the  rate  per  cent,  of  the  solution. 
Hence  : 

_  1,206  r  (t°  +  273)        12  r  (t°  +  273) 

100  M  ~M~ 

I  have  deduced  equation  (4)  for  convenience  in  ascertaining 
and  comparing  osmotic  pressures.  Thus,  sugar  is  CuH22On. 
Hence  for  sugar,  M  =  (12  X  H)  +  (1  X  22)  +  (16  X  11)  =  342. 
For  a  2-per-cent.  sugar  solution,  r  =  2.  Therefore  at  15°  C.  we 
have  the  osmotic  pressure  according  to  equation  (4)  as  follows  : 

p  =  12  X  2  (15  +  273)  =  20>2  lb_  per  gq_  .n 
342 

By  actual  experiment  p  was  found  to  be  20  Ib.  per  sq.  in.  under 
these  conditions  ;  and  Van't  Hoff  's  law  of  osmotic  pressure  has 
been  repeatedly  proved  by  similar  tests.  From  the  above  state- 
ment it  is  clear  that  osmosis  is  far  from  being  a  vague  or  feeble 
force. 

When  due  to  a  rise  in  temperature,  or  for  other  reasons, 
ground-water  at  any  given  point  begins  to  dissolve  a  mineral, 

1  Elements  of  Physical  Chemistry,  by  J.  Livingston  R.  Morgan,  New  York,  John 
Wiley  &  Son,  p.  96. 


452  OSMOSIS    AS    A    FACTOR    IN    ORE-FORMATION. 

that  mineral  is  immediately  forced  by  osmotic  pressure  out  to 
the  extreme  confines  of  the  vessel  holding  the  water.  Let  us 
suppose,  therefore,  that  a  dike-intrusion  has  so  heated  the  sur- 
rounding waters  that  they  have  taken  up  a  burden  of  PbS ;  evi- 
dently, then,  osmosis  will  force  this  PbS  throughout  the  mass 
of  water  into  every  cranny,  crevice,  fissure,  or  cavity.  It  re- 
quires no  convection-currents  to  accomplish  this  distribution, 
although  convection  will  hasten  the  process.  Having  taken  up 
its  full  burden  of  PbS  there  comes  a  period  of  inactivity,  until 
the  temperature  begins  to  fall.  This  fall  of  temperature  will 
be  most  rapid  near  the  surface  of  the  earth  and  it  will  be  most 
rapid  in  the  larger  water  channels,  for  the  reason  that  circula- 
tion there  is  least  retarded. 

In  the  case  of  dike-intrusion,  I  believe  that  the  shrinking  of 
the  dike-matter  will  open  the  largest  crevices  and  channels 
along  the  dike  itself,  and  I  conceive  that  surface-waters  flowing 
into  these  shrinkage-cracks  will  accelerate  the  cooling  near  the 
dike.  Hence,  in  such  cases,  contact  ore-deposits  will  be  found 
on  one  side  of  a  dike,  and  that  side  will  be  the  side  which  orig- 
inally faced  uphill.  The  down-flowing  surface-  or  ground- 
water  will  enter  the  first  crevices  it  meets  and  hasten  the  cool- 
ing there,  and  it  is  quite  evident  that  where  cooling  is  fastest, 
crystallization  of  dissolved  mineral  will  first  begin.  Let  the 
smallest  speck  of  galena  be  crystallized  out,  and  immediately 
osmosis  will  force  more  dissolved  galena  to  that  point,  and  thus 
feed  the  crystal-mass.  Heretofore,  the  deposition  of  ore  nearest 
the  once-molten  dikes  has  been  inexplicable,  but  in  no  other 
place  could  it  have  started,  and,  once  started,  the  tendency 
toward  crystal  growth  must  be  due  entirely  to  osmotic  pressure 

Let  us  consider  for  a  moment  certain  other  conditions  that 
accelerate  cooling,  since  it  is  now  evident  that  much  depends 
upon  the  first  cooling  of  the  solution.  At  the  intersection  of 
two  fissures  the  cooling  should  be  most  rapid,  for  at  that  point 
two  channels  supply  convection-currents.  Hence  the  deposition 
of  the  most  insoluble  minerals  should  occur  first  at  vein-inter- 
sections, a  circumstance  which  is  often  verified  in  known  ore- 
deposits.  Again,  in  fissure  walls  that  have  been  striated  by 
slipping  past  one  another,  the  grooves  form  channels  in  which 
convection-currents  move  most  rapidly,  and,  as  should  be  ex 
pected,  the  most  insoluble  minerals  are  found  in  the  grooves. 


OSMOSIS    AS    A    FACTOR    IN    ORE-FORMATION.  453 

This,  I  believe,  explains  "  Clayton's  law."2  Since  the  richest  min- 
erals are  ordinarily  the  most  insoluble,  I  offer  this  general  propo- 
sition :  "  Bonanzas  should  be  sought  at  points  where  circulation 
has  been  freest,  namely,  in  the  widest  and  most  open  channels." 
Since  the  relative  solubility  of  minerals  has  evidently  played 
so  important  a  role  in  ore-formation,  a  few  suggestions  may 
not  be  out  of  place.  Hot  waters  carrying  metallic  sulphides 
in  solution  must  carry  also  a  great  burden  of  alkaline  salts. 
In  fact,  the  solubility  of  the  metallic  sulphides  is  due  to  the 
presence  of  these  alkaline  salts  which  form  new  ions  with  the 
sulphides,  just  as  potassium  cyanide  dissolves  gold  salts  by 
forming  new  ions  with  the  gold.  One  well-known  geologist 
has  erred  in  assuming  that  the  "  solubility  product "  of  every 
mineral  is  increased  by  the  presence  of  other  minerals  in  solu- 
tion. This,  in  passing,  I  would  say  is  not  so ;  for  it  is  only 
when  new  ions  are  formed  with  the  added  elements,  that  solu- 
bility is  effected,  and  there  are  many  minerals  which  do  not 
combine  to  produce  these  new  ions.  The  metallic  sulphides 
and  the  ions  formed  by  them  have  a  very  low  "  solubility  pro- 
duct "  at  best,  and  when  a  lowering  of  temperature  causes  the 
sulphides  to  crystallize  out,  the  "  solubility  products  "  of  the 
substances  in  solution  are  often  so  increased  that  more  country- 
rock  is  dissolved.  In  this  manner  for  every  particle  of  sulphide 
deposited  by  crystallization,  a  particle  of  country-rock  may  be 
dissolved.  -  This,  I  take  it,  is  the  true  explanation  of  the  so- 
called  "  metasopnatic  replacement "  which  has  been  regarded 
as  a  true  chemical  reaction,  or  precipitation.  I  have  never 
been  able  to  believe  that  galena  and  other  natural  metallic  sul- 
phides are  chemical  precipitates,  and  one  of  my  strongest 
reasons  for  this  disbelief  has  been  the  fact  that  chemical  pre- 
cipitates of  lead  and  similar  sulphides  are  flocculent  and  never 
crystalline.  How  cubical  galena  could  be  precipitated  chemi- 
cally from  solution,  by  any  reducing  agent  in  nature,  has  ever 
been  a  most  serious  stumbling  block.  I  am  convinced  now 
that  practically  all  of  the  hypothetical  equations  written  by 
geologists  to  account  for  ore-deposition  by  chemical  reaction 
are  erroneous.  Many  of  these  equations  can  be  demonstrated 
to  be  false  from  the  laws  of  thermal  chemistry,  and  few  of 


Ore- Deposits  of  the  United  States  and  Canada>  J.  F.  Kemp,  p.  49. 


454  OSMOSIS    AS    A    FACTOR    IN    ORE-FORMATION. 

them  appear  even  plausible  when  viewed  from  a  thermo-chem- 
ical  standpoint.  It  is  not  now  my  purpose  to  tear  down,  but 
to  build  up.  I  am  wholly  in  accord  with  Professor  Kemp  and 
other  geologists  who  voice  the  movement  against  the  chemical 
theories  of  ore-deposition  which  have  so  long  occupied  the 
arena.  It  cannot  be  denied,  however,  that  very  many  ore- 
deposits  have  come  from  minerals  carried  in  solution  to  the 
chambers  where  they  are  now  found. 

It  has  been  urged  in  the  past  that  the  formation  of  ore-depos- 
its from  hot-water  solutions  could  not  have  occurred,  for  two 
reasons :  (1)  Because  the  same  heat  that  would  cause  the  solu- 
tion of  the  precious  minerals  would  also  cause  the  solution  of 
the  rocks  in  which  those  minerals  are  scattered,  and  con- 
versely, cooling  would  precipitate  them  both  together,  and, 
(2)  Because  hot  springs  are  not  now  depositing  metallic  sul- 
phides except  in  very  small  amounts  and  then  only  in  the  midst 
of  a  mass  of  gangue. 

I  trust  that  I  have  indicated  how  osmosis  effects  the  distri- 
bution and  final  concentration  of  minerals,  without  any  appeal 
to  hot-water-spring  theories  or  to  chemical  precipitation  from 
cold-water  theories,  for  I  am  convinced  that  we  must  look  to  the 
laws  of  physical  chemistry  for  an  explanation  of  ore-formation, 
and  not  to  the  laws  of  physics  or  of  chemistry  alone. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  455 


No.  18. 


The  Ore-Deposits  of  Sudbury,  Ontario.* 

BY  CHARLES  W.    DICKSON,   COLUMBIA   UNIVERSITY,    NEW  YORK,  N.   Y. 

(Albany  Meeting,  February,  1903.     Trans.,  xxxiv.,  3.) 

CONTENTS.  PAGE 

PART!.  THE  RELATION  OF  NICKEL  TO  PYRRHOTITE,      ,        .        .  .     455 

Introduction,  .         .         .         .         .                  .         '.,..-.         .  .     455 

Minerals  of  the  Sudbury  Nickel-Region,         .        .         .                  .  .     456 

Pyrrhotites  in  General,  .         .         .         *         .         .         .         .         .  .     458 

The  Origin  of  Pyrrhotite,       .         ...        ...        ,         ...         .  .460 

Nickel  and  Cobalt  in  Pyrrhotite,    .         .         ...         .         .  .     461 

The  Sudbury  Pyrrhotites,       .         .         .        .         .         .        ...     463 

The  Magnetic  Separation  of  Nickeliferous  Pyrrhotite,  .         .        .  ."    466 

The  Nickel-Bearing  Mineral,  .         .         .         .         .        .         .  .470 

The  Non-Magnetic  Residue,    .         .         .         .        .  I  ,  ..        .  .     472 

The  Formula  of  the  Pyrrhotite,      .         .         .         .         .         .        .  .     475 

Summary,       .         .         ...         .         .        .         .         .         .  .     476 

PART  II.  GENESIS  OF  THE  SUDBURY  ORES,        .        .        .        .        .  .     477 

General  Considerations,          *•'*•'       .         .         .         .         .         ,  477 

Classification  of  Pyrrhotites,  ...         .         .         .         .         .  .477 

Value  of  the  Classification,       .         .         .         .         .        .         .  .     478 

The  Sudbury  Pyrrhotite- Deposits, .         .         .        .         .         .         .  .     479 

The  Nickel-Belts,     .         .        .         .        .        .        .        .        .  .480 

Various  Theories  of  the  Origin  of  Nickeliferous  Pyrrhotite,          .  .      .     481 

The  Rossland  Pyrrhotite-Deposits,          .         i        ...         .        .  .     486 

Microscopical  Evidence  of  the  Origin  of  the  Ores;        .        .        .  .     497 

Sudbury  District, .497 

Wallace  Mine,         .         ...        ...         .         .        ....     508 

Rossland,  B.  C.,       •        •  ,      •        •        •        ?        ..'.-.     509 

Ducktown,  Tenn.,    .        .         .         .                  .         .         .         .  .     510 

Summary,       .         .         .         .        .         ......  .     510 

Relation  of  Chalcopyrite  to  Pyrrhotite,   .         .         .         .         .  .513 

Source  of  the  Metals,  .     .         .         .        .. ,.''-.         .                  .  .     514 

Acknowledgments,  .         .         .        .         ...         .        .  516 

I.  THE  RELATION  OF  NICKEL  TO  PYRRHOTITE. 
Introduction. 

The  Sudbury  district  is  to-day  one  of  the  two  great  sources 
of  nickel  in  the  world.     The  peculiar  geological  relations  of 

*  This  paper  was  presented  by  the  author  as  a  dissertation  for  the  degree  of 
Ph.D.  at  Columbia  University,  New  York  City. 


456  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

the  ores  have  long  attracted  attention,  and  widespread  interest 
has  been  aroused  by  the  difference  of  opinion  regarding  their 
origin,  whether  as  igneous  segregations  or  as  precipitates  from 
solution.  The  writer  has  endeavored  to  attack  this  problem 
with  the  aid  of  microscopical  and  petrographical  methods. 
The  field-work  of  these  investigations  was  carried  on  during 
the  summers  of  1901  and  1902,  and  the  material  collected  was 
worked  up  at  Columbia  University,  New  York,  during  the  ses- 
sions of  1901-02  and  1902-03. 

As  a  necessary  preliminary,  it  was  thought  advisable  to  in- 
vestigate carefully  the  chemical  composition  and  geological 
relations  of  pyrrhotite,  as  well  as  the  mineralogical  associations 
of  the  Sudbury  ores. 

Minerals  of  the  Sudbury  Nickel- Region. 

Pyrrhotite  and  chalcopyrite,  associated  with  fragments  of 
the  inclosing  rock,  are  the  predominant  minerals  of  the  Sud- 
bury deposits.  The  nickel-mineral  pentlandite,  which  is  the 
principal  source  of  this  metal,  is  distributed  through  all  the  ore- 
bodies  in  greater  or  less  amount.  Its  matrix  is  almost  univer- 
sally pyrrhotite,  though  a  number  of  exceptions  occur,  notably 
at  the  Copper  Cliff  mine. 

This  mine,  which  has  furnished  a  number  of  interesting 
minerals,  contains  in  the  lower  levels  some  massive  ore,  com- 
posed very  largely  of  chalcopyrite  intimately  associated  with 
pentlandite.  Other  samples  from  the  same  place  consist  of 
pyrite  and  marcasite,  also  with  an  intimate  mixture  of  pent- 
landite. 

Millerite  is  encountered,  though  rarely.  In  a  sample  from 
the  Copper  Cliff  mine,  the  writer  found  small  bunches  of  hair- 
like  crystals  of  this  mineral  in  the  cavities  of  some  radiating 
pyrite  mixed  with  calcite.  It  has  also  been  reported  in  a  num- 
ber of  other  cases.  The  millerite  is  undoubtedly  secondary, 
and  was  probably  derived  from  pre-existing  pentlandite. 

Polydymite  (Ni4S5,  with  one  part  of  nickel  replaced  by  iron) 
containing  platinum  was  described  by  Clarke  and  Catlett.1 

Kiccolite,  gersdorffite,  danaite,  and  arsenopyrite  (containing 
cobalt)  occur  in  several  localities  in  Denison  township,  though 

1  American  Journal  of  Science,  Third  Series,  vol.  xxxvii.,  No.  221,  p.  372  (May, 
1889). 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  457 

the  association  is  not  exactly  similar  to  that  of  the  typical 
deposits. 

Pyrite  is  by  no  means  uncommon,  and  Walker  has  described 
a  nickeliferous  variety  (over  4  per  cent,  of  nickel)  from  the 
Murray  mine.  A  number  of  samples  of  this  mineral  from  the 
Copper  Cliff  mine  were  associated  with  secondary  quartz,  cal- 
cite,  and  millerite.  On  analysis,  they  yielded  from  a  trace  to 
over  3  per  cent,  of  M,  which,  however,  may  be  due  to  an  inti- 
mate mixture  of  pentlandite  or  millerite. 

Samples  of  a  compact,  whitish  or  steel-gray  mineral,  contain- 
ing a  considerable  amount  of  pentlandite,  were  submitted  by 
the  writer  to  Professor  Penfield,  who  considers  it  to  be  massive 
marcasite.  The  analyses  conform  to  the  formula  FeS2,  and 
show  the  presence  of  from  2  to  4  per  cent,  of  !N"i,  probably  as 
pentlandite. 

Sperrylite  (PtAs2)  was  originally  found  in  the  gossan  at  the 
Vermilion  mine.  The  writer  has  also  isolated  it  from  the  un- 
altered chalcopyrite  of  the  Victoria  mine  (see  p.  463). 

Galena  occurs  rarely  in  streaks  through  the  pyrrhotite,  e.  g., 
at  the  Mount  Nickel  mine,  Blezard  township.2 

Native  copper  is  reported  in  a  few  instances  in  leaves  in  the 
associated  rocks.  Secondary  copper-minerals  are  rare;  but 
bornite  is  occasionally  seen. 

Small  masses  of  titaniferous  magnetite  (with  as  much  as  18 
per  cent,  of  TiO2)  are  at  times  found. 

This  list  is  probably  not  complete,  but  represents  the  most 
important  minerals  found  by  the  writer  or  recorded  by  others. 

S.  H.  Emmens3  describes  what  he  calls  several  new  species 
of  nickel-minerals  from  Sudbury.  But  the  doubtful  purity  of 
his  material  and  the  analytical  methods  employed  do  not  war- 
rant the  recognition  of  these  new  species.4 

As  a  preliminary  to  the  discussion  of  the  relation  of  the 
nickel  to  the  pyrrhotite  and  its  associates,  a  brief  review  of  our 
knowledge  of  pyrrhotites  will  be  given ;  since  the  uncertainty 

2  Specimen   kindly  furnished  by  Prof.  W.  G.  Miller,  Provincial  Geologist  of 
Ontario. 

3  Journal  of  the  American  Chemical  Society,  vol.  xiv.,  p.  205  (1892). 

.  4  S.  L.  Penfield,  On  Pentlandite  from  Sudbury,  Ont. ,  Can.,  with  Remarks 
upon  Three  Supposed  New  Species  from  the  Same  Region,  American  Journal  of 
Science,  Third  Series,  vol.  xlv.,  No.  270,  p.  493  (June,  1893). 


458 

which  prevails  regarding  the  exact  chemical  composition  of 
pyrrhotites  is  probably  not  generally  appreciated  by  students 
of  ore-deposits . 

Pyrrhotites  in  General. 

For  many  years  the  composition  of  pyrrhotite  has  presented 
to  chemists  and  mineralogists  a  most  difficult  and  interesting 
problem,  to  a  large  extent  still  unsolved. 

Various  writers  have  applied  to  this  mineral  formulas  which 
range  from  Fe3S4  to  Fe16Sl7.  In  general  terms  it  is  usually  ex- 
pressed as  FenSn+1.  By  some  it  is  regarded  simply  as  FeS 
with  impurities.5  Others  consider  it  a^  varying  molecular  mix- 
tures of  different  sulphides,  as  nFeS  +  Fe2S3  or  nFeS  +  FeS2. 
Bodewig's 6  and-  Doelter's  7  formula  was  FenS12. 

In  other  words,  "  pyrrhotite  "  is  regarded,  not  as  a  mineral 
in  the  true  sense  of  the  term,  but  as  a  series  of  minerals,  dif- 
fering slightly  from  each  other  in  the  relative  proportions  of 
their  constituents.  If  this  is  the  correct  view,  the  case  is 
unique.  Homologous  chemical  series  are  by  no  means  uncom- 
mon, but  in  these  there  is  always  a  gradual  change  in  the  prop- 
erties of  the  different  members ;  the  extremes  being  so  entirely 
unlike  as  hardly  to  be  recognizable  components  of  the  same 
group.  There  seems,  however,  to  be  little,  if  any,  difference 
between  pyrrhotites  represented  by  Fe3S4  and  Fe16Sir  It  should 
thus  be  possible  to  grade  imperceptibly  from  the  monosulphide, 
FeS,  to  the  disulphide,  FeS2,  when  a  pyrrhotite  with  the  com- 
position of  pyrite  would  result.  But  such  a  view  does  not  seem 
reasonable,  and  is  opposed  to  some  of  the  fundamental  laws  of 
chemistry.  It  seems  more  reasonable  to  consider  many  of  the 
so-called  "  pyrrhotites  "  as  mixtures  of  other  sulphides  with  this 
mineral,  and  to  regard  the  latter  as  of  a  definite  composition. 

A  fact  which  may  have  an  important  bearing  on  this  ques- 
tion is  that  of  the  magnetic  permeability  of  different  pyrrho- 
tites. In  the  preparation  of  various  samples,  as  noted  later  in 
this  paper,  some  were  observed  to  be  much  more  magnetic  than 

5  Weinschenk,  Groth's  Zeitschrift  fur  Krystallographie  und  Mineralogie,  vol.  xvii., 
p.  499  ;  Lorenz,  Ber.  d.  chem.  Ges.,  p.  1501  (1891). 

6  Groth's  Zeitschrift,  vol.  vii.,  p.  180. 

7  Tschermak's  Mineralogische  und  petrographische  Mittheilungen,  N.  F.,  vol.  vii.,  p. 
544.     A  synopsis  of  the  results  obtained  by  different  writers  will  be  found  in  the 
Handbuch  der  Mineralogie,  Hiutze,  vol.  i.,  p    621  ct  xeq.  (1901). 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  459 

others,  the  strength  of  attraction  by  a  small  magnet  being,  in  a 
general  way,  proportional  to  the  percentage  of  iron.  Further 
investigation  along  this  line  may  lead  to  important  results. 

It  should  be  borne  in  mind,  however,  that  lack  of  care  in 
the  preparation  of  samples  for  analysis  may  account  for  many 
discrepancies,  especially  as  few  pyrrhotites  are  entirely  free 
from  other  sulphides  in  more  or  less  intimate  mixture. 

The  inaccurate  methods  of  analysis,  and  difficulties  of  manip- 
ulation, will  also  cause  many  errors.  That  the  reliability  of 
many  analytical  methods  is  open  to  question  is  shown  by  the 
animated  controversies  of  experts  in  recent  years.8  Errors 
amounting  to  0.75  per  cent,  in  the  estimation  of  sulphur  are 
not  uncommon,  and  in  many  cases  they  are  possibly  larger. 
The  iron-results  are  also  apt  to  be  unreliable. 

In  a  number  of  determinations  on  the  same  sample  Haber- 
mehl 9  obtained  results  in  which  the  sulphur  varied  from 
39.10  to  39.71— a  difference  of  0.61,  and  iron  from  60.28  to 
60.79 — a  difference  of  0.51  per  cent.  When  we  consider  the 
theoretical  compositions  represented  by  the  compounds  varying 
from  FeS  to  FeS2  it  is  seen  that  a  comparatively  small  error 
would  change  the  formula  calculated  from  the  analysis.  The 
calculated  composition  for  different  formulas  would  be  as 
follows : 


Formula. 

Iron. 
Per  Cent. 

Sulphur. 
Per  Cent. 

Formula. 

Iron. 
Per  Cent. 

Sulphur, 
Per  Cent. 

FeS  . 

Fe15S16  . 
FenS12  . 

.     63.61 
.     62.06 
.     61.60 

36.39 
37.94 
38.40 

Fe8S9 

Fe7S8 
FeS9 

60.80. 
60.40' 
46.60 

39.20 
39.60 
53.40 

A  few  analyses  made  by  prominent  workers  (see  Table  I.) 
will  show  the  wide  variation,  both  in  the  analytical  results  and 
in  the  recorded  specific  gravity  of  the  mineral.  The  latter  varies 
very  widely  (3.98  to  4.80)  and  probably  indicates  the  doubtful 
purity  of  the  sample.  Where  the  total  (as  in  analysis  ~No.  1) 
is  over  101  per  cent.,  any  calculations  based  on  the  result  will 
be  wholly  misleading,  and  it  is  safe  to  say  that  many  others 
recorded,  while  not  indicating  such  an  excess,  are  equally  un- 
reliable for  this  purpose. 

8  Gladding  and  Lunge,  Journal  of  the  American  Chemical  Society,  vols.  xvi.,  xvii., 
and  xviii.  (1894  to  1896). 

9  Obcrhessische  Gesellschaft  fur  Natur-  und  Heilkunde,  vol.  xviii.,  p.  97  (1879). 


460  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

TABLE  I. — Analyses  of  Pyrrhotite. 


1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Fe 

63  82 

63  15 

63  35 

62  62 

63  41 

62  04 

61  17 

60  83 

58  00 

S  

37.36 

36  35 

35.91 

37  38 

36.29 

38.08 

38  83 

39  17 

42  00 

Total  
Sp.  gr  
Formula.  . 

101.18 
3.98 
Nearly 
FeS. 

99.50 
4.62 
Nearly 
FeS. 

99.26 
4.787 
Nearly 
FeS. 
(Fe  in 
excess.) 

100.00 
4.80 
Nearly 
FeS. 

99.70 
""FeS."" 

100.12 
4.497 
Fe13S14. 

100.00 
4.546 

Fe9S10. 

100.00 
4.580 
Fe8S9. 

100.00 
Fe4S§. 

No.  1.  Nenntmansdorf,  Geinitz,  N.  Jahr.,  1876,  609. 

No.  2.  Tavetsch,  Gutknecht,  cited  by  Kenngott,  N.  Jahr.,  1880,  1,  164. 

No.  3.  Seelasgen,  Rammelsberg,  Poyy.  Ann.,  1864,  cxxi.,  368. 

No.  4.  Brazil,  Berthier,  Ann.  Mines,  1835,  vii.,  531. 

No.  5.  Jeliza,  Servia,  Losanitsch,  Ber.  d.  Chem.,  1892,  xxv.,  880. 

No.  6.  BoreV,  Palfy,  Groth's  ZeiL,  xxx.,  184,  and  xxvii.,  101. 

No.  7.  Bodemais,  Graf  Schaffgotsch,  Pogg.  Ann.,  1840,  1.,  533. 

No.  8.  Hartzburg,  Kammelsberg,  Pogg.  Ann.,  1864,  cxxi.,  356. 

No.  9.  Chile,  Mennier,  Cosmos,  1869,  3d  series,  v.,  581. 

The  above  results  are  taken  from  C.  Hintze's  Hdb.  der  Min., 
vol.  i.,  pp.  653  and  654  (1901). 

Altogether  apart,  however,  from  the  considerations  outlined 
above,  pyrrhotite,  as  we  know  it,  is  not  constant  in  composi- 
tion ;  and  an  adequate  explanation  of  the  variations  in  its  com- 
position is  one  of  the  problems  of  the  future. 

The  Origin  of  Pyrrhotite. 

Little  is  known  of  the  conditions  under  which  pyrrhotite  is 
formed  in  nature,  except  that  a  strongly-reducing  atmosphere 
is  necessary.  Those  synthetic  reproductions  of  the  mineral, 
which  have  not  been  made  under  conditions  analogous  to  those 
of  nature,  do  not  aid  materially  in  explaining  its  origin. 

Doelter,10  however,  by  heating  ferrous  chloride  to  250°  C. 
in  an  atmosphere  of  carbonic  acid  and  hydrogen  sulphide  gas, 
produced  pyrrhotite  much  like  the  natural  mineral  and  having 
a  composition  represented  by  FenS12.  He  also  produced  it  by 
the  action  of  H2S  gas  on  solutions  of  ferrous  sulphate,  carbon- 
ate, chloride,  and  silicate.  Other  methods  of  "preparation  do 
not  appear  to  have  any  direct  bearing  on  the  natural  formation 
of  the  mineral. 


10  Tschermak's  Mittheilungen,  vol.  vii.,  pp,  85,  86. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


461 


Nickel  and  Cobalt  in  Pyrrhotite. 

Nickel  is  universally  recognized  as  an  associate  of  pyrrho- 
tite,  and  in  few  cases  has  it  proved,  when  looked  for,  to  be  en- 
tirely lacking.  Whether  the  nickel  is  an  essential  constituent 
of  the  pyrrhotite,  replacing  part  of  the  iron,  or  whether  it  is 
present  as  a  separate  compound,  is  still  a  disputed  question.  It 
is  hoped,  however,  that  the  results  here  presented  will  help  to 
clear  this  matter  up  to  a  great  extent. 

The  percentage  of  nickel  varies  widely  in  different  pyrrho- 
tites.  Those  occurring  in  metamorphosed  sedimentary  and 
acidic  schistose  rocks  are  notably  low  in  nickel,  while  in  those 
associated  with  basic  igneous  rocks,  especially  of  the  gabbro 
family,  it  may  range  from  a  trace  to  a  proportion  economi- 
cally valuable.  Cobalt  nearly  always  accompanies  the  nickel, 
though  usually  in  very  subordinate  amount. 

Tables  II. ,  III.,  and  IV.  give  the  nickel-contents  of  representa- 
tive pyrrhotites  of  these  two  classes.  Those  of  the  first  class 
rarely  carry  more  than  0.5  per  cent,  of  nickel,  while  those 
from  basic  eruptives  usually  exceed  this  limit,  some  of  the 
Rossland  examples  being  notable  exceptions. 

TABLE  II. — Percentages  of  Nickel  and  Cobalt  in  Pyrrhotites 

Generally. 


Ni. 

Co. 

Ni. 

Co. 

ONTARIO. 
1.  Dalhousie  twp.   Lanark  co.. 

0.23 

trace 

BRITISH  COLUMBIA. 
1.  West  Kootenay  

0.16 

o 

2   Dalhousie  twp  '  Lanark  co 

0  11 

trace 

*>   Kennedy  Lake  VI 

0  16 

0  16 

trace 

j    3   Deer  Creek  V  I 

1  70 

4   Galway  twp     Peterboro'  co 

0  16 

trace 

'    4   West  Kootenay 

0  14 

trace 

5   Galway  twp     Peterboro1  co 

0  10 

trace 

5  Crawford  Bay 

0  05 

6.  Galway  twp     Peterboro'  co.. 

0  05 

trace 

1    6  Jarvis  Island  -    . 

0  28 

trace 

•  7   Victoria  co 

0  15 

trace 

i    7   Rossland 

0  °3 

8   Rainy  River  District  

0.13 

trace 

1    8.  Rossland  

0  13 

trace 

9   District  of  Nipissing 

3  30 

trace 

9   Kootenay  Lake 

0  68 

10.  District  of  Nipissing  

2.10 

trace 

!  SWEDEN,  ETC. 

QUEBEC 

1   Klefva             

1  08 

0  07 

1   Ottawa  co 

0  13 

o 

i    2   Klefva 

1  50 

0  08 

2  Ottawa  co  

1  68 

3   Klefva 

2  03 

0  10 

3  Calumet  Island 

1  48 

4   Sagmyrna 

0  50- 

4   Calumet  Island  

4.06 

0  33 

0  80 

5   Pontiac  co  

1  50 

trace 

5    Krageroe 

1  75 

NOVA  SCOTIA. 

6.  Varallo  

1  20- 

1   Cape  Breton  co  

0  10 

trace 

1  44 

NEW  BRUNSWICK. 
1   St.  Stephen  

1  82 

0  17 

UNITED  STATES. 
il    Gap  Mine   Pa 

1  75 

0  10 

2   St  Stephen  

trace 

2  Gap  Mine  Pa 

1  00- 

to 
4.00 

3.  Anthonv's  Nose,  N.  Y  

3.00 
0.30 

NOTE. — The  nickel-mineral  gersdorffite  occurred  in  association  with  some  of 
these  pyrrhotites,  so  that  in  part  the  nickel  found  may  mean  an  admixture  of  this 
mineral. 


462  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

Ontario. — 1.  Pyrrhotite  with  pyrite  in  white  translucent  quartz  and  hornblende; 
2.  Pyrrhotite  with  pyrite  in  quartz-rnica-diorite  (Nos.  1  and  2  occur  in  dark-gray 
diorite,  which  cuts  gneiss)  ;  3.  Pyrrhotite  in  dark-gray  gneissoid  rock  ;  4.  Mas- 
sive pyrrhotite  ;  5.  Massive  pyrrhotite  with  pyrite,  chalcopyrite,  and  quartz  ;  6. 
Massive pyrrhotite  with  chalcopyrite,  quartz,  and  feldspar  (other  samples  from  Gal- 
way  gave  from  a  trace  to  0.15  per  cent,  of  nickel.  The  pyrrhotite  is  associated 
with  bands  of  gneiss,  mica-schist,  and  quartzite  ;  i.  e.,  the  deposits  are  fahlbands, 
like  those  of  Norway,  which  are  likewise  poor  in  nickel) ;  7.  Massive  pyrrhotite; 
8.  Massive  pyrrhotite  with  a  small  amount  of  quartz  from  the  Huronian  schists  of 
English  river ;  9  and  10.  Pyrrhotites  with  small  amounts  of  chalcopyrite  in  a 
gangue  of  grayish-green  diorite.  (Pyrrhotites  occurring  in  light-  and  dark-gray 
gneissoid  rocks  from  Frontenac  county,  Ont.,  Schreiber  (Thunder  bay),  Darlington 
bay  (Lake  of  the  Woods),  and  numerous  other  localities  all  contained  nickel,  but 
only  in  traces. ) 

Quebec. — 1.  Massive  pyrrhotite  from  Eardley  township  ;  2.  Pyrrhotite  in  part 
massive,  in  part  disseminated  through  a  gangue  of  quartz,  feldspar,  and  horn- 
blende ;  3.  Small  quantity  of  pyrrhotite,  etc.,  in  a  quartz-amphibolite  ;  4.  Massive 
pyrrhotite  with  a  little  quartz  gangue  (the  associated  rocks  of  3  and  4  are  diorites,. 
which  cut  a  series  of  gneisses  and  limestones)  ;  5.  Massive  pyrrhotite. 

Nova  Scotia. — Pyrrhotite  in  a  siliceous  gangue  from  Leitche's  creek. 

New  Brunswick. — Pyrrhotite  with  a  little  chalcopyrite  and  a  small  amount  of 
quartz  gangue,  or  diorite  and  quartz.  (The  association  is  much  like  that  of  Sud- 
bury.  Various  samples  from  the  same  locality  yield  from  a  trace  to  4  per  cent,  of 
nickel. ) 

British  Columbia. — 1.  Pyrrhotite  in  quartz,  feldspar,  and  hornblende  ;  2.  Mas- 
sive pyrrhotite  in  a  gangue  of  quartz,  garnet,  calcite,  and  hornblende  ;  3.  Massive 
pyrrhotite  with  chalcopyrite  in  a  quartzose  gangue  (from  the  Two  Sisters  and 
Crow  claim)  ;  4.  Pyrrhotite  and  chalcopyrite  in  a  dark-green  rock  ;  5.  Pyrrhotite 
in  association  with  a  small  amount  of  chalcopyrite,  graphite,  quartz,  mica,  and 
feldspar  ;  6.  Pyrrhotite  with  chalcopyrite  in  a  gangue  of  quartz-green  diorite  ;  7 
and  8.  Massive  pyrrhotite  with  chalcopyrite  in  massive  eruptive  rocks,  the  ore- 
bodies  lying  between  gabbros  and  surrounding  porphyries  and  diabases  ;  9.  Pyr- 
rhotite with  pyrite  and  chalcopyrite  in  garnet  and  quartz. 

The  above  Canadian  examples  are  taken  from  vols.  vi.  to  xi.  of  the  Reports  of 
the  Canadian  Geological  Survey. 

Sweden,  etc. — Pyrrhotites  in  dark  eruptive  rocks,  principally  gabbros  (authority, 
Schnabel's  Handbook  of  Metallurgy. ) 

Gap  Mine,  Pa. — Pyrrhotite  with  chalcoyrite,  pyrite,  etc.,  in  the  outer  portions 
of  basic  igneous  rock-masses,  which  may  be  metamorphorsed  to  amphibolites. 

Mine  at  Anthony's  Nose,  N.  Y. — Pyrrhotite  in  association  with  feldspar,  pyrox- 
ene, hornblende,  and  quartz  ;  the  walls  being  acidic  gneisses.  (Authority  for 
this  and  the  preceding  examples,  The  Nickel-Mine  at  Lancaster  Gap,  by  J.  F. 
Kemp,  Trans.,  xxiv.,  620,  883,  1894.) 

The  relation  of  the  nickel-content  to  the  mode  of  origin  of 
the  pyrrhotites  and  the  inclosing  rock  will  be  considered  sub- 
sequently. 

One  of  the  purposes  of  this  investigation  has  been  to  test 
the  validity  of  the  view  generally  held,  that  in  the  Sudbury 
pyrrhotites  the  nickel  and  cobalt  replace  the  iron  isomor- 


THE    OhE-DEPOSITS    OF    SUDBUKY,  ONTARIO.  468 

phously.  Another  purpose  has  been  to  try  to  find  a  definite 
formula  for  the  sulphide  of  this  district,  with  the  idea  of  com- 
paring it  with  similar  minerals  from  other  localities. 

The  Sudbury  Pyrrhotites. 

The  Sudbury  nickel-region,  as  treated  in  this  paper,  will  be 
considered,  for  convenience,  as  including  the  deposits  of  simi- 
lar nature  in  the  adjoining  Algoma  district,  as  well  as  those 
in  the  immediate  vicinity  of  the  town  of  Sudbury. 

The  ore  mined  in  this  region  consists  chiefly  of  a  mixture  of 
pyrrhotite  and  chalcopyrite,  intimately  associated  with  more 
or  less  country-rock.  The  pyrrhotite  carries  the  nickel,  while 
the  chalcopyrite  appears  to  be  quite  free  from  that  element.11 
Table  III.  gives  the  nickel  and  copper  in  typical  samples  of  the 
ore  of  some  of  the  leading  Sudbury  mines,  as  taken  from  the 
catalogue  of  the  Ontario  mineral  exhibit  at  the  Buffalo  Pan- 
American  Exposition  of  1901,  and  similar  data  regarding  a 
number  of  nearly-pure  pyrrhotites  from  claims  in  various  parta 
of  Algoma,  taken  from  the  reports  of  the  Canadian  Survey. 
These  Algoma  deposits  have  the  same  geological  relations — i.  e.r 
they  are  closely  associated  with  an  altered  gabbro  or  norite. 

The  average  contents  of  nickel,  copper,  and  cobalt  in  the 
ore  smelted  since  1892  are  given  in  Table  IV.  The  state- 
ments of  Messrs.  Turner  and  Walker,  Table  V.,  show  that 
gold,  silver,  and  the  metals  of  the  platinum  group  are  constant 
constituents  of  the  ore,  though  present  only  in  small  quanti- 
ties. 

Sperrylite,  the  arsenide  of  platinum  (PtAs2),  was  first  recog- 
nized in  the  decomposed  products  of  chalcopyrite  and  pyrrho- 
tite at  the  Vermilion  mine.  The  platinum  in  the  unaltered 
ore  occurs  as  sperrylite,  as  proved  by  the  writer.12  T.  L. 
Walker13  has  shown  that  the  sperrylite  is  associated  with  the 
chalcopyrite,  rather  than  the  pyrrhotite.  Recent  investiga- 
tions seem  to  confirm  this  view,  as  sperrylite  has  been  found 
associated  with  copper-minerals  in  several  other  places. 

11  Thus,  Nos.  3  and  5  in  Table  III.,  which  are  largely  chalcopyrite,  contain  but 
little  nickel. 

12  American  Journal  of  Science,  Fourth  Series,   vol.  xv.,  No.  86,  p.  137  (Feb.,. 
1903). 

13  Idem,  vol.  i.,  No.  2,  p.  110  (Feb.,  1896). 


464 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


Mr.  Turner's  estimate,  given  in  columns  A  and  B,  Table  IV., 
probably  presents  fair  averages  of  the  general  run  of  the  ore. 
The  figures  under  A  may  give  a  good  idea  of  the  ore  of  the 
Creighton  mine,  while  that  from  Copper  Cliff  may  run  up  to 
7  per  cent,  of  copper  and  3  per  cent,  of  nickel,  according  to  the 
particular  level  from  which  the  ore  was  taken  (copper  predomi- 
nating in  the  upper,  and  nickel  in  the  lower  levels).  Column  B 
is  based  on  the  composition  of  the  matte  produced,  as  shown 
in  Table  V.,  column  I. 


TABLE  III. — Nickel  and  Cobalt  in  Sudbury  and  Algoma  Pyrrhotites. 


Ni. 

Cu. 

Ni. 

Cu. 

SUDBURY. 

1    Victoria  mine 

Per 
Cent. 
3  50 

Per 

Cent. 
4  50 

ALGOMA. 
1.  Lome  township 

Per 
Cent. 

1  95 

Per 
Cent. 
0 

2   Copper  Cliff  mine  

9.25 

0.51 

2.  Lome  township  

2  80 

0 

3   Copper  Cliff  mine               .  . 

1  25 

23  78 

3   Nairn  township  

1  95 

trace 

4  Stobie  mine  

2.99 

0.37 

4.  Drury  township  

2.01 

trace 

5   Stobie  mine   .            

0  64 

24  23 

5   Denison  township  

1  80 

0 

6   No  2  mine 

4  70 

0  38 

6   Levack  township 

4  13 

7    No.  2  mine  

1.87 

13.76 

7.  Levack  township  

3  00 

trace 

8   No  3  mine     Frood 

4  85 

0  42 

8   Levack  township 

1  96 

trace 

9   No.  4  mine  

4.33 

1.39 

9.  Morgan  township  

3  30 

10    No  4  mine 

4  15 

2  49 

11   Creighton  mine  

7.03 

1.81 

12   No  2  extension 

4  32 

0  35 

13   Worthington  mine  

3.00 

3.00 

NOTE. — The  Sudbury  figures  are  from  the  catalogue  of  the  mineral  exhibit  of  On- 
tario at  the  Pan-American  Exposition  of  1901,  except  those  of  the  Worthington 
mine,  which  are  the  result  of  a  number  of  analyses  of  average  samples,  obtained 
through  the  kindness  of  R.  E.  Booraem,  New  York  City. 

The  Algoma  figures  are  taken  from  reports  of  the  Geological  Survey  of  Canada. 
Most  of  the  samples  were  massive  pyrrhotite,  with  a  small  amount  of  chalcopy- 
rite.  The  copper  per  cent,  was  not  reported. 

TABLE  IV. — Averages  of  Smelters'  Assays  of  Sudbury  Ores, 
from  1892  to  1900. 

1892.  1893.       1894.  1895.  1896.       1897.      1898.  1899.       1900.        A.  B. 

Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct.  Per  Ct. 

Cu,    .        .     3.19  2.38        3.14  2.73        2.54        2.86        3.43        1.59        1.50        2.00 

Ni,    .        .     3.36  2.21        2.92  2.67        2.67        2.08        2.28         1.67        3.50        2.50 

Co,   .        .    0.10  0.08        0.07 

NOTE. — The  figures  for  the  several  years  aret^  en  from  the  Sixth  Report  of  the 
Ontario  Bureau  of  Mines  (1896)  and  Mineral  Industry,  vol.  ix.  (1900).  The  returns 
for  1900  seem  too  low.  Columns  A  and  B,  furnished  by  President  A.  P.  Turner, 
of  the  Canadian  Copper  Co.,  contain  (A)  an  estimate  of  certain  ores  of  that  com- 
pany, and  (B)  a  general  average  based  on  the  composition  of  the  matte  produced 
from  a  mixture  of  all  its  ores. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  465 

TABLE  V. —  Composition  of  Sudbury  Mattes. 

i.  n. 

Per  Cent. 

Copper,     ....  14  percent.  25.92 

Nickel,     ....  17  per  cent.  ")  ^  ^ 

Cobalt,     .         .         .         .  0.5  to  0.6  per  cent.  / 

Gold,       ....  trace  0.000075 

Silver,      .        .         .         .  0.5  to  1  oz.  per  ton.  0.001775 

Platinum,         .         .         .  0.25  to  0.5  oz.  per  ton.  0.000430 

Palladium,       .         .         .  0.25  to  0.5  oz.  per  ton.  present 

Iridinm,           .         .         .  0.000056 

Osmium,          .         .         .             0.000057 

Rhodium,        .         .         .  present 

Iron,                .         .         .  2.94 

Sulphur,          .         .         .  22.50 

I.  Average  furnished  by  President  A.  T.  Turner  for  mattes  of  the  Canadian 
Copper  Co. 

II.  Analysis  of   the  matte  from  the  Murray  mine,  given  by  T.  L.  Walker, 
American  Journal  of  Science,  Fourth  Series,  vol.  i.,  No.  2,  p.  112  (Feb.,  1896). 

To  ascertain  as  accurately  as  possible  the  average  nickel-  and 
cobalt-contents  of  the  general  run  of  the  pyrrhotite  from  the 
whole  region,  a  number  of  analyses  of  carefully-selected  mate- 
rial were  made  by  the  writer. 

The  pyrrhotite  was  coarsely  crushed  and  the  mineral  picked 
out  as  pure  as  possible,  under  a  lens  when  necessary.  From 
the  massive  varieties  good  samples  were  easily  obtained  ;  but  in 
other  cases  the  pyrrhotite  was  so  intimately  mixed  with  chalco- 
pyrite  and  rock  that  it  was  very  difficult  to  obtain  satisfactory 
samples,  some  rock  always  adhering  to  the  sulphide.  The  re- 
sults, given  in  Table  VI.,  show  that  the  percentage  of  nickel 
and  cobalt  in  the  pyrrhotite,  calculated  to  the  pure  mineral,  is 
fairly  constant  over  a  wide  area,  embracing  all  the  principal 
mines  and  prospects.  The  pyrrhotites  include  both  coarse-  and 
fine-grained  massive  varieties,  and  those  mixed  with  more  or 
less  rock  and  chalcopyrite.  The  object  was  to  determine,  as 
far  as  practicable,  only  the  nickel  existing  as  a  component  of 
the  pyrrhotite,  if  it  occurred  as  such.  In  the  case  of  the 
coarse-grained  varieties,  where  the  nickel-mineral  pentlandite 
is  often  to  be  recognized,  this  was  carefully  rejected,  as  far  as 
possible.  But  the  difficulty  of  this  separation  accounts  for  the 
fact  that  some  of  these  varieties  show  less  nickel  than  the  fine- 
grained ones,  although  the  former  are  usually  considerably 
richer.  Had  the  coarse-grained  samples  been  treated  in  their 

30 


466 


THE    ORE-DEPOSITS 


original  condition,  the  results  would  have  been  more  uniform. 
Subsequent  work  proves  that  a  large  part,  at  least,  of  the  nickel 
is  not  a  constituent  of  the  pyrrhotite.  The  results  of  these 
tests,  therefore,  represent  the  nickel  which  is  most  intimately 
associated  with  pyrrhotite  and  does  not  appear  in  visible  par- 
ticles of  pentlandite. 

Cobalt  is  always  very  subordinate  in  amount,  bearing  a  ratio 
between  1  :  40  and  1  :  50  to  the  nickel. 


TABLE  VI. — Nickel,  Cobalt,  etc.,  in  Sudbury  Pyrrhotites. 


Location. 

Insol. 

Cu. 

Ni. 

Co. 

Niin 
Pure  Pyr- 
rhotite. 

1    Elsie  (a) 

Per  Cent. 
2.00 

Per  Cent, 
trace 

Per  Cent. 
2  40 

Per  Cent. 
0  06 

Per  Cent. 
2  46 

2    Elsie  (b)  

3.45 

trace 

2  35 

0.05 

2  44 

3    Stobie  (a)  

1.50 

trace 

3  00 

0  08 

3  05 

4.  Stobie  (b)  

4.00    - 

trace 

2  05 

0  05 

2  15 

5.  Frood,  No.  3  mine  (a)  

0.40 

trace 

2.35 

0.05 

2  40 

6.  Frood,  No.  3  mine  (b)  

5.00 

trace. 

2.34 

0.06 

2.48 

7    Mount  Nickel 

2  20 

3  00 

0  07 

3  06 

8.  Copper  Cliff,  No.  4  mine  (a)... 
9.  Copper  Cliff,  No.  2  mine  (b)... 
10.  Copper  Cliff,  No.  5  mine  (c)... 
11    Creighton  (a) 

1.10 
5.00 
0.50 
3  25 

trace, 
trace, 
trace, 
trace 

3.24 
3.70 
3.47 
3  84 

0.06 
0.08 
0.08 
0  10 

3.30 
4.00 
3.50 
4  00 

12    Creighton  (b) 

0  50 

trace 

2  26 

0  06 

2  32 

13.  Gertrude  (a)       .  . 

5  00 

trace 

3  83 

0.11 

4  05 

14    Gertrude  (b)  

6  00 

trace 

3  61 

0  09 

4  00 

15.  Victoria  (a)  

0  50 

trace. 

3.3H 

0  07 

3.40 

16.   Victoria  (b)  

0.40 

trace. 

3.14 

0  08 

3.20 

17.  Levar-k  

3.20 

trace. 

2.80 

288 

18.  North  Range  

4.10 

trace. 

2.22 

232 

NOTE. — These  analyses,  and  others  by  the  writer,  were  made  in  duplicate  or 
triplicate  to  insure  the  greatest  possible  accuracy. 

1.  Coarse  pyrrhotite  with  a  small  amount  of  chalcopyrite  and  rock  ;  2.  Compact 
fine-grained  pyrrhotite,  with  a  small  amount  of  rock  ;  3.  Massive  fine-grained 
pyrrhotite  ;  4.  Pyrrhotite  and  chalcopyrite  in  diorite  ,  5.  Pure,  coarse  pyrrhotite  ; 
6.  Fine-grained  pyrrhotite  ;  7.  Massive  pyrrhotite  ;  8.  Coarse  pyrrhotite.  9,  10, 
11.  Massive  fine-grained  pyrrhotite ;  12.  Coarse  pyrrhotite  ;  13,  14.  Massive  pyr- 
rhotite ;  15.  Massive  fine-grained  pyrrhotite;  16.  Coarser  than  No.  15,  but  with 
more  chalcopyrite  ;  17.  Massive  pyrrhotite  (Tuff  &  Stobie' s  property)  ;  18.  Coarse^ 
massive  pyrrhotite  from  Wisner  township. 

The  Magnetic  Separation  of  Nickeliferous  Pyrrhotite. 

Many  experiments  have  been  performed  in  recent  years  to 
effect  a  commercial  magnetic  separation  of  the  nickel  in  pyr- 
rhotite ores;  or,  for  scientific  purposes,  to  determine  the  con- 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  467 

dition  of  the  nickel  in  this  mineral.  The  commercial  elimina- 
tion of  the  nickel  is  probably  an  impossibility,  and  the  scientific 
problem  is  only  now  approaching  a  solution. 

S.  H.  Emmens  14  refers  to  the  work  of  Habermehl  (1879),  who 
effected  a  separation  of  European  nickeliferous  pyrrhotite  into 
magnetic  and  non-magnetic  portions. 

T.  J.  McTighe,  in  1890,  applied  magnetic  separation  in  the 
treatment  of  Canadian  ores;  and  in  1892  T.  A.  Edison,  in  ap- 
plying for  a  U.  S.  Patent,  said : 

"  I  have  discovered  that  where  magnetic  pyrites,  called  pyrrhotite,  is  nickel- 
iferous, as  it  usually  is  to  a  more  or  less  extent,  the  nickel  is  not  distributed  gen- 
erally throughout  the  whole  body  of  the  pyrrhotite,  but  certain  crystals  are  pure 
pyrrhotite  or  magnetic  pyrites,  while  other  crystals  have  some  of  the  iron  replaced 
by  nickel  and  sometimes  by  cobalt,  and  that  the  crystals  containing  the  nickel  and 
cobalt  are  considerably  less  magnetic  than  the  pure  pyrrhotite." 

Emmens  himself  made  some  crude  experiments  on  material 
from  the  Gap  mine,  Pa.,  and  from  Sudbury,  and  obtained  two 
products,  the  non-magnetic  being  considerably  richer  in  nickel 
than  the  original  ore. 

Shortly  after,  David  H.  Browne 15  contributed  a  very  valua- 
ble article  on  the  same  subject.  He  shows  the  existence  of  a 
rich  nickel-mineral  in  the  ores  from  the  Copper  Cliff,  Evans, 
and  Stobie  mines,  in  the  Sudbury  district,  and  also  that  it  can 
be  separated  by  rough-crushing  and  hand-picking,  after  first 
removing  the  magnetic  part.  His  analyses 16  show  that  the  non- 
magnetic residue  bears  a  close  resemblance  to  the  pentlandite 
described  by  Penfield. 

Probably  the  most  extensive  series  of  experiments  for  a  com- 
mercial separation  were  those  made  by  J.  ST.  Judson,  of  the 
Wetherill  Separating  Co.,  in  1900.  The  results  have  never 
been  published ;  but  Mr.  Judson  has  very  kindly  placed  them 
in  the  hands  of  the  writer,  and  a  partial  abstract  is  here  pre- 
sented. 

The  material  operated  on  was  nearly  pure  pyrrhotite  from 
Copper  Cliff,  containing,  by  analysis,  Ni,  3.14 ;  Cu,  0.42 ;  and 
Fe,  49.78  per  cent.  The  magnetic-separation  products,  with 

14  Second  Report,  Ontario  Bureau  of  Mines,  p.  163  (1892).     Journal  of  the  Ameri- 
can Chemical  Society,  vol.  xiv.,  No.  10,  p.  369  (1892). 

15  Engineering  and  Mining  Journal,  vol.  Ivi ,  No.  23,  p.  565  (Dec.  2,  1893). 

16  Nos.  5  to  8  in  Table  XL  of  this  paper. 


468 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


different  current-strengths,  and  the  analysis  of  each,  are  given 
in  Table  VII. 

TABLE  VII. — Magnetic  Separation  of  Pyrrhotite  by  the  Wetherill 
Separator.  First  Experiment — Material  Crushed  to  No.  30  Mesh. 


Product 

No. 

52 
11 

5 
la 
2-5« 

Amperes. 

Magnetic 
Product. 

Analyses. 

Magnetic  Portion. 

Total  Percentage  of  Metal  in 
Magnetic  Portion. 

Ni. 

Cu. 

Fe. 

Ni. 

Cu. 

Fe. 

1 
15 
15 
28 
tails 
1 

Per  Cent. 
90.11 
7.65 
0.78 
0.92 
0.54 
90.11 
9.89 

Per  Cent. 
2.46 
10.83 
9.68 
1.76 
0.70 
2.46 
9.33 

Percent. 

0.22 
0.78 
2.55 
13.58 
2.64 
0.22 
2.21 

Percent. 
53.60 
14.80 
13.25 
20.10 
11.25 
53.60 
14.97 

Per  Cent. 

70.58 
26.38 
2.42 
5.87 
0.13 
70.58 
29.42 

Percent. 

47.48 
14.37 
4.79 
29.99 
3.35 
47.48 
52.52 

Per  Cent. 
97.02 
2.27 
0.21 
0.37 
0.12 
97.02 
2.98 

a  Making  only  two  products — i.  e.,  magnetic  and  non-magnetic — at  1  ampere. 

The  results  show  that  with  a  current-strength  of  1  ampere 
90.11  per  cent,  of  the  total  sample  was  magnetic,  and  this  con- 
tained 2.46  per  cent,  of  Ni,  or  the  equivalent  of  70.58  per  cent, 
of  the  total  metal  in  the  original  pyrrhotite ;  that  is,  only  29.42 
per  cent,  of  the  total  nickel  was  concentrated  in  the  non-mag- 
netic portion  (making  only  two  products).  The  second  and 
third  products  (15  amperes)  were  highly  nickelif erous ;  but  as 
they  contained  less  than  a  third  of  the  total  nickel  in  the  ore, 
the  loss  in  the  magnetic  portion  was  very  heavy. 

In  the  next  experiment,  the  first  magnetic  product,  at  1  am- 
pere (amounting  to  90.11  per  cent,  of  the  total),  containing  M, 
2.46;  Cu,  0.22;  and  Fe,  50.62  per  cent,  was  again  treated, 
using  a  weaker  current.  The  results  are  shown  in  Table  VIII. 

TABLE  VIII. — Magnetic-Separation  Product  No.  1  of  Table  VII. 
Second  Experiment  (No.  30  Mesh). 


1. 
Magnetic 

2. 

Analyses. 

Product 
No. 

Amperes. 

Portion 
of  Part 
Treated. 

Portion 
of  Total. 

Ni. 

Cu. 

Fe. 

1 
2 
3 
4 
5 
6 

t 

f 

tails 

Per  Cent. 
33.61 
54.15 
4.64 
1.79 
2.35 
3.47 

Per  Cent. 
30.28 
48.79 
4.18 
1.61 
2.12 
3.13 

Per  Cent. 
1.93 
2.08 
3.46 
3.70 
3.95 
10.60 

Per  Cent. 
0.08 
0.13 
0.18 
0.51 
0.90 
2.44 

Per  Cent. 
56.65 
55.60 
53.00 
41.25 
23.80 
20.20 

THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


469 


Column  1  gives  the  percentage  of  the  part  treated  which 
was  magnetic  with  the  different  current-strengths  indicated; 
column  2,  the  percentage  of  the  total  sample  which  was  mag- 
netic under  the  same  conditions  (e.  g.,  90.11  X  33.61  =  30.28). 
The  portion  magnetic  at  -f%  ampere  (about  one-third  of  the 
total)  still  contained  nearly  2  per  cent,  of  Ni ;  so  the  loss  was 
still  very  great,  while  the  non-magnetic  concentrate  was  not 
very  greatly  enriched. 

All  the  products  of  these  two  experiments  were  then  mixed, 
crushed  to  pass  through  60-mesh  and  treated  as  shown  in 
Table  IX. 

TABLE  IX. — Magnetic  Separation  of  Mixed  Sample  Crushed  to 
Pass  No.  60  Mesh.      Third  Experiment. 


Product 
No. 

Amperes. 

Magnetic 
Portion. 

Analyses. 

Ni.                      Cu. 

Fe. 

Per  Cent,  of 

Per  Cent.            Per  Cent.            Per  Cent. 

Total. 

1 

44.26 

1.69                 0.13                 55.50 

2 

41.96 

2.16                  0.18 

54.80 

3 

i 

0.37 

2.16                  0.26 

50.30 

4 

0.37 

4.19                 0.70        |         32.50 

5 

• 

0.49 

5.29                 0.93 

24.55 

6 

2 

1.13 

8.96                 0.97 

20.85 

7 

3 

1.38 

13.55                 0.76 

21.55 

8 

4 

3.95 

10.29                 0.46 

22.35 

9 

5 

4.19 

12.71                 0.60 

19.60 

10 

C 

» 

0.89 

4.17                 3.18 

12.65 

11 

28 

0.77 

1.53                14.36 

19.65 

12 

tails 

0.52 

0.38                 1.64 

i 

8.25 

At  J  ampere,  44.26  per  cent,  of  the  sample  was  magnetic,  and 
the  product  contained  l.(19  per  cent,  of  Ni.  At  J  ampere, 
86.22  per  cent,  was  magnetic,  and  the  product  contained  1.92 
per  cent,  of  Ni.  If  the  remainder,  13.78  per  cent.,  were  consid- 
ered as  the  non-magnetic  concentrate,  we  would  have  a  com- 
paratively rich  nickel-ore,  but  the  losses  in  the  magnetic  portion 
are  so  great  that  a  commercial  separation  by  this  method  is  out 
of  the  question.  All  the  other  experiments  led  to  the  same 
conclusion.  Intermediate  products,  rich  in  nickel,  were  easily 
obtained ;  but  in  no  case  was  the  nickel  in  the  magnetic  por- 
tion reduced  to  such  an  extent  that  it  could  be  economically 
rejected. 

D.  P.  Shuler,  Sudbury,  Ont.,  has  recently  (1902)  taken  out 
patents  for  a  process  whereby  he  proposes  to  eliminate  the 


470  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

copper  from  the  nickel-iron  portion  by  magnetic  concentration, 
and  subsequently  to  convert  the  latter,  after  roasting,  into  a 
nickeliferous  pig-iron.  The  copper-nickel  concentrate  will,  of 
course,  be  treated  separately  for  its  metallic  content.  This 
seems  to  be  the  most  fruitful  field  for  investigation  now  open 
in  this  connection,  and  about  the  only  method  of  treatment 
which  promises  to  yield  results  capable  of  industrial  application. 
The  Nickel-Bearing  Mineral.17— Prof.  S.  L.  Pentield18  first 
•definitely  proved  the  existence  of  pentlandite  in  the  ores  from 
the  Sudbury  nickel-copper  mines.  Later,  David  H.  Browne 19 
showed  that  pentlandite  was  the  principal  nickel-bearing  min- 
eral. On  the  assumption  that  the  ores  were  the  result  of  a 
magmatic  segregation  from  an  original  fused  magma,  he  tried 
to  show  that  the  coarser  the  grain  of  the  pyrrhotite,  and  the 
deeper  it  lies  below  the  surface,  the  more  nickel  exists  as  pent- 
landite. On  the  other  hand,  the  finer-grained  the  ore,  and  the 
more  rapidly  it  has  cooled  from  the  fused  state  (i.  e.,  the  nearer 
it  is  to  the  surface),  the  more  nickel  exists  as  an  element  replac- 
ing the  iron  in  the  pyrrhotite.  As  will  appear  later  in  this 
paper,  however,  this  relation  does  not  hold  good. 

In  order  to  determine  as  nearly  as  possible  how  much  of  the 
nickel  occurs  as  a  separate  mineral,  and  how  much,  if  any,  re- 
places iron,  and  also  to  ascertain  the  composition  of  the  nickel- 
mineral,  several  series  of  experiments  were  made  by  the  writer. 

First  Series  of  Experiments. — A  number  of  representative 
samples  of  pyrrhotite  were  ground  to  pass  through  100-mesh 
and  the  non-magnetic  portion  was  removed  as  completely  as 
possible  by  repeated  treatment  with  a  small  horse-shoe  magnet. 
The  nickel-contents  of  the  original  samples  are  given  in  column 
I.,  and  those  of  the  magnetic  concentrate  in  column  II.,  Table  X. 
The  nickel  is  seen  to  have  been  materially  reduced,  and  the 
results  seemed  to  indicate  a  pretty  constant  quantity  remaining 
with  the  magnetic  part.  Further  experiments,  however,  showed 
that  this  was  purely  an  accidental  relation. 

Second  Series  of  Experiments. — The  original  samples  were 
coarsely  crushed  and  the  magnetic  portion  was  sized  between 

17  A  preliminary  note  on  this  subject  was  published  in  the  Engineering  and  Min- 
ing Journal,  vol.  Ixxiii.,  No.  19,  p.  660  (May  10,  1902),  by  the  writer. 

18  .American  Journal  of  Science,  Third  Series,  vol.  xlv.,  No.  270,  p.  493  (June, 
1893). 

19  Engineering  and  Mining  Journal,  vol.  Ivi.,  No.  23,  p.  565  (Dec.  2,  1893),  and 
School  of  Mines  Quarterly,  vol.  xvi.,  No.  4,  p.  297  (July,  1895). 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


471 


40-  and  60-mesh,  then  freed  as  well  as  possible  from  non-mag- 
netic material,  crushed  between  60-  and  80-mesh  and  again 
concentrated.  By  successive  treatments  the  mineral  was  finally 
reduced  to  a  fine  powder.  The  ultimate  product  was  then  as- 
sayed for  nickel.  As  shown  in  column  III.,  Table  X.,  the  nickel 
was  much  reduced,  but  not  entirely  eliminated. 

Third  Series  of  Experiments. — To  see  if  it  were  possible  to  still 
further  reduce  the  nickel-content,  a  number  of  samples  were 
very  carefully  prepared.  They  were  coarsely  crushed  and  the 
purest  mineral  selected.  This  was  crushed  to  pass  through  10- 
on  20-mesh,  and  the  finer  material  was  rejected.  All  the  non- 
magnetic portion  was  eliminated  and  the  concentrate  was  then 
crushed  to  20-  on  40-mesh,  the  finer  part  being  again  rejected. 
The  operations  were  repeated  until  the  ore  was  finally  ground 
in  an  agate  mortar,  the  non-magnetic  part  being  very  carefully 
removed  each  time.  The  nickel  in  the  final  concentrate  is 
given  in  column  IV.,  Table  X. 

TABLE  X. — Experiments  in  the  Magnetic  Concentration  of  Nickel- 
iferous  Pyrrhotite. 


Location.                       ^  Ja 

II. 

Ni. 

III. 

Ni. 

~Pe7 
Cent. 
0.98 
0.68 
1.05 
0.75 
0.70 
0.83 
1.20 

Tib" 

0.80 

IV. 

Ni. 

Per 
Gent. 
1.  Elsie  mine  2.44 

Per 
Cent. 
2.22 
2.14 
2.07 
2.14 
2.00 
2.32 
2.25 

'2.30' 
2.46 

Per 

Cent. 

Fine-grained  pyrrhotite. 
Fine-grained  pyrrhotite. 
Coarse-grained  pyrrhotite. 
Medium-grained  pyrrhotite. 
Coarse-grained  pyrrhotite. 
Coarse-grained  pyrrhotite. 
Coarse-grained  pyrrhotite. 
Fine-grained  pyrrhotite. 
Massive  pyrrhotite. 
Fine-grained  pyrrhotite. 

2    Stobie  mine                          3  05 

3.  Frood  mine  2.40 

0.65 
0.70 

4.  Mount  Nickel  mine  3.06 
5.  Copper  Cliff,  No.  2  mine.  4.00 
.6.  Copper  Cliff,  No.  4  mine.  3.30 
7.  Creighton  mine  (a)  2.32 
Creighton  mine  (b)  4.15 
8    Gertrude  mine  4  00 

0.70 
0.45 

9.  Victoria  mine  3.40 

a  Nickel  with  a  trace  of  cobalt. 

The  results  show  conclusively  that  the  nickel  present  is  not 
replacing  part  of  the  iron  in  the  pyrrhotite,  but  exists  as  a  sep- 
arate mineral.  The  fact  that  all  the  nickel  could  not  be  elim- 
inated by  the  methods  used  does  not  indicate  that  even  the 
amount  that  remained  was  an  essential  part  of  the  pyrrhotite, 
as  several  factors  enter  which  render  its  complete  removal 
practically  impossible.  In  the  first  place,  the  nickel-mineral 
is  very  intimately  associated  with  the  magnetic  pyrites;  and 
even  a  minute  adhering  fragment  of  the  latter  will  cause  it  to 


472 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


be  carried  over  with  the  magnetic  portion.  It  is  also  to  be 
noted  that  the  nickel-mineral  itself  is  slightly  magnetic,  and  in 
the"  form  of  a  powder  is  attracted  by  even  a  small  magnet. 

As  a  result  of  these  experiments  I  feel  justified  in  saying 
that  all  the  nickel,  in  the  Sudbury  ores  at  least,  occurs  as  a 
separate  mineral,  and  that  in  this  district  there  does  not  exist 
a  true  nickeliferous  pyrrhotite,  in  the  sense  that  the  nickel  iso- 
morphously  replaces  part  of  the  iron  in  that  mineral. 

Experiments  on  Swedish  and  Norwegian  ores  of  a  similar 
nature  show  that  a  large  part  of  the  nickel  can  be  eliminated 
by  magnetic  concentration ;  and  taking  these  results,  in  con- 
nection with  the  foregoing,  it  is  pertinent  to  ask,  "  Is  there 
such  a  thing  as  a  true  nickeliferous  pyrrhotite  ? " 

The  results  show  that  even  with  the  most  careful  treatment, 
a  commercial  separation  of  the  nickel  by  magnetic  concentra- 
tion is  prohibited  by  the  considerable  loss  of  nickel  involved. 

The  Non-Magnetic  Residue.™ — Analyses  of  the  non-magnetic 
residues,  roughly  freed  from  impurities,  were  made  to  get  an 
idea  of  their  compositions. 

The  small  amount  of  copper  was  estimated  as  chalcopyrite, 
and  the  necessary  amounts  of  iron  and  sulphur  deducted.  The 
ratios  of  Fe  :  Ni :  S  (taken  as  1)  were  then  calculated,  and  the 
results  are  given  in  Table  XL 

TABLE  XI. — Analyses  of  the  Non-Magnetic  Residue  from 
Pyrrhotites.a 


Location. 

Cu. 

Total 
Fe. 

Total 

S. 

Ni. 

Per 
Cent. 
31.65 
32.25 
33. 
29.71 
35. 
35. 
34. 
34. 

Co 

~PeT 
Cent. 

0.65 
0.84 
30 
|0.60 
35 
30 
30 
70 

Fe.6 

S.6 

Ratios.  (S  =  1.00.) 

S. 

Ni  +Co. 

Fe. 

1.  Victoria  mine  
2.  Frood  mine  

Per 
Cent. 
0-95 
0.84 
1.20 
0.80 
0 
0 
0 
0 

Per 
Cent. 
28.50 
29.36 
29.50 
27.11 

Per 

Cent. 
31.92 
32.85 
34.25 
30.30 

Per 
Cent. 
27.66 
28.65 
28.45 
26.40 
29.80 
30.30 
29.60 
29.90 

Per 

Cent. 
30.96 
3-2.04 
32.80 
29.46 
34.35 
33.50 
33.35 
33.90 

1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 

0.570 
0.565 
0.550 
0.565 
0.56 
0.571 
0.571 
0.56 

0.514 
0.512 
0.50 
0.515 
0.50 
0.52 
0.51 
0.505 

3.  Creighton  mine  
4.  General  sample  
5.  Copper  Cliff  minec... 
6.  Copper  Cliff  minec  .. 
7.  Evans  mine  
8.  Stobie  mine  



0  For  the  sake  of  uniformity  the  following  revised  atomic  weights  are  used 
throughout :  Ni,  58.69  ;  Co,  58.99  ;  Fe,  56.02  ;  8,  32.07. 

6  After  deducting  the  necessary  amounts  to  form  chalcopyrite  with  the  copper 
present. 

c  Analyses  by  D.  H.  Browne  ;  Nos.  5  and  8  contained  some  pyrrhotite  ;  Nos.  6 
and  7  were  purer.  Engineering  and  Mining  Journal,  vol.  Ivi. ,  No.  23,  p.  565  (Dec- 
2,  1893). 

20  The  residue  is  spoken  of  for  convenience  as  being  non-magnetic,  although  in 
reality  slightly  so. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


473 


The  striking  uniformity  of  the  ratios  obtained  at  once  indi- 
cated the  similarity  of  the  mineral  in  all  these  cases  ;  and 
further  work  on  carefully-purified  material  confirms  this  view. 

The  pyrrhotite  from  the  Creighton,  Worthington,  and  Frood 
mines  shows  considerable  amounts  of  the  non-magnetic  material, 
in  pieces  up  to  0.75  in.  in  diameter,  fairly  pure,  and  specimens 
from  these  localities  were  chosen  as  affording  the  best  material 
to  work  on. 

The  ore  was  first  roughly  crushed  and  the  pyrrhotite  re- 
moved by  a  magnet.  The  larger  non-magnetic  fragments  were 
taken  and  picked  over  under  a  lens,  carefully  discarding  any 
that  was  even  suspected  of  containing  pyrrhotite. 

The  samples  were  then  crushed  successively  to  pass  through 
No.  20,  No.  40,  No.  60,  No.  80,  and  No.  100  mesh,  each  time 
discarding  the  fines  and  going  over  them  with  a  magnet,  exam- 
ining under  a  lens,  and  removing  all  foreign  material  till  they 
were  too  fine  to  treat  in  this  way.  They  were  finally  ground 
in  an  agate  mortar  and  again  gone  over  with  a  weak  magnet, 
which  attracted  the  mineral  but  little  and  served  to  remove 
any  tracer  of  pyrrhotite  that  might  remain.  In  this  way  the 
samples  were  obtained  as  pure  as  it  is  practically  possible 
to  get  them,  and  they  were  ready  for  analysis ;  the  results  are 
shown  in  Table  XII. 

TABLE  XII. — Analyses  of  Nickel- Bearing  Mineral." 


Location. 

Cu. 

Per  Cent. 
0 
0 
0 
0 

Ni. 

Co. 

Fe. 

s. 

Ratios.    (S  =1.00.) 

S. 

1.00 
1.00 
1.00 
1.00 

Ni  +  Co. 

Fe. 

1.  Creighton  
2.  Worthington... 
3.  Frood  

PerCent. 
34.82 
33.70 
34.98 
34.23 

Per  Cent. 
0.84 

0.78 
0.85 
0.85 

Percent. 
30.00 
29.17 
30.04 
30.25 

Per  Cent. 
32.90 
32.30 
33.30 
33.42 

0.589 
0.583 
0.58S 
0.573 

0.518 
0.517 
0.513 
0.518 

4.  Copper  Cliff6. 

a  The  small  amount  of  residue  consisted  of  siliceous  gangue.  These  analyses 
were  made  in  the  laboratory  of  the  School  of  Mining,  Kingston,  Ont.,  which  was 
kindly  placed  at  the  writer's  disposal. 

6  Penfield,  American  Journal  of  Science,  Third  Series,  vol.  xlv.,  No.  270,  p. 
493  (June,  1893). 

The  composition  of  the  non-magnetic  residue  at  once  sug- 
gests pentlandite,  and  as  such  Penfield  describes  the  sample 
he  examined  (No.  4  in  Table  XII.). 


474  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

The  pentlandite  from  Lillehammer,  Norway,  corresponds 
very  closely  to  it  in  physical  properties,  but  carries  a  lower  per- 
centage of  nickel  (20  to  22  per  cent.) 

The  Sudbury  mineral  occurs,  in  part,  finely  disseminated 
through  the  pyrrhotite,  so  that  it  cannot  be  detected,  even  with 
the  aid  of  a  lens,  and  partly  in  larger  grains  and  segregations, 
at  times  an  inch  in  diameter.  Usually  it  possesses  the  charac- 
teristic platy  structure  and  octahedral  parting,  though  this  is 
at  times  obscured.  On  fresh  fracture,  the  mineral  has  a  light 
steel-gray  or  silver-white  color,  which  soon  changes  on  ex- 
posure to  the  peculiar  and  characteristic  light  bronze-yellow. 
When  fresh  and  massive  it  is  with  difficulty  to  be  distinguished 
from  the  fresh  pyrrhotite,  but  on  a  slight  superficial  oxidation 
the  difference  becomes  quite  pronounced. 

The  Lillehammer  pentlandite  has  a  ratio  of  FeS  :  NiS  of 
about  2  : 1,  and  its  formula  is  given  as  2FeS  -f  NiS.  Penfield 2I 
gives  the  ratio  of  the  Sudbury  mineral  as  (Fe  -f  Ni) :  S  =  1:1, 
or  (Fe  -f  Ni)  S.22  By  a  reference  to  Table  XII.  it  will  be  seen 
that  the  ratio  (Fe  +  M)  :  S  is  (1)  11.07  :  10;  (2)  11  :  10 ;  (3) 
11.03  :  10 ;  and  (4)  10.91  :  10 ;  that  is,  there  is  an  excess  of  the 
metallic  constituents  over  the  amount  required  by  the  formula 
(Fe  -f  Ni)S.  The  same  excess  is  indicated  in  the  analyses  of 
less  pure  material  given  in  Table  XI.  This  relation  is  con- 
stant and  cannot  be  regarded  as  accidental,  especially  since  the 
analyses  of  the  purest  samples  from  different  localities  show 
the  ratio  to  be  constant  at  11  :  10.  Just  what  this  peculiarity 
signifies  it  is  difficult  to  say ;  but  it  seems  to  indicate  that  the 
structure  of  the  pentlandite  molecule  is  more  complicated  than 
that  represented  by  (Fe  +  Ni)S,  even  though  it  is  advantageous 
to  represent  minerals  by  the  simplest  possible  formulas. 

An  excess  of  sulphur  over  the  metal  is  by  no  means  uncom- 
mon in  minerals  (e.g.,  in  pyrrhotite,  poly dy mite,  beyrichite, 
etc.) ;  but  an  excess  of  metallic  contents  seem  unique. 

21  Loc.  cit.     The  analysis  given   by  Professor  Penfield,   in  this  paper,  agrees 
almost  exactly  with  those  made  by  the  writer,  but  by  a  slight  error  in  calculation, 
his  analysis  worked  out  exactly  to  the  formula  (Fe  +  Ni)S,  instead  of  showing  an 
excess  of  metallic  constituents,  as  is  actually  the  case  ;  that  is,  the  ratio  of  (Fe  +  Ni) : 
S  in  the  material  examined  by  Professor  Penfield  is  almost  11 : 10,  instead  of  1  : 1 
as  given. 

22  Nickel  and  cobalt  being  taken  together. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  475 

Such  a  formula  as  (Fe  -f-  Ni)uS10  is  not  convenient;  but  it 
appears  to  be  the  only  means  of  expressing  the  results  of 
analysis. 

Another  interesting  feature  is  the  ratio  of  nickel  to  iron, 
which  is  quite  constantly  also  nearly  11  :  10,  while  that  of 
nickel  to  cobalt  is  about  42  :  1. 

An  intimate  mixture  of  some  sub-sulphide  with  what  might 
be  regarded  as  normal  pentlandite  [(N"i  -f  Fe)S]  is,  of  course, 
a  possibility ;  but  if  this  is  the  case  it  must  be  in  a  definite  and 
constant  ratio,  as  the  mineral  shows  the  same  phenomenon 
throughout  the  whole  district. 

But  this  is  a  mere  speculation.  There  is  no  direct  evidence 
on  which  to  base  the  assumption,  and  at  present  it  seems  most 
reasonable  to  imagine  a  peculiar  molecular  arrangement  of  the 
atoms  of  the  mineral  itself.  As  the  matter  now  stands,  how- 
ever, the  relations  are  unexplained,  and  must  be  the  subject  of 
further  investigation  before  a  satisfactory  conclusion  is  reached. 

The  Formula  of  the  Pyrrhotite. 

A  large  number  of  the  magnetically-separated  samples  were 
analyzed,  in  an  attempt  to  determine  the  formula  of  the  pyr- 
rhotite,  and  with  a  fair  amount  of  success.  A  number  of  fac- 
tors had  to  be  taken  into  consideration,  and  tended  to  render 
the  results  in  some  cases  rather  unsatisfactory,  so  that  absolute 
uniformity  was  not  attained. 

The  nickel  present  was  calculated  to  pentlandite  on  the  basis 
of  the  ratios  given  above,  and  the  necessary  amounts  of  iron 
and  sulphur  were  deducted.  As  there  was  a  persistent,  though 
varying,  amount  of  magnetite  in  all  the  samples,  it  was  neces- 
sary to  determine  this.  The  estimation  of  the  oxide  (Fe304)  in 
the  presence  of  the  magnetic  sulphide  presented  considerable 
difficulty,  and  this  is  probably  the  main  cause  of  the  discrep- 
ancies. 

After  a  number  of  experiments,  it  was  found  that  by  treating 
the  sample  with  a  dilute  (10  per  cent.)  solution  of  nitric  acid, 
the  pyrrhotite  could  be  largely  removed,  while  the  magnetite 
was  but  little  affected.  The  separated  sulphur  was  removed 
by  means  of  bromine  and  carbon  bisulphide ;  and  after  several 
treatments  the  residue  of  magnetite  was  obtained  pure,  and  the 
iron  was  estimated  by  titration.  The  nature  of  the  various 


476  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

operations  involves  the  possibility  of  some  loss,  especially  as  the 
amount  of  magnetite  is  comparatively  small;  but,  on  the 
whole,  the  method  answered  very  well.  The  great  majority 
of  the  analyses  indicated  that  the  pyrrhotite  could  be  repre- 
sented by  the  formula  Fe8S9,  while  two  or  three  worked  out  to 
Fe7S8  and  Fe9S10 ;  so  that  the  former  can  be  regarded  as  the 
most  probable  for  the  pyrrhotite  from  the  Sudbury  district. 

For  purposes  of  comparison,  a  number  of  pyrrhotites,  as  pure 
as  it  was  possible  to  obtain  them,  from  various  localities,  were 
further  purified  by  magnetic  concentration  and  analyzed.  One 
from  Rossland,  B.  C.,  conformed  to  Fe8S9,  one  from  Anthony's 
Nose,  N.  Y.,  to  Fe7S8,  as  did  also  a  sample  from  Enter- 
prise, Ont.23 

As  absolute  uniformity,  even  in  the  material  from  a  limited 
district,  was  not  obtained,  it  would  not  be  wise  to  draw  general 
conclusions,  or  attempt  to  make  any  general  applications,  with- 
out an  exhaustive  study  of  more  representative  material. 

It  seems,  however,  a  justifiable  conclusion  from  the  work  so 
far  that  the  pyrrhotite  from  the  nickel-region  of  Sudbury  is  of 
fairly-uniform  composition,  and  is  best  represented  by  the  for- 
mula Fe8S9. 

Summary. 

In  recapitulation,  the  main  facts  may  be  summed  up  briefly 
as  follows  : 

1.  Our  present  conception  of  the  constitution  of  pyrrhotite 
is  very  unsatisfactory.     The  nature  and  associations  of  the  min- 
eral are  such  that  analyses  are  often  misleading,  and  a  great 
deal  of  careful,  systematic  work  is  necessary  as  a  basis  for  gen- 
eralisations of  any  value. 

2.  The  conditions  under  which  pyrrhotite  is  formed  in  nature 
are  still  very  little  understood. 

3.  Nickel  is  universally  associated  with  pyrrhotite  in  greater 
or  less  amount,  though  in  but  few  instances  is  it  present  in  quan- 
tities of  economic  importance. 

4.  The  Sudbury  pyrrhotites   are  very  uniform   over  large 
areas,  as  to  metallic  contents  and  associated  minerals. 

5.  Aside  from  the  copper-  and  nickel-minerals,  the  others 

23  This  pyrrhotite  is  associated  with  a  remarkable  deposit  of  molybdenite,  which 
has  recently  been  exploited. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  477 

are  of  small  economic  importance,  except,  perhaps,  sperrylite, 
which  is  furnishing  an  increasing  amount  of  the  world's  supply 
of  platinum. 

6.  The  magnetic  separation  of  the  nickel  from  pyrrhotite  is 
out  of  the  question  commercially. 

7.  The  nickel  occurs  in  the  pyrrhotite  as  the  so-called  pent- 
landite,  and  not  as  an  essential  constituent  of  this  mineral. 

8.  Nearly  all  the  pentlandite  can  be  separated  from  the  pyr- 
rhotite by  magnetic  methods ;   but  peculiar  physical  conditions 
seem  to  render  its  absolute  elimination  an  impossibility. 

9.  The  pentlandite   does  not  conform  to  the  generally-ac- 
cepted formula  (Fe  -f-  Ni)S.     The  metallic  constituents  are 
always  in  excess  of  the  sulphur  by  a  constant  ratio  of  11  :  10. 
But,  as  yet,  no  satisfactory  explanation  of  this  phenomenon  can 

be  advanced. 

» 

10.  The  pyrrhotite  from  Sudbury  can  best  be  represented  by 
the  formula  Fe8S9. 

11.  Pyrrhotite  and  magnetite  can  be  separated  by  a  10-per 
cent,  solution  of  nitric  acid  with  fairly-satisfactory  results. 

II.  GENESIS  OF  THE  SUDBURY  ORES. 

General  Considerations. 

For  convenience,  pyrrhotites  may  be  divided  into  two  main 
classes,  according  to  their  geological  relations. 

1.  Those  of  the  first  class  occur,  often  with  more  or  less  py- 
rite  and  chalcopyrite,  as  lenses  in  acidic  gneisses  and  schists. 
These  lenticular  masses  generally  conform  to  the  foliation  of 
the  schists,  and  are  often  repeated  and  connected   by  leaner 
zones,  like  fahlbands.     Such  deposits  are  of  world-wide  distri- 
bution ;  and,  wherever  found,  generally  carry  pyrrhotite  low  in 
nickel,  seldom  containing  more  than  0.5  and  usually  less  than 
0.25  per  cent. 

2.  The  second  class  also  is  widely  distributed.     The  deposits 
are  likewise  lenticular  in  shape,  but  they  are  associated  with 
basic  igneous  rocks,  usually  of  the  gabbro  type,  or  their  meta- 
morphic   equivalents.     Another  characteristic  feature  is,  that 
while  they  lie  well  within  the  limits  of  the  eruptive  rock,  they 
generally  occur  at  or  near  its  contact  with  other  rocks,  such  as 
granite,  mica-schist,  porphyry,  or  diabase.     The  pyrrhotite  is 


478  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

always  associated  with  more  or  less  chalcopyrite  and  pyrite,  and 
at  times  with  the  rarer  minerals,  pentlandite,  sperrylite,  and 
gersdorffite.  The  characteristic  minerals  of  the  basic  rock  are 
also  intimately  mixed  through  the  prevailing  sulphides.  Nickel 
is  almost  invariably  present,  at  times  reaching  the  amount  of 
10  per  cent.  Generally,  however,  from  2  to  4  per  cent.,  as  at 
Sudbury,  would  be  a  fair  average.  In  Norway  and  Sweden  the 
average  is  lower. 

It  should  be  added  that  the  above  general  statements  as  to 
the  nickel-contents  of  the  two  classes  of  pyrrhotite-deposits  i& 
subject  to  some  important  exceptions. 

3.  Outside  of  these  two  classes,  pyrrhotite  is  found  at  times 
in  considerable  quantity  in  true  fissure-veins;  but  this  occur- 
rence is  relatively  unimportant. 

Types  of  the  first  class,  as  represented  by  the  Phillips  mine,, 
at  Anthony's  Nose,  N.  Y.,  the  Ducktown,  Tenn.,  deposits,  and 
numerous  fahlbands  in  various  parts  of  Ontario,  Norway,  and 
Sweden,  are  believed  to  be  replacement-deposits  along  crushed 
zones. 

To  the  second  class  of  deposits  an  igneous  origin  has  been 
attributed  in  recent  years  by  some  of  the  ablest  workers  in  this 
field  of  geology.  The  sulphides  are  regarded  as  original  rock- 
constituents,  and  it  is  thought  that,  being  among  the  first  min- 
erals to  crystallize  in  a  cooling  rock-magma,  they  became  con- 
centrated in  their  present  position  before  the  rock  solidified. 

It  is  well  established  that  rock-magmas — especially  the  more 
basic — tend  to  divide  into  fractional  parts  of  varying  acidity. 
What  forces  produce  this  "  magmatic  differentiation "  is  not 
clearly  understood. 

There  seems  to  be  excellent  evidence  to  prove  that  many  de- 
posits of  magnetite  (always  titaniferous),  chromite,  and  cor- 
undum have  originated  in  this  way.  That  is,  they  are  simply 
excessively  basic  developments  of  magma,  in  which  the  mineral 
in  question  is  a  normal,  or  common,  accessory  constituent. 

These  deposits,  however,  consist  of  oxidized  compounds; 
and  their  segregation  presents  fewer  theoretical  difficulties  than 
does  that  of  the  sulphides. 

Value  of  the  Classification. — Quite  apart,  however,  from 
theories  of  origin,  the  distinction  above  made  as  to  geological 
relations  is  of  the  utmost  importance  from  an  economic  stand- 
point. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  47& 

This  view  of  the  relative  value, of  the  pyrrhotites  in  acid 
and  basic  rocks,  as  nickel-ores,  is  strongly  urged  by  Professors 
Adams  and  Kemp  in  valuable  papers  which  appeared  about 
the  same  time.24 

The  Sudbury  Pyrrhotite-Deposits. 

In  studying  the  origin  of  pyrrhotite  of  the  second  class,  par- 
ticular attention  has  been  paid  to  the  Sudbury  deposits.  Ref- 
erence will,  however,  be  made  to  similar  deposits  elsewhere 
when  necessary. 

Before  proceeding  with  the  consideration  of  the  origin  of  the 
ores,  it  will  be  necessary  to  give  a  brief  account  of  the  geology 
of  the  deposits,  especially  as  the  ideas  formerly  held  have  been 
recently  much  modified.  The  Canadian  Geological  Survey  ha& 
lately  paid  particular  attention  to  the  district,  and  it  is  now 
recognized  that  its  relations  are  much  more  complex  than  wa& 
at  first  thought.  In  his  preliminary  report  on  the  district,  Dr. 
A.  E.  Barlow,25  who  has  had  charge  of  the  work,  gave  some 
general  ideas  of  the  nature  of  the  rocks  and  the  extent  of  the 
ore-bodies.  But  the  field-work  was  not  completed  at  the  time, 
and  many  new  facts  have  been  collected  during  the  past  season; 
hence,  his  final  views  on  the  subject  will  not  be  presented  until 
the  full  report  is  issued.  Meanwhile,  the  question  must  be 
considered  with  the  understanding  that  some  of  the  previously- 
presented  conceptions  are  subject  to  revision. 

The  deposits  are  prevailingly  lenticular,  pinching  out  in  both 
directions  and  conforming  to  the  general  strike  of  the  inclos- 
ing Huronian  strata.  The  ore  always  occurs  in,  and  contains 
fragments  of,  a  basic  and  altered  eruptive  of  the  gabbro  type. 

The  ore-bodies  may  occur  either  well  within  this  eruptive  or 
at  its  contact  with  the  other  prevailing  rocks  of  the  district, 
namely,  granite  or  granite-gneiss,  quartzite,  or  the  metamor- 
phosed representative  of  a  series  of  basic  sedimentaries,  now 
termed  "  greenstones  "  by  the  Survey. 

Dr.  Barlow  says  his  investigations  prove  that  the  normal 

24  F.  D.  Adams,  Preliminary  Eeport  on  the  Geology  of  a  Portion  of  Central 
Ontario,   Annual  Report  of  the  Geological  Survey  of  Canada,    vol.    vi.,  Report  J 
(1892-93).     On  the  Igneous  Origin  of  Certain  Ore-Deposits,  Journal  of  the  Gen- 
eral Mining  Association  of  the  Province  of  Quebec,  vol.  ii.,  pp.  35  to  53  (1894-95). 
J.  F.  Kemp,  The  Nickel-Mine  at  Lancaster  Gap,  Trans.,  xxiv.,  620  (1894). 

25  Summary  Report  of  the  Geological  Survey  Department  of  Canada  (1901). 


480  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

or  type-rock  associated  with  the  deposits  is  a  member  of  the 
gabbro  family  of  rather  exceptional  character.  It  nearly  always 
has  traces  of  a  broad,  ophitic  structure,26  and  the  presence  of 
hypersthene  or  enstatite  justifies  its  classification  as  a  norite. 
Considerable  original  quartz  is,  at  times,  present.  In  general, 
the  rock  consists  of  a  basic  plagioclase,  hypersthene,  or  ensta- 
tite, augite,  biotite,  hornblende,  and  quartz,  with  smaller  quan- 
tities of  accessories.  Associated  with  the  nickel-bearing  norite 
and  grading  into  it,  is  a  rock  which  is  called  "  micro-pegma- 
tite." Microscopically  studied,  the  change  consists  in  the  grad- 
ual assumption  of  a  reddish  color  and  an  increase  in  quartz  and 
feldspar.  The  hornblende  is  replaced  by  biotite  and  the  pla- 
gioclase by  orthoclase. 

The  Nickel-Belts. — Three  main  belts  of  these  norites  and 
associated  micro-pegmatites  are  now  recognized,  designated  as 
the  northern,  middle,  and  southern  belts,  respectively.  They 
are,  at  present,  mapped  as  separate,  but  genetically  and  miner- 
alogically  they  are  essentially  identical.  The  northern  belt 
runs  from  the  old  Ross  mine  (Foy  township)  ESE.  to  Bowell, 
where  it  branches.  The  limits  of  the  smaller  branch  have  not 
been  ascertained,  but  the  larger  trends  to  the  north  and  con- 
nects with  the  large  area  of  basic  rocks  to  the  west  of  Lake 
Wahnipitae.  The  middle  band  begins  in  Levack  township  to 
the  southwest  of  the  northern,  and  runs  in  a  southwesterly 
direction  across  Windy  lake  to  Trill. 

The  southern  and  most  important  belt  begins  in  scattered 
patches  in  Drury  township  (south  of  Trill),  which  unite  and 
extend  unbrokenly  NE.  for  over  32  miles  into  Denison  town- 
ship, where  a  maximum  width  of  over  4  miles  is  attained. 
Here  it  is  divided  into  two  by  an  intrusion  of  coarse  "  augen  " 
granite-gneiss.  The  northern,  or  more  important,  branch  pur- 
sues a  northeasterly  direction  through  Garson  township  (south 
of  Lake  Wahnipitae).  The  southern  branch  crosses  the  Ver- 
milion river  and  passes  through  Copper  Cliff,  where  it  rejoins 
the  other. 

It  will  thus  be  seen  that  the  norite  belt  forms  a  sort  of  rough 
and  somewhat  disconnected  ellipse,  the  center  of  which  is  occu- 
pied by  the  basin  of  later  silicified  volcanic  tuffs,  and  sur- 
rounded by  the  so-called  Laurentian  acidic  gneisses. 

26  This  was  found  by  the  writer,  also,  to  hold  true  as  a  general  rule. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  481 

The  unraveling  of  the  complex,  which  was  formerly  included 
under  the  general  name  of  "  greenstone,"  has  proved  a  very 
difficult  problem.  The  results  seem  to  show  that  it  can  be 
broken  up  into  several  series,  comprising  eruptives,  metamor- 
phosed sediments,  and  some  as  to  whose  true  nature  it  is  diffi- 
cult to  decide. 

The  relation  of  the  granite  intrusions  also  presents  a  difficult 
problem.  These  granites  in  many  places,  undoubtedly,  cut 
some  of  the  basic  rocks  in  close  proximity  to  the  ore-bodies,  but 
in  other  places  they  seem  to  be  earlier  than  these. 

The  geologists  of  the  Canadian  Survey  are  now  of  the  opin- 
ion that  these  granite  rocks  are  intruded  into  rocks,  largely  of 
sedimentary  origin,  and  classed  as  greenstones,  but  that  these 
intrusions  are  earlier  than  the  ore-bearing  norite.  The  problem 
is  complicated  by  the  close  similarity  in  mineralogical  and 
chemical  composition  of  the  so-called  altered  sediments  and  the 
basic  eruptives,  and  by  the  excessive  metamorphism  which  all 
have  undergone. 

The  points  at  issue  are  probably  not  yet  finally  settled,  and  a 
great  deal  of  careful  work  will,  no  doubt,  be  necessary  before 
the  last  word  is  spoken.  In  the  absence  of  the  full  Survey  re- 
port,'the  matter  is  in  a  very  unsatisfactory  state,  but  we  may 
confidently  expect,  in  Dr.  Barlow's  final  utterance,  a  contribu- 
tion of  great  scientific  and  practical  value,  shedding  much  light 
on  the  question. 

Various  Theories  of  the  Origin  of  Nickeliferous  Pyrrhotite. 

A  brief  statement  of  the  views  held  hitherto  by  prominent 
workers  in  this  field  is  appropriate  here. 
Dr.  Bell 27  brings  out  the  following  points : 

1.  That  this  area  was  the  seat  of  volcanic  activity,  with  ex- 
plosive violence  on  a  large  scale. 

2.  The  greenstones  along  certain  lines  hold  an  abundance  of 
angular  fragments  of  other  rocks,  especially  quartzite,  and  this 
brecciated  condition  appears  to  be  favorable  to  the  accumula- 
tion of  ore.     (Blezard,  Stobie,  Copper  Cliff,  etc.)     In  fact,  the 
ore-masses  always  consist  of  a  breccia,  of  sulphides  and  country- 
rock  in  angular  and  rounded  fragments  of  all  sizes. 

27  Annual  Report  of  the  Geological  Survey  of  Canada,  vol.  v.,  Report  F  (1890-91). 

31 


482  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

3.  The  ore-bodies  are  lenticular  and  parallel  to  the  strike  of 
the  inclosing  rocks. 

4.  The.  chalcopy  rite  in  large  masses  is  generally  nearly  pure, 
but  the  pyrrhotite  is  always  mixed  with  a  certain  amount  of 
stony  matter.     This  may  indicate  that  the  former  has  segre- 
gated from  the  original  mixture  by  some  secondary  process. 

5.  The  chalcopyrite  is  often  in  the  form  of  branching  strings 
and    partly    surrounds    stony   inclusions.      In    some    of    the 
brecciated  ore-deposits   in   Levack   township,  the  spiaces   be- 
tween the    greenstone  fragments  are  filled,   partly  with   sul- 
phides and  partly  with  light-colored  crystalline  granite  vein- 
matter. 

6.  The  intimate  association  with  the  greenstone  appears  to 
indicate  that  they  have  originated  first  from  a  state  of  fusion, 
but  have  been  more  or  less  modified  by  other  agencies.     The 
presence  of  crystals  of  feldspar,  quartz,  apatite,  etc.,  together 
with  laminated  iron  pyrites  and  galena,  indicates  the  action  of 
solutions. 

7.  Both  elastics  and  eruptives  have  suffered  extensive  meta- 
morphism. 

Yon  Foullon28  also  calls  attention  to  the  metamorphosed 
and  brecciated  condition  of  the  diorite  (more  properly'  nor- 
ite,  or  altered  gabbro ;  Bell's  greenstone)  and  to  the  fact  that 
this  appears  tov  be  the  most  favorable  place  for  ore-deposits. 
Along  a  line  of  fracture  which  can  be  traced  from  the  Domin- 
ion (Blezard)  mine  to  the  Vermilion,  very  similar  deposits  pre- 
vail, so  it  must  be  considered  that  the  fracture  caused  them. 
There  is  also  a  fracture-line  from  the  Copper  Cliff  to  the 
McConnell  mine  in  Denison  township,  along  which  ore  out- 
crops, accompanied  by  diorite  and  a  breccia  of  gneiss  and 
quartz-syenite.  He  then  adds  that  the  ores  are  not  deposited 
from  solution,  but  are  of  igneous  origin,  because  they  occur  in 
an  eruptive  rock. 

Dr.  F.  D.  Adams,29  speaking  of  The  Igneous  Origin  of  Cer- 
tain Ore-Deposits,  claims  such  an  origin  for  both  the  Sudbury 
and  Norwegian  pyrrhotites  in  gabbro.  He  thinks  the  ores  se- 
gregated according  to  Soret's  principle,  and  the  formation  of 
the  minerals  was  determined  according  to  Fournet's  series. 

28  Jdhrbueh  der  kaiserlich-koniglichen  geologischen  Reichsanstalt,  vol.  xlii.  (1892). 

29  Canadian  Mining  Review,  vol.  xiii.,  No.  1,  p.  3  (Jan.,  1894). 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  483 

Philip  Argall 30  also  points  out  the  faulted  nature  of  the  dis- 
trict. He  considers  that  a  leaching-out  of  the  nickel  and  cop- 
per from  the  greenstones  in  which  they  were  originally  formed, 
and  a  concentration  and  precipitation  along  favorable  zones,  is 
a  more  reasonable  explanation  than  that  of  magmatic  differen- 
tiation. 

E.  Renshaw  Bush 3l  says,  the  schists  in  Denison  and  Graham 
townships  in  the  vicinity  of  the  nickel-bearing  greenstones 
carry  pyrrhotite  in  grains  and  aggregates  between  the  layers. 
He  suggests  the  aqueous  origin  of  the  ores  for  the  following 
reasons : 

1.  Because  of  the  tendency  of  the  sulphides  to  occur  along 
planes  of  contact  and  fracture,  and  the  impregnation  of  the 
rock  near  such  planes. 

2.  Because  the  ore-bodies    occur    at    the    contact  between 
structurally-different  rocks.  • 

3.  Because  of  the  impregnation  of  the  schistose  areas  near 
the  greenstones. 

Merritt 32  thinks  that  a  secondary  concentration  is  necessary 
to  explain  certain  features  of  the  ore-bodies,  viz.:  the  presence 
of  native  copper;  the  "horses"  of  barren  country-rock,  ce- 
mented by  ore ;  the  "  fluccan "  observed  across  certain  de- 
posits; and  the  sharply-brecciated  nature  of  some  of  the 
"  horses." 

D.  H.  Browne,33  in  an  article  on  Segregation  in  Ores  and 
Mattes,  seeks  to  draw  an  analogy  between  a  pot  of  matte,  in 
which  he  found  that  the  nickel  and  copper  sulphides  tended  to 
separate  somewhat,  and  the  Sudbury  ore-bodies,  where  it  is 
seen  that  pyrrhotite  and  chalcopyrite,  to  a  certain  extent,  form 
separate  masses. 

Prof.  J.  F.  Kemp 34  appeals  to  the  laws  of  thermo-chemistry 
to  explain  the  Sudbury  deposits.  As  is  well  known,  in  a  fused 
mass  or  solution  the  order  of  formation  of  compounds  is  de- 
termined by  the  amount  of  energy  (heat)  which  they  develop 

30  Proceedings  of  the  Colorado  Scientific  Society,  vol.  iv.,  p.  395  (1891-93). 

31  The  Sudbury  Nickel  Region,  Engineering  and  Mining  Journal,  vol.  lyii.,  No. 
11,  p.  245  (Mar.  17,  1894). 

32  Trans.,  vols.  xvii.,  293  (1888-89),  and  xxiv.,  755  (1894). 

38  School  of  Mines  Quarterly,  vol.  xvi.,  No.  4,  p.  297  (July,  1895). 
34  An  Outline  of  the  Views  Held  To-day  on  the  Origin  of  Ores,  Mineral  Industry, 
vol.  iv.,  p.  755  (1895). 


484  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

on  crystallizing.  If,  now,  the  gabbro  magma  is  considered  as 
an  intrusion  in  which  the  bases  have  been  concentrated  near 
the  walls  by  Soret's  or  some  other  principle,  and  a  stream  of 
sulphuretted  hydrogen  and  sulphurous  anhydride  gases  finds 
a  way  of  escape  along  the  contact,  the  sulphides  would  form  in 
the  order  indicated  above.  This  should  give,  in  order,  the 
sulphides  of  iron,  copper,  and  nickel.  Professor  Kemp,  how- 
ever, recognizes  that  in  this  case  nickel  should  be  associated 
with  the  copper,  not  the  iron  sulphide. 

Professor  Vogt's  views  on  this  subject  are  well  known.35  He 
considers  that  on  account  of  the  close  chemical  and  mineral- 
ogical  relations  of  these  deposits  the  world  over,  they  can  be 
explained  only  by  a  common  general  chemical  process.  He 
also  emphasizes  the  fact  that  there  is  a  regular  transition  from 
the  pure  ore,  on  the  one  hand,  to  normal  rock,  on  the  other,  by 
a  gradual  decrease  of  sulphides.  He  claims  further  support 
for  his  theory  in  the  facts  that  titaniferous  magnetite  is  often 
present  in  the  ore;  that  the  platinum-metals,  which  are  re- 
garded as  essentially  of  igneous  origin,  are  found  in  Sudbury; 
and  that  eruptive  magmas  can  dissolve  considerable  quantities 
of  sulphides.  The  last  seems  to  be  shown  by  the  fact  that  basic 
blast-furnace  slags  often  contain  from  3  to  5  per  cent,  of  CaS 
and  MnS ;  from  4  to  6  per  cent,  of  FeS ;  and  from  6  to  8  per 
cent,  of  ZnS,  etc.  His  conclusion  is  that  the  sulphides  are  un- 
doubtedly derived  from  original  eruptive  magmas  by  a  process 
of  differentiation  according  to  Soret's  principle,  influenced  by 
other  factors,  of  which  gravity  may  be  important. 

T.  L.  Walker 36  says  that  near  the  nickel-deposits  the  basic 
eruptives  are  more  or  less  completely  altered  by  metamorphism, 
while  farther  away  the  change  is  less,  till  practically  unaltered 
rock  is  found.  He  also  brings  out  the  very  important  fact  that 
some  at  least  of  the  granites,  in  contact  with  the  nickel-bearing 
greenstones,  formerly  held  to  be  of  Lauren tian  age,  are  really 
younger  than  the  greenstones.  This  is  well  seen  at  the  Murray 
mine,  where  the  "  younger  granite  "  sends  apophyses  into  the 
surrounding  greenstones. 

35  Sulphidische  Ausscheidungen  von  Nickelsulphiderzen.  Zeitschrift  fur  prak- 
tische  Geology,  vol.  i.,  No.  4,  p.  125  (Apr.,  1893). 

56  Geological  and  Petrographical  Studies  of  the  Sudbury  Nickel  District.  Quar- 
terly Journal  of  the  Geological  Society,  vol.  liii.,  No.  209,  p.  40  (Feb.,  1897). 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  485 

Breccias  are  also  formed  in  places  by  the  inclusion  of  angu- 
lar fragments  of  greenstone  in  the  granite.  Similar  examples 
are  seen  in  the  granites  south  of  the  Blezard  mine  and  the 
coarse-grained  gneiss  north  of  the  Copper  Cliff,  which  is  essen- 
tially the  same  rock. 

In  direct  opposition  to  the  views  of  Professor  Vogt,  another 
eminent  European  geologist,  Prof.  R.  Beck37  (Freiberg),  may 
be  quoted.  Professor  Beck  in  his  admirable  work  on  ore- 
deposits  (Fig.  18)  pictures  a  polished  section  of  mixed  ore  and 
rock  from  the  Murray  mine,  near  Sudbury,  showing  its  brec- 
ciated  nature.  Such  an  association,  he  claims,  could  not  result 
from  a  direct  magmatic  segregation,  but  must  have  been  due 
to  a  separation  of  the  ore,  during  or  after  the  metamorphism. 

Speaking  of  the  Norwegian  nickel-deposits,  Professor  Beck 
says  there  are  weighty  considerations  opposed  to  the  theory  of 
a  direct  igneous  origin  of  the  ores. 

1.  On  physical  grounds  it  is  very  difficult  to  understand  how 
the  molten  sulphides  penetrated  so  far  into  the  cool,  surround- 
ing rocks  (schists)  as  Yogt  figures  it. 

2.  On  the  basis  of  a  microscopical  examination  of  the  ore, 
he  considers  that  the  corrosion  of  the  residue  of  the  rock- 
minerals  in  the  ore  is  due  to  solution  by  water,  especially  as 
most  of  the  ore  occurs  in  very  strongly  metamorphosed  parts 
of  the  gabbro,  and  that  here  the  ore-separation  appears  later 
than  the  metamorphism.    In  Figs.  16  and  17 38  the  relations  are 
shown.     The  gabbro  and   norite,  associated  with   the  ore,  is 
nearly  always  changed  to  amphibolite,  or-  garnet-amphibolite, 
and  the  ore  seems  to  have  followed  the  metamorphic  changes, 
or  in  some  cases  to  have  been  contemporaneous  with  them. 
The  conclusion  is  that  the  important  concentration  of  the  ore 
took  place  daring  the  regional  metamorphism,  and  later  by  the 
aqueous  method. 

Posepny,39  referring  to  the  Sudbury  ore-bodies,  claims  that  an 
igneous  origin  is  a  "  chemical  impossibility."  But  the  conten- 
tion is  not  borne  out,  when  we  consider  that  pyrrhotite  is  one 
of  the  commonest  of  the  early  crystallizations  from  the  gabbro 
magma. 

37  Lehre  von  den  Erzlagerstdtten  (1901). 

38  Op.  tit,  pp.  41  and  42. 

39  The  Genesis  of  Ore-Deposits,  p.  146  (1902). 


486 

S.  F.  Emmons40  is  of  the  opinion  that  the  ore  has  been  con- 
centrated by  percolating  waters  along  lines  of  faulting  and 
brecciation. 

The  Rossland  Pyrrhotite-Deposits. 

By  way  of  comparison,  a  word  about  the  Rossland,  B.  C., 
pyrrhotites  may  not  be  out  of  place.  The  writer  has  to  thank 
R.  "W.  Brock,  of  the  Geological  Survey  of  Canada,  who  has 
been  one  of  the  chief  workers  in  this  province,  for  the  latest 
data. 

The  ore-bodies  here,  while  not  carrying  nickel  in  any  quan- 
tity, have  the  same  general  associations  as  at  Sudbury;  and  it 
is  now  fully  established  that  they  are  of-  secondary  aqueous 
origin. 

During  the  trial  of  the  suit  of  the  Iron  Mask  Mining  Co. 
against  the  Centre  Star  Co.,  in  1899,  evidence  was  submitted 
by  Messrs.  Clarence  King,  Waldemar  Lindgren,  and  R.  "W. 
Raymond  as  to  the  nature  of  these  deposits.41 

Stated  briefly,  the  Rossland  district  forms  part  of  a  huge  sys- 
tem, reaching  from  Cape  Horn  to  the  Arctic,  and  has  been 
involved  in  the  enormous  dynamic  and  volcanic  effects  which 
this  region  has  undergone  from  early  geological  times.  Follow- 
ing the  folding  of  the  dynamic  periods,  the  deposition  of  min- 
eral matter  in  the  fissures  and  along  lines  of  weakness  took 
place.  In  connection  with  most  of  the  ore-bodies  three  types 
of  rocks  are  represented. 

1.  A  monzonite,  often  carrying   pyrrhotite,  and  with   the 
original  structure  more  or  less  obliterated. 

2.  A  darker,  coarser-grained  rock  of  the  gabbro  family,  con- 
sisting of  augite  and  triclinic  feldspar,  with  little  or  no  ortho- 
clase. 

3.  The  third  is  composed  largely  of  hornblende  and  orthoclase. 
These  types  are  doubtless  local  variations  of  the  same  magma, 

but  of  successive  flows. 

The  veins  are  considered  as  distinctly  of  the  fissure-type,  and 
many  of  them  are  of  the  "shear-zone"  variety — i.  e.,  consist- 
ing of  a  number  of  more  or  less  parallel  seams,  with  little  dis- 
placement and  no  open  fissures.  The  depth  of  the  fissuring 

40  Geological  Distribution  of  the  Useful  Metals  in  the  United  States,  p.  65,  this 
volume. 

41  Records  of  the  Supreme  Court  of  British  Columbia,  1899. 


THE    ORE-DEPOSITS    OF   SUDBURY,  ONTARIO. 


487 


FIG.  1. — MOUNT  NICKEL  MINE. 
Photograph  of  polished  section  of  ore. 
The  light  is  chalcopyrite  and  pyrrhotite  ; 
the  dark  is  gangue  and  rock.   .  Slightly 
enlarged. 


FIG.  2. — MOUNT  NICKEL,  MINE. 
Photograph  of  polished  section  of  ore  and 
rock,  showing  brecciated  character.    Slightly 
enlarged. 


FIG.  3. — MOUNT  NICKEL  MINE. 
Polished  section   of  massive  ore  with 
unreplaced  rock  (dark).     Pyrrhotite  and 
chalcopyrite  indistinguishable  in  the  pho- 
tograph.    Slightly  enlarged. 


FIG.  4. — STOBIE  MINE. 

Photograph  of  polished  section  of  ore  (light), 
with  angular  and  rounded  rock-fragments  (dark). 
Slightly  enlarged. 


488 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


FIG.  5. — MOUNT  NICKEL  MINE. 
Photomicrograph  of  rock  containing  ore, 
showing  the  ore  in  parallel  veinlets 
through  the  rock-minerals.  The  white  is 
feldspar  containing  ore  (dark),  and  granu- 
lar and  fibrous  hornblende  and  hyper- 
sthene  (shaded).  Field,  2.5  mm. 


FIG.  6. — STOBIE  MINE. 
Photomicrograph  of  ore-rock.    The  dark 
is  ore  in  veinlets,  etc.     The  white  is  feld- 
spar, and  the  shaded  is  hypersthene,  often 
with  ore  in  the  cleavages.    Field,  2.5  mm* 


FIG.  7/— MOUNT  NICKEL  MINE. 
Drawn  from  blue-print  of  photomicro- 
graph, showing  the  ore  in  veinlets  through 
the  rock-minerals.  The  dark  is  mostly 
pyrrhotite,  the  white  is  feldspar,  and  the 
shaded  is  hypersthene.  Field,  2.5  mm. 


FIG.  8. — STOBIE  MINE. 
Drawn  from  blue-print  of  photomicro- 
graph, showing  the  ore  (dark)  sharply 
outlined  against  the  fresh  hypersthene- 
(shaded)  and  feldspar  (white),  and  enter- 
ing  the  cleavages.  Field,  2.5  mm. 


THE   ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


489 


FIG.  9. — ELSIE  MINE. 
Photograph  of  polished  section  of 
ore  (light),  showing  the  irregular,  vein- 
like  replacement  of  the  rock  (dark). 
Slightly  enlarged. 


FIG.  10.— COPPER  CLIFF  MINE. 
Photograph  of  polished  section  of 
ore,  showing  the  vein-like  character 
of  the  sulphides.  The  pyrrhotite  has 
been  touched  out  with  Chinese  white 
to  form  a  contrast  with  the  chalcopy- 
rite  (dark).  Slightly  enlarged. 


FIG.  11. — COPPER  CLIFF,  No.  2,  MINE. 

Photograph  of  polished  section  of  ore  and  rock,  showing  the  brecciated 
character,  and  the  vein-like  nature  of  the  ore  (light),  and  the  centers  of  un- 
replaced  rock  (dark).  The  sulphides  are  brought  out  by  touching  up  with 
Chinese  white.  Slightly  enlarged. 


490 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


FIG.  12. — ELSIE  MINE. 
Photomicrograph  of  ore-rock,  showing 
altered  feldspar  (white)  with  parallel  vein- 
lets  of  ore  (dark)  and  irregular  patches  of 
pale-green  hornblende  (shaded).  Field, 
2.5  mm. 


FIG.  13.— COPPER  CLIFF,  No.  2,  MINE. 

Photomicrograph  of  ore-rock,  showing 
ore  (dark)  replacing  fibrous  and  granular 
hornblende  (shaded),  and  entering  cracks 
and  cleavages.  The  white  is  feldspar  and 
quartz.  Field,  2.5  mm. 


FIG.  14. — CREIGHTON  MINE. 
Drawn  from  blue-print  of  photomicro- 
graph, showing  the  ore  in  veinlets,  through 
altered  hornblende,  chlorite,  and  biotite 
(shaded).  The  white  is  feldspar  and  quartz. 
Field,  2.5  mm. 


FIG.  15. — VICTORIA  MINE. 
Drawn  from  blue-print  of  photomicro- 
graph, showing  sulphides  (dark)  between 
and  surrounding  fibers  of  hornblende  and 
biotite  (shaded),  and  entering  cleavages. 
The  white  is  quartz  and  feldspar.  Calcite 
is  also  present.  Field,  2.5  mm. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


491 


FIG.  16. — GERTRUDE  MINE. 
Drawn   from  blue-print  of  photomicro- 
graph, showing  the  sulphides  (dark)  parallel 
to  the  fibers  of  the  hornblende  (shaded). 
The  white  is  feldspar.     Field,  2.5  mm. 


FIG.  17. — GERTRUDE  MINE. 
Drawn  from  blue-print  of  photomicro- 
graph, showing  sulphides  (dark)  parallel 
to  the  cleavages  of  the  fibrous  hornblende 
(shaded),  and  following  the  changes  of  di- 
rection. Field,  2. 5  mm. 


FIG.  18. — CREIGHTON  MINE. 
Photomicrograph  of  ore  with  small  resi- 
dues of  hornblende,  feldspar,  and  quartz, 
partly  replaced.     Field, -2.5  mm. 


FIG.  19. — GERTRUDE  MINE. 
Photomicrograph  of  ore-rock,  with  ore 
(dark)  replacing  the  hornblende  and  bio- 
tite  (shaded)  along  cracks  and  cleavages. 
The  white  is  feldspar  and  quartz.  Field, 
2.5  mm. 


492 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


FIG.  20. — GERTRUDE  MINE. 

Photograph  of  polished  section  of  ore,  showing  unreplaced  rock  (dark). 
The  light  is  pyrrhotite  and  the  shaded  is  chalcopyrite.  Slightly  en- 
larged. 


FIG.  21* — CREIGHTON  MINE. 

Photograph  of  polished  section  of  ore,  showing  the  vein-like  nature 
of  the  sulphides.  The  light  is  pyrrhotite  and  the  dark  is  chalcopyrite. 
Slightly  enlarged. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


493 


FlG.   22. — WORTHINGTON    MlNE. 

Photograph  of  polished  section  of  ore,  showing  irragular  patches  of 
unreplaced  schistose  rock.     Slightly  enlarged. 


FIG.  23. — WORTHINGTON  MINE. 

Photograph  of  polished  section  of  ore,  showing  round  and  angular 
fragments  of  unreplaced  rock.     Slightly  enlarged. 


494 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 


FIG.  24. — COPPER  CLIFF  MINE. 

Drawn   from    blue-print   of    photomicrographs,    showing  ore    (dark) 
between  the  grains  and  fibers  of  the  rock-minerals.     Field,  2.5  mm. 


FIG.  25. — PHOTOMICROGRAPH  OF  ORE  FROM 

THE  EAST  TENNESSEE  MINE. 
The  white  mineral  is  calcite.    The  dark  min- 
eral is  chalcopyrite,  which  has  entered  cracks 
and  fissures  in  the  calcite.    Magnified  40  diame- 
ters. 


FIG.  26. — PHOTOMICROGRAPH  OF  ORE  FROM 

THE  EAST  TENNESSEE  MINE. 
The  white  mineral  is  actinolite.  The  dark 
mineral  is  chalcopyrite,  which  has  filled  even 
minute  cracks  in  the  shattered  actinolite  and 
has  replaced  it  when  crushed  and  altered. 
Magnified  17.3  diameters. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  495 

permitted  a  circulation  of  deep-seated  thermal  waters  and  a 
deposition  of  the  chemicals  carried  in  solution  along  the  lines 
of  weakness  by  a  decomposition  and  replacement  of  the  rock- 
minerals.  The  final  result  is  either:  (1)  a  deposition  of  the 
ore  on  one  plane  or  fissure  of  the  "  shear-zone,"  or  (2)  a  re- 
placement of  the  rock  between  two  planes,  or  (3)  the  replace- 
ment of  a  whole  zone,  and  so  on  with  endless  variations.  The 
replacement  of  the  rock-minerals  by  ore  (largely  chalcopyrite 
and  pyrrhotite)  took  place  molecule  by  molecule,  producing 
what  is  really  a  pseudomorph.  The  replacement  is  well  seen 
near  the  Iron  Horse  mine,  where  large  diallages  or  augites  have 
changed  to  ore,  while  the  surrounding  country-rock  was  only 
partly  transformed. 

The  replacement  has,  at  times,  been  so  intense  that  an  almost 
solid  body  of  sulphides  (with  quartz  and  calcites)  results.  In 
other  places  the  original  rock,  more  or  less  modified  and  silici- 
fied,  has  been  only  partly  replaced  and  impregnated  with  ore. 

Messrs.  King,  Lindgren,  and  Raymond  were  practically  unan- 
imous in  their  interpretation  of  the  phenomena  of  the  district, 
which  agrees  very  closely  with  that  of  the  Canadian  Geological 
Survey,  though  the  more  recent  work  shows  that  slight  modi- 
fications of  the  rock  relations  are  necessary. 

Briefly,  the  geology  and  relative  ages  of  the  rocks  of  the 
mining-district  are  as  follows  : 42 

1.  The  oldest  series  represented  is  classed  as  the  Kootenay 
volcanic  group,  consisting  of  augite-porphyrites,  tuffs,  ash-beds, 
etc.,  of  Palaeozoic  age. 

2.  Next  comes  a  granite  or  grano-diorite  (Nelson  granite), 
probably  Jurassic. 

3.  The  Rossland  monzonite,  probably  post-Jurassic. 

4.  Conglomerate,  probably  Tertiary. 

5.  Alkali  (Rossland)  granite  and  syenite. 

The  ores  may  occur  in  any  of  the  rocks  older  than  the  alkali 
granite.  This  granite,  whose  main  development  is  outside  the 
limit  of  the  Trail  Creek  sheet,  is  probably  a  Tertiary  eruptive, 
and  its  dikes  have  penetrated  all  through  the  Rossland  district. 

As  it  happens,  the  principal  mineralization  is  in  the  augite- 
porphyrites  and  monzonite,  probably  on  account  of  the  fractur- 

42  See  Trail  Creek  map  (1897),  and  Summary  Reports  ( 1896-1900)  of  the  Geological 
Survey  of  Canada. 


496  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

ing  and  cutting  of  these  rocks  by  dikes,  together  with  their 
relative  solubility.  The  chief  factor  controlling  the  location  of 
the  mineralization  seems  to  have  been  the  alkali-granite  contact 
and  its  system  of  dikes,  the  eruption  of  which  immediately  pre- 
ceded the  formation  of  the  ore-bodies.  The  deposits  are  found 
where  the  dikes  are  particularly  abundant. 

The  monzonite  is  the  chief  center  of  mineralization,  but  it 
is  not  to  be  considered  as  a  volcanic  neck,  with  the  augite  por- 
phyrites  and  tuffs  as  part  of  the  cone.  These  latter  are  much 
older  and  are  cut  by  the  Nelson  granite.  The  occurrence  of 
the  ore  has  no  relationship  to  the  contact  of  the  monzonite, 
being  found  both  outside  and  inside  its  boundaries  and  in  the 
younger  rocks. 

While  magmatic  differentiation  has  gone  on  to  some  extent, 
the  sulphides  are  not  the  result  of  it,  as  is  proved  definitely  by  the 
work  of  the  Survey. 

A  peculiarity  of  the  rocks  in  which  the  ore  occurs  is  that, 
while  sheared  and  fractured,  they  are  not  brecciated,  the  dy- 
namic movement  having  doubtless  taken  place  under  an  im- 
mense load. 

With  reference  to  the  ore-bodies  themselves,  some  interest- 
ing points  are  brought  out.  The  ore  replaces  the  country-rock, 
partly  or  completely,  starting  from  some  fissure  or  line  of  fis- 
sures and  often  fading  out  gradually,  the  only  "  wall "  being  a 
commercial  (economic)  boundary.  It  may  end  abruptly  at  a 
fissure,  in  some  cases  due  to  a  slip,  which  brought  an  unminer- 
alized  face  against  the  ore. 

Deposits  very  similar  to  those  in  the  eruptives  are  found  in 
the  conglomerate  (No.  4),  which  cannot  be  regarded  in  any 
other  way  than  as  of  secondary  origin. 

The  marked  similarity  of  the  geological  relations  in  Rossland 
and  Sudbury  helps  to  make  clear  some  of  the  more  obscure 
points  in  the  latter  district.  As  the  conditions  of  metamor- 
phism,  however,  were  not  identical,  the  dynamic  movements 
have  manifested  themselves  in  different  ways,  and  it  is  not  sur- 
prising that  there  should  be  striking  dissimilarities.  This  dif- 
ference is  seen  in  the  characteristic  structures  of  the  ore-bodies 
in  the  two  districts.  In  Rossland,  the  fissure  or  shear-zone  type 
of  vein  is  predominant,  with  little  or  no  sign  of  brecciation. 
In  Sudbury,  on  the  other  hand,  where  the  dynamical  move- 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  497 

ments  probably  took  place  under  a  very  small  load,  a  breccia- 
tion  from  faulting  on  a  large  scale,  and  probably  with  consid- 
erable movement,  is  characteristic.  This  will  be  brought  out 
more  clearly  in  speaking  of  the  individual  deposits. 

This  brief  review  indicates  the  wide  differences  of  existing 
opinion  as  to  the  origin  of  pyrrhotite  and  the  various  interpre- 
tations which  have  been  put  upon  the  same  phenomena. 

Microscopical  Evidence  of  the  Origin  of  the  Ores. 

The  evidence  on  which  the  secondary  nature  of  these  ores  is 
here  advocated  is  mostly  altogether  different  in  character  from 
that  already  presented.  It  consists  in  the  relations  between 
the  ores  and  the  rock-minerals,  brought  out  by  microscopical 
examination.  As  no  investigation  of  this  kind  has  been  pre- 
viously made,  the  results  will  be  given  in  some  detail.  Mate- 
rial from  all  the  principal  mining-locations  has  been  studied, 
in  order  to  avoid  laying  too  much  stress  on  local  phenomena 
and  to  emphasize  the  genetic  similarity  of  all  the  deposits  of 
the  district.  The  character  of  the  ore-bodies  in  a  large  way 
will  also  be  briefly  noted  as  throwing  much  light  on  the  gen- 
eral nature  of  the  deposits. 

Sudbury  District. — The  following  separate  localities  in  this 
district  will  represent  its  character : 

1.  Mount  Nickel  Mine,  Blezard  Township. — The  ore  con- 
sists of  pyrrhotite  (both  coarse-  and  fine-grained)  and  a  smaller 
amount  of  chalcopyrite,  through  which  occur  masses  of  almost 
barren  rock,  varying  in  size  from  minute  particles  to  large 
"  boulders,"  or  "  horses."  Near  what  is  considered  as  the  foot- 
wall,  the  chalcopyrite  increases  in  amount  and  the  proportion 
of  barren  rock  is  greater. 

The  deposit  is  a  good  example  of  what  is  best  described  as 
a  "  breccia  ore-body."  Rounded  and  angular  rock-fragments  of 
all  sizes,  with  sulphides  as  a  cementing  material,  are  every- 
where a  striking  characteristic.  Besides  the  brecciation  as  a 
whole,  the  rock  is  often  broken  and  fractured,  and  little  seams 
and  veinlets  of  ore  occur  all  through  it  in  a  very  typical 
manner. 

In  some  of  the  open-cuts  the  ore  is  seen  to  run  in  particular 
streaks  or  bands,  and  may  end  very  abruptly  against  barren 
rock. 


498  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

The  brecciated  character,  as  it  is  seen  in  a  large  way,  is  also 
faithfully  reproduced  in  hand-specimens.  Figs.  1,  2,  and  3, 
from  photographs  of  polished  sections,  show  these  features 
very  well. 

While  brecciation  is  one  of  the  most  striking  characteristics 
of  the  deposit,  evidences  of  faulting  and  shearing  are  not  want- 
ing in  the  slickensided  and  schistose  nature  of  some  of  the 
rocks.  There  are  a  number  of  clayey  seams,  and  some  of  the 
samples  are  decidedly  fibrous.  Along  certain  of  the  lines  of 
crushing  the  rock  is  partly  brecciated  and  partly  slickensided, 
and  here  the  ore  occurs  in  veinlets  and  as  a  cement  for  the 
rock-fragments. 

Under'the  microscope,  the  rock  associated  with  the  ore  is 
black  and  dense,  and  belongs  to  the  gabbro  family.  Hyper- 
sthene  in  fresh  idiomorphic  grains  is  very  abundant,  while 
augite  and  diallage  are  in  subordinate  amount.  The  pyroxenes 
have,  in  part,  been  altered  to  green  fibrous  hornblende.  The 
feldspar  forms  an  irregular  mosaic,  among  the  grains  of  which 
are  fragments  of  hypersthene.43  Biotite  and  quartz  are  spar- 
ingly present. 

The  relations  of  the  sulphides  to  the  rock-minerals  are  well 
shown.  Where  the  pyroxene  is  somewhat  altered  it  becomes 
fibrous ;  and  here  the  sulphides  are  best  developed. 

Chalcopyrite  and  pyrrhotite  form  numerous  veinlets  between 
the  fibers  and  cleavages  of  the  rock-minerals.  In  places,  where 
not  too  massive,  the  sulphides  reproduce  very  faithfully  the 
fibrous  structure  of  the  hornblende,  though  little  of  this  min- 
eral may  remain,  so  that  really  a  pseudomorph  results.  In  one 
place  or  another  all  stages  of  replacement  can  be  seen,  from  a 
few  dust-like  particles  of  sulphides  in  the  hornblende  to  com- 
plete replacement.  Where  the  pyroxene  is  fresh,  the  sulphides 
are  outlined  sharply  against  its  margin,  and  only  enter  cleav- 
ages. In  this  way  grains  of  pyroxene  are  more  or  less  com- 
pletely isolated.  Figs.  5  and  7  show  veinlets  of  sulphides 
through  the  fibrous  minerals. 

The  relations  seem  to  indicate  a  crushed  zone,  in  which  the 
feldspar  has  yielded  and  formed  a  mosaic,  and  along  which  the 
solutions  carrying  the  sulphides  have  acted ;  the  greater  the 

43  The  rocks  from  all  the  localities  examined  show  a  more  or  less  pronounced 
migration  of  the  dark  silicates,  especially  secondary  hornblende,  into  the  feldspar. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  499 

alteration  of  the  rock,  the  more  complete   being  its  replace- 
ment. 

2.  Blezard  (Dominion)  Mine,  Blezard  Township. — The  char- 
acter of  the  deposit  is  very  similar  to  that  of  the  Mount  Nickel, 
showing  the  same  brecciation  and  shearing.     Under  the  micro- 
scope, however,  the  rock  shows  a  more  advanced  stage  of  alter- 
ation than  that  of  Mount  Nickel.     The  pyroxene  has  changed 
to  greenish  fibrous  hornblende  and   chlorite,  which,  in  some 
cases,  makes  up  nearly  the  whole  rock.     The  feldspar  is  largely 
labradorite,  and  often  contains  irregular  fibers  of  hornblende. 
The  pyrrhotite  forms  reticulating  networks  among  the  horn- 
blende fibers,  the  veinlets  of  ore  lying  parallel  to  the  fibers. 

3.  Stobie  Mine,  Blezard   Township. — The  brecciated  char- 
acter is  here  very  pronounced,  and  the  ore  contains  a  large  pro- 
portion of  barren  rock-masses  of  all  sizes,  as  usual  filled  around 
with  sulphides.    Fig.  4  shows  the  prevailing  nature  of  the  more 
massive  ore,  with  its  residual  angular  and  rounded  rock-frag- 
ments. 

Under  the  microscope,  sections  of  rock,  with  a  small  pro- 
portion of  ore,  are  made  up  largely  of  a  fine-grained  mixture 
of  plagioclase  (labradorite  and  anorthite)  and  hypersthene,  with 
small  amounts  of  augite,  diallage,  and  biotite ;  and  magnetite, 
apatite,  and  zircon  as  accessories.  Quartz,  in  varying  amount, 
is  also  characteristic.  The  hypersthene  is  quite  abundant,  and 
forms  idiomorphic  and  rounded  grains  and  irregular  aggre- 
gates; it  shows  the  usual  microscopical  characters  of  this  min- 
eral. The  pyroxenes  are,  as  a  rule,  quite  fresh,  but  form  a  mo- 
saic with  the  feldspar,  probably  due  to  crushing.  Along  certain 
lines,  however,  the  pyroxenes  have  altered  to  a  pale-green 
uralitic  hornblende  or  chlorite. 

The  relations  of  the  sulphides  to  the  rock-minerals  are  strik- 
ing. Following  the  direction  of  the  altered  zones,  the  sulphides 
are  most  prominently  developed.  A  veinlet  of  chalcopyrite 
€an  be  traced  across  one  of  the  sections,  following  the  cleavages, 
and  between  the  fibers  of  hornblende  and  around  the  fresher 
grains  of  the  other  minerals  (Fig.  6).  In  other  cases  the  partly- 
altered  pyroxene  has  been  more  or  less  replaced  by  ore,  the  par- 
ticles of  which  are  elongated  in  the  direction  of  the  cleavages, 
and  follow  these  even  when  they  change  their  direction  ab- 
ruptly. When  found  in  connection  with  the  fresher  grains,  the 


500  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

sulphides  simply  inclose  them,  following  their  irregularities  and 
larger  cleavages  (Fig.  8). 

An  increasing  proportion  of  ore  is  accompanied  by  a  corre- 
sponding change  in  the  character  of  the  rock.  The  pyroxenes 
decrease  notably  in  quantity  and  finally  disappear,  giving  place 
to  secondary  green  hornblende,  chlorite,  and  biotite.  Both 
hornblende  and  biotite  are  fibrous,  and  often  show  deformation, 
due  to  strain.  The  hornblende  and  other  secondary  products, 
in  their  turn,  disappear  as  the  ore  increases,  and  various  stages 
of  their  replacement  can  be  traced  from  an  almost  pure  silicate, 
containing  a  few  specks  of  ore,  to  pure  sulphide.  In  interme- 
diate cases  the  sulphides  may  preserve  very  perfectly  the 
fibrous  structure  of  the  hornblende  or  biotite,  with  little  shreds 
of  the  mineral  marking  its  original  form.  In  purer  ore,  still, 
the  dark  silicates  disappear  almost  entirely,  and  the  feldspar  is 
filled  with  inclusions  of  ore  and  changed  to  a  confused  aggre- 
gate of  secondary  products. 

In  the  latter  cases  the  amount  of  quartz  has  increased  nota- 
bly and  remains  as  clear  irregular  patches  through  the  ore. 

4.  Frood,  or  No.  3  Mine,  McKim  Township. — The  ore  con- 
sists of  coarse-  and  fine-grained    pyrrhotite  and  chalcopyrite. 
The  latter  at  times  occurs  in  almost  pure  masses,  and  is  most 
abundant  towards  the  walls.     Barren  rock-fragments  occur  all 
through  the  ore-body,  presenting  the  usual  breccia,  cemented 
by  sulphides. 

Microscopic  sections  show  that  the  rock  has  undergone  con- 
siderable alteration.  No  traces  of  original  pyroxene  could  be 
found.  The  secondary  hornblende  is  bleached  and  ragged, 
and  is  intimately  associated  with  the  sulphides,  as  is  the  biotite, 
which  is  also  plentiful.  Feldspar  in  many  cases  is  subordinate, 
while  there  is  a  notable  amount  of  clear  quartz,  which  is  ap- 
parently secondary.  Calcite  also  appears  in  small  quantities. 
The  sulphides  are  always  found  in  connection  with  the  dark 
silicates,  and  replace  them  to  a  greater  or  less  extent. 

5.  Elsie  Mine,  Snider  Township,  and  Murray  Mine,  McKim 
Township. — The  ore-body  (Elsie)  is  situated  well  within  the 
basic  rocks,  the  granite  contact  being  some  distance  off.     The 
ore  is  largely  pyrrhotite,  with  a  varying    amount  of  chalco- 
pyrite, which  increases  towards  the  foot-wall.     The  ore  is  in 
places  largely  mixed  with  rock  and  may  become  subordinate 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  501 

in  amount,  even  in  the  midst  of  the  deposit.  Nearly  every 
piece  of  ore  shows  a  characteristic  breccia  of  rock  in  a  matrix 
of  sulphides,  the  rock  being  either  practically  barren  or  having 
veinlets  of  mineral  irregularly  through  it  (Fig.  9).  There  are 
many  evidences  of  movement,  as  shown  by  the  numerous  clay 
seams  impregnated  with  sulphides  and  in  the  schistose  and 
slaty  character  of  the  gabbro,  which  is  often  polished  and 
slickensided.  There  are  also  examples  of  what  appear  to  be 
fault-planes  and  fissures,  filled  with  a  mixture  of  tremolite, 
quartz,  calcite,  and  ore,  the  latter  very  evidently  having  been 
introduced  subsequent  to  the  movement.  The  structure  at  the 
Murray  mine  is  very  similar  to  that  at  the  Elsie,  except  that 
the  granite  contact  is  close  to  the  ore-body.  The  granite  pierces 
the  associated  "  greenstones  "  (altered  sediments  ?)  and  is  un- 
doubtedly younger. 

Microscopic  sections  of  rock  with  a  large  amount  of  ore  show 
that  most  of  the  pyroxenes  have  changed  to  green  fibrous  horn- 
blende, though  original  hypersthene  more  or  less  altered  is  still 
recognizable.  The  feldspar  is  much  crushed,  and  is  in  an  ad- 
vanced stage  of  alteration,  and  often  contains  hornblende  fibers, 
and  parallel  veinlets  of  pyrrhotite  along  the  cleavages  (Fig.  12). 

The  relation  of  the  sulphides  to  the  rock-minerals  is  of  the 
usual  type,  i.e.9  the  replacement  proceeds  along  and  between  the 
hornblende  fibers  and  lines  of  weakness  and  cleavage  in  other 
minerals. 

6.  Mines  Around  Copper  Cliff  in  Snider  and  McKim  Town- 
ships.— This  group  includes  the  following  mines  of  the  Cana- 
dian Copper  Co. :  Copper  Cliff",  No.  1,  No.  2,  No.  4,  and  No.  5, 
in  different  stages  of  development.  Some  of  the  deposits  are 
entirely  surrounded  by  "  greenstones,"  while  others  have  the 
granite-gneiss  as  one  of  the  so-called  "  walls."  Dr.  Barlow,  of 
the  Geological  Survey  of  Canada,  is  of  the  opinion  that  the 
ore-bearing  norite  often  occurs  in  more  or  less  completely  iso- 
lated passages  in  the  "  greenstones,"  and  may  consist  almost 
entirely  of  ore. 

No.  2  mine  (and  extension)  affords  a  typical  example  of  the 
"  breccia  ore-body."  The  contact  is  right  at  the  granite,  and 
the  ore-bearing  rock  has  numerous  small  dikes  of  the  latter 
through  it,  and  in  this  case,  at  least,  it  seems  to  be  indisputa 
ble  that  the  granite  is  the  younger.  Near  the  contact  the 


502  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

granite  contains  a  small  amount  of  ore,  and  samples  at  times 
consist  of  both  acid  and  basic  rock  impregnated  with  sulphides. 
The  brecciated  structure  is  very  pronounced,  and  veinlets  of 
ore  occur  everywhere  through  the  rock  (Fig.  11).  There  is 
also  evidence  of  shearing,  and  secondary  quartz-stringers  are 
common. 

The  Copper  Cliff  mine  belongs  to  the  same  brecciated  type 
and  has  yielded  a  large  number  of  minerals  of  secondary  origin. 
(See  Part  I.) 

No.  1  mine  in  places  exhibits  a  very  abrupt  transition  from 
rich  ore  to  barren  rock.  A  short  distance  from  the  ore-body 
the  rock  is  slightly  mineralized,  but  on  a  close  examination  it 
is  seen  that  the  ore  always  occurs  in  small  crevices  or  parting- 
planes,  or  other  lines  of  weakness. 

Under  the  microscope,  thin  sections  show  that  the  rock 
varies  from  an  almost  pure  hornblende  variety,  with  other 
minerals  in  subordinate  amount,  to  more  acid  varieties,  but  in 
all,  the  dark  silicates  are  in  excess.  Nearly  all  the  pyroxene 
has  been  altered  to  fibrous  green  hornblende,  though  in  some 
sections  traces  still  remain.  Quartz  is  often  quite  abundant, 
and  the  usual  accessories  are  present.  The  granular  nature  of 
the  feldspar,  and  the  bent  and  twisted  hornblende  and  biotite, 
indicate  severe  crushing.  The  sulphides  abut  sharply  against 
the  fresher  minerals,  but  when  they  are  fibrous  and  broken, 
they  tend  to  occur  between  the  fibers  and  grains,  more  or  less 
complete  replacement  resulting.  (Fig.  13). 

As  the  amount  of  ore  increases,  the  dark  silicates  disappear 
largely,  leaving  areas  of  clear  quartz  and  feldspar,  with  the 
ore  sharply  defined  against  their  boundaries  (Fig.  24).  Where 
the  effects  of  crushing  are  most  pronounced,  the  sulphides  are 
best  developed,  and  then  the  replacement  extends  from  these 
centers  along  the  cleavages  and  between  the  hornblende  fibers,, 
resulting  in  a  more  or  less  complete  substitution  of  ore. 

7.  Creighton  Mine,  Near  the  Boundary  Between  Snider  and 
Creighton  Townships. — This  mine,  which  has  recently  been 
developed  by  the  Canadian  Copper  Co.,  is  perhaps  one  of  the 
most  remarkable  nickel-deposits  in  the  world.  The  ore-body 
is  very  large,  and  the  ore  is  above  the  average  in  richness  and 
purity.  Mining  is  carried  on  in  a  huge  open-cut,  200  ft.  or 
more  across  and  about  100  ft.  deep,  in  solid  ore,  with  a  shaft 
from  the  bottom  of  the  pit. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  503 

The  ore,  which  is  largely  pyrrhotite  with  more  or  less  chal- 
copy  rite,  however,  contains  many  masses  of  barren  diorite 
(norite)  all  through  it,  presenting  a  very  characteristic  breccia. 
The  rock-fragments  vary  in  size  from  minute  particles  to  large 
"  boulders,"  and  are  both  rounded  and  angular.  Where  the 
ore  is  not  too  massive  to  obscure  the  relations,  it  presents  much 
the  appearance  of  a  conglomerate  cemented  by  sulphides,  with 
numerous  ramifying  veinlets  along  the  fracture-planes  of  the 
rock.  Through  the  ore-body  are  a  number  of  intrusions  of  a 
coarse  granitic  rock,  which  often  includes  fragments  of  the 
diorite  (norite)  breccia.  This  rock  is  itself  not  heavily  miner- 
alized, but  where  it  has  included  fragments  of  the  basic  rock 
these  are  more  or  less  replaced  by  ore,  and  the  replacement 
may  extend  to  the  acid  rock  itself  to  a  lesser  extent. 

From  the  evidence  collected  it  would  appear  that  this  gran- 
itic rock  had  been  intruded  into  and  had  included  fragments 
of  the  diorite  at  the  time  of,  or  after,  its  brecciation.  These 
fragments  have  then  been  partly  replaced  by  ore,  the  minerali- 
zation extending  slightly  to  the  acid  rock. 

There  are  also  two  dense  fine-grained  diabase  dikes  cutting 
sharply  through  the  ore-body  and  having  well-defined  contacts. 
These  are  considered  as  among  the  youngest  rocks  of  the  dis- 
trict. While  they  are  usually  considered  to  have  cut  through 
the  ore  after  its  formation,  there  is  a  possibility,  if  the  theory 
of  igneous  origin  is  left  out  of  the  question,  of  their  being  pre- 
vious to  the  formation  of  the  deposits. 

They  do  not  include  fragments  of  the  ore,  and  their  only 
mineralization  is  along  fissures  and  joint-planes,  the  introduc- 
tion of  the  sulphides  being  very  evidently  later  than  the  intru- 
sion. There  has  also  been  a  movement  in  the  dikes  themselves 
since  their  formation,  as  they  are  composed  of  numerous  verti- 
cal and  parallel  divisions  with  smooth  polished  faces,  along 
which  sulphides  at  times  occur.  If  the  dikes  were  in  place 
previous  to  the  formation  of  the  ore,  their  compact  fine-grained 
texture  would  be  unfavorable  to  the  action  of  the  ore-bearing 
solutions,  except  along  parting-planes,  while  the  more  coarsely 
crystalline  and  crushed  diorite  would  offer  an  easy  passage  for 
the  circulating  waters. 

No  conclusive  evidence  of  faulting  or  shearing  could  be 
found  in  the  main  pit,  but  in  several  of  the  test-pits  sunk  in 


504  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

the  vicinity,  to  determine  the  extent  of  the  ore-body,  abundant 
proof  was  available.  In  these,  the  rock  associated  with  the 
ore  has  been  severely  crushed  and  squeezed,  so  that  it  presents 
a  schistose  and  slickensided  appearance,  and  is  often  much  like 
an  amphibolite-schist,  with  seams  of  ore  on  the  parting-planes. 

If  these  pits  are  in  a  continuation  of  the  main  body  of  ore, 
as  seems  probable,  we  have  two  different  structures  resulting 
from  an  unequal  distribution  of  the  dynamic  force  which 
caused  them,  and  probably  also  due  to  local  differences  in  the 
rocks  themselves. 

In  the  neighborhood  of  the  Creighton  mine,  and  towards 
Copper  Cliff,  the  granite  frequently  cuts  the  basic  rocks  and 
sends  dikes  through  them.  What  the  relation  of  these  rocks 
is  to  the  ore-bearing  variety  could  not  be  accurately  deter- 
mined. 

Under  the  microscope,  the  diorite,  or  altered  norite,  presents 
a  somewhat  gneissoid  appearance,  with  a  large  part  of  the 
pyroxenes  altered  to  fibrous  green  hornblende  and  chlorite. 
Quartz  is  present  in  variable  amount. 

The  sulphides  (Fig.  14)  are  best  developed  where  the  effects 
of  crushing  are  most  apparent.  Some  of  the  dark  silicates 
have  altered  to  indefinite  aggregates  of  secondary  products, 
which  are  spotted  all  through  with  ore  and  may  even  be  en- 
tirely replaced.  The  veinlets  of  sulphides  typically  follow 
along  the  cleavages  of  hornblende  and  feldspar,  which  shows  in 
some  cases  an  advanced  stage  of  alteration.  Fig.  18  shows  mas- 
sive ore,  with  only  small  residues  of  unreplaced  rock-minerals. 

The  coarse  granitic  dikes  contain  abundant  quartz  and  feld- 
spar, and  where  they  include  fragments  of  the  basic  rock  these 
show  partial  replacement,  which  also  extends  to  the  minerals 
of  the  acid  rock. 

8.  Gertrude  Mine,  Creighton  Township. — Besides  the  usual 
breccia,  which  is  very  pronounced,  there  is  abundant  evidence 
of  shearing  in  the  different  deposits  under  development  (Fig. 
20).  In  No.  1  pit  the  ore  ends  very  abruptly  against  a  wall  of 
sheared  diorite,  which  is  only  slightly  mineralized  along  the 
shear-planes. 

Along  this  contact,  and  penetrating  the  rock  breccia,  a  num- 
ber of  small  granite  dikes  have  been  intruded,  which  are 
slightly  mineralized.  Sheared  diorite,  together  with  actinolite 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  505 

and  other  secondary  minerals,  impregnated  with  ore,  is  notice- 
able in  all  the  pits  which  have  been  opened  up.  As  these  pits 
are  in  line,  it  is  probable  that  the  faulting  movement  embraced 
them  all,  but  from  lack  of  exposures  between,  the  fault-line 
could  not  be  traced. 

The  brecciation  and  shearing,  as  well  as  the  intrusion  of  the 
granite,  evidently  took  place  previous  to  the  introduction  of 
the  ore,  as  all  are  more  or  less  impregnated  \vith  mineral, 
either  as  veinlets  or  between  parting-planes. 

Under  the  microscope,  the  ore- rock  is  seen  to  consist  very 
largely  of  actinolitic  and  chloritic  hornblende,  with  other  min- 
erals of  lesser  amount. 

The  relation  of  the  sulphides  to  the  rock-minerals  is  quite 
typical  (Figs.  16, 17,  and  19).  Where  the  hornblende  is  of  the 
fibrous  variety,  it  is  usually  associated  with  ore,  and  all  stages 
of  progressive  replacement  can  be  seen.  In  samples  with  a 
large  proportion  of  the  ore,  the  more  compact  grains  of  horn- 
blende, as  well  as  the  feldspar  and  quartz,  are  left  as  isolated 
patches  in  a  ground-mass  of  sulphides,  while  the  fibrous 
variety  has  nearly  all  disappeared. 

9.  Victoria  Mine,  Denison  Township. — The  ore  consists  of 
pyrrhotite,  with  chalcopyrite,  which  increases  in  quantity  to-- 
wards  the  foot-wall  in  a  typical  rock-breccia.     There  is  a  fault 
passing  through  the  deposit,  and  in  the  secondary  minerals 
formed  (actinolite,  mica,  etc.)  the  ore  occurs  in  veinlets  clearly 
later  than  the  movement.     There  is  also  a  considerable  devel- 
opment of  quartz  and  calcite  intimately  mixed  through  the 
ore,  which  cannot  be  considered  as  original  igneous  products. 

The  microscope  shows  the  ore-rock  to  be  the  usual  altered 
norite  with  the  minerals  of  a  diorite.  Green  fibrous  and  gran- 
ular hornblende  is  predominant.  One  of  the  most  noticeable 
features  is  the  large  amount  of  quartz  and  calcite  which  re- 
mains spotted  through  the  ore  when  the  other  minerals  have 
largely  disappeared.  The  replacement  of  the  hornblende  and 
biotite  by  sulphides  is  well  shown  (Fig.  15).  The  pyrrhotite 
has  many  hornblende  fibers  through  it  and  enters  the  cleavages 
of  the  other  minerals  in  a  typical  manner. 

10.  Worthington  and  Mitchener  Mines,  Drury  Township. — 
The  ore-rock  at  the  Worthington  is  bounded  on  the  south  by  a 
band  of  dark  schistose  rock  of  sedimentary  origin,  and  to  the 

32 


506  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

south  of  this  there  is  quartzite.  The  Mitchener  mine,  about 
0.5  mile  west  of  the  Worthington,  is  surrounded  by  the  quartz- 
ite. Two  varieties  of  rock  are  met  with  in  the  ore-bodies, 
namely,  coarse-  and  line-grained.  The  coarse-grained  variety 
is  sheared  and  slickensided,  and,  as  a  rule,  contains  little  ore, 
but  when  it  does,  it  is  in  the  form  of  veinlets  and  along  the 
parting-planes.  The  fine-grained  rock  has  been  brecciated, 
instead  of  sheared,  and  numerous  rock-fragments  of  different 
sizes,  surrounded  and  cemented  by  sulphides,  remain  in  the 
ore-bodies  (Figs.  22  and  23).  Through  the  ore-body  there  are 
also  numbers  of  small  lenticular  masses  of  schistose  diorite, 
giving  the  ore  somewhat  the  appearance  of  an  "  augen  "  gneiss. 
These  are  evidently  residual  portions  of  the  rock  which  have 
escaped  replacement,  and  clearly  show  that  the  introduction  of 
the  ore  was  subsequent  to  the  movement  which  caused  the 
shearing  and  brecciation. 

The  ore  at  the  Worthington  is  often  very  rich,  and  the  nickel- 
mineral  pentlandite  occurs  quite  abundantly. 

The  fault  which  occurs  at  the  Victoria  seems  to  be  continued 
through  Denison  township,  embracing  the  deposits  containing 
niccolite  and  gersdorffite,  through  the  Worthington,  and  gradu- 
ally dying  out  towards  the  Mitchener. 

Under  the  microscope,  it  is  seen  that  the  original  structure 
of  the  rock  has  been  almost  entirely  obliterated,  and  green- 
fibrous  hornblende  and  chlorite  are  the  most  abundant  minerals, 
and  often  show  the  effects  of  severe  crushing.  As  the  quan- 
tity of  ore  increases,  the  amount  of  secondary  products  (epi- 
dote,  etc.)  increases  also,  and  the  feldspar  is  more  or  less  altered 
and  peppered  with  sulphide  grains.  Quartz  is  often  present  in 
large  amount.  Progressive  replacement  can  be  traced  in  both 
the  irregular  aggregates  and  the  fibrous  masses  of  hornblende 
and  biotite.  In  many  cases,  the  introduction  of  the  sulphides 
appears  to  start  along  cleavages,  gradually  spreading  and  uniting 
till  only  isolated  patches  of  rock-minerals  remain,  or  the  whole 
may  be  replaced,  leaving  no  trace  of  the  original  structure.  In 
this  way,  reticulating  networks  of  sulphide  veinlets  form  all 
through  the  rock,  oftentimes  ramifying  through  the  areas  of 
quartz  and  separating  the  individual  grains.  Samples  of  the 
coarse  diorite  containing  ore  present  much  the  same  features — 
i.  e.j  a  branching  network  of  sulphide  veinlets  between  the 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  507 

fibers  and  along  cleavages  of  hornblende,  etc.,  and  separating 
the  different  rock-minerals. 

11.  Levack  Township  Deposits. — On  the  northwest  are  the 
large  deposits  in  Levack  township  on  the  western  side  of  the 
nickel-belt.     These  deposits  have  been  thoroughly  prospected 
and  opened  up  to  show  their  extent,  and  promise  to  be  large 
contributors  of  ore  in  the  future. 

To  the  north  and  west  the  contact  is  on  the  large  granite- 
area,  formerly  mapped  as  Laurentian,  but  which  may  prove 
to  be  much  later.  At  the  contact  the  ore-bearing  diorite  and 
granite  are  mixed  up,  and  the  acid  rock  is  impregnated  with 
ore  for  a  short  distance,  though  not  to  the  same  extent  as  the 
basic  rock. 

The  brecciated  nature  of  the  ore-body  is  very  pronounced, 
and  is  emphasized  on  the  weathered  exposures,  where  pebbles 
and  boulders  of  rock  stand  out  from  the  oxidized  sulphides  of 
the  gossan. 

The  vein-like  nature  of  the  sulphides  is  everywhere  seen, 
and  is  especially  well  shown  in  the  diamond-drill  cores. 

As  seen  under  the  miscroscope,  the  rock  consists,  as  usual, 
largely  of  secondary  fibrous  green  hornblende,  and  shows  many 
evidences  of  severe  crushing  in  the  bent  and  twisted  horn- 
blende fibers  and  the  granular  aggregates  of  hornblende  and 
feldspar.  The  minerals,  also,  have  a  marked  undulatory  ex- 
tinction. The  feldspar  is,  at  times,  in  idiomorphic  individuals, 
giving  the  rock  a  somewhat  diabasic  aspect. 

Good  examples  of  the  relation  of  ore  to  rock-minerals  are 
presented  in  some  of  the  sections.  One  shows  a  large  frag- 
ment of  fibrous  hornblende  which  has  been  bent  and  twisted, 
with  pyrrhotite  between  the  fibers,  following  all  the  curves  and 
leaving  the  comparatively  fresh  fibers  intact.  In  other  places 
the  pyrrhotite  has  replaced  the  uralitic  hornblende  to  a  greater 
or  less  extent,  in  some  cases  with  such  delicacy  as  to  preserve 
the  original  fibrous  structure  perfectly.  Where  the  feldspar 
and  hornblende  form  granular  aggregates,  the  sulphides  form 
a  mass  of  radiating  veinlets  around  and  between  the  grains, 
leaving  the  nucleus  unreplaced. 

12.  North  Eange.     Location,  W.  D.  16,  Wisner  Township. — 
On   the   northern   extension   of  the  nickel-belt  a  number  of 
promising  deposits  have  been  opened  up,  but  so  far  have  not 
passed  the  "prospect"  stage. 


508  THE    ORB-DEPOSITS    OF    SUDBURY,  ONTARIO. 

Deposits  with  good  showing  have  been  exploited  in  lot  6, 
concession  3,  Norman  township  (Whistle  mine);  in  Bowell 
township,  W.  D.  35,  150,  151,  and  155,  but  lack  of  transporta- 
tion-facilities has  been  a  serious  drawback  to  more  active  work. 
The  ore-rock  is  a  fine-grained  altered  norite,  shading  to  a 
coarser  and  more  granitic  variety  to  the  south,  and  bounded 
on  the  north  by  the  so-called  Laurentian  granite. 

As  far  as  could  be  determined  from  the  limited  exposures, 
the  ore-bodies  are  very  similar  to  those  farther  south.  That 
is,  they  consist  of  a  breccia  of  almost  barren  rock  cemented  by 
sulphides  and  with  irregular  veinlets  of  ore  running  through 
them.  Besides  the  prevailing  brecciation,  there  has  been  shear- 
ing, and  numbers  of  samples  of  schistose  rock  are  found  seamed 
with  ore,  especially  on  the  parting-planes. 

Microscopically,  the  rock  is  seen  to  be  composed  largely  of 
secondary  hornblende  and  chlorite,  both  fibrous  and  granular. 
Feldspar  is  often  in  idiomorphic  crystals,  giving  the  rock  a 
decided  ophitic  structure.  The  structure  of  the  sulphides  is 
decidedly  vein-like,  some  of  the  veinlets  continuing  across  the 
sections  and  having  numerous  accessory  ramifications.  The 
ore  is  most  closely  associated  with  the  hornblende,  and  follows 
between  the  fibers  and  grains,  conforming  to  all  the  irregulari- 
ties and  replacing  it  partly  or  wholly,  often  preserving  the 
fibrous  structure  very  well.  As  the  amount  of  ore  increases, 
the  alteration  of  the  rock-minerals  becomes  more  pronounced, 
and  the  sulphides  spread  all  through  the  section,  forming  a 
very  characteristic  secondary  network  of  reticulating  veinlets. 

The  Wallace  Mine,  Near  ike  Mouth  of  the  White-fish  River,  Lake 
Huron. — This  deposit  lies  outside  what  is  commonly  under- 
stood as  the  "nickel-belt."  While  essentially  the  same  in  some 
respects,  so  that  it  must  be  considered  as  genetically  similar,  it 
presents  certain  peculiar  features  of  its  own. 

The  mine  is  of  historic  interest,  and  was  opened  up  as  early 
as  1847  for  copper.  A  year  later  it  was  discovered  that  the 
ore  carried  nickel,  and  a  sample  containing  about  two-fifths 
rock,  analyzed  by  Dr.  T.  Sterry  Hunt,  yielded  more  than  8  per 
cent,  of  this  metal.  After  a  series  of  disasters,  and  the  loss  of 
trial-shipments  on  Lake  Huron,  the  mine  was  abandoned  in 
1867,  and  work  has  not  since  been  resumed.  The  deposit 
occurs  at  the  junction  of  two  small  dikes  of  so-called  diorite,  in- 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  509 

truded  in  the  country  quartzite.  The  quartzite  at  the  contact 
is  very  black  and  dense,  and  has  been  sheared  and  slickensided. 

Some  large  masses  of  heavily-mineralized  ore-rock  on  the 
dump,  which  have  resisted  oxidation,  show  a  decidedly  brecci- 
ated  structure,  with  sulphides  (pyrrhotite,  pyrite,  and  chalco- 
pyrite)  cementing  the  fragments. 

The  junction  of  the  dikes  seems  to  have  been  the  center  of 
dynamic  disturbances,  which  caused  the  brecciation  and  shear- 
ing, and  formed  a  favorable  place  for  the  circulation  and  con- 
centration of  ore-bearing  solutions  on  a  small  scale. 

There  seems  little  doubt  that  the  ore  was  precipitated  from 
solution,  and  the  relations  are  very  suggestive  when  compared 
with  those  of  the  Sudbury  deposits. 

The  microscope  shows  that  the  rock  has  been  severely 
crushed  and  presents  a  typical  mosaic  in  places.  The  horn- 
blende is  both  granular  and  fibrous,  and  gives  the  rock  a  schis- 
tose appearance.  The  rock  is  also  much  more  acidic  than  the 
Sudbury  types,  and  contains  a  good  deal  of  orthoclase  and 
quartz,  often  in  the  form  of  a  micropegmatite,  differing  in  this 
respect  also  from  the  others.  The  ore  is  mainly  in  veinlets, 
surrounding  and  penetrating  the  remaining  rock-fragments, 
and  replacing  the  dark  silicates  (hornblende  and  biotite)  to  a 
greater  or  less  extent.  As  the  amount  of  ore  increases,  the  dark 
silicates  largely  disappear,  and  the  feldspar  is  broken  up  into 
grains,  inclosed  by  ore,  and  this,  together  with  quartz,  is  left  to 
a  large  extent  unreplaced,  while  the  remaining  fragments  of 
hornblende  contain  sulphides  along  the  cleavages  and  between 
fibers. 

The  Rossland,  B.  (7.,  District. —  The  Josie  Mine.44 — The  micro- 
structure  of  the  Rossland  ore  is  so  strikingly  similar  to  that 
from  Sudbury  that  a  brief  reference  will  be  made  to  it. 

The  rock  usually  associated  with  the  ore  is  a  monzonite,  more 
or  less  altered.  The  specimens  examined  were  samples  of  vein- 
matter  from  the  Josie  (Le  Roi  No.  2)  mine,  and  presented  a 
decidedly  altered  and  schistose  appearance,  and  contained 
pyrrhotite  and  chalcopyrite.  Thin  sections  show  that  the  rock 
is  more  or  less  silicified,  and  consists  largely  of  secondary 
fibrous  hornblende  and  biotite,  and  a  smaller  amount  of  feld- 
spar with  many  fragments  of  the  dark  silicate  through  it. 

44  Material  kindly  furnished  by  George  H.  Dickson,  Rossland,  B.  C. 


510  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

The  relation  of  the  sulphides  and  rock-minerals  is  also  very 
similar  to  that  of  the  Sudbury  examples. 

They  are  intimately  associated  with  the  dark  silicates  and 
form  veinlets  between  the  hornblende  and  biotite  fibers,  and 
extend  from  these  in  the  form  of  reticulating  networks,  which 
in  places  wholly  replace  the  minerals  involved.  Where  asso- 
ciated with  the  more  granular  silicates  and  quartz,  the  sulphides 
form  veinlets  along  the  cleavages  and  around  the  grains  and 
present  the  same  features  as  the  Sudbury  ore,  and  can  only  be 
explained  as  due  to  a  secondary  introduction  by  means  of  cir- 
culating, ore-bearing  solutions. 

The  Ducktown,  Tenn.,  Deposits. — Figs.  25  and  26 45  show  the 
relations  of  the  ore- and  rock-minerals  in  the  Ducktown  copper- 
deposits. 

An  inspection  will  show  that  these  are  very  similar  to  some 
of  the  Sudbury  examples.  Professor  Kemp  considers  that  ore- 
bearing  solutions  entered  along  zones  of  crushing  or  faulting, 
where  the  material  was  of  a  more  or  less  open  texture,  and 
replaced  silicates  and  other  minerals;  the  sulphides  often  in- 
sinuating themselves  into  the  broken  silicates  and  abutting 
sharply  against  the  fresher  specimens.  In  this  connection  he 
says  :  "  It  therefore  seems  probable  that  the  replaced  material 
consisted  of  the  crushed  and  greatly  comminuted  country-rock, 
which  in  this  condition  would  prove  an  easier  prey  to  the  ore- 
bearing  solutions.  Where  the  crushing  was  most  severe,  the 
large  ore-bodies  are  found.  Unless  some  factor  of  this  sort 
exercised  an  influence,  it  seems  strange  that  the  process  of  re- 
placement should  cease  so  sharply  against  perfectly  fresh  and 
unchanged  representatives  of  the  presumably  replaced  min- 
erals." 

Summary. 

The  above  results  are  given  in  some  detail,  even  at  the  risk 
of  repetition.  But  in  a  problem  of  this  kind  it  is  all-import- 
ant that  the  facts  should  be  clearly  presented,  so  as  to  obtain 
a  grasp  of  the  entire  situation  and  avoid  a  narrow  interpreta- 
tion based  on  one  or  two  occurrences,  which  might  not  be 
typical  of  the  whole. 

The  investigations  covering  the  whole  field  of  the  nickel- 

45  From  Professor  Kemp's  paper,  The  Deposits  of  Copper-Ores  at  Ducktown, 
Term.,  Trans.,  xxxi.,  255,  256  (1901). 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  511 

range  show  that  all  tne  deposits  have  certain  prominent  fea- 
tures in  common. 

1.  Brecciation,  with  accompanying  faulting,  and  shearing  are 
everywhere  characteristic.     This 'is  shown  not  only  on  a  large 
scale,  but  is  also  corroborated  by  the  microscopical  relations. 

2.  The  main  brecciation  and  shearing  took  place  previous  to 
the  formation  of  the  ore-bodies  proper. 

3.  The   abrupt  change  from   massive   sulphides    to  barren 
rock,  so  often  noticed,  seems  irreconcilable  with  the  theory  of 
magmatic  segregation,  and  it  is  also  difficult  to  imagine  how 
the  included  rock-fragments  could  retain  their  angular  form  if 
they  were  once  part  of,  or  floated  in,  a  molten  magma. 

4.  The   ore  prevailingly  occurs  as   a  cement  for  the  brec- 
ciated  rock-fragments  and  along  shear-planes. 

5.  The  rocks  associated  with  the  ore  are  all  members  of  the 
gabbro  family  and  can  generally  be  referred  to  norite. 

6.  The  rocks  are    more    or   less    altered    and    now  resem- 
ble diorite,  the  original  pyroxene  having  in  nearly  all  cases 
changed  to  a  fibrous  green  hornblende  and  chlorite.     Where 
original  pyroxene  remains  (e.  g.,  at  the  Stobie  and  Mount  Nickel 
mines),  the  structure  is  markedly  brecciated. 

7.  The  effects  of  metamorphism   and   the   development  of 
secondary  hornblende  are  most  marked   near  the  ore-bodies, 
and  diminish  away  from  them.46 

8.  In  general,  the  more  complete  the  alteration  of  the  rock, 
the  more  complete  has  been  its  replacement  by  sulphides. 

9.  The  relation  of  the  ore  to  the  rock-minerals  is  practically 
identical  throughout  the  whole  district.     In  all  cases  the  ten- 
dency of  the  sulphides  is  to  occur  along  planes  of  weakness 
and  in  connection  with  the  fibrous  minerals. 

Occasionally  the  relations  of  the  pyrrhotite  to  the  silicates 
suggest  that  it  is  an  original  constituent  of  the  rock  and  one 
of  the  first  minerals  to  crystallize  from  the  magma.  This  is 
seen  at  times  in  the  less  altered  specimens  some  distance  from 
the  ore-bodies. 

The  amount  of  this  apparently  original  pyrrhotite  is,  how- 
ever, always  very  subordinate,  and  is  probably  no  more  than 
might  reasonably  be  expected  in  a  gabbro. 

46  Compare  Walker,  Quarterly  Journal  of  the  Geological  Society,  vol.  liii.,  No.  209, 
p.  47  etseg.  (Feb.,  1897). 


512  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

So  that  while  a  small  percentage  of  the  pyrrhotite  may  be 
original,  the  main  contention  still  holds,  namely,  that  the  sul- 
phides are  essentially  and  predominantly  secondary. 

10.  Secondary  quartz  and  ealcite  are  often   present  in  the 
ore  in  appreciable  amount,  while  they  are  insignificant  or  lack- 
ing at  a  little  distance.47 

11.  Sulphides  are  practically  lacking  in  the   rock  a  short 
distance  from  the  ore.     The   rock-fragments  included  in  the 
deposit  are  also  comparatively  free  from  ore,  except  in  veinlets. 

12.  The  relation  of  the  magnetite  to  the  rock-minerals  is  in 
marked   contrast  to  that  of  the  sulphides,  the  former  being 
always  in  more  or  less  rounded  grains  in  the  dark  silicates  and 
generally  primary. 

13.  With  regard  to  the  relations  of  the  sulphides  to  the  rock- 
minerals  themselves,  several  different  types  might  be  differen- 
tiated.   These  types  are,  however,  all  alike  in  kind,  and  several 
may  occur  in  a  single  specimen. 

(a)  Replacement  starting  between  and  extending  along  the 
fibers  of  hornblende,  often  resulting  in  a  pseudomorph  of  ore 
after  this  mineral. 

(6)  Replacement  along  cleavages  of  the  more  compact  and 
less  altered  minerals,  breaking  them  up  into  grains  and,  at 
times,  forming  complete  pseudomorphs. 

(c)  Replacement  between  crystals  and  fragments  of  the  same 
or  different  minerals,  often  extending  into  the  mineral  sub- 
stance, when  it  could  be  classed  under  (a)  or  (b). 

(d)  Replacement  along  planes  or  zones  of  parting  and  shear- 
ing, the  veinlets  being  in  general  parallel  and  ramifying  through 
the  neighboring  minerals  as  indicated  in  (a),  (6)  and  (c). 

(e)  In  the  more  crushed  and  granular  examples,  where  the 
rock-minerals  are  much  altered,  the  sulphides  are  peppered  all 
through  them  and  form  an  intricate  and  ramifying  network  of 
veinlets  in  the  rock,  at  times  completely  replacing  the  minerals 
around  certain  centers. 

(/)  The  dark  silicates  fall  the  easiest  prey  to  the  ore-bearing 
solutions,  but  many  instances  are  noted  in  which  the  feldspar 
suffers.  This  is  generally  the  case  where  the  crushing  and 
shearing  have  been  most  severe  and  the  mineral  is  partly  or 
wholly  changed  to  secondary  products.  As  a  rule,  though  not 

47  Walker,  Joe.  cit. 


THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO.  513 

invariably,  this  change  is  especially  noticeable  where  the  min- 
eralization of  the  rock  is  most  pronounced. 

14.  A  comparison  of  the  Sudbury  deposits  with  those  of 
Rossland,  B.  C.,  and  Ducktown,  Tenn.,  shows  many  remarkable 
and  essential  points  of  similarity.  These  deposits  are  now 
proved  beyond  all  reasonable  doubt  to  be  of  secondary  aqueous 
origin,  and  this,  aside  from  direct  evidence,  points  strongly  to 
a  similar  origin  for  the  Sudbury  occurrences. 

Relation  of  Chalcopyrite  to  Pyrrhotite. — From  the  massive  na- 
ture of  the  sulphides,  very  little  can  be  accurately  determined 
as  to  the  paragenesis  of  the  minerals.  There  are,  however, 
certain  relations  existing  between  the  chalcopyrite  and  the  pyr- 
rhotite  which  may  help  to  explain  it. 

1.  In  a  number  of  cases  where  copper  is  predominant,  the 
ore  consists  of  numerous  small  parallel  veinlets  of  pyrrhotite 
and  chalcopyrite  very  intimately  associated.     This  is  well  illus- 
trated by  examples  from  the  Copper  Cliff  and  Creighton  mines 
(Figs.  10  and  21).     The  same  relation  is  a  prominent  feature  of 
the  Rossland  ore,  and  hand-specimens  from  the  two  localities 
are  almost  indistinguishable. 

2.  The  chalcopyrite  is  usually  most  strongly  concentrated 
near  the  outside  of  the  deposits,  especially  towards  the  so-called 
foot-wall.     As  a  rule,  the   proportion  of   chalcopyrite  in  the 
main  ore-body  is  rather  small,  and  it  tends  to  form  fairly-pure 
masses  without  much  pyrrhotite.     Taking  these  facts  into  con- 
sideration, it  seems  likely  that  the  pyrrhotite  at  first  constituted 
the  largest  part  of  the  ore-body.     Later,  due  to  some  dynamic 
movement,  opening  up  passages  through  the  ore-bodies,  espe- 
cially towards  the  outer  limits,  copper-bearing  solutions  entered 
and  deposited  their  mineral  contents  among  the  rock-masses 
and  partly  replaced  pyrrhotite  along  certain  lines.     In  some 
deposits,  as  at  the   Copper  Cliff,  where  copper-minerals  pre- 
dominate, the  fracturing  may  have  been  greater  and  the  solu- 
tions more  active  or  concentrated. 

It  is  also  possible  that  the  copper  disseminated  in  the  upper 
part  of  the  ore-bodies,  now  eroded,  has  been  secondarily  de- 
posited by  downward-moving  currents,  but  this  does  not  seem 
to  have  been  the  case  to  any  great  extent.  In  the  first  place, 
there  is  very  little  in  the  way  of  an  oxidized  gossan,  and  the 
ground-water  level  is  comparatively  near  the  surface.  Secondly, 


514  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

there  is  little,  if  any,  indication  of  this  secondary  change  in  the 
way  of  enriched  sulphides  which  accompany  the  process.  . 

Pyrrhotite  is  quite  generally  admitted  to  be  a  product  of 
primary  concentration  by  upward-moving  solutions  in  a  strongly 
reducing  atmosphere,  and  if  any  considerable  concentration  by 
downward-moving  waters  had  taken  place,  we  would  expect  to 
find  the  pyrrhotite  largely  oxidized  or  removed  entirely.  It  is, 
however,  a  notable  fact  that  when  the  thin  surface-covering  is 
removed,  the  pyrrhotite  appears  perfectly  fresh  and  with  no 
appreciable  admixture  of  secondary  minerals,  such  as  are 
formed  in  the  process  of  secondary  enrichment. 
.  Source  of  the  Metals. — What  the  exact  sequence  of  events 
leading  up  to  the  formation  of  the  ore-bodies  and  the  immedi- 
ate source  of  the  metallic  contents  was,  is  not  yet  satisfactorily 
settled.  The  question  involves  many  intricate  problems,  both 
of  a  local  and  a  general  nature,  and  with  the  evidence  at  hand 
an  authoritative  discussion  would  be  premature. 

The  metamorphic  processes  appear  to  have  been  very  com- 
plicated, and  are  still  more  obscured  by  the  later  alteration  due 
to  the  mineralizing  solutions. 

Pyrrhotite  is  a  product  of  many  metamorphic  processes  and 
may  be  formed  in  any  of  the  classes  designated  by  Lindgren — 
dynamo,  hydro-thermal,  solfataric,  or  contact.48 

Under  which  head  the  metamorphism  of  the  Sudbury  dis- 
trict could  be  accurately  classified,  it  is  difficult  to  say.  Indeed, 
it  might  be  considered  as  a  combination  dynamo,  hydro-thermal, 
and  solfataric.  From  a  study  of  the  history  of  the  district, 
however,  it  is  quite  evident  that  it  was  a  region  of  vulcanism 
and  metamorphic  processes  on  a  large  scale,  and  the  immense 
stores  of  heat  and  energy  involved  could  be  readily  available  as 
stimulators  of  the  circulation  and  chemical  activity  of  the  min- 
eral solutions,  so  that  the  theory  of  an  aqueous  origin  presents 
nothing  at  all  unreasonable. 

Hvdrogen  sulphide  is  so  common  a  constituent  of  mineral 
and  thermal  springs  that  its  presence  in  the  mineral  solutions 
can  be  assumed.  From  the  nature  of  the  deposits,  the  ore- 
bearing  solutions  were  probably  highly  charged  with  alka- 

48  W.  Lindgren,  Nevada  City  and  Grass  Valley  Districts,  Seventeenth  Annual 
Report,  U.  S.  Geological  Survey,  Pt.  II.,  p.  90  (1895-96). 


THE    ORE-DEPOSITS    OF    SUDBURY,   ONTARIO.  515 

line  carbonates  and  hydrogen  sulphide,  but  with  subordinate 
amounts  of  carbon  dioxide. 

The  microscopical  investigations  show  that  the  dark  silicates 
are  often  bleached  and  robbed  of  iron,  or  else  "  resorbed," 
forming  aggregates  of  magnetite  grains.  It  is  thus  possible 
that  a  certain  amount  of  the  iron  was  derived  from  the  altera- 
tion of  the  minerals  of  the  replaced  zone  as  well  as  from  extra- 
neous sources.  The  source  of  the  nickel  may,  to  some  extent, 
have  been  the  associated  rocks,  which  contain  small  amounts, 
but  it  seems  more  probable  that  the  larger  part  was  derived 
from  greater  depths  traversed  by  the  circulating  waters. 

Many  of  those  who  are  familiar  with  the  district,  and  who 
have  discarded  the  theory  of  a  direct  "  magmatic  segregation," 
still  consider  that  there  was  a  preliminary  concentration  of 
metals  with  the  intrusion  of  the  norite,  and  that  the  ore-bodies 
assumed  their  present  position  and  dimensions  by  subsequent 
processes. 

This  may,  to  a  certain  extent,  be  true,  and  the  presence  of 
small  quantities  of  what  appears  to  be  original  pyrrhotite  in 
the  ore-rock  is  cited  in  support  of  this  view.  Moreover,  this 
theory  does  not  involve  many  of  the  difficulties  of  the  first. 
Still,  a  consideration  of  the  whole  subject  and  the  relations  in- 
volved seems  to  indicate  that  this  "  preliminary  concentration  " 
was  comparatively  slight,  and  appeal  must  be  made  to  a  more 
distant  source  of  the  metals,  probably  minutely  disseminated  in 
the  rocks  through  which  the  depositing  solutions  passed. 

In  conclusion,  it  might  be  safely  stated  that  at  present  the 
whole  weight  of  the  evidence  points  to  the  secondary  forma- 
tion of  the  Sudbury  ore-bodies  as  replacements  along  crushed 
and  faulted  zones,  with  only  minor  indications  of  open  cavities. 

Previous  observers  have  naturally  been  impressed  by  the 
massive  character  of  the  sulphides,  in  which  are  found  the  min- 
erals of  the  inclosing  rock,  and  this  seems  to  fall  in  readily 
with  the  idea  of  an  igneous  origin. 

The  clue  to  the  interpretation  of  the  matter,  however,  ap- 
pears to  be  furnished  by  the  leaner  material,  where  the  relations 
have  not  been  obscured  or  obliterated  by  the  excessive  develop- 
ment of  the  sulphides. 

The  universal  association  of  these  ores  with  essentially  simi- 
lar rocks  is  also  striking.  That  the  norite  (or  gabbro)  has  an 


516  THE    ORE-DEPOSITS    OF    SUDBURY,  ONTARIO. 

intimate  connection  with  the  development  of  the  ores  cannot  be 
doubted,  but  in  just  what  way  they  are  related  is  not  clear. 

After  a  review  of  the  ideas  held  of  these  and  similar  deposits 
elsewhere,  it  will  be  seen  that  the  evidence  adduced  in  support 
of  the  igneous  hypothesis  can  be  equally  well,  if  not  better,  in- 
terpreted on  the  basis  of  replacement,  while  many  of  the 
observed  phenomena  cannot  be  satisfactorily  explained  on  the 
assumptions  of  the  old  hypothesis. 

With  the  additional  light  thrown  on  the  subject  by  these  in- 
vestigations, there  seems  to  be  no  reasonable  doubt  left  as  to 
the  true  nature  of  the  deposits,  and  it  may  be  confidently  ex- 
pected that  future  work  will  give  additional  weight  to  the  views 
here  advanced. 

Finally,  with  regard  to  my  personal  connection  with  the 
matter,  it  may  be  well  to  say  that,  in  taking  up  the  work,  I 
went  into  the  field  with  an  open  mind  and  for  the  sole  purpose 
of  interpreting  the  phenomena  as  they  were  presented  by  the 
facts,  without  being  hampered  by  any  preconceived  theories.  I 
had  always  been  taught  to  regard  the  deposits  as  essentially  of 
igneous  origin,  and  this  theory  was,  of  course,  uppermost  in  my 
mind.  But  as  instance  after  instance  of  the  relations  in  the 
field  was  presented  in  the  different  deposits,  the  "  igneous J> 
theory  was  not  sufficient  to  explain  the  facts.  Then,  on  calmly 
studying  the  material  collected  in  the  laboratory,  the  convic- 
tion became  a  certainty,  and  I  present  my  views  only  for  the 
purpose  of  throwing  as  much  light  as  possible  on  these  compli- 
cated problems. 

Aside  from  the  main  contention  that  the  deposits  are  replace- 
ments, any  arguments  advanced  as  to  the  actual  source,  manner 
of  concentration,  and  paragenesis  of  the  ore  may  be  regarded 
as  largely  tentative  and  as  inviting  discussion,  by  which  we  may 
hope  to  arrive  at  more  definite  conclusions  as  to  the  actual  pro- 
cesses and  sequence  of  events,  culminating  in  these  remarkable 
bodies  of  ore  as  we  find  them  to-day. 

Acknowledgments. — The  writer  wishes  especially  to  acknowl- 
edge his  indebtedness  to  Professor  Kemp,  of  Columbia  Univer- 
sity;  Dr.  Goodwin,  Director  of  the  School  of  Mining,  Kingston, 
Ontario;  Prof.  W.  G.  Miller,  Provincial  Geologist  of  Ontario; 
and  J.  "Walter  Wells,  late  Chemist  to  the  Ontario  Bureau  of 
Mines,  for  assistance  and  kindly  interest  in  the  work. 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       517 

No.  19. 


The  Genesis  of  the  Copper-Deposits  of  Clifton- Morenci, 

Arizona.* 

BY  WALDEMAR  LINDGREN,    WASHINGTON,    D.    C. 

(Lake  Superior  Meeting,  September,  1904.     Trans.,  xxxv.,  511.) 
CONTENTS. 

PAGE 

Topography  and  Geology,     .         .         ....         .        ,                 .  .  518 

Occurrence  and  General  Features  of  Ore-Deposits,        .  520 

Metamorphic  Processes,         .        .        .         ...         .         .         .  .  522 

Contact-Metaraorphism,          .         .         .         .         .         .         .         .  .  522 

Hydrothermal  Metamorphism,        .         .         .         .         .         ,         .  .  529 

Kelation  of  Contact-  and  Hydrothermal  Metamorphism,        .         .  .  530 

Processes  Due  to  Oxidation  and  Hydration  in  the  Oxidized  Zone,  .  531 

Sulphate  Waters,     .'        .         .         .        .        i        •'        .        .  .532 

Processes  in  Fissure- Veins,      .         .        .      •  >      ,.    \    .         .  .  532 

Oxidation  of  Chalcocite,                   .......  534 

Oxidizing- Processes  in  Limestone, 535 

Oxidizing-Processes  in  Shale,  .                  .        .         .         .         .  .  536 

Paragenesis,   .         ..-,..        ...        .         .        .  .  536 

Characteristics  of  Deposits,   .         .         .        .        ....        .         .         .  .  537 

Deposits  of  Carbonates  and  Oxides  in  Limestone  and  Shale, .         .  537 

Fissure-Veins  and  Related  Deposits  of  Morenci  Type,  ....  539 

The  Coronado  Type  of  Veins,        .    '    .         ;'        .        .        .         .  .  543 

Gold-Bearing  Veins,       .         .         .         . 544 

Conditions  of  Ground-Water,        .         .         .         .         .         .         .         .  .  544 

Depth  of  Oxidized  Zone,       .        .         .        .        .        .        .        .        .  .  545 

Fluid-Inclusions,  .        .         .        .        .         .        .         .         .         .         .  .  545 

In  Granite,     .         .....        .        •        .         .         .        .        .  .  546 

In  Metamorphic  Limestones,  .         .         .         .         .         .         ,         .  .  545 

In  Porphyry, .         .         .         .         ,         .        .         ...         .         .  ,  545 

In  Vein-Quartz,      .         .  '     .         .         .        .        .        .        .        .  .  549 

Summary  of  Genesis,    .        ^  '••     *      .'.         .         ,         ....    .  .  55^ 

Genetic  Classification,   .       ..     ...       .*         .       ..        ....         .  .  555 

THE  following  pages  are  a  resume  of  some  of  the  conclusions 
reached  during  a  study  of  the  copper-deposits  near  Clifton. 
The  field-work  was  finished  in  1902  and  a  complete  report  is 
now  in  the  press.  A  preliminary  description  of  the  district 
was  published  in  1903,  in  Bulletin  U.  S.  Geological,  Survey,  No. 
213,  pp.  133-140. 

*  Published  by  the  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 


518      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

The  Clifton  mines,  always  important,  are  at  present  the 
largest  in  the  territory,  the  output  in  1902  having  reached 
50,000,000  Ib.  of  copper,  chiefly  divided  between  the  two  prin- 
cipal producers,  the  Arizona  and  the  Detroit  copper  companies. 
The  Shannon  Copper  Co.  also  contributed  to  this  figure,  and  its 
output  has  greatly  increased  since  then.  The  total  output  of 
the  district  to  the  end  of  the  year  1903  is  estimated  at  a  value 
of  about  $49,000,000. 

TOPOGRAPHY  AND  GEOLOGY. 

Clifton  is  situated  on  the  San  Francisco  river,  a  few  miles 
above  its  confluence  with  the  Gila  river,  in  the  southeastern  part 
of  the  territory,  and  not  many  miles  from  the  New  Mexican 
boundary.  An  irregular  mountain  region,  without  well-defined 
ranges,  lies  here  north  of  the  broad,  detritus-filled  valley  of  the 
Gila  river,  which  has  an  elevation  of  about  3,000  feet.  The 
highest  elevations  in  the  mountains  scarcely  attain  8,000  feet. 

Between  the  San  Francisco  river  and  Eagle  creek,  both  trib- 
utaries to  the  Gila  river  from  the  north,  a  core  of  older  rocks  of 
about  70  sq.  miles  is  exposed,  consisting  of  pre-Cambrian  gran- 
ites, Cambrian  quartzites,  Paleozoic  limestones,  and  a  capping- 
formation  of  Cretaceous  beds — all  intruded  by  post-Cretaceous 
granitic  porphyries.  This  older  core,  which  seems  to  represent 
the  broken-down  edge  of  the  great  plateau-province,  is  com- 
pletely surrounded  and  largely  covered  by  volcanic  flows  of 
Tertiary  age,  including  basalts,  andesites  and  rhyolites,  which 
have  been  extensively  eroded ;  hence  the  lack  of  regularity  so- 
plainly  apparent  in  the  mountain  complex. 

The  copper-deposits  are  all  contained  in  the  older  rocks  and 
distinctly  antedate  the  Tertiary  lavas. 

The  sedimentary  rocks  rest  on  a  basement  of  red,  coarse 
granite,  forming  two  great  buttresses,  the  Coronado  and  the 
Copper  King  mountains,  both  rising  more  than  3,000  ft.  above 
the  San  Francisco  river. 

The  Paleozoic  series  consists  of  the  following-named  forma- 
tions : 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       519 

Modoc  limestone.  Up  to  200  ft.  thick,  heavy-bedded,  gray  limestones  of 
(Lower  Carboniferous.)  great  purity,  with  some  equally  pure  dolomites  at  the 

base. 
Morenci  shale.  100  ft.  of  clay-shales,  sometimes  underlain  by  75  ft.  of 

(Devonian  ?)  argillaceous  limestone. 

Longfellow  limestone.        Up  to  400  ft.  of  limestones,  partly  cherty  and,  near 
( Ordovician. )  the  base,  containing  sandy  beds.     Some  of  these  strata 

are  dolomitic. 

Coronado  quartzite.  200   ft.    of    reddish,    quartzitic   sandstones    resting    on 

(Cambrian?)  granite.      Lowest   member   is   a   quartzitic  conglom- 

erate. 

The  three  upper  divisions  contain  characteristic  fossils,  while 
only  a  few  small  Lingula  shells  have  been  found  in  the  Coronado- 
quartzite. 

The  Cretaceous  series  rests  unconformably  on  the  Modoc 
limestone  and  consists  of  a  succession  of  clay-shales  and  dark 
sandstones  at  least  200  ft.  thick.  Scant  fossils  indicate  that  it 
belongs  to  the  Fort  Benton  horizon. 

Gentle  dips,  rarely  above  20°  and  generally  directed  west- 
ward, characterize  the  sedimentary  rocks. 

All  of  the  above-mentioned  rocks  are  intruded  by  a  great 
stock  of  porphyry  which  extends  in  a  northeasterly  direction 
between  the  foothills  near  Eagle  creek  across  to  the  great  Cop- 
per King  granite  ridge  overlooking  San  Francisco  river.  The 
main  stock,  which  is  about  8  miles  long  and  up  to  a  mile  and 
a  half  wide,  breaks  up,  at  the  southwest  end,  into  a  network 
of  irregular  dikes  and  sheets,  and,  at  the  northeast,  into  a  sys- 
tem of  northeasterly-trending  dikes  cutting  through  the  granite. 
Laccolithic  masses  of  porphyry  occur  in  the  Cretaceous  shales 
and  sandstones.  The  rock  of  the  main  stock  ranges  from  a 
granite-porphyry  to  a  quartz-monzonite  porphyry.  The  sills 
and  laccoliths  are  usually  composed  of  diorite-porphyry,  but  the 
different  types  of  rock  are  clearly  facies  of  the  same  magma, 
connected  by  transitions  and  forming  a  single  geological  unit. 
Dikes  of  diabase  occur  in  a  few  places. 

The  intrusion  of  the  poryhyry  took  place  during  the  latest 
Cretaceous  or  the  earlier  Tertiary,  and  was  accompanied  by 
great  disturbances  in  the  immediately  adjoining  rocks,  particu- 
larly well  noticeable  in  the  Paleozoic  sediments ;  but  these  dis- 
turbances of  the  strata  did  not  extend  far  from  the  contacts. 

The  intrusion  of  the  porphyry  was  followed  by  important 


520       GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

structural  movements.  The  surface  of  the  granite,  together 
with  the  whole  covering  sedimentary  series,  was  buckled  into 
dome-shaped  folds  and  then  extensively  fractured,  the  blocks 
sinking  successively  deeper  towards  the  valley  and  settling  un- 
equally around  the  two  great  buttresses,  or  "  horsts,"  the  Coro- 
nado  and  Copper  King  mountains,  the  maximum  throw  of  the 
normal  faults  being  3,000  feet. 

An  epoch  of  erosion  followed,  but  floods  of  Tertiary  lavas 
soon  surrounded  and  largely  covered  the  old  rocks  which  have 
only  lately  emerged  by  the  energetic  action  of  a  second  epoch 
of  erosion.  The  effects  of  the  large  faulting-movements,  which 
preceded  the  lavas,  are  still  visible  in  the  greater  topographic 
features  of  the  region,  especially  in  the  bold  escarpment  of  the 
Copper  King  ridge. 

OCCURRENCE  AND  GENERAL  FEATURES  OF  THE  ORE-DEPOSITS. 

The  geographical  distribution  of  the  copper-deposits  is  prac- 
tically coextensive  with  the  great  porphyry  stock  and  its  dike- 
systems.  The  deposits  occur  either  in  the  porphyry  or  close  to 
its  contacts,  or  along  dikes  of  porphyry  in  some  other  rock. 
Areas  in  which  no  intrusions  have  taken  place  are  practically 
barren.  This  intimate  connection  with  the  porphyry  is  certainly 
a  most  important  fact.  There  is  only  one  small  division  of  de- 
posits which  deviates  from  this  rule — namely,  that  connected 
with  the  diabase-dikes. 

Practically  all  types  of  deposits  contain  copper  as  the  most 
valuable  metal.  Gold  and  silver  occur,  as  a  rule,  only  in  minute 
quantities,  except  in  some  of  the  outlying  districts  where  they 
become  of  more  importance.  The  two  most  important  mining- 
centers,  Morenci  and  Metcalf,  which  are  3  miles  apart,  are 
both  situated  at  the  main  contact  of  the  porphyry  stock  and 
the  series  of  Paleozoic  limestones.  Elsewhere  the  intrusive 
rock  generally  adjoins  granite  or  Cretaceous  sediments. 

The  ores  consist  of  chalcocite,  chalcopyrite,  malachite,  azu- 
rite,  chrysocolla,  brochantite,  cuprite,  and  native  copper.  Covel- 
lite  and  bornite  are  practically  absent.  Brochantite,  a  basic 
copper  sulphate,  is  very  commonly  present,  especially  in  the 
oxidized  veins  in  porphyry ;  and,  in  fact,  constitutes  in  places  an 
important  ore.  On  account  of  its  similarity  to,  and  intimate 
intergrowth  with,  malachite  it  has  usually  been  overlooked. 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       521 

The  following-named  minerals  have  been  found : — Native 
copper,  native  gold,  quartz,  chalcedony,  rutile,  magnetite, 
hematite,  limonite,  pyrolusite,  coronadite  (a  new  mineral, 
chiefly  PbO  and  Mn02),  cuprite,  pyrite,  chalcopyrite,  zinc- 
blende,  galena,  molybdenite,  chalcocite,  diopside,  tremolite, 
garnet,  epidote,  muscovite,  chlorite,  serpentine,  asbestos,  kao- 
lin, willemite,  calamine,  dioptase,  chrysocolla,  copper  pitch  ore, 
morencite  (a  new  mineral,  chiefly  a  ferric  silicate),  calcite,  dolo- 
mite, zinc  carbonate,  malachite,  azurite,  libethenite  (copper 
phosphate,  not  previously  found  in  the  United  States),  brochan- 
tite,  al unite,  gypsum,  spangolite  (basic  chloro-sulphate  of  cop- 
per and  aluminum),  chalchanthite,  goslarite,  epsomite  and  ger- 
hardtite  (a  basic  copper  nitrate  forming  green  crusts  on  weath- 
ered surfaces  of  porphyry,  and  associated  in  these  with  a  cop- 
per chloride,  possibly  atacamite). 

The  deposits  with  payable  copper-ore  take  many  widely  dif- 
fering forms,  as  follows  : — 

Deposits  in  limestone  and  ghale,  not  connected  with  fissure-veins. 

Irregular  bodies  near  contacts  of  main  stock  or  dikes. 

Tabular  bodies  near  contacts  of  main  stock  or  dikes  following  stratification. 

Tabular  bodies,  following  contacts  of  porphyry  dike  (all  of  these  carry  oxi- 
dized ores,  almost  exclusively  ;  rarely  chalcocite). 
Fissure-veins. 

Normal  veins  in  porphyry  or  in  any  of  the  other  rocks  near  porphyry-con- 
tacts. Include  central  veins  and  surrounding  partly- replaced  porphyry 
forming  together  a  lode.  Carry  chalcocite  as  the  important  ore  ;  in  upper 
levels  also  sometimes  oxidized  ores. 

Normal  veins,  following  porphyry  dikes  in  granite.  Chalcocite  and  oxidized 
copper-ores. 

Normal  veins  following  diabase-dikes.      Chalcocite  and  oxidized  copper-ores. 
Stock-werks.     Irregular  disseminations  in  porphyry,  quartzite  and  other  rocks. 

Contain  chalcocite  and  oxidized  copper-ores. 

The  above  classification  is  based  on  occurrence  and  form,  and 
a  more  general  genetic  system,  given  below,  shows  a  somewhat 
different  arrangement. 

Native  copper,  all  of  the  oxy-salts  of  copper,  and  chalcocite 
are  wholly  secondary  minerals  produced  by  direct  or  indirect 
oxidation  from  primary  pyritic  ores.  In  all  of  the  divisions 
given  above,  this  primary  ore  consists  of  pyrite  and  chalco- 
pyrite, with  some  zinc-blende  and  molybdenite.  The  scant 
gangue  of  the  veins  consists  of  quartz,  while  the  deposits  in 

33 


522       GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

the  first  division  are  usually  accompanied  by  garnet,  epidote> 
magnetite,  diopside,  tremolite,  or  their  products  of  oxidation. 

METAMORPHIC  PROCESSES. 

The  region  described  in  this  paper  is  practically  unaffected 
by  regional  or  dynamic  metamorphism,  and  even  the  ordinary 
hydro-metamorphism  has  altered  the  rocks  but  little,  produc- 
ing some  slight  changes  in  granite  and  porphyry  and  introduc- 
ing cherts  into  the  limestones.  Epidote,  chlorite,  and  a  little 
pyrite  are  apt  to  develop  in  the  hornblendic  phases  of  the 
porphyry. 

Contact- Metamorphism. 

Contacts  of  porphyry  with  sedimentary  rocks  often  show  typi- 
cal instances  of  this  metamorphism.  The  granite-porphyry  and 
the  quartz-monzonite  porphyry  show  themselves  most  effective 
in  this  direction,  while  there  is  usually  but  little  metamorphic 
action  at  the  contacts  of  the  diorite-porphyry.  The  effect 
seems  in  direct  proportion  to  the  amount  of  quartz  contained 
in  the  porphyry.  Granite  and  quartzite  are  unaltered;  the 
shales  and  sandstones  of  the  Cretaceous  series  are  hardened 
and  baked.  The  shales  change,  as  a  rule,  only  at  the  imme- 
diate contact,  to  dense,  greenish  hornfels. 

The  Paleozoic  limestone-series  comes  in  contact  with  the- 
main  stock  in  two  places — at  Morenci  and  at  Metcalf.  In  both 
places  extensive  copper-deposits  are  encountered.  Dikes  also 
occur  at  both  places  and  along  some  of  these  radiating  out 
into  the  unaltered  areas  the  metamorphic  processes  may  be 
examined  to  best  advantage. 

In  studying  the  phenomena  along  dikes,  it  is  found  that  the 
metamorphism  varies  greatly  in  the  different  strata,  and  even 
in  apparently  similar  limestone  layers  there  may  be  great  dif- 
ference in  the  degree  of  alteration.  A  well-defined  dike  50  ft. 
wide  on  Modoc  mountain  was  studied  with  special  care  as  it 
cut  through  all  of  the  formations  present.  Where  contained 
in  the  Longfellow  limestone  the  metamorphism  extends  at  most 
20  ft.  outward  into  the  limestone,  and  generally  only  a  few  feet. 
Garnet,  epidote,  diopside,  specularite,  and  magnetite  are  the 
minerals  which  form  abundantly  by  metasomatic  replacement 
along  the  contacts,  and  intergrown  with  them  are  chalcopyrite, 
pyrite,  and  zinc-blende,  unquestionably  of  contemporaneous 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.        523 

formation.  The  contact  metamorphic  limestone  has  certainly 
a  very  different  composition  from  the  unaltered  rock,  and  it  is 
apparent  that  much  silica,  iron,  copper  and  zinc,  at  least,  have 
been  added.  Epidote  often  forms  in  considerable  quantities 
close  to  the  contacts,  while  a  little  farther  away  garnet  prevails. 
The  Morenci  shales  overlying  the  Longfellow  limestone  are 
hardened  and  baked,  but  not  materially  altered  in  compo- 
sition. Finally,  when  the  dike  enters  the  pure  limestone  of  the 
Modoc  formation,  garnet  forms  in  enormous  quantities  from 
the  latter ;  the  metamorphism  exerted  by  the  dike  here  merges 
into  that  affecting  the  whole  block  of  limestone,  due  to  the  con- 
tact of  the  main  stock  of  porphyry. 

The  principal  metamorphic  area  at  Morenci  is  about  2  miles 
long;  its  width  is  from  1,000  to  1,500  feet.  The  Modoc  forma- 
tion, however,  has  been  affected  to  an  extraordinary  degree, 
and  extends  as  a  stratum  of  garnet  and  magnetite  2,000  ft. 
distant  from  the  contact  between  almost  unaltered  Devonian 
and  Cretaceous  sediments. 

The  Longfellow  limestone,  though  somewhat  irregularly 
altered,  is,  next  to  the  contact,  generally  transformed  into  a 
coarsely  granular  rock  of  garnet,  epidote,  diopside,  magnetite, 
pyrite,  zinc-blende,  and  chalcopyrite,  and  there  is  a  most  de- 
cided change  of  composition,  chiefly  consisting  in  additions  of 
silica  and  iron.  Other  parts  are  less  altered,  but  contain  much 
magnetite,  together  with  the  sulphides  mentioned,  disseminated 
through  a  medium-grained  crystalline  mass  of  the  carbonates 
of  lime  and  magnesia.  The  development  of  magnetite,  metaso- 
matically,  is  a  most  pronounced  feature  of  the  process.  Look- 
ing at  the  formation  as  a  whole;  sulphur,  iron,  copper  and  zinc 
have  certainly  been  added,  and  probably  also  silica  and  mag- 
nesia. Large  masses  of  magnetite,  locally  used  as  a  flux,  have 
been  mined  at  this  horizon. 

The  Morenci  shales  have  suffered  a  change  to  dense,  green- 
ish hornfels  with  a  development  of  amphibole  and,  in  places, 
also  muscovite.  Pyrite  and  magnetite  are  also  present,  but  on 
the  whole,  the  change  in  composition  is  probably  slight. 

The  Modoc  limestone,  containing  about  96  per  cent,  of  car- 
bonate of  lime,  has  proved  extremely  susceptible,  and  over  large 
areas  at  Morenci,  as  well  as  at  Metcalf,  it  is  converted  to  a 
massive  sheet  of  lime-iron  garnet ;  magnetite  is  usually  present; 


524      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

epidote  and  oxidized  copper-ores  are  also  of  frequent  occur- 
rence. This  transformation,  involving  large  additions  of  silica 
and  ferric  iron  is  very  noteworthy,  as  the  evidence  is  entirely 
micontrovertible.  Analyses  of  the  garnet  and  of  the  unaltered 
limestone  are  given  in  my  report,  now  in  press. 

The  contacts  of  the  sedimentary  series  and  the  porphyry  are 
sharp  and  show  no  evidence  of  assimilation.  All  of  the  con- 
tact metamorphic  rocks,  when  unaffected  by  oxidation,  are  very 
compact  and  hard,  atmospheric  waters  finding  great  difficulty 
in  attacking  them.  Considering  that  great  amounts  of  carbon 
dioxide  have  been  expelled  during  the  metamorphism,  it  is 
clear  that  a  great  shrinkage  of  volume  should  have  taken  place 
if  no  additions  of  material  had  been  received.  Such  a  reduc- 
tion of  volume  has  evidently  not  taken  place,  and  I  believe  that 
any  loss  has  been  fully  balanced  by  gains  from  material  con- 
tained in  magmatic  solutions. 

The  question  whether  contact  metamorphic  rocks  simply  rep- 
resent a  recrystallization,  or  whether  they  have  received  addi- 
tional substance  from  the  cooling  magma,  is  a  most  important 
one.  Prof.  Rosenbusch  believes  that  little  or  no  additional 
substance  has  been  received  and  considers  that  it  is  possible  to 
determine  the  original  character  of  metamorphic  rocks  from 
their  present  composition.1  This  idea  has  recently  been  fol- 
lowed out  by  Dr.  J.  Barrell  in  his  study  of  certain  contact  meta- 
morphic rocks  of  Montana.  In  this  paper2  he  advances  the  fol- 
lowing generalization  that  "  carbonic  acid  is  only  expelled 
where  the  siliceous  impurities  of  the  limestone  are  sufficient  to 
combine  with  the  lime  set  free."  Based  on  this  he  obtains  the 
further  result  that  a  great  loss  of  volume  has  taken  place  and 
that  it  is  possible  to  calculate  original  constituents  (kaolin, 
silica,  magnesite,  and  calcite)  from  any  given  rock  more  or  less 
altered  to  wollastonite,  garnet,  epidote,  etc.  If  these  statements 
are  really  meant  as  generalizations,  as  would  appear  from  the 
paper,  they  are  not  supported  by  convincing  proofs.  Magmatic 
additions,  though  mentioned,  are  not  considered  important. 

1  Man  kann  es  also  als  ein  Gesetz  aussprechen  dass  bei  der  Kontakt-meta- 
morphose  urn  Tiefengesteine  das  Eruptivgestein  nur  physikalisch  und  im  allge- 
meinen  nicht  durch  Stoffabgabe  cliemisch  wirkte.  Mikroskopische  Physiographic, 
3ded.,  p.  85. 

3  The  Physical  Effects  of  Contact-Metamorphism,  American  Journal  of  Science, 
vol.  xiii.,  pp.  279  to  296  (April,  1902). 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENGI.       525 

Prof.  Zirkel  says3  that  in  nearly  all  cases  the  contact-meta- 
m orphic  rocks  simply  represent  a  recrystallization  of  original 
constituents.  He  believes  that  the  contact-metamorphism  sim- 
ply took  place  by  reason  of  the  pressure  and  heat  exerted  by 
the  molten  rock,  and  speaks  rather  slightingly  of  the  view  that 
substance  from  the  magma  can  be  transferred  to  the  surround- 
ing strata,  although  admitting  that  in  one  or  two  cases  it  seems 
to  have  happened.  Hawes,  as  is  well  known,  proved — in  the 
case  of  the  Albany  contact-zone — an  increase  of  silica  towards 
the  contact  and  also  a  certain  amount  of  boron  which  appeared 
to  have  been  given  off  by  the  granite.  Prof.  Brogger,  to  whom 
we  owe  a  most  careful  description  of  the  Kristiania  contact- 
zone,  says,  that  on  the  whole,  the  alteration  seems  to  involve 
chiefly  a  recrystallization,  although  certain  of  the  phenomena 
strongly  suggest  local  accession  of  material,  though  rather  from 
adjacent  strata  than  from  the  intrusive  body. 

This  seems  a  rather  crushing  array  of  authoritative  testimony 
from  the  petrographic  side  and  it  has  even  been  intimated  by 
Prof.  Klockmann,4  in  a  recent  paper  combatting  the  theory  of 
transfer  of  material  from  magmas  to  sediments,  that  it  ought 
to  be  sufficient  to  settle  the  question.  While  I  do  not  doubt 
in  the  least  the  correctness  of  the  conclusions  drawn  in  indi- 
vidual cases  by  such  eminent  authors  as  Professors  Rosenbusch 
and  Zirkel,  it  is  certain  that  contact-metamorphism  manifests 
itself  in  many  various  ways,  and  that  the  particular  phases  con- 
nected with  mineral  deposits  have  been  rather  conspicuously 
neglected  by  many  petrographers,  whose  data  and  statements 
in  regard  to  the  occurrence  of  ores,  even  in  ordinary  rocks, 
have  always  seemed  to  me  to  suffer  somewhat  from  lack  of 
detail  and  precision. 

On  the  other  hand,  many  French  authors,  among  these  Prof. 
Michel-Levy,  and,  lately,  Prof.  J.  H.  L.  Yogt,5  of  Kristiania,  to- 
gether with  a  growing  number  of  younger  scientific  men,  have 
strongly  contended  that  many  substances  are  given  off  by  the 
cooling  magma  and  enter  the  adjoining  strata.  This  view  is 

3  Lehrbbch  der  Petrographie,  2d  ed.,  vol.  i.,  p.  587,  588. 

4  Zeitschrift/iir  Praktische  Geologic,  vol.  xii.,  p.  78  (March,  1904). 

5  See  Trans.,  xxxi.,  637  to  640  and  The  Genesis  of  Ore-Deposits,  p.  648,  2d  ed. 
(1902). 


526       GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

shared  by  myself  and  expressed  in  a  recent  paper  on  contact- 
metamorphic  deposits.6 

The  truth  seems  to  be  that  in  many  cases  no  perceptible  ac- 
cession of  substance  from  the  magma  has  taken  place,  while 
perhaps,  equally  often,  important  additions  have  been  received. 
How  far  the  heat  and  the  gases  from  the  intruded  magma  will 
penetrate,  and  what  effects  they  will  produce,  depend  on  many 
factors.  As  shown  above,  the  composition  of  the  magma  is 
sometimes  a  factor  of  importance.  In  case  of  the  Morenci  con- 
tact-zone, the  quantity  of  substance  available  seems  to  stand  in 
direct  relation  to  the  quantity  of  quartz  in  the  porphyry.  In 
many  intrusive  magmas  there  may  be  a  very  small  quantity  of 
water  present ;  the  access  of  material  may  then  be  slight  and  the 
contact-phenomena  mostly  due  to  the  heat  of  the  rock.  The  dif- 
ference in  susceptibility  of  the  various  beds  is  also  strongly 
marked ;  all  investigators  agree  on  this  point.  In  this  district 
impure  and  very  compact  limestones  resist  alteration  much 
more  than  coarse-grained  pure  rocks  of  the  same  kind;  and 
the  change  in  composition  in  the  case  ot  clay-shales  is  extremely 
slight. 

Study  of  the  Morenci  contact-zone,  as  a  whole,  proves  conclu- 
sively that  most  important  accessions  of  substance  have  been 
received.  The  rocks  inside  of  the  altered  zone  contain  an 
enormous  quantity  of  sulphur,  iron,  copper,  and  zinc.  Iron  is, 
of  course,  contained  in  the  unaltered  rocks  to  some  slight  ex- 
tent, but  in  nothing  like  the  quantities  accumulated  in  the 
contact-zone ;  sulphur,  copper  and  zinc  in  noticeable  amounts 
are  absent  from  the  unaltered  rocks.  Were  they  present,  to 
the  extent  of  a  small  fraction  of  the  percentage  contained  in  the 
contact-zone,  they  could  be  detected,  either  directly  or  through 
the  products  of  their  surface-oxidation.  The  minerals  in  which 
these  substances  are  contained  were  certainly  formed  contempo- 
raneously with  the  ordinary  contact-minerals  of  the  district, 
like  garnet,  diopside  and  epidote. 

The  metasomatic  development  of  magnetite  in  pure  lime- 
stones which  has  recently  been  questioned  by  Prof.  Klockmann 
may  be  observed  in  almost  countless  localities  at  Morenci  and 
Metcalf,  both  in  the  field  and  under  the  microscope.  It  is 

6  Trans.,  xxxi.,  226-244  (1901)  and  The  Genesis  of  Ore-Deposits,  p.  716,  2d  ed. 
(1902). 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       527 

known  that  iron  was  not  contained  to  this  extent  in  the  original 
rock,  but  to  demonstrate  its  actual  derivation  in  each  case  is, 
of  course,  difficult.  The  question  becomes  clear  only  when  we 
compare  the  contact-zone  as  a  whole  with  the  original  unal- 
tered rocks.7 

It  seems  very  strange  that  any  one  can  doubt  the  possibility 
"of  such  additions,  and  overlook  what  must  happen  when  a 
magma  in  aqueous  fusion  is  suddenly  brought  up  to  higher 
levels  and  strongly  ionized  water-gas  above  the  critical  temper- 
ature is  largely  released  from  its  bonds.  It  must  of  necessity 
contain  dissolved  substances.  Even  at  comparatively  low  tem- 
peratures water  is  one  of  the  most  powerful  solvents  known, 
and  its  action,  when  a  perfect  gas,  is  probably  far  in  excess  of 
that  at  100°  or  200°  C.  It  is  well  known  that  some  rapidly 
congealed  rocks,  like  the  "  pitch  stone  "  from  Saxony,  contain 
up  to  8  per  cent,  of  water,  indicating  an  amount  of  water- 
gas  which,  per  cubic  meter  of  magma,  would  at  -f  4°  C.  cor- 
respond to  from  250  to  300  liters.8  All  magmas  may,  of  course, 
not  have  contained  this  amount.  The  water-gas  seems  to  have 
penetrated  the  limestones  like  a  sponge,  inducing  extreme 
molecular  mobility.  Even  should  we  deny  any  additions  of 
substance,  a  most  remarkable  transferring  of  substance  has 
certainly  taken  place  in  the  rock,  as  shown,  for  instance,  by 
large  crystals  of  garnet  developing  in  limestones  of  uniform 

7  Professor  Kloekmann's  article,  which  is  really  intended  to  prove  that  no  im- 
portant deposits  of  magnetite  can  have  a  contact-metamorphic  origin  and  that  no 
important  material  can  be  transferred  from  cooling-magmas  to  adjoining  sedi- 
ments, was  published  in  Zeitschrift  fur  Praktinche  Geologie,  vol.  xii.,  p.  78  (1904). 
Among  the  arguments  used  is  one  referring  to  the  content  of  alumina  in  epidote, 
and  to  the  improbability  of  transfer  of  that  metal  from  magma  to  limestone.     At 
Morenci  the  massive  epidote  is  usually  confined  to  the  immediate  vicinity  of  the 
contacts,  and  I  fully  believe  that  some  transfer  of  alumina  has  actually  occurred. 
Regarding  the  occurrence  of  that  mineral  within  the  contact-metamorphic  zone, 
but  at  some  distance  from  the  actual  contact,  it  is  not  likely  that  the  alumina  repre- 
sents an  addition  from  the  magma,  but  it  is  certain  that  under  the  peculiar  condi- 
tions obtaining  during  the  metamorphism  the  alumina  to  no  small  degree  shared 
in  that  wonderful  molecular  mobility  which  characterized  the  whole  process. 

When,  however,  Prof.  Klockmann  refers  to  garnet  as  an  essentially  aluminous 
mineral,  a  typographical  error  must  surely  have  occurred.  All  garnets  do  not 
contain  alumina,  and  the  contact-metamorphic  garnets  at  Morenci  and  Metcalf 
are  throughout  andradites  or  lime-iron  garnets. 

8  E.  Weinschenk,  Vergleichende  Studien  ueber  den  Kontakt-Metamorphismus, 
Zeitschrift  der  deutschen  Geologuschen  Gesellschaft,  vol.  liv.,  p.  443  (1902\ 


528       GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

composition  containing  far  less  iron  and  silica  than  the  amounts 
required  by  the  newly-formed  mineral.  In  a  chapter  on  inclu- 
sions cogent  proof  will  be  brought  that  the  magma  actually 
was  accompanied  by  water  that  contained  a  large  amount  of 
substances  in  solution. 

A  misapprehension  of  the  character  of  contact-deposits  seems 
to  exist  in  many  quarters,  as  shown,  for  instance,  by  Prof. 
Klockmann,9  in  considering  the  presence  of  minerals  contain- 
ing boron,  fluorine,  etc.,  as  necessary  to  prove  the  contact- 
metamorphic  character  of  these  deposits.  To  such  arguments 
I  would  reply  that  the  character  of  magmatic  waters  evidently 
varies  greatly  in  different  magmas.  Some  may  carry  large 
quantities  of  the  substances  mentioned,  as  shown  by  the  presence 
of  tourmaline,  cassiterite  and  other  minerals  in  the  contact-met- 
amorphic  rocks,  while  others  may  be  almost  wholly  deficient 
in  them,  and,  instead,  carry  sulphur,  copper,  iron,  and  other 
metals.  In  the  Clifton  group  of  deposits,  I  would  be  inclined 
to  consider  molybdenum  a  characteristic  constituent,  taking 
the  place  of  tungsten  in  the  tin-deposits.  Any  attempt  to  re- 
duce the  wonderful  variety  in  the  contact-metamorphic  deposits 
to  a  single  pattern  is  doomed  to  failure. 

In  a  short  paper  dealing  with  contact-metamorphic  deposits 
in  North  America,10 1  emphasized  the  irregular  form  of  most 
ore-deposits  of  this  kind  and  declared  that  they  only  occur 
close  to  the  contact  or,  at  most,  a  hundred  feet  away.  As  a  re- 
sult of  wider  observations  I  would  modify  this  statement;  as 
far  as  we  know  at  present,  they  may  occur  several  hundred  or 
even  2,000  ft.  away  from  the  contact.  In  fact,  disseminated 
sulphides  and  magnetite  occur  at  Morenci  as  far  as  2,000  ft. 
from  the  main  contact. 

A  tabular  form  of  deposits  often  noted  is  usually  due  to  the 
strongly  marked  difference  in  susceptibility  of  the  various  beds. 
Wherever  the  deposits  have  been  enriched  by  oxidation  the 
form  may  be  more  or  less  dependent  upon  these  changes. 

Mr.  W.  H.  Weed  has  noted  the  tabular  shape  in  contact- 
deposits  at  Cananea,  Mexico,  and  makes  the  form  a  basis  of 
classification.11  I  do  not  believe,  however,  that  distance  from 

9  Zeitschrift/iir  Praktische  Geologic,  vol.  xii.,  p.  75. 

10  Trans.,  xxxi.,  226  (1901). 

11  Ore-Deposits  near  Igneous  Contacts,  p.  364,  this  volume. 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       529 

contact  (within  limits  given  above)  and  shape  are  at  all  essen- 
tial, and  can  find  no  mineralogical  difference  between  deposits 
varying  in  these  respects. 

Hydrothermal  Metamorphism. 

Both  the  porphyry-  and  the  contact-zone  are  traversed  by  fis- 
sure-veins which  carry  pyrite  with  a  small  quantity  of  chalcopy- 
rite,  zinc-blende  and  molybdenite,  whenever  oxidation  has 
not  changed  these  minerals.  These  pyritic  veins  are  of  low — 
generally  unpayable — tenor ;  they  consist  of  prevailingly  gran- 
ular or  massive,  very  rarely  crustified,  minerals  with  a  little 
quartz-gangue,  and  are  believed  to  have  been  formed  by  pyri- 
tic replacement  along  well-defined  fissure-planes.  In  the  por- 
phyry these  veins  are  surrounded  by  very  wide  zones  in  which 
the  rock  is  greatly  altered  by  the  introduction  of  sericite  and 
pyrite,  and  this  applies  to  Metcalf  as  well  as  to  Morenci.  At 
the  latter  place  almost  the  whole  of  Copper  mountain,  contain- 
ing the  most  important  lodes,  is  thus  altered.  The  process 
which,  in  my  complete  report,  is  elucidated  by  many  analyses, 
produces  bleached  rocks  of  varying  hardness  in  which  all  of 
the  feldspar  has  been  replaced  by  sericite  and  some  pyrite. 
The  biotite  and  hornblende  are  transformed  into  chlorite  and 
serpentine,  while  the  silica  of  the  rock  remains  almost  constant. 
All  of  the  lime  and  soda  is  eliminated,  while  potash  is  greatly 
increased.  No  carbonates  are  formed  during  this  process. 

Little  alteration  is  noted  where  fissure-veins  cut  through 
contact-metamorphic  shale,  nor  when  highly  altered  garnet- 
magnetite  rock  forms  the  walls,  but  in  unaltered  or  slightly 
metamorphosed  limestone  a  change  is  observed,  For  a  short 
distance  from  the  vein — a  few  inches  or  a  few  feet — the  rock 
is  bleached  and  proves  to  have  been  converted  into  tremolite, 
more  rarely  diopside,  with  disseminated  pyrite,  chalcopyrite, 
and  zinc-blende,  all  more  or  less  intimately  intergrown  with 
magnetite.  This  alteration  involves  a  loss  of  carbon  dioxide 
and  some  lime,  as  well  as  addition  of  silica,  iron,  magnesia, 
and  the  sulphides  mentioned  above.  More  rarely  argilla- 
ceous limestones  are  altered  to  sericitic  minerals  with  magne- 
tite and  sulphides.  Magnetite  has  not  been  observed  in  the 
massive  pyritic  veins,  although  it  occurs  in  the  altered  country- 
rock. 


530      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

Relation  of  Contact  and  Hydrothermal  Metamorphism. 

The  alteration  of  limestone  along  fissure-veins  to  tremolite 
(or  diopside)  with  magnetite  and  sulphide  is,  so  far  as  I  know,  a 
novel  one.  Ordinarily,  limestone  alters  next  to  fissure.-veins  to 
dolomite  or  quartz  or  jasperoids.12  The  addition  of  silica  and 
iron  and  the  mineralogical  trend  of  the  hydrothermal  process 
at  Morenci  undoubtedly  connects  it  in  some  way  with  contact- 
metamorphism,  making  it  probable  that  the  alteration  took 
place  at  high  temperature  comparatively  soon  after  the  solidi- 
fication of  the  porphyry. 

At  first  glance,  it  might  seem  plausible  to  assign  all  the 
changes  which  have  taken  place  in  the  metamorphic  zone  to 
the  same  hydrothermal  alteration  which  has  affected  the  por- 
phyry along  the  fissure-veins.  This  view,  however  tempting, 
is  surely  incorrect.  Instead  of  one  set  of  phenomena,  there  are 
two  related  and,  in  part,  superimposed  processes.  Among  the 
proofs  of  this  are  the  absence  of  sericitization  in  the  porphyry 
of  many  dikes  which  have  exerted  strong  contact-metamor- 
phism. Further,  the  entire  independence  which  the  masses  of 
extremely  altered  garnet-magnetite  rock  show  in  regard  to  the 
fissure-veins,  and  their  distinct  dependence  on  contact  of  dikes 
and  main  stock.  The  vein-alteration  produces  dull,  earthy 
rocks  from  the  limestone,  while  contact-metamorphism  results 
in  hard,  compact  and  granular  rocks.  On  the  other  hand, 
there  is  undoubtedly  a  certain  relation  between  the  two  pro- 
cesses for  amphibole  (and  pyroxene)  occurs  in  the  true  contact- 
metamorphic  rocks,  and  the  intergrowth  of  magnetite  and 
pyrite  is  characteristic  of  both.  I  should,  therefore,  conclude 
that  after  the  completion  of  the  contact-metamorphism,  prop- 
erly speaking,  and  after  the  consolidation  of  the  porphyry,  an 
extensive  fissuring  took  place  and  solutions  derived  from  the 
cooling  porphyry,  probably  ascending  and  laterally  extending 
from  this  rock,  flowed  through  these  fissures.  Everything  in- 
dicates that  these  solutions  were  closely  related  to  those  which 
emanated  from  the  magma  at  the  moment  of  intrusion  and,  in 
fact,  similar  in  general  composition. 

As  to  the  quantitative  relation  of  contact-metamorphism  and 
hydrothermal  metamorphism,  it  is  difficult  to  speak  with  ab- 

12  W.  Lindgren,  Metasomatic  Processes  in  Fissure- Veins,  Trans.,  xxx.,  578  to  692. 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       531 

solute  certainty.  In  some  parts  of  the  contact-metamorphic 
rocks  small  seams  with  sulphides  and  magnetite  are  very  abund- 
ant (for  instance,  in  the  Yuvapai  mine)  and  it  is  not  easy  to  say 
how  much  of  this  should  be  credited  to  each  form  of  alteration, 
for  the  sedimentary  rocks  were  evidently  solid  during  the  in- 
trusion, and  seams  filled  with  sulphides  may  well  have  formed 
in  them.  Generally  speaking,  they  would  be,  and,  in  fact,  are 
at  present  much  less  permeable  to  solutions  than  the  porphyry, 
as  shown  by  the  slight  depth  which  oxidation  has  attained  in 
them,  and  it  is  believed  that  the  hydrothermal  solutions  were 
chiefly  confined  to  cracks  and  fissures  in  contradistinction  to 
the  much  more  searching  action  of  gaseous  water.  The  facts 
above  given  show  indeed  how  slight  is  the  lateral  spread  of 
alteration  from  the  veins  in  limestone.  That  the  solutions 
producing  the  contact-metamorphism  effected  such  intense  re- 
sults is  probably  due  to  the  existence  of  a  far  greater  degree 
of  heat  and  gas-pressure. 

Processes  Due  to  Oxidation  and  Hydration  in  the  Altered  Zone. 

Under  influence  of  surface-waters  (but  protected  from  direct 
oxidation),  chlorite  and  serpentine  form  from  the  tremolite  and 
diopside  of  the  contact-zones,  while  garnet  is  little  altered. 
Under  direct  oxidizing-action,  garnet  changes  to  limonite  and 
quartz,  while  lime  is  probably  carried  away  as  carbonate. 
Tremolite  and  related  minerals  are  similarly  affected.  Magne- 
tite oxidizes  to  hematite  and  limonite,  many  large  bodies  of 
which  are  mined  for  fluxing-purposes.  Pyrite  changes  by 
direct  oxidation  into  ferrous  sulphate  and  free  sulphuric  acid ; 
the  ferrous  sulphate  upon  further  oxidation  yields  ferric  sul- 
phate and  the  latter  is  easily  decomposed  into  basic  sulphates, 
ferric  hydrates  and  free  acid;  ferric  sulphate  is  also  ready  to 
attack  pyrite  and  other  sulphides,  changing  them  to  sulphates 
and  being  itself  reduced  to  ferrous  sulphate. 

This  cycle  of  reactions  will  finally  transform  all  of  the  sul- 
phides present  into  various,  more  or  less  soluble,  oxy-salts.  A 
large  part  of  the  pyrite  will  be  changed  to  limonite.  Such 
"  iron  caps  "  are  seen  at  the  outcrops  of  many  veins  in  regions 
where  oxidation  proceeds  undisturbed  by  erosion,  but  in  this 
region  they  are  generally  absent. 

The  veins  are  marked  by  siliceous  outcrops,  either  entirely 


532       GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

barren  or  containing  small  amounts  of  oxidized  copper-ores. 
N"o  basic  ferric  sulphates  have  been  seen  either  in  the  mines 
or  on  the  surface.  The  waters  percolating  downwards  must 
soon  have  lost  their  oxygen  and,  for  the  alteration  at  greater 
depths,  ferrous  sulphate  and  dilated  sulphuric  acid  are  prob- 
ably the  only  reagents  of  importance  resulting  from  the  py- 
rite.  It  is  clear  that  the  upper  part  of  the  veins  have  not 
been  formed  by  simple  oxidation  of  pyrite  and  accumulation 
of  limonite. 

Direct  oxidation  of  chalcopyrite  yields  cupric  and  ferrous 
sulphates,  while  the  zinc-blende  produces  zinc  sulphate;  both 
of  these  processes  are  in  evidence  wherever  the  disseminated 
sulphides  in  the  metamorphic  rocks  are  exposed  to  oxidation. 
The  general  order  of  attack  of  oxygen  is  usually  stated  as 
follows : — Arsenopyrite  (most  easily  attacked),  pyrite,  chalco- 
pyrite, blende,  galena  and,  finally,  chalcocite  (most  difficultly 
attacked).  This  rule  is  probably  true  only  for  one  set  of  con- 
ditions as  to  mass,  aggregate  and  character  of  solutions.  Very 
marked  exceptions  from  it  occur  at  Morenci. 

Sulphate  Waters. — Descending-waters  from  a  lode  of  decom- 
posing pyrite,  chalcopyrite  and  zinc-blende  should  contain 
chiefly  ferrous,  cupric  and  zinc  sulphates,  together  with  free 
sulphuric  acid.  The  first  two  salts  are  easily  soluble,  but  far 
more  so  is  the  zinc  sulphate. 

Cuprous  sulphate  is  stable  only  under  certain  conditions  and 
is  not  believed  to  be  an  important  reagent,  though  it  may  form 
during  subsidiary  or  intermediate  reactions.  Its  presence  in 
any  mine-waters  has  not  been  satisfactorily  proved. 

In  this  district,  some  moisture  percolates  the  upper  workings, 
as  shown  by  efflorescences  and  stalactites  of  sulphates,  but  the 
mines  are  practically  dry.  In  the  porous  porphyry  the  mois- 
ture spreads  easily,  while  the  hard  metamorphic  rocks  offer  con- 
siderable resistance. 

Processes  in  Fissure-  Veins. — Below  the  region  of  oxidizing- 
influences  the  veins  consist  of  pyrite,  chalcopyrite  and  zinc- 
blende,  while  the  upper  few  hundred  feet  contain  chalcocite 
and  oxidized  copper-ores.  The  most  important  action  of  the 
descending  sulphate  solutions  has  been  a  development  of  chal- 
cocite by  the  action  of  cupric  sulphate  on  primary  py rite-ore ; 
this  process  began  at  the  time  the  veins  were  first  touched  by 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON,MORENCI.       533 

oxidizing  waters,  and  continues  to  some  extent  to  the  present 
time. 

If  secondary  deposition  of  sulphides  has  taken  place  accord- 
ing to  Schuermann's  reactions,  they  should  be  arranged  in  the 
upper  zones  of  the  deposit  in  the  following  order: — (Top), 
galena,  zinc-blende,  chalcocite,  bornite,  chalcopyrite  and  pyrite. 
(Bottom.) 

In  Morenci,  practically  only  chalcocite  thus  forms.  The  first 
of  the  primary  minerals  attacked  is  the  zinc-blende  which  ap- 
pears to  be  rapidly  transformed,  first  into  covellite  and  then 
into  chalcocite,  as  follows : 

ZnS  +  CuS04  =  ZnS04  +  CuS. 

Chalcopyrite,  present  only  in  small  quantities,  is  probably 
attacked  at  the  same  time.  The  zinc  sulphate  is  carried  away 
and  no  zinc  minerals  appear  in  the  upper,  oxidized  part  of  the 
veins. 

Contrary  to  the  list  just  given  above,  blende  is  thus  attacked 
before  the  pyrite.  The  conversion  of  pyrite  to  chalcocite  may 
be  studied  in  all  stages  of  the  process;  it  is  a  molecular  re- 
placement attacking  the  pyrite  from  cracks  and  fissures,  and 
gradually  eliminating  it  entirely.  However,  even  in  the  best 
chalcocite-ores  residual  pyritic  cores  ordinarily  remain.  Dr. 
Stokes  has  shown  that  the  reaction  at  +  100°  C.  and  -f  200°  C. 
proceeds  as  follows : 

5  FeS2  +  14  CuS04  -f  12  H20  =  7  Cu.2S  +  5  FeS04  -f-  9  H2S04 
-f-  3  H2S04,  the  last  H2S04  being  formed  by  oxidation  of  the 
sulphur  of  FeS2.  It  is  probable  that  the  reaction  likewise  goes 
on,  though  more  slowly,  between  -f  100°  C.  and  -|-  20°  C.,  the 
range  probably  existing  in  the  deposit  during  the  period  of  oxi- 
dation. Mr.  H.  V.  Winchell's  reaction13  necessitates  sulphur- 
ous acid  as  a  reagent,  the  presence  of  which  seems  unlikely. 
The  equations  given  by  Prof.  Van  Hiseu  for  the  formation  of 
secondary  copper  sulphides  seem  improbable,  as  they  require 

13  Synthesis  of  Chalcocite  and  Its   Genesis  at  Butte,  Montana,  Bulletin  of  the 
Geological  Society  of  America,  vol.  xiv.,  pp.  269-276. 

14  Some  Principles  Controlling  the  Deposition  of  Ores,  Trans.,  xxx.,  101,  111, 
112. 


534      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

the  presence  of  free  oxygen,  and  as  they  are  generally  based 
on  cuprous  sulphate. 

By  this  process  of  alteration  the  massive  pyritic  veins  have 
been  transformed  into  almost  solid,  dull,  sooty  chalcocite;  and 
the  zones  of  dissemination  surrounding  them  in  the  porphyry 
have  changed  into  low-grade  chalcocite-ores.  The  process  is  ac- 
companied by  the  formation  of  some  kaolin,  quartz,  chalcedony, 
and  probably  also  opal.  No  sericite  forms.  The  kaolin  develops 
metasomatically  at  the  expense  of  the  sericite,  and  sulphuric 
acid  was  evidently  the  reagent.  Alunite  is  in  places  formed  in 
the  same  manner.  Extremely  large  amounts  of  ferrous  sulphate 
must  have  been  carried  away  during 'this  process. 

Oxidation  of  Chalcocite. — After  a  large  part  of  the  chalcocite 
in  the  lode  had  been  formed,  there  came  a  time  when  erosion 
and  degradation,  working  faster  than  oxidation,  began  to  expose 
the  upper  part  of  the  chalcocite-zone  to  active  and  direct  attack 
by  oxygen.  Practically  all  of  the  veins  are  in  this  stage.  The 
present  zones  of  active  oxidation  are  therefore  due,  not  to  direct 
oxidation  of  the  primary  lode,  but  to  the  destruction  of  the  upper 
horizon  of  the  chalcocite-zone.  As  reagents,  there  are  here  fer- 
rous sulphate,  sulphuric  acid,  cupric  sulphate  and  free  oxygen. 
Any  ferric  sulphate  present  would  soon  be  reduced  to  ferrous 
salt  by  the  abundant  pyrite.  Chalcocite  changes  to  cuprite  and 
cupric  sulphate,  sometimes  with  an  intermediate  stage  of  cov- 
ellite. 

2  Cu2S  +  0  =  2  CuS  +  Cu,0  and  CuS  +  40  =  CuS04. 

Cuprite  partly  reduced  to  metallic  copper  is,  in  fact,  abundantly 
present  in  the  upper  limit  of  the  chalcocite-zone. 

Cu20  +  H2S04=  Cu  +  CuS04  +  H20. 

By  some  process  not  quite  elucidated,  chalcocite  may,  in  places,, 
change  directly  into  native  copper.  The  zone  of  cuprite  and 
metallic  copper  has  rarely  great  vertical  extension,  for  the 
reason  that  both  minerals  are  rapidly  converted  into  cupric  sul- 
phate, brochantite,  malachite,  azurite  and  chrysocolla;  but  these 
products  are  soon  dissolved  by  free  sulphuric  acid  from  pyrite, 
a  mineral  which  tenaciously  remains  until  the  last,  and  descend 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       535 

as  soluble  sulphates  to  enrich  the  upper  part  of  the  chalcocite 
zone. 

In  the  Copper  Mountain  veins,  contained  in  porphyry,  oxi- 
dized copper-minerals  are  almost  entirely  absent,  probably  be- 
cause of  the  great  amount  of  free  sulphuric  acid  present.  The 
chalcocite  disappears  at  from  100  or  200  ft.  below  the  surface, 
and  the  lode  consists  of  a  rusty  mass  of  sericitized  porphyry, 
with  considerable  amounts  of  remaining  pyrite  and  efflores- 
cences of  cupric  sulphate.  The  last  particles  of  pyrite  only 
disappear  close  to  the  surface. 

In  places,  chalcocite  may  change  directly  into  brochantite 
or  malachite.  Cupric  oxide  (melaconite  or  tenorite)  has  not 
been  found. 

Oxidizing  Processes  in  Limestone. — The  processes  which  have 
resulted  in  the  oxidized  deposits  now  forming  irregular  or  tab- 
ular masses  in  limestone  or  shale,  and  not  connected  with  fis- 
sures, are  materially  different  from  those  occurring  in  the  lodes. 
In  most  cases  the  original  material  consisted  of  disseminated 
lean  pyritic  ores,  containing  pyrite,  chalcopyrite,  zinc-blende, 
and  magnetite,  locally  more  or  less*  concentrated  in  irregular 
masses,  or  following  certain  strata-  or  dike-contacts.  Free  oxy- 
gen and  sulphuric  acid,  ferrous  and  cupric  sulphates,  with  an 
abundance  of  calcium  carbonate,  formed  the  reagents.  Though 
oxygen  and  carbon  dioxide  may  in  part  have  produced  limonite 
and  malachite  directly  from  pyrite  and  chalcopyrite,  the  most 
important  reactions  doubtless  were  those  between  calcium  car- 
bonate and  sulphate  solutions,  partly  derived  from  nearer  the 
surface. 

2  CuSQ4  -t-  2  CaC03  -f  H2O  =  (CuOH)2,  C03,  +  2  CaS04  + 

C02  +  H2S04. 
3  CuS04  -f-  3  CaC03  +  H20  =  (CuOH)2,  Cu  (C03)2  -f  3  CaS04 

+  C02. 

In  the  first  case  malachite,  in  the  second  azurite  forms,  to- 
gether with  gypsum.  The  latter  mineral,  though  largely  car- 
ried away  in  solutions,  is  not  uncommon  in  these  deposits  at 
Morenci.  Ferric  hydrate  will  be  produced  from  ferrous  sul- 
phate and  calcium  carbonate.  Thus,  in  general,  is  explained 
the  constant  occurrence  in  these  deposits  of  malachite,  azurite 


536      GENESIS    OP    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

and  limonite.  Crusts  of  replacing-malachite  and  azurite  fre- 
quently surround  residual,  rounded  masses  of  limestone.  The 
gangue  of  garnet  and  magnetite  alters  to  ferric  hydrate  and 
quartz.  Chrysocolla  forms  when  silica  is  plentiful ;  zinc-min- 
erals are  not  uncommon  in  these  deposits,  and  efflorescences  of 
the  zinc  and  magnesia  sulphates  sometimes  cover  the  tunnel- 
walls.  During  the  process  outlined  above,  lime  is  almost 
wholly  eliminated,  while  alumina  forms  residual  concentra- 
tions. 

Oxidizing  Processes  in  Shale. — Disseminated  cuprite  in  beds 
of  Morenci  shale  is  a  common  occurrence,  and  some  of  the 
large  ore-bodies  of  the  Manganese  Blue  mine  were  of  this 
character.  It  occurs  as  flakes  on  the  bedding-planes,  or  in 
small  replacement-veins,  sometimes  accompanied  by  distinctly- 
later  malachite  and  by  limonite.  These  occurrences  seemed 
difficult  to  explain,  but  light  is  thrown  on  them  by  recent  ex- 
periments by  Dr.  E.  Kohler,15  who  shows  that  solutions  of  cupric 
sulphate,  filtered  through  kaolin,  become  hydrolyzed  by  adsorp- 
tion. The  copper  is  precipitated  as  oxide,  and  sulphuric  acid 
is  set  free.  (Experiments'are  now  in  progress  which  seem  to 
indicate  that  the  Morenci  shale  possesses  remarkable  power  of 
adsorbing  copper  from  aqueous  solutions.) 

Azurite  also  occurs  frequently  in  shale,  as  shown  by  the 
second  ore-body  in  the  Detroit  mine.  Large  crystals  of  that 
mineral  develop  here,  metasomatically,  in  a  metamorphic  shale 
composed  of  sericite  and  amphibole.  Cases  have  been  observed 
where  azurite  envelops  masses  of  un decomposed  pyrite  accom- 
panied by  a  little  limonite.  During  the  oxidizing  process  the 
alumina  possesses  considerable  mobility.  It  is  dissolved  by  sul- 
phuric acid  from  clay-shale  and  forms  certain  aluminous  min- 
erals, notably  sericite.  The  aluminium  sulphate  formed  is  ex- 
tremely soluble  in  water,  and  thus  easily  transported.  At  many 
places  in  the  mines  of  Morenci,  pure  kaoli-n  forms,  together 
with  azurite  and  malachite. 

Paragenesis. 
The  minerals  formed  during  successive  stages  are  as  follows  : 

15  Adsorptionsprozesse  als  Faktoren  der  Lagerstattenbildung  und  Lithogenesis, 
Zeitschriftfur  praktische  Geohgie,  vol.  xi.,  p.  49  (1903). 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       537 


VEINS. 

Primary  Processes.  Pyrite,  chalcopyrite,  zinc-blende,  molybde- 

nite (rarely  magnetite),  sericite,  quartz,  rarely 
tremolite,  diopside  and  epidote. 

Introduction  of  iron,  sulphur,  zinc,  copper, 
.molybdenum,  potassium  and  silica.      Elimi- 
nation of  calcium  and  sodium. 
Processes  of  Oxidation.  (     Chalcocite  (rarely  covellite,   chalcopyrite, 

,      I  and  bornite),  quartz,  chalcedony,  kaolin,  alu- 
Action  of  sulphate  solu-  I     . 

tions  without  oxygen.  J  m  ®'  . 

Introduction   of    copper.      Elimination    of 

L  zinc,  some  iron  and  sulphur. 
f      Cuprite,  native  copper,  brochantite,  malaj 
I  chite,  chrysocolla  (rarely  azurite),  chalchan- 
Action   of  directly  oxi-J  thite,  limonite,  quartz. 

dizing  solutions.  Introduction  of  carbon  dioxide.     Elimina- 


>tion  of  sulphur,  together  with  some  iron  and 
copper. 
CONTACT-DEPOSITS. 

Primary  Processes.  Pyrite,  magnetite,  chalcopyrite,  zinc-blende, 

molybdenite,  specularite,  garnet,  epidote,  di- 
opside, tremolite,  quartz. 

Introduction  of  much  iron  and  silica,  to- 
gether with  copper,  zinc,  molybdenum,  sul- 
phur, possibly  magnesia.  Elimination  of 
carbon  dioxide  and  probably  some  lime. 

Processes  of  Oxidation.  Limonite,  malachite,  azurite,  cuprite,  rarely 

native  copper  and  chalcocite,  copper-pitch  ore, 
chrysocolla,  goslarite,  zinc  carbonate,  wille- 
mite,  calamine,  pyrolusite,  quartz,  calcite, 
chlorite,  serpentine. 

Introduction  of  carbon  dioxide  and  addi- 
tional copper.  Elimination  of  calcium,  sul- 
phur, some  zinc  and  iron. 

CHARACTERISTICS  OF  DEPOSITS. 

Deposits  of  Carbonates  and  Oxides  in  Limestone  and  Shale. 

The  important  occurrences  of  these  ore-bodies  are  found  in 
the  Longfellow,  Manganese  Blue,  Detroit,  Copper  Mountain, 
Montezuma,  and  Shannon  mines. 

They  contain  practically  all  of  the  oxy-salts  of  copper  known 
from  the  district;  but  chiefly  malachite,  azurite  and  cuprite, 
with  very  subordinate  amounts  of  native  copper  and  chalco- 
cite. The  accompanying  minerals  consist  of  limonite,  manga- 
nese peroxide,  kaolin,  and  soft,  yellowish  material  which,  in  a 
large  proportion  of  deposits,  generally  proves  to  be  decompos- 

34 


538       GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

ing  and  hydrated  forms  of  tremolite,  diopside,  garnet,  or  epi- 
dote.  Some  deposits  of  chrysocolla  and  limonite  occur,  how- 
ever, in  unaltered  limestone,  and  the  cuprite-bearing  shales  are 
not  accompanied  by  any  gangue  except  a  little  limonite.  The 
copper-minerals  are  sometimes  formed  by  crustification,  but 
replacements  in  shale  or  lime  are  almost  equally  common. 

The  form  is  sometimes  wholly  irregular,  but  there  is  a 
marked  tendency  towards  a  tabular  form  following  certain 
strata  evidently  favorable  for  deposition.  The  horizontal  ex- 
tent varies  greatly,  but  rarely  exceeds  300  or  400  ft.,  and  the 
two  dimensions  are  apt  to  be  approximately  equal.  The  thick- 
ness ranges  from  1  to  30  ft.  and  is  sometimes  more.  Regular 
boundaries  rarely  occur,  and  the  pay-ore  easily  shades  off  into 
the  country-rock.  In  the  Manganese  Blue  and  the  Detroit 
mines  several  superimposed  ore-bearing  horizons  are  found 
within  300  ft.  of  the  surface.  The  Longfellow  deposit  has  the 
form  of  an  inverted  pyramid. 

Acidic  porphyry  is  found  in  the  immediate  vicinity  of  all  de- 
posits. Some  of  them  immediately  adjoin  the  contact  of  the 
main  stock,  but  others  show  decided  dependence  upon  dikes 
of  porphyry ;  one  class  of  deposits  forms  tabular  masses  along 
the  contacts  of  dikes ;  others,  such  as  the  Detroit,  the  Manga- 
nese Blue,  and  the  Longfellow,  lie  between  two  or  three  por- 
phyry dikes,  the  latter  being  largely  barren,  except  for  some 
disseminated  chalcocite.  Fissures  antedating  the  oxidation, 
but  subsequent  to  the  contact-metamorphism,  have  sometimes 
influenced  the  form  by  guiding  the  descending  waters. 

The  deposits  may  be  found  in  any  of  the  Paleozoic  horizons 
between  the  Coronado  quartzite  and  the  Cretaceous  beds. 
They  frequently  crop  at  the  surface,  azurite  appearing  to  resist 
decomposition  quite  obstinately. 

Driving  laterally,  or  sinking  deeper  from  these  ore-bodies,  is 
apt  to  develop  hard  limestone  with  typical  contact-metamor- 
phic  minerals  and  scattered  pyritic  ores.  The  very  confident 
conclusion  has  been  drawn  that  the  majority  of  these  deposits 
have  been  formed  by  the  oxidation  of  irregular  or  tabular 
masses  of  low-grade  pyritic  ores,  such  as  the  lower  mine-work- 
ings have  disclosed  in  such  abundance,  for  instance,  in  the 
Yavapai  mine. 

An  enrichment  accompanied  the  oxidation,  both  on  account 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCT.        539 

of  reduction  in  volume  and  introduction  of  additional  copper 
as  sulphate.  The  oxidation  does  not  reach  the  water-level 
which  is  far  below  the  present  workings,  but  acts  most  irregu- 
larly, sometimes  leaving  fresh  metamorphic  limestone  near  the 
surface  and  again  penetrating  along  fissures  to  a  depth  of  400 
feet. 

The  above  explanation  does  not  fit  all  of  these  deposits,  for 
some  are  unaccompanied  by  evidence  of  contact-metamorphism 
and  have  probably  primarily  been  formed  by  the  action  of 
thermal,  vein-forming  waters,  and  others  are  entirely  of  sec- 
ondary origin,  being  deposited  in  shales  and  in  the  clays  along 
important  faults  by  migrating  sulphate  solutions.  The  oxida- 
tion of  the  present  ore-bodies  followed  the  faulting  movement 
and  probably  began  at  a  rather  early  epoch  of  Tertiary  times. 

Fissure-  Veins  and  Related  Deposits  of  Morenci  Type. 

Fissure-veins  with  a  northeasterly  or  northerly  trend,  but  of 
no  great  individual  length,  follow  the  entire  length  of  the  por- 
phyry stock,  but  are  especially  developed  between  Morenci  and 
Metcalf  and  on  Copper  King  mountain.  The  most  prominent 
lode  system  at  Morenci  extends  for  about  2  miles,  and  consists 
of  a  number  of  shorter-linked  and  branching  fissures,  forming 
two  belts  slightly  curved  towards  the  southeast.  One  of  them 
lies  in  porphyry  within  a  few  hundred  feet  of  the  contact  and 
comprises  the  principal  mines  of  the  district — the  West  Yan- 
kee, the  Humboldt,  and  the  Copper  Mountain.  The  other  and 
parallel  system  traverses  the  metamorphic  rocks  a  few  hundred 
feet  southeast  of  the  contact. 

The  dip  is  steep  to  the  NW.  or  SE.  and  the  system  is  thus 
a  conjugated  one,  bearing  every  evidence  of  origin  by  com- 
pressive  stress. 

Outcrops  are  very  poor,  frequently  wholly  unrecognizable, 
and  it  is  most  difficult  to  trace  the  veins  on  the  surface.  Low- 
grade  malachite,  chrysocolla,  and  brochantite-ores  are  con- 
tained in  the  outcrops  of  some  veins.  Large  masses  of  limo- 
nite  while  common  enough  in  the  oxidized  contact-metamor- 
phic  deposits  do  not  usually  occur  in  the  vein-croppings. 

Underground  exposures  always  show  one  or  more  well-de- 
fined walls  frequently  polished  and  striated.  The  faulting- 
movement  on  these  fissures  is  slight. 


540      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

In  the  majority  of  these  deposits  there  is  a  central  vein  which 
ordinarily  is  4  ft.  wide  or  less,  but  may  sometimes  expand  to  50 
ft. ;  it  is  composed  of  nearly  massive  sulphides,  arid  closely  fol- 
lows the  fissure.  In  the  porphyry,  this  is  surrounded  by  a 
much  wider  zone  of  altered  rock  which  may  constitute  ore; 
the  central  vein  and  the  altered  zone  together  are  characterized 
as  a  "  lode."  In  almost  all  of  the  veins  the  following  vertical 
distribution  of  ores  is  noted : 

SURFACE  ZONE.  {  From  50  to  20°  ft  deep  from  the  cr°PPings-     Contains  oxi- 

l      dized  copper-minerals  or  is  barren. 
p  7          /  From  100  to  400  ft.  in  vertical  extent ;   possibly  more  in 

l      places.     Contains  clialcocite  and  pyrite. 

PYEITIC  ZONE  I  Begins  ^rom  2^  to  600  ft.  below  the  surface.    Contains  pyrite, 
I     chalcopyrite  and  zinc-blende. 

It  has  been  shown  that  the  minerals  of  the  two  upper  zones 
have  been  derived  from  those  of  the  pyritic  zone  by  processes 
of  direct  and  indirect  oxidation  ;  that  the  chalcocite  is  wholly 
formed  by  replacement  of  pyrite  effected  by  solutions  of  cupric 
sulphate ;  that  secondary  covellite,  chalcopyrite  and  bornite  only 
occur  in  very  small  amounts.  Also,  that  the  surface-zone  is 
derived  from  the  chalcocite-zone  by  its  direct  oxidation.  It 
has  further  been  emphasized  that  the  pyritic  zone  is  generally 
very  poor ;  that  the  chalcocite-zone  produces  the  richest  ore, 
and  that  the  surface-zone  is  always  poor  and  sometimes  barren. 

The  pyritic  part  of  the  veins  is,  with  good  reason,  believed 
to  represent  the  primary  deposition  of  sulphides  along  the  fis- 
sures. It  contains  a  small  amount  of  quartz-gangue  with  inti- 
mately intergrown  pyrite,  zinc-blende  and  chalcopyrite;  the 
two  last-named  minerals  are  present  only  in  small  quantities; 
molybdenite  also  occurs.  A  well-defined  foot-wall  is  usually 
present,  while  the  hanging-wall  may  be  more  or  less  indistinct 
or  represented  by  several  subordinate  fissures.  The  deposition 
seems  to  have  been  chiefly  effected  by  metasomatic  replace- 
ment of  crushed  and  sheeted  porphyry,  or  metamorphic  rock. 
The  zone  of  altered  rock  surrounding  the  vein  consists  of  seri- 
citized  and  pyritic  porphyry  when  the  vein  is  in  this  rock,  and 
may  then  be  very  wide.  In  the  hard,  metamorphic  limestone 
and  shale,  this  zone  is  narrow  and  shows  either  an  amphibo- 
litic  or  a  sericitic  alteration  and  contains  besides  pyrite,  chal- 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       541 

copyrite  and  zinc-blende  intergrown  with  magnetite,  a  mineral 
absent  from  the  vein  proper.  In  the  chalcocite-zone,  commer- 
cially the  most  important,  magnetite  has  largely,  but  rarely 
wholly,  replaced  the  pyrite,  both  in  the  massive  veins  and  in 
the  zones  of  pyritization  and  sericitization  surrounding  them 
at  a  certain  depth.  It  is  generally  sharply  separated  from  the 
pyritic  zone,  the  transition  taking  place  within  a  surprisingly 
short  distance.  Below  this  limit,  evidence  of  chalcocitization 
can  only  be  found  along  fissure-planes.  The  uppermost  part  of 
the  chalcocite-zone  is  invariably  the  richest.  The  massive  py- 
rite veins  form  pure,  dull  black  chalcocite,  or  a  mixture  of 
pyrite  and  chalcocite.  This*  constitutes  high-grade  ore  with 
more  than  5  per  cent,  of  copper — ranging  up  to  70  per  cent. — 
while  the  pyritized  porphyry  turns  into  low-grade  ores  with 
from  2  to  5  per  cent,  of  copper. 

To  these  large  bodies  of  low-grade  ore  the  recent  great  de- 
velopment of  the  district  is  due.  In  some  mines,  which  are 
generally  on  the  lower  slopes,  or  in  the  bottoms  of  canyons,  the 
chalcocite  begins  almost  at  the  surface.  At  Morenci,  situated 
high  up  on  the  hills,  the  depth  from  the  surface  is  rarely  less 
than  200  ft.  The  depth  on  the  vein  attained  by  the  chalcocite- 
zone,  from  the  level  where  direct  oxidation  begins  to  the  upper 
limit  of  the  pyrite-zone,  varies  greatly ;  it  is  sometimes  less 
than  100  ft.,  while  under  Copper  mountain  the  average  would 
somewhat  exceed  200  ft.  Directly  below  the  summit  it  is  300 
ft.,  and  its  lower  limit  in  some  cases  has  not  yet  been  reached. 
In  general,  the  upper  limit  would  be  represented  by  a  curved 
line  somewhat  less  convex  than  the  contours  of  the  mountain. 
The  lower  limit  seems  to  be  flatter,  but  great  irregularities 
exist,  due  no  doubt  to  exceptional  conditions  of  circulation  of 
surface-waters. 

The  great  bodies  of  low-grade  ore  are  almost  wholly  con- 
fined to  the  lodes  in  porphyry;  and  the  pay-zone  generally 
contracts  greatly  when  contact-metamorphic  shales  or  lime- 
stones are  entered.  Stopes  of  low-grade  ore  range  from  a  few 
feet  to  100  ft.  or  more  in  width ;  many  are  200  ft.  long  and 
have  been  stoped  for  the  same  vertical  distance.  The  great 
body  of  concentrating  ore  between  the  two  Humboldt  walls, 
which  dip  against  each  other,  is  about  300  ft.  long,  up  to  200 
ft.  wide,  and  has  been  stoped  200  ft.  high.  Values  gradually 


542        GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

decrease  on  both  sides  unless,  as  sometimes  happens,  cut  off 
by  fissures  on  one  or  both  sides.  The  limit  is  thus  usually 
simply  determined  by  the  lowest  grade  of  ore  workable.  Seri- 
citization  and  chalcocitization  has  spread  considerably  farther, 
laterally,  than  is  indicated  by  the  2.5  or  3  per  cent,  of  copper 
contained  in  the  lowest  grade  of  ore  mined. 

The  ore-shoots  of  Copper  mountain  are  thus  materially  dif- 
ferent from  those  usually  found  in  gold-  and  silver-veins.  Their 
greatest  extent  is  horizontal  rather  than  vertical,  and  their  size 
depends  more  upon  conditions  of  circulation  of  surface-waters 
than  upon  the  primary  distribution  of  copper  in  the  vein. 
Prospecting  for  reserves  must  proceed  laterally  rather  than 
towards  extreme  depth. 

The  surface-zone  is  always  richest  near  the  lowest  limit  of 
oxidation  where  cuprite  and  native  copper  form  from  chalco- 
cite.  The  upper  part  contains  poorer  ores  of  malachite,  bro- 
chantite,  etc.,  and  may  be  entirely  barren. 

In  the  Copper  Mountain  veins  the  chalcocite  apparently 
changes  directly  to  cupric  sulphate  ;  and  other  copper  oxy-salts 
are  practically  absent.  The  pyrite  remains,  in  part,  rusty  and 
accompanied  by  limonite,  until  near  the  surface,  where  it  finally 
disappears.  The  surface-zone  is  thus  directly  derived  from  the 
chalcocite-zone  by  gradual  erosion  and  oxidation,  indicating 
that  the  latter  is  not  a  very  recent  development. 

Two  of  the  principal  faults  of  the  district  cut  across  the  Mo- 
renci  veins  and  dislocate  them.  Some  of  the  ore-bodies  are 
clearly  faulted,  so  that  rich  chalcocite-ore  is  brought  opposite 
leached  and  barren  surface-rock.  Brecciated  zones,  accompany- 
ing this  faulting,  contain  fragments  of  chalcocite-ore.  In  all> 
the  evidence  is  pretty  clear  that,  at  least  a  part  of  the  chalco- 
cite-zone had  already  been  formed  when  the  faulting  took 
place,  and  that,  consequently,  the  beginning  of  chalcocitization 
and  oxidation  must  be  placed  in  the  earlier  or  middle  part  of 
Tertiary  times. 

Descriptions  of  chalcocite-ores  from  other  districts  show  that 
the  secondary  sulphides  develop  at  a  point  just  below  the 
water-level.  In  none  of  the  important  mines  in  this  district 
has  the  water-level  been  reached;  it  is  probably  far  below  the 
present  workings.  Chalcocite  may  now  form  in  the  upper 
part  of  the  zone,  in  places  away  from  fissures  and  faults,  where 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       543 

sulphate  solutions  are  slowly  descending  and  free  oxygen  scarce, 
but  I  doubt  very  much  whether  it  is  now  forming  in  the  lower 
part  of  that  zone.  I  regard  the  chalcocite-zone  as  formed 
about  an  ancient,  gradually-receding  water-level.  During  the 
early  Quaternary,  that  level  was  evidently  several  hundred  feet 
higher  than  at  present,  but  the  occurrences  of  the  chalcocite 
appear  to  require  a  still  higher  stand,  such  as  existed  during 
the  probably  moist  climate  of  the  middle  Tertiary. 

The  payable  deposits,  as  a  rule,  lie  at  high  elevations,  and  no 
large  deposits  have  been  opened  on  the  lower  slopes  of  Chase 
Creek  canyon,  or  along  its  bottom.  The  lower  down  on  the 
slope  a  deposit  is  located,  the  nearer  to  the  surface  will  the 
chalcocite-zone  be  found.  Chalcocite-ores  do  occur,  in  fact,  in 
veins  along  the  bottom  of  Chase  Creek  canyon,  but  the  mineral 
shows  only  as  a  slight  coating  on  pyrite.  This  topographical 
distribution  is  the  more  remarkable  when  it  is  recalled  that 
Chase  Creek  canyon  antedates  the  early  Quaternary  conglom- 
erates (Gila  formation)  and  that,  therefore,  oxidation  would 
apparently  have  had  a  long  time  in  which  to  act.  It  confirms 
the  conclusions  as  to  the  great  age  of  the  chalcocite-zone  and 
emphasizes  the  very  slow  rate  at  which  oxidation  works. 

Chalcocite-ores  and  oxidized  ores  forming  a  "  stock- werk " 
of  seams  in  porphyry  (at  Metcalf  mines),  or  in  quartzite  (at 
the  East  Yankee  mine),  or  occurring  as  disseminations  in  por- 
phyry dikes  (West  Yankee  lode  and  Shannon  mine),  in  general 
correspond  to  the  descriptions  of  the  altered  zones  surrounding 
the  veins.  They  pre-suppose  an  earlier  sericitization  and  py- 
ritization  effected  by  the  primary  vein-forming  solutions. 

The  fault-planes  of  the  principal  epoch  of  dislocations  are 
later  than  the  Morenci  veins  and  generally  barren,  but  may 
locally  contain  "  drag  "  or  cuprite-ores  deposited  from  migrating 
sulphate  solutions  by  processes  of  adsorption. 

The  Coronado  Type  of  Veins. 

Almost  the  only  representative  of  the  Coronado  type  of 
veins  is  the  Coronado  lode,  which  outcrops  on  the  summit  of 
Coronado  ridge  about  2,000  ft.  above  Metcalf.  It  presents  the 
feature  unusual  for  a  fissure-vein  of  following  one  of  the  prin- 
cipal faults  of  the  district  with  a  throw  ranging  from  1,000  to 
2,000  ft.,  and  it  is  traceable  for  nearly  2  miles,  finally  disap- 


544      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

pearing  towards  the  west  under  the  basaltic  foothills  of  Eagle 
creek.  The  fault-zone,  which  is  from  50  to  200  ft.  wide,  is 
followed  by  a  diabase  dike  which  has  been  crushed  and  partly 
deformed.  Oxidized  ores,  malachite,  azurite  and  chrysocolla, 
of  medium  to  poor  grade,  occupy  irregular  shoots  in  the  sur- 
face-zone, but  are  replaced  at  a  depth  of  from  200  to  300  ft.  by 
chalcocite-ores.  At  some  points  the  latter,  however,  reach 
the  surface.  Explorations  during  the  last  two  years  are  re- 
ported to  have  developed  large  bodies  of  these,  even  at  a  depth 
of  500  ft.  below  the  surface.  The  evidence — as  far  as  it  goes — 
here,  too,  points  to  secondary  origin  of  chalcocite  and  its  de- 
rivation from  pyritic  ores,  but  here,  as  well  as  at  Morenci,  the 
maximum  depth  attained  by  the  secondary  chalcocite  has  not 
been  fully  demonstrated. 

The  Coronado  lode  was  formed  later  than  the  Morenci  type 
of  veins  and  subsequent  to  the  intrusion  of  diabase,  which  is 
younger  than  the  porphyries  of  Morenci  and  Metcalf.  Regard- 
ing the  relative  age  of  the  diabase  and  the  fault-fissure,  the  evi- 
dence is  hardly  conclusive.  It  seems  as  if  the  dike  had  been 
intruded  during  the  epoch  of  faulting,  and  the  solutions  de- 
positing the  copper  certainly  followed  the  intrusion  of  the  dike. 

Gold-Searing  Veins. 

Gold,  silver  and  lead  are  practically  absent  from  the  prin- 
cipal deposits,  but  it  is  an  interesting  fact  that  they  begin  to 
appear  in  many  of  the  outlying- veins  somewhat  distant  from 
the  central  mass  of  porphyry.  These  veins,  in  which  copper  is 
apt  to  play  a  less  important  part,  have  not  as  yet  attained  much 
importance  from  an  economic  standpoint. 

CONDITIONS  OF  GROUND- WATER. 

Permanent  water  has  not  thus  far  been  encountered  in  any 
of  the  mines  in  the  whole  district  with  which  this  paper  deals. 
Morenci  is  situated  on  the  hills  from  800  to  1,500  ft.  above  the 
principal  streams,  Chase  creek  and  Eagle  creek ;  and  the  deepest 
workings  in  no  place  reach  farther  than  600  ft.  below  the  surface. 
A  little  seepage  from  the  surface  takes  place  in  case  of  heavy 
rains,  or  from  the  local  water-supply ;  and  some  drifts  and  cross- 
cuts underneath  the  town  are  somewhat  damp,  especially  in  the 
Manganese  Blue  and  Arizona  Central  mines.  The  mines  at 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       545 

Metcalf  are  situated  on  Shannon  mountain  from  500  to  1,200  ft. 
above  Chase  creek,  and  here,  too,  the  workings  are  dry,  ex- 
cepting one  place  in  the  Shirley  tunnel  where  a  winze  struck 
some  standing  water.  The  few  shafts  and  prospects,  sunk  in 
the  bottom  of  Chase  creek,  are  the  only  places  containing  per- 
manent water.  The  Copper  King  mine,  situated  a  few  hun- 
dred feet  below  the  summit  of  the  mountain  of  the  same  name, 
has  a  shaft  600  ft.  deep;  some  crevices  containing  water  have 
been  found  in  it,  but  they  soon  drained  out  and  no  more  has 
since  come  in. 

The  present  stand  of  the  water-level, -except  along  the  creeks, 
is  practically  unknown.  It  probably  rises  as  a  slightly  curved 
surface  from  the  creek-levels  towards  the  high  hills.  The 
total  amount  of  water  stored  below  this  water-level  is  probably 
small. 

DEPTH  OF  OXIDIZED  ZONE. 

The  presence  of  products  of  direct  or  indirect  oxidation 
shows  the  depth  to  which  the  oxidizing-waters  or  the  sulphate 
solutions  have  penetrated;  but  the  porphyry  and  the  metamor- 
phosed limestones  should  be  separated,  because  they  act  very 
differently.  In  that  part  of  Copper  mountain  which  has  been  ex- 
plored, the  average  depth  of  the  lower  limit  of  the  chalcocite- 
zone  is  400  ft.,  but  it  increases  in  places  to  500  or  even  600  ft. 
To  this  depth  from  the  surface,  the  sulphate  solutions  descended, 
and  along  important  fissures  they  may  have  gone  somewhat 
farther.  The  solutions  not  only  followed  fissures,  but  pene- 
trated the  porous,  sericitized  porphyry  with  considerable  ease. 
On  the  other  hand,  the  altered  limestones  and  shales  are  very 
compact,  non-porous  and  impervious.  Where  circulation  was 
facilitated  by  fissures,  as  in  the  Manganese  Blue  and  the  Joy 
mines,  the  rocks  may  be  partly  oxidized  to  a  depth  of  400  ft., 
but  this  is  generally  a  maximum.  There  is  no  well-defined 
plane  expressing  the  depth  of  oxidation,  which,  on  the  contrary, 
proceeds  very  capriciously,  fresh  sulphides  being  frequently 
found  very  close  to  the  surface. 

FLUID-INCLUSIONS. 

Fluid-inclusions  have  been  observed  in  the  quartz-grains  of 
granite,  quartzite,  porphyry  and  vein-quartz  occurring  in  this 
district.  There  is  nothing  uncommon  in  this;  it  is,  indeed,  the 


546      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

ordinary  condition  of  affairs.  As  these  fluid-inclusions,  beyond 
doubt,  contain  aqueous  solutions,  it  may  be  regarded  as  certain 
that  such  fluids  were  present  when  the  quartz-grains  in  ques- 
tion were  formed.  It  is  the  purpose  of  the  following  para- 
graphs to  call  attention  to  certain  phenomena  in  these  inclu- 
sions which  have  not  been  described  previously. 

In  Granite. — Inclusions,  filled  with  a  fluid  and  a  bubble  of 
gas,  occur  abundantly  in  the  quartz-grains  of  all  of  the  granites 
examined.  They  are  of  rare  occurrence,  though  not  unknown 
in  the  feldspars.  The  form  is  round  or  elliptical,  or  may  be 
that  of  a  negative  quartz-crystal  with  prism  and  pyramid.  The 
size  averages  perhaps  0.02  mm.  The  relation  of  volume  be- 
tween the  fluid  and  the  bubble  varies  considerably  among 
inclusions  in  the  same  grain.  In  the  smaller  inclusions  the 
bubble  frequently  is  in  active  motion.  Heated  to  40°  or  50° 
C.  there  is  no  perceptible  change  in  volume  of  fluid  or  bubble, 
and  consequently  it  may  be  considered  certain,  that  the  fluid  is 
not  liquid  carbon  dioxide,  which  has  sometimes  been  observed 
in  the  granites,  but  chiefly  water.  In  some,  but  by  no  means 
all,  of  the  inclusions  there  is  also  a  solid  body  contained  in  the 
fluid ;  in  some  cases  this  is  a  transparent  cube,  in  others,  and 
more  commonly,  an  irregular  grain  or  a  rod  of  the  solid  mate- 
rial. This  also  has  occasionally  been  observed  and  described 
in  granites  from  other  districts. 

In  Metamorphic  Limestones. — The  metamorphism  of  the  lime- 
stone to  garnet,  epidote,  diopside,  quartz  and  other  minerals 
took  place  under  conditions  of  high  temperature  and  pres- 
sure, and  almost  certainly  in  the  presence  of  aqueous  solutions 
in  fluid  or  gaseous  form.  It  is  a  curious  fact  that  these  min- 
erals only  very  exceptionally  contain  fluid-inclusions.  The 
quartz-grains  formed  seem  entirely  homogeneous  and  free  from 
these  interpositions.  Only  one  or  two  very  small  inclusions 
with  moving  bubble  were  noted.  The  same  applies  to  the  gar- 
net and  other  heavy  minerals.  The  calcite  would  hardly  be 
expected  to  preserve  any  such  inclusions  on  account  of  its  per- 
fect cleavage. 

In  Porphyry. — The  inclusions  in  the  porphyry  are  again  prac- 
tically confined  to  the  quartz.  They  occur  chiefly  in  the  pheno- 
crysts,  but  also  in  the  quartz  of  the  ground-mass,  although  they 
are  here  usually  very  small.  Naturally,  the  diorite-porphyries 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCT.       547 

are  poor  in  inclusions,  but  they  appear  abundantly  in  the  gran- 
ite-porphyries and  the  quartz-monzonite  porphyries  with  which 
the  ore-deposits  are  chiefly  connected.  They  are  found  through- 
out the  Metcalf  granite-porphyry,  which  is  characterized  by 
large  bi-pyramidal  quartz-phenocrysts,  and  they  are  almost 
equally  common  in  the  smaller  quartz-crystals  of  the  Copper 
mountain  porphyry  of  Morenci.  The  sericitization  of  the  por- 
phyry affects  them  but  little,  for  the  quartz-grains  of  the  por- 
phyries are  very  rarely  altered  by  this  process.  In  specimens 
taken  from  the  oxidized  zone  near  the  surface,  many  of  the  in- 
clusions are  empty,  probably  due  to  the  cracking  of  the  grains, 
and  the  attending  expulsion  of  the  highly-compressed. fluid. 

The  peculiar  feature  of  these  fluid-inclusions  is  that,  as  a 
rule,  they  contain,  besides  the  gas-bubble,  an  extremely  sharply- 
defined  cube  of  transparent  material,  and  a  smaller  opaque 
particle.  The  invariable  recurrence  of  this  association  is  a 
proof  that  these  bodies  are  not  accidental  inclusions,  but  were 
present,  dissolved  in  the  fluid,  at  the  time  the  quartz  crystal- 
lized and  imprisoned  the  drop  of  solution. 

The  inclusions  are  elliptical,  irregularly  rounded,  or  show 
the  form  of  their  host,  that  is,  a  hexagonal  pyramid  with  short 
prism.  Their  size  ranges  from  those  barely  visible  up  to  0.02 
mm.  in  diameter;  the  latter  being  about  the  maximum.  A 
frequently  recurring  size  is  0.012  mm.  Their  distribution  in 
the  phenocrysts  is  irregular ;  they  are  not  ranged  along  any 
given  plane  or  surface.  Moving  bubbles  are  often  noted  in  the 
smaller  inclusions.  'Heating  to  40°  and  up  to  80°  C.  does  not 
noticeably  affect  the  relation  of  fluid  cube  and  gas ;  they  do  not 
therefore  consist  of  carbon  dioxide,  but  of  some  aqueous  solu- 
tion. The  proportion  of  volume  between  bubble  and  inclusion 
is  not  constant ;  many  of  them  contain  large  gas-bubbles,  while 
in  others  they  may  be  quite  small.  To  some  extent  this  may 
be  explained  by  leaking,  but  comparing  a  great  number  in  very 
fresh  rocks  there  certainly  appears  to  be  considerable  variation 
in  this  proportion.  The  fluid  is  colorless.  ' 

As  to  the  cube  of  transparent  salt,  it  is  very  sharply  defined 
and  well  developed.  In  polarized  light  the  cube  appears  iso- 
tropic.  Its  size  varies,  but  is  usually  of  about  the  same  volume 
as  the  bubble,  and  occupies  from  4  to  15  per  cent,  of  the  vol- 
ume of  the  inclusion.  Such  cubes  have  been  sometimes  ob- 


548      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

served  before,  especially  in  inclusions  contained  in  quartz  crys- 
tals; and  in  some  cases  they  have  been  proved  to  consist  of 
sodium  chloride.  They  have  also  been  noted  in  quartz  pheno- 
crysts  of  certain  Cornish  granite-porphyries.  In  the  present 
case  the  small  size  of  the  inclusions,  and  especially  the  degree 
of  alteration  and  oxidation  to  which  most  of  the  specimens 
have  been  subjected,  renders  experimental  determination  of  the 
salt  impracticable,  at  least  with  the  material  in  hand  at  present. 
It  may  be  said,  however,  that  in  all  probability  the  substance 
is  sodium  chloride.  Several  inclusions  were  measured  to  de- 
termine the  degree  of  saturation  when  the  substance  was  dis- 
solved in  the  fluid,  assuming  that  it  is  Nad,  and  that  the  liquid 
is  a  saturated  Solution  of  the  same  salt  at  ordinary  temperature. 
Results  indicate  that  this  was  ordinarily  from  5  to  20  per  cent, 
above  the  maximum  amount  soluble  in  water  under  ordinary 
conditions.  In  one  case  it  was  found  that  the  water  must  have 
contained  45  per  cent,  of  salt.  Most  of  the  inclusions  also  con- 
tain a  small  opaque  particle,  generally  measuring  only  a  frac- 
tion of  the  volume  of  the  bubble  or  the  cube.  It  has  no  dis- 
tinct form ;  occasionally,  rod-shaped  outlines  may  be  observed, 
but  ordinarily  it  is  so  small  that  it  only  appears  as  a  black 
speck.  Examined  in  reflected  light,  one  unusually  large  parti- 
cle seemed  decidedly  black,  while  another  inclusion,  contained 
also  in  a  Copper  Mountain  porphyry,  seemed  distinctly  reddish 
in  transmitted  light. 

These  inclusions  are  certainly  a  characteristic  feature  of  the 
granite-porphyries  of  Morenci  and  Metcalf.  They  prove,  I 
think,  conclusively,  that  the  acid  porphyry-magma  was  accom- 
panied by  notable  quantities  of  aqueous  solutions  containing  a 
large  quantity  of  a  salt,  which  probably  was  E"aCl;  and  also  a 
smaller  amount  of  some  compound  containing  one  or  several  of 
the  heavy  metals.  From  what  follows,  it  is  extremely  probable 
that  this  compound  is  largely  ferric  oxide.  It  may  well  also 
contain  copper,  although  a  direct  evidence  of  this  cannot  be 
furnished. 

These  observations  gain  in  interest  when  it  is  considered  that 
the  porphyry  has  caused  a  strong  metamorphism  of  adjoining 
limestone,  the  principal  feature  of  which  is  an  acquisition  of 
silica  and  iron,  which  in  all  probability  were  given  off  by  the 
porphyry.  It  is  now  shown  that  the  magma  contained  heavy 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       549 

metals  in  aqueous  solution.  Very  likely  these  solutions  also 
contained  much  silica,  but  it  should  be  remembered  that  this 
material  would  most  likely  have  been  deposited,  upon  the  cool- 
ing of  the  rock,  on  the  walls  of  the  inclusion,  and  in  such  a  case 
it  would  naturally  have  the  crystallographic  orientation  of  the 
host  from  which  the  new  substance  could  not  readily  be  distin- 
guished. 

It  is  perhaps  a  significant  fact  that  these  inclusions  are  ab- 
sent in  the  diorite-porphyries,  which,  as  a  rule,  have  no  con- 
nection with  the  copper-deposits. 

As  to  the  quantitative  importance  of  the  inclusions,  it  may  be 
estimated  that  in  some  specimens  they  make  up  a  very  percep- 
tible percentage  of  the  rock  volume. 

In  Vein-Quartz. — The  results  of  the  examinations  of  the  por- 
phyries encouraged  a  search  in  the  vein-quartz.  In  a  greatly 
altered  pyritic  porphyry  from  the  Butler  and  London  tunnel  at 
Morenci,  the  ground-mass  is  silicified  and  contains  irregular 
replacement-veinlets  of  quartz,  which  were  found  to  contain  in- 
clusions entirely  similar  to  those  in  the  porphyritic  quartz  with 
cubic  and  opaque  body.  In  some  cases  three  small  opaque 
masses  were  found  in  one  inclusion. 

At  Metcalf  the  granite  close  to  the  porphyry  is  greatly  shat- 
tered and  cemented  by  veinlets  of  quartz  with  scattered  and 
minute  foils  of  specularite  and  occasionally  some  pyrite.  The 
quartz  of  the  granite  has  the  usual  fluid-inclusions  mentioned 
above.  The  cementing-veinlets  of  granular  quartz  are  full  of 
remarkably  beautiful  and  fairly  large  (up  to  0.02  mm.)  inclu- 
sions of  the  usual  rounded  or  pyramidal-prismatic  form.  Most 
of  these  contain  bubble,  cube  and  opaque  body.  The  bubble 
varies  as  usual  in  its  relative  size ;  the  cube  is  sharply  defined 
and  of  the  size  described  under  the  inclusions  in  porphyry.  In 
a  few  of  the  inclusions  the  dark  bodies  are  unusually  large  and 
have  a  rounded  flat  form ;  they  are  here  translucent  with  red- 
dish color,  and  there  can  be  little  hesitation  in  identifying  them 
as  ferric  oxide  or  specularite.  In  some  inclusions  small  grains 
or  crystals,  beside  the  cube,  and  occasionally  transparent  matter 
adhering  to  the  wall,  are  also  found.  All  this  shows  that 
the  same  or  very  similar  solutions,  which  formed  a  part  of  the 
magma,  deposited  quartz  in  the  immediately  surrounding  rock 
or  in  the  solidified  porphyry  itself.  It  is  clear  that  these  solu- 


550      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

tions  must  have  been  very  hot  and  probably  also  under  great 
pressure,  since  they  held  dissolved  not  only  much  larger  quan- 
tities of  salt  than  can  be  taken  up  by  water  at  ordinary  tem- 
perature, but  also  a  substance,  which  probably  is  ferric  oxide, 
entirely  insoluble  under  ordinary  conditions.  This  directly 
connects  the  solutions  contained  in  the  magma  with  those 
which  deposited  quartz  shortly  after  the  intrusion  and  shows 
that  the  general  quartz-cementation  which  occurred,  closely 
following  the  consolidation  of  the  magma,  is  probably  not  due 
to  atmospheric  waters,  but  to  eruptive  after-effects. 

In  the  next  place,  the  strong  pyritic,  primary  fissure-veins 
were  examined,  which  cut  across  both  porphyry  and  metamor- 
phosed limestcme  at  Morenci.  They  are  associated  with  a  little 
normal,  coarsely  crystalline,  vein-quartz.  Specimens  from  the 
Montezuma  vein  from  different  places  showed  typical  vein- 
quartz  full  of  fluid-inclusions,  either  irregularly  arranged  or  in 
places  following  certain  planes  in  the  grains.  The  quartz- 
grains  often  show  cry  stall  ographic  outlines,  are  occasionally 
speared  by  smaller  quartz-prisms  and  are  associated  with  a  few 
large  irregular  grains  of  pyrite.  Though  some  of  the  inclu- 
sions are  irregular,  the  majority  have  rounded  outlines,  more 
seldom  bi-pyramidal.  The  size  ranges  up  to  0.012  mm.  The 
relation  of  bubble  and  cavity  is  not  constant;  many  inclusions 
are  empty,  no  doubt  due  to  leaking,  for  the  quartz  is  consider- 
ably crushed.  No  change  is  apparent  upon  heating  the  slide 
to  40°  and  even  to  80°  C.  Almost  always  the  inclusion  con- 
tains solid  bodies.  Cubes,  so  abundant  in  the  porphyries,  are 
of  rare  occurrence  and  seldom  well-developed.  Most  frequent 
are  transparent  adhesions  to  the  wall,  rod-like  masses,  pyra- 
midal crystals,  or  irregular  grains.  None  seem  to  act  on 
polarized  light,  possibly  on  account  of  the  minute  size.  In 
most  cases  the  inclusions  also  contain  one  or  two  minute  opaque 
bodies,  which  cannot  be  further  determined.  In  a  few  inclu- 
sions the  solid  material  is  so  abundant  as  to  cause  the  bubble 
to  assume  an  elongated  form. 

Entirely  similar  inclusions  are  found  in  the  quartz  of  the 
Humboldt  vein,  occurring  as  branching-veinlets  in  porphyry. 

The  granite  along  Chase  creek,  half  a  mile  above  the  foot  of 
the  Longfellow  incline,  contains  many  quartz-veins  with  pyriter 
chalcocite  and  molybdenite.  The  quartz  contains  fluid-inclu- 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       551 

sions,  though  many  of  the  cavities  are  empty.  Most  of  the  in- 
clusions contain  some  solid  material ;  a  few  of  these  are  imper- 
fect cubes ;  most  common  are  transparent  adhesions  to  the 
walls,  while  many  also  contain  opaque  bodies. 

These  observations  indicate  that  the  quartz  in  the  fissure- 
veins  was  formed  in  the  presence  of  aqueous  solutions  of  prob- 
ably several  salts.  The  cubes,  so  prominent  in  the  porphyry 
and  in  some  probably  earlier  veinlets  of  quartz,  seem  to  be 
less  uniformly  present  in  those  of  the  regular  veins.  It  also 
follows  that  the  solutions  were  very  hot,  for  they  contained  a 
much  larger  proportion  of  salts  than  can  be  dissolved  at  ordi- 
nary temperature  or  even  at  -j-  100°  C.  The  opaque  bodies 
indicate  that  some  combination  of  the  heavy  metals  was  also 
present  in  the  waters. 

The  quartz-veinlets,  connected  with  the  processes  of  forma- 
tion of  chalcocite  and  of  copper  carbonates,  contain  only  few 
and  small  inclusions,  in  which,  thus  far,  nothing  but  the  fluid 
and  the  bubble  have  been  observed. 

SUMMARY  OF  GENESIS. 

It  has  been  shown  that  the  intrusions  of  stocks  and  dikes  of 
granite-porphyry  and  quartz-monzonite  porphyry,  which  took 
place  in  late  Cretaceous,  or  early  Tertiary  times,  produced  an 
important  contact-metamorphism  in  shales  and  limestones  of 
Paleozoic  age,  which  happened  to  adjoin  them.  This  meta- 
morphism  resulted  in  metasomatic  development  of  garnet,  epi- 
dote,  diopside,  and  other  silicates,  accompanied  by  pyrite,  mag- 
netite, chalcopyrite,  and  zinc-blende.  The  sulphides  are  not 
later  introductions,  but  contemporaneous  with  the  other  contact 
minerals. 

The  contact-zone  received'  very  substantial  additions  of 
iron  oxides,  silica,  sulphur,  copper,  and  zinc,  enough  to  form 
good-sized  deposits  of  pure  magnetite  and  low-grade  deposits 
of  chalcopyrite  and  zinc-blende,  all  of  which  are  entirely  un- 
known in  the  sedimentary  series  away  from  the  porphyry. 

In  view  of  the  evidence,  I  consider  it  impossible  that  circu- 
lating atmospheric  waters  have  effected  these  changes.  The 
occurrences  of  metamorphosed  rocks  are  manifold  and  found 
under  many  varying  conditions;  there  is  only  one  common  fac- 
tor and  that  is  the  presence  of  the  porphyry.  It  is  shown  that 


552      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

the  porphyry  magma  contained  much  water  which  held  dis- 
solved various  salts,  among  them  some  of  the  heavy  metals. 
Sodic  chloride  and  ferric  oxide  prohably  predominated.  I  be- 
lieve that  it  contained  all  of  the  substances  mentioned  above, 
and  that  large  quantities  of  this  gaseous  solution  (for  the  criti- 
cal temperature  must  have  been  exceeded)  dissolved  in  the 
magma  were  suddenly  released  by  diminution  of  pressure  as 
the  magma  reached  higher  levels,  and  forced  through  the  ad- 
joining sedimentary  beds  ;  the  purest  and  most  granular  lime- 
stones suffering  the  most  far-reaching  alteration  and  receiving 
the  greatest  additions  of  substance.  It  is  thus  held  that  a  di- 
rect transfer  of  material  from  cooling  magma  to  adjacent  sedi- 
ments took  place.  The  formation  of  garnet  indicates  large 
gains  of  ferric  oxide  and  silica.  If  the  magmatic  waters  car- 
ried iron  only  as  ferric  oxide  some  of  it  must  have  been  reduced 
to  magnetite  during  the  metamorphism,  for  the  latter  mineral 
is  much  more  common  than  the  specularite.  These  contact 
metamorphic  deposits  often  occur  at  the  immediate  contact 
of  the  main  porphyry  stock  and  the  limestones.  But  more 
commonly  they  seem  to  be  connected  with  dikes  of  the  same 
porphyry  close  to  the  principal  mass,  these  dikes  being  proba- 
bly more  highly  charged  with  magmatic  waters. 

It  is  shown  that  fissures  and  extensive  shattering  developed 
both  in  porphyry  and  altered  sediments  after  the  congealing  of 
the  magma,  and  that  these  fissures  and  seams  were  cemented 
by  quartz,  pyrite,  chalcopyrite,  and  zinc-blende ;  forming  nor- 
mal veins  largely  of  the  type  of  replacement-veins.  The  amount 
of  copper  contained  in  these  is  usually  small,  though  in  places 
possibly  large  enough  to  form  pay-ore.  The  bulk  of  the  veins 
consists  of  pyrite.  Two  classes  of  veins  may  be  distinguished. 
The  usual  type  is  practically  always  connected  with  granite- 
porphyry  or  quartz-monzonite  porphyry ;  it  occurs  in  this  rock 
or  along  dikes  of  the  same.  The  smaller  division  consists  of 
those  connected  in  their  occurrence  with  diabase  dikes.  The 
genesis  of  the  former  type  will  first  be  discussed. 

As  far  as  the  metallic  minerals  are  concerned  there  is  a 
striking  similarity  between  the  veins  connected  with  porphyry 
and  the  contact-metamorphic  deposits,  the  only  difference  being 
in  the  magnetite,  which  does  not  occur  in  the  veins  proper  and 
only  subordinately  in  certain  of  the  altered  wall-rocks.  A  rela- 


GENESIS    OP    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI.       553 

tionship  is  also  clearly  seen  in  the  remarkable  action  of  the 
vein-solutions  on  the  adjoining  wall-rock  wherever  this  is  lime- 
stone, tremolite  and  diopside  being  formed  in  it  by  replace- 
ment. On  the  whole,  iron  and  silica  are  the  main  substances 
added,  during  contact-metamorphism,  as  well  as  during  the 
vein-formation. 

A  study  of  the  fluid-inclusions  in  the  vein-quartz  proves  con- 
clusively that  the  veins  were  formed  by  aqueous  solutions  and 
that  these  solutions  were  at  a  high  temperature,  for  they  con- 
tained various  salts,  in  part,  those  of  heavy  metals,  probably 
iron,  which  have  separated  out  during  the  cooling  of  the  crys- 
tallized quartz.  This  entirely  eliminates  the  possibility  of  de- 
position by  cold  surface-waters  and  points  to  two  or  three  even- 
tualities. Deposition  by  atmospheric  waters  heated  by  contact 
with  the  cooling  porphyry,  or  deposition  by  ascending  mag- 
matic  waters,  or,  finally,  by  a  mixture  of  both.  In  any  case  the 
metals  must  be  derived  from  the  porphyry,  or  from  deep-seated 
sources  below  the  porphyry,  for,  as  stated  above,  the  presence 
of  porphyry  is  the  only  common  factor  in  all  occurrences.  It 
is  clear  that  a  positive  solution  of  these  problems  must  be  most 
difficult,  but,  here  again,  the  fluid-inclusions  offer  the  only  di- 
rect evidence.  In  the  quartz-seams  penetrating  the  granite 
near  the  porphyry-contact  at  Metcalf,  inclusions  were  found 
which  are  indistinguishable  from  those  characteristic  of  the 
quartz-phenocrysts  in  the  porphyry,  and  it  must  be  concluded 
that  the  same  highly  heated  and  highly  charged  solutions 
were  -active  in  both  cases.  This  directly  connects  some  of 
the  probably  earlier  quartz-veins  with  magmatic  water  and 
is  evidence  of  considerable  importance.  The  vein-quartz  of 
Morenci  contains  inclusions  which,  in  some  cases,  are  identical 
with  those  in  the  porphyry,  and  in  other  cases  slightly  different 
from  them,  but  always  indicate  highly  heated  solutions.  The 
metasomatic  action  of  the  waters  proves  them  to  have  been  rich 
in  silica  and  various  salts,  among  them  some  of  the  heavy 
metals,  but  entirely  deficient  in  carbon  dioxide.  Considering 
this  evidence,  together  with  the  similarity  of  the  products  of 
these  processes  with  those  of  contact-metamorphism,!  think  it 
certain  that  parts  of  the  mineral  solutions  were  directly  derived 
from  and  formed  part  of  the  porphyry  magma,  and  I  believe  it 
is  probable  that  they  were  entirely  derived  from  this  source. 

35 


554      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

It  seems  likely,  that  the  fissuring,  which  took  place  after  the 
cooling,  opened  vents  of  escape  for  magmatic  waters  under 
heavy  pressure  at  lower  levels,  and  that  they  ascended  on  these 
fissures  depositing  the  heavy  metals  and  the  silica  and  acquir- 
ing at  the  same  time  carbon  dioxide  from  the  sediments  which 
they  traversed. 

As  to  the  depth  at  which  deposition  took  place,  no  positive 
evidence  is  available  on  account  of  lack  of  data  concerning  the 
extent  of  erosion.  But  from  stratigraphic  consideration,  it  is 
not  likely  that  the  depth  from  surface  was  more  than  two  or 
three  thousand  feet.  The  cause  of  the  deposition  was  no  doubt 
a  decrease  in  temperature,  just  as  the  deposits  are  formed  in 
the  cooled  fluid-inclusions.  I  think  it  likely  that,  in  most 
cases,  the  solutions  were  present  as  liquids,  for,  assuming  that 
the  waters  communicated  with  the  surface,  neither  pressure  nor 
temperature  could  have  been  high  enough  to  reach  the  critical 
point.  Probably  this  does  not  matter  very  much,  for  the  proper- 
ties of  water  appear  to  be  very  similar  for  some  distance  each 
side  of  this  point.  Copper,  iron  and  zinc  are  practically  the  only 
important  metals  present  in  the  main  deposits  close  to  the  main 
porphyry  stock ;  but  it  is  interesting  and  suggestive  to  note 
that  gold  begins  to  appear  in  veins  which  are  located  some  dis- 
tance away  from  the  central  porphyry. 

The  veins  connected  with  diabase  dikes  are  few  in  number, 
and  the  opportunity  for  their  study  has  been  limited.  It  seems 
risky,  therefore,  to  express  a  definite  opinion  on  their  genesis, 
except  that  the  copper  and  iron  sulphides  in  all  probability  were 
derived  from  the  diabase  itself,  either  by  means  of  magmatic  or 
heated  atmospheric  waters. 

The  deposits  thus  far  described  are,  in  general,  of  low-grade, 
only  rarely  containing  enough  copper  to  be  classed  as  econom- 
ically important.  Those  in  shale  or  limestone  consist  of  dis- 
seminated sulphides,  in  places  irregularly  concentrated,  or  accu- 
mulated along  certain  strata,  according  to  the  well-defined  tend- 
ency of  contact-metamorphism.  Those  in  porphyry  consist  of 
heavy  veins  of  pyrite  and  a  small  amount  of  other  sulphides, 
surrounded  by  zones  of  dissemination  of  the  same  sulphides. 

It  remained  for  the  surface-waters,  as  erosion  gradually  ex- 
posed the  deposits,  to  alter  and  enrich  them  in  manifold  forms. 

From  the  evidence  presented  above,  it  must  be  concluded 


GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCT.       555 

that  some  of  the  deposits,  especially  the  fissure-veins,  were  laid 
bare  by  erosion,  and  attacked  by  surface-waters  at  an  early 
date,  probably  before  the  principal  faulting-movement,  and 
certainly  before  the  eruption  of  the  Tertiary  basalts  and  rhyo- 
lites.  Oxidation  has  thus  acted  on  them  for  a  very  long  period. 

The  irregular  and  tabular  deposits  of  oxidized  ore  in  lime- 
stone and  shale  have  been  formed,  partly  by  direct  oxidation 
of  sulphides  and  partly  by  the  influence  of  sulphate  solutions 
derived  from  widely  disseminated  chalcopyrite  due  to  contact- 
metamorphism ;  a  great  enrichment  has  taken  place,  due  to 
decrease  of  volume  and  addition  of  copper  from  the  circulating 
sulphate  solutions.  Some  of  the  oxidized  deposits  in  shale,  how- 
ever, may  be  wholly  due  to  adsorption,  exerted  by  the  kaolin  in 
the  shale  on  these  sulphate  solutions. 

In  the  veins,  and  especially  in  those  which  traverse  the  por- 
phyry stock,  or  follow  porphyry  dikes,  the  history  is  more 
complicated.  It  has  been  shown  that  oxidation  dates  back 
to  Tertiary  times,  and  that  the  water-level  then  was  con- 
siderably higher  than  it  is  at  the  present  time.  By  action 
of  descending  sulphate  solutions  on  pyrite,  chalcocite  was 
deposited  very  extensively,  and  very  likely  the  great  ver- 
tical extent  of  the  chalcocite-zone,  ordinarily  from  200  to 
500  ft.,  is  due  to  slow  and  gradual  changes  in  the  water- 
Jevel.  Disintegration  and  erosion  removed  the  iron-cap  (the 
products  of  direct  oxidation  of  the  primary  vein)  and  began  to 
oxidize  the  exposed  chalcocite-zone.  In  practically  all  of  the 
veins,  the  surface-zone  of  poor  ore  is  due  to  the  direct  oxi- 
dation of  chalcocite.  The  solutions  from  this  part  descend  and 
add  richness  to  the  upper  part  of  the  remaining  chalcocite- 
zone.  But  at  the  present  low  stand  of  the  water-level,  and  the 
exceedingly  dry  climate,  the  lower  limit  of  the  chalcocite-zone 
is  probably  almost  stationary. 

The  copper-deposits  of  Clifton  and  Morenci  are  thus  believed 
to  have  been  formed  primarily  by  mineral-laden  magmatic 
waters,  partly  acting  as  gas  and  partly  as  liquids,  and  in 
both  cases  derived  from  a  magma  of  granite-porphyry.  These 
solutions  were  evidently  directly  released  from  the  magma 
without  a  preliminary  concentration  in  pegmatitic  or  aplitic 
dikes,  which,  indeed,  do  not  occur  in  this  district  in  association 
with  the  porphyry.  It  is  perhaps  superfluous  to  emphasize 


556      GENESIS    OF    THE    COPPER-DEPOSITS    OF    CLIFTON-MORENCI. 

that  these  conclusions  are  not  generalizations,  and  that  this  mode 
of  origin  is  not  necessarily  that  of  all  other  metalliferous  veins. 
The  earlier  processes  of  magmatic  origin  produced  low-grade 
deposits  of  pyritic  ores,  and  the  final  concentration  to  payable 
ore-bodies  has  chiefly  been  effected  by  descending  and  oxidiz- 
ing surface-waters  of  atmospheric  origin. 

GENETIC  CLASSIFICATION. 

The  following  scheme  of  genetic  classification  of  the  deposits 
is  presented : 

I.  FIRST  EPOCH.  Formed  during  the  consolidation  of  porphyry 

by  laterally  moving  water-gas. 

a.  Contact  metamorphic  deposits. — Irregular  or  tabular  dis- 
seminations in  shale  or  limestone,  sometimes  fol- 
lowing stratification  planes  or  dike  contacts.  Ores 
consist  of  pyrite,  chalcopyrite,  zinc-blende  and  mag- 
netite. Generally  unpayable. 

II.  SECOND  EPOCH.    Formed  shortly  after  the  consolidation  of 

the  porphyry  by  ascending  hot,  magmatic  waters. 
Continued  on  porphyry,  granite  or  more  or  less 
altered  sedimentary  rocks. 

a.  Fissure-veins. — Lode-systems    or  single  veins.     Cen- 

tral seams  of  pyrite,  chalcopyrite  and  zinc-blende 
accompanied  by  wide  zones  of  sericitization  and 
pyritization  of  the  porphyry.  Generally  unpayable. 

b.  Stock-werks  and  irregular  disseminations. — Same  charac- 

ter of  mineralization.     Unpayable. 

III.  THIRD  EPOCH.  Fissure-veins  formed  by  ascending-waters 

shortly  after  the  intrusion  of  diabase. 

IV.  FOURTH  EPOCH.     Deposits   formed  by  descending  atmos- 

pheric waters  acting  on  Classes  I.,  II.  and  III. 

a.  Concentrations  by  direct  oxidation  and  secondary  chalco- 

cite-dcposition  in  type  I.     Payable. 

b.  Concentrations  by  direct  oxidation  and  secondary  chalco- 

cite-deposition  in  type  Ila.     Payable. 

c.  Concentrations  by  direct  oxidation  and  secondary  chalco- 

cite-deposition  in  type  lib.     Payable. 

d.  Deposits  caused  by  sulphate-waters  along  otherwise  barren 

fault-planes.     Occasionally  payable. 

e.  Deposits   caused   by   sulphate-waters   along  shale    beds. 

Partly  payable. 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       557 


No.  20. 
The  Copper-Deposits  at  San  Jose,  Tamaulipas,  Mexico. 

BY  J.   F.  KEMP,  NEW  YORK,  N.  Y. 

(Washington  Meeting,  May,  1905.    Trans.,  xxxvi.,  178). 
CONTENTS. 

PAGE 

I.  Introduction,  ....         .......     557 

1.  Situation, .        .        .557 

2.  Geology,       . ...        .559 

IL   Eruptive  Rocks, v.         .         .         .         .        .     561 

1.  Deep-Seated  Eruptives,          .         .        ...        .         .         .  562 

(a)  Nephelite-Syenite,        .         .                  .  .  .  .  .562 

(b)  Gabbro,         .         ..."..".  .  .  .  .563 

2.  Laccolith,     .         .      '  .~      .      .  .    '     .         .'  .  .  .  .563 

3.  Dikes,   .         ,       ..         .    '    .         .         ,         .  .  j.  .  .565 

(a)  Tinguaite,      .  .  .  .         .  .        '.         .        .     565 

(b)  Camptonite,  .  ..  .  .         .  .....     566 

(c)  Vogesite,       .  .  .'  .     '  .        .  .     ^,        '*        .567 

(d)  Olivine-Basalt,  .  -     .  .  •  .      ".  .         .        ..       .567 

4.  Surface-Flow,      '.,   .  k  .  .  ...  .        .        '.        .567 

(a)  Basalt,  .         .         .         ...'..        .         .567 

III.  Contact- Effects,      .        .         ....         .         .         .        „        .567 

IV.  Genetic  Conclusions,      .    '     .         .        .         .         .         .         .         .        .     574 

1.  Recrystallization  Process,      .     •    .••    /    .         ...  •.  ..  575 

2.  Absorption  Process,                *        .        .         .                  .  .  .  .579 

3.  Process  by  Contributions  from  the  Eruptive,          .        .  .  ,  .  579 

4.  Oxidized  Ores,        .        .        .      '.        .        .       '„      ..  .  .  581 

I.  INTRODUCTION.* 

1.  Situation. — From  Monterey  in  the  State  of  Nuevo  Leon, 
the  Sierra  Madre  mountains  stretch  away  to  the  southeast  and 
present  a  steep  front  to  the  northeast.  The  Monterey  and  Mexi- 
can Gulf  railway,  which  connects  Monterey  with  Tampico,  fol- 
lows their  general  line  with  its  road-bed  a  few  miles  out  from  the 
foothills.  At  a  distance  of  100  miles  from  Monterey  it  passes 
through  the  town  of  Linares,  and  from  Linares  one  can  see  far 
away  to  the  southeast  the  peaks  of  another  group  of  mountains 

*  For  much  assistance  and  cordial  interest  in  the  preparation  of  this  paper,  I  de- 
sire to  express  my  acknowledgments  to  E.  D.  Self,  General  Manager  of  the  mines 
at  San  Jose,  and  to  W.  H.  Nichols,  Jr.,  President  of  the  San  Carlos  Copper  Co. 


558       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 


rising  from  the  general  plateau  and  forming  a  more  eastern 
uplift  distinct  from  the  main  mountain  system.  The  outlying 
group  is  the  San  Carlos  range,  and  is  one  of  extreme  geoldgical 
interest  because  of  its  nephelite-syenites  and  rare  types  of 
associated  eruptives.  These  have  been  recently  described  by 
George  I.  Finlay,1  who  was  my  companion  during  the  trip 
upon  which  the  observations  for  the  present  paper  were  made. 
The  San  Carlos  mountains  extend  east  and  west,  and  are  about 
15  miles  long.  Their  highest  point,  Pic  de  Diablo,  which  is 
just  south  of  San  Jose,  has  been  determined  by  aneroid  to  be 


FIG.  1.  —  MAP  OF  NORTHEASTERN  PART  OF  MEXICO,  THE  CIRCLE  SHOWING  THE 
LOCATION  OF  THE  SAN  JOSE  DEPOSITS. 

6,000  ft.  above  sea-level.  The  peaks  are  rugged,  and  have  pre- 
cipitous escarpments,  surrounding  inner  amphitheaters.  They 
are  clothed  with  a  noble  growth  of  pines  in  the  upper  portions 
and  receive  enough  precipitation  to  support  a  number  of 
brooks,  which,  however,  except  in  the  wet  season  or  imme- 
diately after  heavy  storms,  are  lost  in  the  gravel  of  the  arroyos 
below.  The  range  soon  dies  out  to  the  east  of  San  Jose.  Its 
main  mass  lies  to  the  south. 


1  The  Geology  of  the  San  Jose  District,  Tamaulipas,  Mexico,.  J.wia/s  of  the  New 
York  Academy  of  Sciences,  vol.  xiv.,  pp.  247  to  318  (1901-03). 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       &59 

San  Jose,  the  little  town  where  the  copper-mines  are  located, 
is  situated  in  a  valley  on  the  northern  side  of  the  mountains. 
Its  arroyo  leads  out  to  the  northeast,  and  the  pass  to  the  south 
goes  around  the  eastern  extremity  of  the  nephelite-syenite,  over 
a  divide,  and  south  to  the  town  of  San  Carlos.  San  Jose  is 
about  40  miles  from  Linares,  with  which  it  is  connected  by  a 
good  road  across  a  plain  covered  with  the  familiar  growths 
of  cactus  and  mesquit,  so  characteristic  of  northern  Mexico. 
The  construction  of  a  railway  between  San  Jose  and  Linares  is 
nearly  finished. 

2.  Geology. — From  Linares  to  San  Jose  the  country-rocks  are 
generally  concealed  by  the  soil,  but  at  the  ford  over  the  creek 
near  Pretil  shales  are  to  be  seen,  in  which  a  brief  search  failed 
to  reveal  fossils.  As  one  nears  the  mountains,  however,  heavy 
strata  of  limestone  rise  gradually  until  the  road  follows  the 
arroyo  in  a  quite  narrow  canyon  with  cliffs  on  either  side. 
Finally,  having  crossed  the  strata  of  outwardly-dipping  lime- 
stone, the  town  of  San  Jose  is  met,  resting  upon  the  carved  and 
eroded  remains  of  a  great  exposure  of  eruptive  rock. 

Detailed  study  shows,  however,  that  the  eruptive  area  is 
surrounded  on  all  sides,  except  the  south,  by  the  limestones, 
which  rest  upon  the  porphyry  and  dip  away  outwardly.  There 
is  no  doubt,  therefore,  that  we  have  to  do  with  an  eroded  lac- 
colith of  eruptive  rock,  which  has  heaved  up  the  limestones 
into  their  present  positions  and  which  has  been  cut  off  on  the 
south  by  the  nephelite-syenite,  probably  along  a  fault.  These 
features  are  shown  on  the  geological  map,  Fig.  2,  reproduced 
with  a  few  modifications  from  Dr.  Finlay's  paper,  in  which  it 
forms  Plate  VIII. 

The  altitude  of  the  village  of  San  Jose  is  approximately 
2,250  ft.  above  sea-level.  The  hills  of  porphyry  within  the 
laccolithic  valley  rise  from  500  to  600  ft.  higher,  are  steep,  and 
obviously  present  what  the  physiographers  call  a  young  topog- 
raphy. A  bore-hole  sunk  since  my  visit  shows  the  laccolith  to 
be  over  1,000  ft.  thick  at  the  Santo  Domingo  mine.  The  sur- 
rounding ridge  of  limestone  and  on  the  south  the  syenite  reach 
the  elevations  marked  on  the  map  at  the  several  stations.  The 
limestone  rim  thus  rises  at  its  lowest  summit  750  ft.  above  the 
valley,  and  at  its  maximum  1,550,  while  the  nephelite-syenites 
attain  heights  of  from  2,500  to  3,000  ft.,  and  at  the  Pic  de 
Diablo  (not  shown  on  the  map)  3,750  ft.  above  it. 


560       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 


GKEOLOGICA.L  IMAiP 
OF  THE 

SAN  JOSE  DISTRICT 

TAMAULIPAS,  MEXICO 


FIG.  2. — GEOLOGICAL,  MAP  OF  THE  SAN  JOSE  DISTRICT. 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       561 

The  limestone  is  a  rather  fine-grained  bluish  variety,  where 
it  has  not  been  exposed  to  contact-metamorphism.  It  is  be- 
lieved to  be  Cretaceous  and  to  belong  to  the  very  thick  forma- 
tion which  is  such  a  prominent  feature  of  northeastern  Mexico. 
It  is  almost  entirely  devoid  of  fossils.  I  only  succeeded  in 
finding  one  poorly-preserved  belemnite  and  one  larger  form 
resembling  an  Exogyra,  the  latter  in  a  rock  altered  to  a  white 
marble  by  the  neighboring  eruptive.  R.  T.  Hill  has  reported 
that  a  formation  probably  the  same  with  this  limestone,  but 
.in  the  valley  of  the  Miquehuana,  which  is  west  of  Victoria  and 
southwest  from  San  Jose,  though  still  in  the  State  of  Tamauli- 
pas,  is  20,000  ft.  thick.2  As  many  earlier  observers  have  re- 
marked, the  limestone  most  closely  resembles  in  its  appearance 
the  Palaeozoic  limestones  of  the  eastern  United  States  and  es- 
pecially the  Siluro-Cambrian  ones  of  the  Great  Valley,  which, 
like  the  Mexican  occurrence,  are  singularly  lacking  in  fossils. 
Near  San  Jose  we  have  neither  the  top  nor  the  bottom  of  the 
series,  but  there  are  certainly  from  1,000  to  2,000  ft.  exposed. 
The  limestone  is  well  bedded  and  it  at  times  contains  streaks  of 
black  flint  or  chert.  From  the  central  eruptive  area  it  dips 
radially  outward  and  is  therefore  in  the  form  of  the  great  eroded 
dome,  so  characteristic  of  laccolithic  intrusions.  On  the  south, 
however,  where  the  mountains  of  nephelite-syenite  cut  off  the 
limestone,  this  structure  does  not  hold,  and  it  is  believed  that 
the  nephelite-syenite  was  elevated  by  faulting  before  the  intru- 
sion of  the  laccolith. 

II.  ERUPTIVE  ROCKS. 

The  eruptive  rocks  are  of  exceptional  scientific  interest  be- 
cause of  the  rare  types  represented.  They  will  be  briefly  de- 
scribed in  their  order  of  age  from  the  oldest  to  the  latest,  so 
far  as  the  succession  can  be  made  out.  The  following  varieties 
are  present :  Irregular  masses  of  nephelite-syenite  and  gabbro ; 
the  laccolith  of  diorite-porphyry ;  about  50  dikes  in  all  -of  tin- 
guaite,  diabase,  camptonite,  and  vogesite  ;  finally  a  surface-flow 
of  basalt.  While  some  of  these  names  are  not  generally  famil- 
iar, a  few  explanatory  sentences  under  each,  as  taken  up  below, 
will  serve  to  tie  them  up  to  varieties  which  have  long  been 
well  established. 

2  K.  T.  Hill.     The  Cretaceous  Formations  of  Mexico,  etc. ,  American  Journal  of 
Science,  Third  Series,  vol.  xlv.,  No.  268,  p.  309  (April,  1893). 


562       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

1.  Deep-Seated  Eruptives. 

(a)  Nephelite-Syenite. — The  oldest  of  the  eruptives  is  the  nephe- 
lite-syenite  which  constitutes  the  high  peaks  to  the  south.  It 
is  a  rather  coarsely  crystalline  rock,  which  for  all  practical  pur- 
poses may  be  likened  to  a  granite.  It  is  a  peculiar  variety  of 
syenite  in  that  it  contains  the  mineral  nephelite.  The  rock  is 
sometimes  nearly  pure  feldspar  and  nephelite,  and  is  light  in 
color.  Again,  it  has,  with  these  two,  more  and  more  black 
hornblende  and  pyroxene,  until  it  becomes  dark  gray.  Almost 
always  honey-yellow  titanites  are  visible  to  the  eye.  The  sev- 
eral varieties  have  been  fully  described  by  Dr.  Finlay. 

The  following  chemical  analysis,  made  by  Dr.  Henry  S. 
Washington,  illustrates  the  composition  of  one  of  the  varieties : 
Si02,  58.40;  A12O3,  20.25;  Fe20s,  1.78;  FeO,  2.41 ;  MgO,  0.49; 
CaO,  3.11;  Na20,  7.01;  K20,  5.39;  H20  (110°),  0.27;  H20 
(ign.),  0.57;  Ti02,  0.25;  P265,  0.20;  S03,  0.06;  C12,  0.2;  total, 
100.21  per  cent.  This  shows  a  typical  nephelite-syenite  rich  in 
feldspar.  Dr.  Finlay  estimated  the  percentage-composition  of 
the  several  minerals  by  measuring  areas  in  thin  sections,  and, 
for  three  varieties  of  the  rock,  his  results,  showing  the  in- 
creasing amounts  of  the  dark  silicates,  are  as  follows  : 

Percentage  Percentage  Percentage 

of  Areas.  of  Areas.  of  Areas. 

Orthoclase 60.0  12.0  5.6 

Plagioclase 5.0 

Nephelite 25.0  18.0  13.2 

Augite 1.0  23.0  13.9 

Hornblende 40.0  60.5 

Biotite 2.2 

Magnetite 8.0  2.7  0.4 

Titanite 0.7  2.0  2.8 

Apatite 1.2  1.4 

Total 99.7  98.9  100.0 

Average  size  of  grain 0.36mm.  0.2mm.  0.16  mm. 

The  coarsely  crystalline  texture  of  the  syenite  proves  it  to 
be  a  rock  which  has  consolidated  far  below  the  surface,  slowly 
and  under  pressure.  Its  present  elevated  position  is  believed 
to  be  due  to  faulting,  as  earlier  stated.  It  is  older  than  the 
porphyry,  but  whether  it  is  older  than  the  limestones  was  not 
determined,  because  in  no  place  could  the  two  be  found  in  con- 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       563 

tact.  Whether,  therefore,  the  syenite  formed  an  old  land-area 
and  shore  along  which  the  limestones  were  laid  down  on  the 
sea-bottom,  or  whether  it  was  intruded  into  them  and  later 
faulted  into  its  present  position,  we  do  not  know.  It  is  possi- 
ble, however,  that  the  question  could  be  solved  at  the  western 
end  of  the  range. 

(b)  Gabbro. — This  rock  was  found  in  three  places,  two  near 
each  other  and  mapped  as  one  along  the  road  from  San  Jose  to 
the  Yegonia  mine,  and  one  in  a  gulch  northwest  of  the  village. 
Recent  work  has  shown  the  former  to  be  somewhat  more  ex- 
tensive than  is  given  on  the  map.  The  exposures  are  deeply 
weathered  and  rusty  brown.  The  fresh  specimens  are  grani- 
toid in  texture,  medium  grained  and  dark  gray.  The  constitu- 
ent minerals  are  plagioclase,  biotite,  augite,  titanite,  magnetite, 
apatite,  pyrite,  and  zircon.  This  rock  was  called  a  diorite  by 
Dr.  Finlay  on  account  of  its  moderately  acidic  feldspar,  but  in 
order  to  be  clear  to  readers  more  especially  familiar  with  rock- 
names  employed  in  mining-districts,  and  on  account  of  the  pre- 
ponderating augite,  it  is  here  called  gabbro.  The  analyses 
of  slightly  differing  varieties,  made  by  Dr.  Finlay,  are :  Si02, 
45.75  (48.49);  A1203,  18.51  (18.99);  Fe203,  6.55  (9.59);  FeO, 
6.02  (1.00);  MgO,  5.06  (5.05);  CaO,  11.85  (10.78);  JSTa2O,  3.41 
(3.47);  K20,  2.35  (1.42);  ^a20,  trace  (nil);  H20  (100°),  0.06 
(0.10);  H2O  (ign.),  0.20  (0.55);  total,  99.76  (99.44)  per  cent. 

These  analyses  show  the  rock  to  be  a  rather  basic  variety, 
but  one  which  does  not  differ  in  any  extraordinary  degree  from 
those  of  many  gabbros.  The  syenite  and  gabbro  are  two  char- 
acteristically deep-seated  rocks. 

2.   The  Laccolith. 

The  next  in  order  of  formation  is  the  rock  constituting  the 
laccolith,  which  is  here  described  under  the  general  name 
diorite-porphyry.  This  eruptive  combines  the  features  of  a 
deep-seated  rock  with  those  of  a  dike  or  sheet.  It  is  visibly 
porphyritic,  but  the  ground-mass,  as  often  happens  in  lacco- 
lithic  types,  is  subordinate  and  it  may  almost,  if  not  quite,  dis- 
appear. The  rock  therefore  shades  texturally  into  a  very  feld- 
spathic  diorite,  and  in  the  diamond-drill  cores  and  some  of  the 
deeper  exposures  it  can  with  difficulty  be  separated,  by  the  eye 
alone,  from  the  whiter  varieties  of  syenite.  The  rock  is  named 


564      COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

in  accordance  with  the  underlying  conception  that  igneous 
varieties  belonging  to  the  andesite-diorite  series  vary  from  glassy 
and  felsitic  surface-flows  of  true  typical  andesites;  through 
porphyritic  varieties  with  increasingly  abundant  phenocrysts, — 
the  andesite-porphyries  of  the  dikes  and  sheets, — on  through 
those  with  less  and  less  ground-mass, — the  diorite-porphyries, 
in  laccoliths  and  stocks, — to  the  granitoid  diorites  in  the  batho- 
liths  and  deep-seated  masses.  As  the  phenocrysts  are  very 
abundant  and  the  ground-mass  almost  disappears  in  most  of  the 
exposures  of  the  laccolith,  diorite-porphyry  best  describes  the 
rock.  The  name  andesite  was  used  by  Dr.  Finlay,  and  while  I 
regard  with  misgivings  any  change  in  a  nomenclature  already, 
although  unavoidably,  confusing,  the  term  "  diorite-porphyry  " 
is  coincident  with  the  usage  of  Whitman  .Cross  in  the  folios  and 
papers  on  the  San  Juan  region  of  Colorado,  where  analogous 
laccoliths  occur  in  many  mining-districts.  It  is  hoped  that  it 
will  therefore  be  most  significant  to  readers  interested  in  min- 
ing-geology. 

The  diorite-porphyries  are  light  yellow  to  bluish  gray  in  color 
and  vary  by  insensible  gradations  from  more  basic  to  more 
acidic  facies.  They  contain  plagioclase,  orthoclase,  augite,  bio- 
tite,  magnetite,  titanite,  zircon,  and  at  times  quartz  in  consid- 
erable quantity.  The  ground-mass  is  fully  crystallized  and  the 
contrasts  are  much  less  between  it  and  the  phenocrysts  than 
are  usually  seen  in  surface-flows.  But  this  relation  always 
holds  in  the  laccoliths  and  intruded  sheets,  as  all  observers  are 
well  aware. 

An  analysis,  made  by  Dr.  Finlay,  gave  the  following  results  r 
Si02,  62.31;  A1203,  18.63;  Fe203, .2.38;  FeO,1.33;  MgO,  0.60; 
CaO,  5.91 ;  ^a20, 4.97  ;  K20,  3.52 ;  P205,  0.07 ;  H20(110°),  0.16 ; 
H20  (ign.),  0.07;  total,  99.98  per  cent. 

This  analysis  indicates  a  rather  acidic  variety.  Column  I.  of 
the  analyses  on  the  following  page  gives  the  percentage-com- 
position of  the  several  minerals  obtained  by  recasting  the  anal- 
ysis. Column  II.  gives  the  percentage-composition  of  a  still 
more  acidic  variety,  a  dacite-porphry,  obtained  by  measuring 
the  diameters  of  the  minerals  in  thin  sections. 

No  biotite  is  tabulated  under  column  I.,  because,  although 
present  in  very  small  quantities,  its  complicated  composition 
prevents  its  calculation. 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,  MEXICO.       565 

Percentage- Composition  of  a  Dacite-Porphyry. 

i.  n. 

Per  Cent.  Per  Cent. 

Plagioclase 60.0  32.0 

Orthoclase 20.6  25.0 

Pyroxene 6.6  16.0 

Magnetite 3.5  6.7 

Quartz 8.9  17.0 

Biotite 2.4 

Accessories 0.9 


Total 99.6  100.0 

The  diorite-porphyry  is  the  most  important  rock  connected 
with  the  ore-formation,  since  it  has  produced  the  garnet-zones 
and  has  apparently  occasioned  the  introduction  of  the  ore,  as 
will  be  later  described.  Messrs.  Aguilera  and  Ordonez,  who 
have  published  a  short  note  about  the  rock  and  its  contact-zones, 
speak  of  it  as  an  andesitic  diorite.3 

Where  exposed  near  the  contact-zones,  the  diorite-porphyry 
is  at  times  supplied  with  pyrite  which  appears  throughout  the 
rock  and  which  follows  the  innumerable  tiny  fissures  ramifying 
through  it  in  every  direction. 

The  diorite-porphyry  is  found  in  the  great  laccolithic  mass 
and  also  as  innumerable  dikes,  penetrating  the  gabbro  and  es- 
pecially the  limestone,  where  the  latter  has  been  opened  up  in 
the  mines.  It  constitutes  the  greater  part  of  the  San  Jose 
valley,  its  unbroken  extent  being  chiefly  prevented  by  the  in- 
clusions of  limestone,  which  resemble  islands  in  the  midst  of 
the  eruptive  mass. 

It  may  be  that  there  is  more  than  one  intrusion  of  the  dioritic 
rock.  Considerable  range  in  mineralogy  is  exhibited;  and 
while  no  positive  field-evidence  could  be  secured,  and  while  the 
amount  of  the  varieties  must  be  small  as  compared  with  the 
main  mass,  yet  the  possibility  may  be  considered. 

The  diorite-porphyry  is  later  in  age  than  the  gabbro,  since  it 
cuts  the  latter  in  dikes.  It  is  also  later  than  the  syenite,  since 
along  the  contacts  it  shows  the  effects  of  chilling  and  becomes 
denser. 

3.  Dikes. 

(a)  Tinguaite. — Dikes  of  this  interesting  rock  cut  the  diorite- 
porphyry  in  every  direction  and  one  in  particular  runs  clear 

3  Bosquejo  geologico  de  Mexico,  Boktin  del  Institute  geologico  de  Mexico,  Nos.  4, 
5,6,  p.  222  (1897). 


566       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

across  the  valley  from  limestone-wall  to  limestone-wall.  Tin- 
guaites  are  dense,  dark-green  rocks  closely  allied  to  phonolites, 
but  containing  the  soda-pyroxene  segirite  in  great  abundance, 
together  with  nephelite  and  orthoclase.  A  little  plagioclase, 
titanite,  magnetite,  and  in  some  varieties  a  great  deal  of  analcite, 
complete  the  list  of  the  minerals.  Fine  phenocrysts  of  ortho- 
clase are  sometimes  abundant,  but  again  the  rock  appears  as  a 
dense,  green,  felsitic  one,  and  then  has  analcite  as  a  rule. 

Two  analyses  of  the  analcite-tinguaites,  one  made  by  H.  8. 
Washington,  the  second  by  Gr.  I.  Finlay,  are  as  follows  :  SiO, 
52.83(49.42);  Ti02,  0.16  (not  det.) ;  A1203,  20.70  (22.99);  Fe2O3, 
2.84  (2.70);  FeO,  1.19  (1.89);  MgO,  0.41  (0.45);  CaO,  1.00 
(2.59);  IsTa20,  9.94  (9.63);  K20,  4.97  (4.21);  H20  (110°),  0.37 
(not  det.) ;  H20  (ign.),  5.28  (5.73) ;  P205,  0.03  (not  det.) ;  01,  0.06 
(not  det);  total,  99.62  (99.99)  per  cent. 

The  tinguaite  dikes  have  been  intruded  after  the  formation 
of  the  ore  and  the  garnet-zones.  They  cut  the  latter  and  are 
met  in  several  places  in  the  mines.  They  also  appear  as  far  as 
20  miles  away  from  the  syenite,  both  towards  San  Carlos  and 
towards  Linares.  Mr.  Self  concludes  that  these  dikes  become 
more  abundant  as  one  leaves  San  Jose  in  each  of  these  direc- 
tions. In  other  parts  of  the  world  tinguaites  have  proved  to 
be  characteristic  associates  of  nephelite-syenites  and  it  is  quite 
natural  that  they  should  occur  near  San  Jose.  So  far  as  we 
know,  they  do  not  cut  the  syenite,  but  are  limited  to  the  sur- 
rounding rocks. 

(b)  Camptonite. — In  great  contrast  with  the  green  dikes  of  tin- 
guaite are  a  number,  of  dark  basaltic  habit,  which  display  long, 
black,  slender  prisms  of  hornblende  on  fresh  fractures.  They 
proved  on  microscopic  examination  to  be  the  basaltic  rock 
whose  chief  dark  silicate  and  predominant  mineral  is  chestnut- 
brown  hornblende,  and  which  contains  also  a  little  augite,  pla- 
gioclose,  magnetite,  and  apatite.  An  analysis  by  Dr.  Finlay 
yielded:  Si02,  42.49;  A1203,  17.68;  Fe203,  5.12;  FeO,  5.90; 
MgO,  5.28;  CaO,  15.81;  Na20,  4.29;  K20,  2.97;  H20,  0.38; 
total,  99.92  per  cent. 

The  camptonite  is  thus  a  very  basic  rock.  Elsewhere  it  is  a 
rather  characteristic  associate  of  nephelite-syenite  and  its  occur- 
rence at  San  Jose  is  quite  in  accord  with  the  general  rule. 

The  camptonites  cut  the   nephelite-syenite,  the  diorite-por- 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       567 

phyry,  and  the  limestone.  They  are  also  later  than  the  ore. 
No  intersections  have'  been  found  which  would  establish  their 
relative  ages  as  compared  with  the  other  dikes. 

(c)  Vogesite. — A  4.5-ft.  dike  of  this  interesting  rock  has  been 
found,  which  consists  chiefly  of  orthoclase,  hornblende,  and 
augite,  but  there  are  also  small  quantities  of  magnetite,  plagio- 
clase,  titanite,  and  biotite.    It  is  practically  a  very  basic  syenite, 
of  which  hornblende  makes  up  the  major  part  of  the  rock. 

(d)  Olivine- Basalt. — One  other  dike  of  olivine-bearing  basalt 
was  found  by  Dr.  Finlay  in  the  syenite  area  5  miles  south  of 
San  Jose.     It  has,  however,  no  connection  with  the  ores. 

4.  Surface-Flow. 

Basalt. — There  is  also  a  remarkable  surface-flow  of  basalt 
which  comes  out  of  the  eastern  side  of  the  San  Carlos  moun- 
tains, in  the  syenite  area,  and  extends  for  4  or  5  miles  down 
the  Arroyo  Grande.  It  is  scoriaceous  and  still  not  greatly  re- 
duced by  erosion.  No  cone  is  associated  with  it  and  it  seems 
to  be  a  fissure-eruption.  It  is  the  last  outbreak  in  the  region. 
The  rock  is  porphyritic  and  consists  chiefly  of  plagioclase, 
augite,  and  magnetite,  with  smaller  amounts  of  biotite,  titanite, 
and  glass.  The  habit  is  basaltic.  An  analysis  by  Gr.  I.  Finlay 
yielded:  Si02,  48.03;  A1203,  20.98;  Fe2O3,  7.06;  FeO,  4.51; 
MgO,  4.43;  CaO,  9.54;  £Ta20,  3.28;  K20,  1.99;  H20  (110°), 
0.21 ;  H20  (ign.),  0.40 ;  total,  100.00  per  cent. 

This  analysis  indicates  a  quite  normal  olivine-free  basalt. 
The  outbreak  had  nothing  to  do  with  the  ores  and  is  5  or  6 
miles  distant  from  the  nearest  mine. 

III.  CONTACT-EFFECTS. 

The  contact-effects  are  limited  to  the  borders  of  the  diorite- 
porphyry  and  the  limestone  and  they  are  variable  in  their  in- 
tensity. The  starting-point  in  their  study  is  the  composition 
of  the  unchanged  limestone,  because  from  this  one  may  infer 
whether  silica  and  the  bases  have  been  added  in  the  meta- 
morphism  or  whether  we  are  dealing  with  the  rearrangement 
and  crystallization  of  materials  already  in  the  limestone  itself. 
Samples  have  been  very  kindly  furnished  me  by  E.  D.  Self, 
one  from  an  exposure  near  the  Yegonia  claim  and  the  other 
from  a  quarry  operated  for  flux  at  the  north  side  of  the  lacco- 


568       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO, 

lithic  valley  and  in  the  surrounding  rim.  Both  were  unaltered 
blue  limestone,  resembling  very  much  the  usual  Cambro-Silu- 
rian  variety  so  abundant  in  the  Great  Valley  of  the  eastern 
United  States.  A  third  sample  was  taken  of  a  white  marble, 
from  the  east  side  of  the  valley  on  Armadillos  hill.  It  came 
from  a  large  mass  of  limestone,  which  had  been  included  in 
the  laccolith,  and  changed  to  a  beautiful,  saccharoidal  marble. 

Vegonia.    Furnace  Quarry.     Marble. 
Per  Cent.         Per  Cent.  Per  Cent. 

Insoluble 5.04  4.31  9.55 

Fe2O3.  A12O3 0.35  0.95  1.28 

CaCO3 94.55  93.83  88.92 

MgCO3 0.58  1.29  0.91 

Total 100.52  100.38  100.66 

These  analyses  indicate  a  limestone  fairly  pure,  so  far  as  in- 
soluble silica  or  silicates  go,  and  one  low  in  magnesia.  It  may 
be  queried  whether  the  analyses  are  representative  of  the  gen- 
eral rock  of  the  section,  where  uninfluenced  by  the  eruptives. 
Broadly  speaking,  it  seems  to  me  that  this  is  probably  not  far 
from  the  truth.  There  are  some  beds  with  chert  observed  in 
the  field  which  would  run  higher  in  silica,  but  these  are  very 
minor  factors  in  the  total.  There  may  be  more  argillaceous 
beds,  yet  any  which  are  markedly  shaly  failed  to  impress  them- 
selves upon  us,  the  section  presenting  a  rather  strikingly  uni- 
form series  of  limestones.  The  analysis  of  marble  shows  a 
higher  percentage  and  it  is  possible  that  all  of  it  was  indigenous 
in  the  original  unaltered  limestone.  This  sample  came  from 
the  specimen  holding  the  still  recognizable  lam.ellibranch  fossil, 
a  type  of  shell  favoring  muddy  bottoms.  We  may  therefore 
be  prepared  to  admit  in  some  parts  of  the  limestone  section 
even  as  much  as  10  per  cent,  of  insolubles.  Still,  as  the  sam- 
ple showed  recrystallization  to  marble,  and  as  it  gave  gelatinous 
silica,  and  probably  therefore  contained  wollastonite,  it  may  also 
be  true  that  some  silica  had  been  introduced.  At  this  point, 
however,  it  is  the  purpose  to  state  facts  rather  than  draw  con- 
clusions, and  further  discussion  is  postponed  to  a  later  page. 

The  simplest  contact-effect  which  has  been  noted  is  the  de- 
velopment of  little  bundles  of  tremolite  in  a  limestone  which 
has  scarcely  lost  its  blue  color.  The  specimen  was  found  on 
the  southwestern  edge  of  the  laccolith  near  the  Santa  Rita 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       569 

trail.  For  the  production  of  the  tremolite  it  would  not  seem 
necessary  to  assume  the  introduction  of  silica  from  outside,  but 
rather  the  recrystallization  of  what  was  probably  already  in 
the  limestone,  under  the  influence  of  heat,  or  hot  waters  from 
the  eruptive. 

The  next  effect  is  to  change  the  blue  limestone  into  white 
marble.  This  change  is  the  rule,  both  with  and  without  the 
further  production  of  garnet  or  other  minerals.  Sometimes 
the  change  to  marble  appears  to  be  the  only  result  brought 
about  by  the  eruptive.  The  marble  is  of  the  usual  variety.  It 
has  no  associated  minerals  prominently  developed  and  has  been 
produced  by  the  recrystallization  of  fairly-pure  calcium  carbo- 
nate with  slight  admixture  of  magnesium  carbonate.  In  one 
interesting  case  observed  on  the  eastern  side  of  the  valley,  and 
already  referred  to,  a  fairly  well  preserved  Exogyra  was  still 
recognizable  in  the  marble. 

The  most  important  and  extensive  contact-effect  is  the  alter- 
ation of  the  limestone  to  garnet  and  other  lime  silicates.  Many 
of  the  hand- specimens  which  appear  to  the  eye  to  be  only  brown 
garnet  are  found  to  be  more  complex  under  the  microscope. 
The  production  of  the  lime  silicates  has  taken  place  on  a  very 
large  scale.  Fig.  2  exhibits  65  different  exposures.  The  focus 
of  change  is  on  the  hill  called  Remedies,  the  summit  of  which 
is  the  mass  of  magnetite  called  the  Piedra  Iman,  or  loadstone. 
The  contact-zones  are  also  extensive  in  Reina  hill,  and  in  a 
general  course  from  the  Santo  Domingo  claim  through  the 
Bretana  and  the  San  Mauricio  towards  and  to  the  Yegonia. 
Around  the  rim,  however,  although  not  absolutely  lacking, 
they  are  much  less  common. 

The  extent  of  the  change  varies  from  scattered  nodules  of 
garnet  in  limestone  up  to  belts  and  masses  many  feet  across. 
In  most  cases  they  lie  along  the  borders  of  the  limestone  and 
porphyry,  but  there  are  occurrences  with  no  visible  limestone 
near,  and  then  the  masses  of  silicates  seem  to  have  resulted 
from  the  complete  alteration  of  included  blocks,  torn  off  by 
the  eruptive. 

The  garnet  and  its  associated  silicates  are  occasionally  in 
banded  or  streaked  formation,  but  more  commonly  they  are 
quite  massive.  Small  vugs  or  cavities  with  crystals  exhibiting 
the  rhombic  dodecahedron  are  not  uncommon.  In  larger  cavi- 

36 


570       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

ties  well-developed  octahedral  crystals  of  pyrite  also  appear, 
and  all  through  the  cavities  and  along  cracks  in  the  garnet,  as 
well  as  included  in  its  substance,  chalcopyrite  and  pyrite  mani- 
fest themselves.  Some  calcite  is  also  occasionally  visible  in  the 
garnet-zones  and,  as  will  be  later  noted,  in  two  or  three  places 
considerable  bodies  of  magnetite  have  been  met,  seamed  in 
every  direction  with  chalcopyrite  and  pyrite.  After  this  gen- 
eral statement  the  more  detailed  discussion  of  the  chemistry 
and  mineralogy  may  be  taken  up  in  connection  with  the  indi- 
vidual minerals. 

The  simplest  change  in  the  alteration  of  the  limestone  to 
silicates  is  the  production  of  wollastonite,  CaO,Si02  (CaO,  48.3 ; 
Si02,  51. 7),  by  the  replacement  of  the  C02  of  the  limestone  with 
Si02.  This  mineral  has  only  been  noted  in  the  microscopic 
way.  It  shows  an  aggregate  of  brightly-polarizing  grains, 
many  of  which  have  a  well-marked  cleavage  with  parallel  ex- 
tinctions. In  many  cases  the  mineral  lacks  the  elongated, 
fibrous  or  prismatic  character  of  the  usual  wollastonite,  but  the 
optical  and  physical  properties  indicate  its  identity. 

The  next  change,  which  involves  the  fewest  chemical  rear- 
rangements, is  the  production  of  diopside,  the  double  bisilicate 
of  lime  and  magnesia,  CaO,Si02,  MgO,SiO2  (CaO,  25.9;  MgO, 
18.5  ;  Si02,  55.6),  which  differs  chemically  from  the  wollastonite 
only  in  the  fact  that  some  magnesia  is  present  with  the  lime. 
The  replacement  of  C02  with  Si02  is  the  only  change  involved. 
The  reaction  is  the  same  as  in  the  case  of  the  tremolite,  which 
has  essentially  the  same  chemical  composition,  but  the  latter 
was  found  in  the  blue  limestone,  while  the  diopside  has  only 
been  observed  in  the  zones  of  silicates.  One  slide  revealed  it 
in  association  with  garnet,  and  calcite.  It  formed  irregular, 
brightly-polarizing,  almost  colorless  grains,  with  its  character- 
istic optical  properties.  The  low  percentage  of  magnesia,  both 
in  the  limestone  and  in  the  eruptive,  has  militated  against  its 
extensive  production,  garnet,  which  requires  no  magnesia,  tak- 
ing natural  precedence. 

The  most  widespread  and  characteristic  mineral  of  the  con- 
tact-zones from  limestone  is  garnet.  Garnet  is,  however,  rather 
a  name  for  a  group  than  for  a  single  species.  The  group  con- 
sists of  orthosilicates  involving  three  molecules  of  H4Si04  and 
having  twelve  bonds  of  affinity  which  are  satisfied  by  three  pro- 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       571 

toxides,  such  as  CaO  and  FeO  ;  and  by  one  sesquioxide,  such  as 
A1203  or  Fe2O3.  By  combinations  of  these,  several  distinct  gar- 
nets can  be  made.  Thus,  3CaO,  Al,03,  3Si02  is  grossularite,. 

Grossularite.  Andradite. 


SiO4  =  Ca.  >Si04  =  Ca. 

e 


\\Si04=Ca. 

the  one  which  has  been  usually  considered  to  be  present  in  the 
zones.  The  fact  that  the  garnets  are  light  brown  or  pale  green 
has  given  rise  to  this  impression  in  the  absence  of  chemical 
analysis,  and  upon  the  basis  of  the  grossularite  molecule  the 
inferences  about  the  constitution  of  the  original  limestone  and 
development  of  the  zones  have  usually  been  reached.  Some 
doubt,  however,  arose  in  my  mind  regarding  the  correctness  of 
this  view  and  a  massive  variety  was  selected  for  analysis.  It 
was  a  pale  reddish  brown  in  color.  The  results  obtained,  in- 
cluding the  molecular  ratios,  are  as  follows  : 

Per  Cent.  Molecular  Ratios. 

SiO2  ......................................................  37.15  619 

A1203  ....................................................      6.98  69 

Fe2O3  ...................................................  19.40  120 

CaO.  ......................................................  32.44  576 

CaCO3  ...................................................       4.20 

Soluble  A  12O3,  Fe2O3  ................................      0.43 

Total  ..............................................  100.60 

It  was  found  on  trial  that  the  sample  contained  some  calcite. 
It  was  therefore  treated  with  very  dilute  hydrochloric  acid  and 
from  the  solution  enough  lime  was  obtained  to  make  4.20 
CaC03.  The  solution  also  yielded  0.43  A1203,  Fe203,  with  per- 
haps a  little  Si02  ;  the  total  was  so  small  that  no  attempt  to 
separate  the  constituents  was  made.  No  visible  magnesia  could 
be  precipitated.  It  is  possible  that  a  little  manganese  was  also 
present  in  the  sample.  It  was  not  specially  sought. 

If  we  recast  the  above  analysis  so  as  to  determine  the  rela- 
tive amounts  of  the  grossularite  and  andradite  molecules,  the 
results  are  as  follows,  using  respectively  the  molecular  ratios  of 
the  alumina  and  ferric  iron  as  the  basis. 


572       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 


Grossularite. 
3CaO  207 

11.60 
6.98 
12.42 

31.00  | 

3CaO 

Andradite. 
360 

20.10 
19.40 
21.60 

61.10 

ALA-. 

69 

Fe.Oo 

120 

3SiO2  

207 

*  ^2^3  

3SiO2. 

360 

There  are  not  sufficient  molecules  of  the  alumina  and  ferric 
iron  to  care  for  all  the  silica  and  lime.  The  excess  of  the 
former  is  619  —  (207  +  360)  =  52,  corresponding  to  3.12  per 
cent.  This  would  lead  one  to  infer  the  presence  of  a  little 
quartz  in  the  sample,  or  else  that  in  the  garnet  th'ere  was  some 
diopside  or  wollastonite,  both  of  which  contain  more  silica  than 
does  garnet.  Yet  in  any  event  the  amount  does  not  seriously 
.affect  the  result.  The  lime  is  as  follows,  576  —  (207  +  360)  =  9, 
corresponding  to  0.5  per  cent.  This  may  be  due  to  the  sup- 
posed diopside  or  wollastonite,  as  just  stated,  or  perhaps  to 
error  in  the  analysis.  It  also  is  not  a  serious  factor.  The 
chief  result  of  importance,  even  admitting  slight  errors  in 
determinations  and  assumptions,  is  to  establish  the  relative 
amounts  of  the  grossularite  and  andradite  molecules.  These 
are  to  each  other  as  31  to  61.1,  or  in  percentages — grossularite, 
33.7 ;  andradite,  66.3. 

The  lime-iron  garnet  must  therefore  be  esteemed  of  very 
great  importance  in  the  chemistry  of  the  production  of  the 
zones,  and  theoretical  discussions  based  on  the  grossularite 
molecule  are  open  to  objection  to  this  extent.  The  importance 
of  the  whole  matter  lies  in  its  bearing  upon  the  question  of  the 
production  of  the  garnet,  whether  by  recrystallization  of  an 
impure  limestone  or  by  contributions  of  silica,  alumina,  and 
iron  from  the  eruptive  to  a  fairly-pure  limestone.  This  ques- 
tion will  be  taken  up  later.  It  may  be  remarked,  however,  that 
Waldemar  Lindgren  4  also  records  the  presence  of  the  andradite 
molecule  in  large  amounts  in  the  zones  at  Morenci,  Ariz., 
although  the  analyses  have  not  yet  been  published. 

In  association  with  the  garnet  is  also  found  vesuvianite,  a  still 
more  complicated  compound,  regarding  whose  exact  formula 
there  has  been  some  difference  of  opinion.  Writing  it  as  it  is 
given  by  F.  "W.  Clarke,5  it  is  HCa5,MgAl3,Si5021,  or  if  we  expand 

*  The  Genesis  of  the  Copper-Deposits  of  Clifton-Morenci,  Arizona,  Trans., 
xxxv.,  511  to  550  (1904)  ;  p.  517,  this  volume. 

5  Bulletin  No.  125,  U.  S.  Geological  Survey,  p.  25  (1895). 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       573 

it  into  a  graphic  form,  which  always  helps  towards  a  clear  under- 
standing, the  following  is  obtained  : 

H— Al  = 
// 
Al 


Si0  =  Ca. 


The  vesuvianite,  as  compared  with  the  other  minerals,  only 
involves  the  addition  to  the  limestone  of  the  same  silica,  alumina, 
and  ferric  oxide,  together  with  hydroxyl  or  hydrogen  ;  and  both 
of  the  last  named  could  easily  be  supplied  by  steam,  conceiv- 
ably dissociated  under  the  pressures  and  temperatures  attendant 
on  igneous  intrusion.  The  vesuvianite  has  been  observed  in 
one  rare  instance  extending  out  as  a  small  vein,  1  in.  wide  by  4 
in.  long,  into  the  limestone,  as  if  it  had  been  formed  on  either 
side  of  a  small  crack  by  the  introduction  of  the  elements  needed 
to  change  over  the  neighboring  limestone.  In  the  general 
mass  of  the  contact-rock  the  microscopic  examination  has  not 
indicated  that  it  is  frequent. 

Of  the  other  silicates,  epidote,  zoisite,  biotite,  albite,  anorthite, 
etc.,  which  are  sometimes  met  in  limestone-contacts,  no  occur- 
rences have  been  noted. 

Magnetite  is  a  contact-mineral  locally  developed  in  irregular 
masses,  which  are  of  very  considerable  size.  On  the  borders 
there  are  intermingled  garnet  and  diopside,  and  throughout 
the  magnetite  are  abundant  veinlets  of  chalcopyrite  and  pyrite, 
but  sections  of  the  magnetite  exhibit  practically  no  transparent 
minerals.  One  prominent  outcrop  gave  the  name  Piedra  Iman, 
or  loadstone,  to  the  summit  of  Remedies  hill.  A  large  mass 
has  been  opened  in  the  Santa  Elena  claim. 

The  magnetite  must  have  been  introduced  in  the  same  way 
as  have  the  silica  and  alumina  which  have  developed  the  sili- 
cates. The  iron  oxide  has  probably  replaced  the  limestone  and 
has  thus  formed  local  contact-masses  different  from  the  usual 
type.  So  far  as  the  available  evidence  goes,  the  introduction 
of  the  magnetite  has  followed  the  garnet  and  diopside  and  has 


574       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

preceded  much  of  the  chalcopyrite  and  pyrite,  since  all  manner 
of  crevices  in  it  are  filled  with  veinlets  of  the  latter. 

In  small  pockety  masses  throughout  the  garnet  and  other 
silicates  calcite  is  occasionally  seen.  It  may  be  either  residual 
limestone  not  changed  over  into  silicates,  or  it  may  be  calcite 
of  secondary  introduction. 

Molybdenite  has  also  been  found  by  E.  D.  Self  to  be  quite 
abundant  in  some  of  the  workings  opened  since  my  visit.  Thus 
in  the  Santa  Elena  adit,  assays  covering  a  considerable  distance 
yielded  from  0.5  to  1  per  cent,  of  MoS2.  In  the  Santo  Do- 
mingo shaft  Mr.  Self  has  observed  it,  apparently  in  a  garnet- 
zone  that  contained  also  vesuvianite.  The  occurrence  of  molyb- 
denite at  San  Jose  corresponds  with  Mr.  Lindgren's  observations 
at  Morenci.  The  home  of  molybdenite  is  in  the  pegmatite 
dikes,  and  it  is  interesting  and  suggestive  to  find  it  also  in  the 
zones,  which  must  likewise  be  ascribed  to  expiring  igneous 
activities. 

The  most  important  copper-mineral  is  chalcopyrite,  quite  in- 
variably in  association  with  pyrite.  The  two  must  have  come 
in  together.  They  appear  not  only  as  inclusions  in  the  silicates, 
but  also  as  veinlets  and  as  coatings  in  cavities.  They  cover  at 
times  the  well-developed  crystals  of  garnet  so  as  to  mold  around 
them  like  a  paste.  The  sulphides  may  themselves  form  large 
masses  analogous  to  the  magnetite  and  thus  yield  the  best 
stopes  of  ore. 

The  usual  oxidized  compounds  malachite,  chrysocolla  and, 
less  often,  cuprite  may  be  seen.  The  mine-waters  from  the 
Santo  Domingo  shaft  yield  appreciable  amounts  of  dissolved 
copper. 

Since  my  visit,  narrow  veinlets  of  sulphide  ore  rich  in  gold 
have  been  discovered  in  the  porphyry  and  far  from  known  lime- 
stone or  garnet-zones,  as  observed  by  Mr.  Self.  These  occur- 
rences suggest  parallels  with  Morenci. 

IV.  GENETIC  CONCLUSIONS. 

Having  the  comprehensive  statement  of  the  minerals  and 
their  relations  to  the  contact-zones  before  us,  we  may  consider 
the  possible,  as  well  as  the  most  reasonable,  methods  whereby 
they  could  have  been  produced.  As  incontrovertible  we  may 
establish  at  the  outset  the  following  premises  : 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       575 

1.  The  garnet-zones  have  been  produced  by  the  action  of  the 
diorite-porphyry  upon  the  limestone. 

2.  The  garnet-zones  are  irrrgular  in  distribution  and  in  size. 
They  are  sometimes  very  thick,  and  again  white  marble  is  alone 
developed  next  the  eruptive. 

3.  The  chemical  compositions  of  the  active  agent,  the  dio- 
rite-porphyry, and  of  the  raw  material,  the  limestone,  are  as 
follows.     Some,  though  probably  not  great,  variation  is  admis- 
sible for  each.     To  these  are  added  the  theoretical  analyses 
of  andradite  and  of  grossularite,  the  most  abundant  molecules 
in  the  zones. 


Diorite-Porphyry. 

Limestone. 

Andradite. 

Per 

fiiO 

Cent. 
tt9  31 

Per  Cent. 

SiO2  

Per  Cent. 
40.0 

Ai  n 

1  Q    £0 

AlA,Fe203 
0.5  to  1.2 
CaCO3  93  to  94 
MgC03...0.5tol.2 

A12O3  

22.7 

AljUj  
TTo  O 

9  '48 

CaO  

37.3 

Stf'  

....     133 

Total..  .. 

100.0 

\f     f\ 

OAfl 

MgU  
CaO  

...      5.91 

Grossularite. 

Na2O 

4.97 

K,O 

3  52 

SiO2  

Per  Cent. 
35.4 

T>  f\ 

&$  

.Oi 

Fe.,O,  .. 

31.5 

±12U  

Total 

,£o 

99  95 

CaO 

33  1 

Total 

100  0 

1.   The  Recrystallization  Process. 

We  may  first  raise  the  question  whether  it  is  conceivable 
that  the  garnet  has  been  produced  from  the  limestone  alone. 
That  is,  are  we  justified  in  believing  that  the  limestone  was 
sufficiently  siliceous  and  argillaceous,  where  we  now  find  the 
zones,  to  have  yielded  the  garnet  and  the  other  silicates  with- 
out contributions  from  the  eruptive  ?  The  belief  that  contact- 
zones  are  formed  in  this  way  is  rather  widespread  and  is  based 
partly  on  general  considerations  and  partly  on  the  following 
specific  cases : 6 

1.  In  studying  the  contact-effects  produced  by  the  famous 
Shap  granite  of  Westmoreland,  England,  upon  amygdaloidal 
and  altered  basaltic  rocks  which  it  crosses,  Alfred  Harker  con- 
cluded that  the  contact-minerals  produced  from  the  amygda- 

6  For  a  general  review  of  views  upon  this  question  with  citations  of  authorities, 
see  W.  Lindgren,  The  Genesis  of  the  Copper-Deposits  of  Clif  ton-Morenci,  Arizona, 
Trans.,  xxxv.,  519  to  524  (1904)  ;  p.  517,  this  volume. 


576       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

loidal  fillings  did  not  involve  new  contributions  from  the  gran- 
ite nor  the  migration  of  the  old  materials  farther  than  -^ 
inch.7 

2.  Great  bodies  of  favorable  eruptive  rocks,  such  as  granite, 
sometimes  break  across  thick  sections  of  sedimentary  rocks  of 
all  sorts,  perhaps  miles  in  extent,  and  yet  produce  extremely 
variable  effects.  Thus  Dr.  Joseph  Barrell  has  described  a  case 
in  the  Elkhorn  district,  Montana.  A  mass  of  granitic  rock  has 
cut  a  thick  sedimentary  series.  It  has  produced  but  slight 
changes  where  it  penetrated  pure  limestones,  the  new  minerals 
scarcely  extending  5  ft.  from  the  contact;  whereas,  where  it 
cut  the  Starmount  limestone,  recognized  to  be  siliceous  and 
argillaceous,  it  has  changed  the  latter  to  a  mass  of  lime  silicates 
and  feldspars  for  a  quarter  of  a  mile  from  the  eruptive.  The 
average  composition  of  the  contact-zone  is,  grossularite,  60 ; 
diopside,  25;  wollastonite,  15;  total,  100  per  cent. 

When  referred  back  to  an  original  limestone  which  would 
yield  this  mixture  Dr.  Barrell8  found  by  recasting  the  mineral- 
ogy that  it  must  have  contained  quartz,  21.3;  kaolinite,  25.0; 
calcite,  46.6;  magnesite,  7.1;  total,  100  per  cent. 

The  magnesite  molecule  was  of  course  combined  with  the 
calcite  in  dolomite.  If  we  express  the  above  in  percentages 
of  oxides  they  will  be,  Si02,  32.9;  A1203,  9.9;  CaO,  26.1;  MgO, 
3.38:  CO2,  24.22;  H20,  3.5;  total,  100  per  cent. 

Dr.  Barrell  does  not  give  any  analyses  of  the  Starmount 
limestone,  but  from  field-observation  he  apparently  esteemed  it 
to  be  sufficiently  siliceous  and  aluminous  to  yield  the  lime  sili- 
cates. On  the  other  hand,  on  p.  291  of  the  paper  in  the  Amer- 
ican Journal  of  Science,  it  is  stated  regarding  the  contact-zones 
from  this  limestone  that 

"  The  rocks  are  dense  and  even-grained  and  without  cracklings  or  infiltrations 
of  quartz  or  calcite.  The  thin  sedimentary  banding  is  still  preserved  with  the 
same  lenticular,  somewhat  concretionary  structure  observed  at  a  distance  from 
the  igneous  intrusions,  and  the  adjacent  layers,  where  of  different  mineral  com- 
position, are  sharply  separated  from  each  other.  Certain  strata  may  show  a  few 

7  Quarterly  Journal  of  the  Geological  Society,  vol.  xlix.,  No.  195,  pp.  368  to  369 
(Aug.,  1893). 

8  Physical    Effects   of    Contact-Metamorphism,    American  Journal  of  Science, 
Fourth  Series,  vol.  xiii.,  No.  76,  pp.  291  to  292  (Apr.,  1902).    See  also  Weed  and 
Barrell,    Twenty-Second  Annual  Report,    U.  S.   Geological  Survey,   Ft.  II.,  p.   399 
(1900-01). 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       577 

per  cent,  of  calcite,  but  this  is  distributed  in  a  manner  which  indicates  that  it  is 
not  a  secondary  addition,  but  on  the  contrary  is  due  to  those  beds  containing 
originally  more  calcium  carbonate  than  could  combine  under  metamorphic  ac- 
tion with  the  quartz  and  kaolin  present.  These  features  sharply  separate  the 
mass  of  Starmount  strata  from  certain  beds,  which  owing  to  special  conditions  do 
show  infiltrations,  as  indicated  by  nuclei  of  quartz  with  fluorite  and  ore  grains." 

Three  paragraphs  further  on  it  is  stated  on  p.  292. 

11  In  the  process  of  metamorphism  this  mass  of  strata  [i.  e.,  the  Starmount]  has 
lost  approximately  28  per  cent,  of  its  weight,  and  45  per  cent,  of  its  volume,  from 
70  to  90  times  its  volume  of  water  vapor  and  320  volumes  of  carbonic  dioxide,  the 
gases  being  measured  at  0°  C.  and  760  mm.'' 

While  it  is  the  purpose  at  this  point  to  state,  with  all  possi- 
ble emphasis,  the  points  favorable  to  the  recrystallization  of 
the  material  in  situ,  and  while  the  perfect  preservation  of  the 
old  bedding  with  the  introduction  of  new  material  may  not  be 
without  difficulties,  yet  one  cannot  but  remark  in  passing  that 
the  production  of  a  rock  "  dense  and  even-grained  and  with- 
out cracklings,"  while  at  the  same  time  losing  "  28  per  cent,  of 
its  weight  and  45  per  cent,  of  its  volume,"  is  also  fraught  with 
other,  perhaps  greater,  difficulties. 

3.  We  sometimes  find  the  zones  of  silicates,  even  in  the  same 
great  stratum  of  limestone,  following  certain  beds  for  a  long 
distance  away  from  the  eruptive,  while  the  beds  on  either  side 
are  white  marble.  The  zones  may  even  be  greatly  contorted 
and  yet  persistent.  Dr.  W.  L.  Austin  has  called  my  attention 
to  a  very  striking  illustration  of  these  relations  at  Sacrificio 
mountain,  Nombre  de  Dios,  Durango,  Mexico,  of  which  a  pho- 
tograph is  reproduced  in  Fig.  3,  in  which  the  zones  are  wollas- 
tonite.  It  would  seem  from  this  as  if  the  siliceous  beds  yielded 
wollastonite,  and  the  neighboring  calcareous  beds,  marble.  No 
doubt  these  cases  strongly  favor  recrystallization  in  situ.  The 
interesting  zones  at  San  Pedro,  N.  M.,  described  by  Messrs. 
Yung  and  McCaffery,9  might  also  be  considered  to  give  addi- 
tional support  when  one  studies  the  map  and  section,  showing 
the  occurrence  of  both  shaly  and  purer  limestones,  but  they 
also  remark  (p.  355),  "  The  limestone  left  in  contact  with  the 
garnet  is  always  more  siliceous  than  the  limestone  further  re- 
moved from  the  ore-body,"  and  as  will  be  brought  out  for  San 
Jose,  it  does  not  seem  probable,  when  the  varying  occurrences 

9  The  Ore-Deposits  of  the  San  Pedro  District,  N.  M.,  Trans.,  xxxii.,  350  (1901). 


578       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

of  the  garnet  rock  are  properly  considered,  that  the  eruptive, 
when  the  garnets  were  developed,  happened  always  to  be  next 
to  a  specially  siliceous  portion. 

Before  we  turn  to  the  considerations  positively  favoring  the 
contribution  of  material  from  the  eruptive,  it  may  be  remarked 
that  wide  experience  has  demonstrated  that  the  development  of 
contact-effects  is,  as  a  rule,  irregular,  showing  great  strength  at 
certain  places  and  a  well-nigh  incomprehensible  failure  at  other, 
apparently  equally  favorable,  points.  We  have  best  accounted 


FIG.  3.— ZONES  OF  WOLLASTONITE  IN  MARBLE,  NOMBRE  DE  Dios, 
DURANGO,  MEX. 

(From  a  photograph  by  W.  L.  Austin.) 

for  these  relations  by  believing  that  the  contact-effects  are  the 
results  of  the  emission  of  gases,  vapors,  and  liquids,  especially 
water  in  its  several  physical  states,  and  that  these  were  freely 
afforded  at  certain  points  and  failed  at  others.  There  is  great 
reason  for  believing  that  this  is  true.  Those  eruptives,  more- 
over, which  fail  to  produce  contact-effects,  are  probably  lack- 
ing in  the  dissolved  gases,  etc.,  and  are  cases  of  relatively  dry 
fusion.10. 

Admitting  the  addition  of  material  from  the  eruptive,  two 
possible  methods  are  to  be  considered.     A  contact-zone  may  be 

10  This  subject  is  briefly  summarized   in  Kemp's  Handbook  of  Rocks,  3d  ed., 
Chapter  IX. 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       579 

due  to  the  fusion  of  the  wall-rock  into  the  eruptive  and  its  con- 
sequent absorption,  yielding  a  product  of  intermediate  composi- 
tion ;  or  it  may  be  due  to  the  emission  of  gases,  vapors  and 
heated  liquids  in  the  process  generally  described  as  hydrother- 
mal.  We  may  consider  the  first  method  at  the  outset. 

2.   The  Absorption  Process. 

The  garnet-zones  at  San  Jose  are  in  a  general  way  interme- 
diate in  composition  between  the  eruptive  and  the  limestones ; 
but,  so  far  as  observation  goes,  they  lack  feldspar  entirely,  and 
this  mineral  ought  not  to  fail  if  absorption  took  place.  More- 
over, the  irregularity  of  distribution ;  the  sharp  contacts ;  the 
obvious  effects  of  chill  on  the  eruptive,  as  shown  by  the  changes 
in  texture  and  the  occasional  presence  of  scattered  garnets  in 
predominating  limestone,  all  militate  against  its  application. 
Experiments,  moreover,  in  the  artificial  production  of  garnets 
of  the  grossularite  type  have  shown  that  when  their  component 
materials  are  fused  together,  or  when  they  themselves  are 
melted,  the  resulting  product  is  anorthite,  melilite,  and  pyrox- 
ene. Therefore,  while  absorption-phenomena  have  been  with 
good  reason  called  into  play  to  account  for  some  contact-phe- 
nomena, as,  for  instance,  the  curious  rocks  at  Pigeon  Bay,  Minn., 
described  by  W.  S.  Bayley ; n  yet  in  the  typical  garnet-zones 
they  have  small  claims  to  confidence. 

3.   The  Process  by  Contributions  from  the  Eruptive. 

In  the  cooling  of  the  eruptive  there  must  have  been  a  stage 
when  the  emissions  were  of  necessity  gaseous,  and  a  later  stage 
when  they  were  liquids,  and  still  a  third  stage  when  meteoric 
waters,  if  such  could  penetrate  to  the  still  heated  eruptive,  must 
have  been  set  in  circulation  by  it  at  temperatures  below  the 
boiling-point,  else  it  is  difficult  to  conceive  of  water  reaching 
the  heated  eruptive  against  steam-pressure,  except  perhaps  very 
locally  and  for  a  brief  season. 

In  his  study  of  the  Clifton  district,  Mr.  Lindgren  has  attrib- 
uted the  garnets  and.  other  silicates  to  the  stage  of  gaseous 
emissions,  particularly  of  water-gas  accompanied  by  silica  and 
iron.  This  is  quite  reasonable,  and  it  may  be  that  at  San  Jose 
the  garnet-zones,  the  magnetite,  and  the  copper-ores  were  formed 

11  Bulletin  No.  109,  U.  S.  Geological  Survey  (1893). 


580       COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO. 

at  this  time.  From  the  evidence  in  hand,  however,  there  seems 
no  reason  to  eliminate  heated  waters  as  also  possible  agents. 
The  chief  and  most  tangible  interest  centers  around  the  ques- 
tion of  the  introduction  of  silica,  iron,  and  perhaps  alumina, 
from  the  eruptive. 

That  these  three  must  have  been  added  to  the  limestone  in 
order  to  produce  the  zones  of  silicates,  the  chemical  analyses 
of  the  unaltered  rock  and  the  field-observations  make  practi- 
cally certain.  Otherwise  we  cannot  easily  understand  how 
limestones  ranging  from  4  to  5  per  cent,  of  insolubles  attain  to 
from  40  to  50  per  cent,  of  silica  and  alumina.  Regarding  the 
silica  and  the  iron  there  is  no  special  chemical  difficulty,  but 
the  alumina  is  perhaps  different.  In  the  general  weathering 
of  rocks,  such  as  granites,  we  usually  consider  the  alumina  as 
the  stable  oxide,  and,  assuming  that  it  remains  comparatively 
unaffected  by  the  natural  agents,  we  calculate  back  to  original 
compositions.  At  the  same  time,  we  have  as  a  suggestive  com- 
pound of  aluminum  the  fluoride,  cryolite,  a  mineral  easily  sol- 
uble in  sulphuric  acid,  with  the  evolution  of  hydrofluoric  acid. 
Its  properties  would  suggest  the  inference  that  at  the  tempera- 
tures and  pressures  prevailing  during  the  cooling  of  a  rather 
deep-seated  intrusive  rock,  it  may  well  happen  that  aluminum  is 
far  from  being  inert.  When  we  compare  its  great  abundance 
in  the  porphyry,  from  18  to  19  per  cent.,  with  the  1  per  cent, 
and  less  in  the  limestone  analyzed,  the  former  seems  to  be  much 
the  more  probable  source. 

Again,  if  we  are  still  favorably  inclined  to  believe  in  an 
original  siliceous  and  argillaceous  composition  of  the  limestone 
and,  recognizing  the  comparative  rarity  of  this  variety  so  far 
as  observation  goes,  if  we  try  to  conceive  of  just  this  variety 
happening  to  be  next  the  eruptive  wherever  we  find  the  garnet- 
zones,  widely  distributed  as  they  are,  both  vertically  and  hori- 
zontally ;  shading  off  as  they  occasionally  do  into  pure  white 
marble,  without  regard  to  original  stratification ;  and  in  neigh- 
boring places  abruptly  failing  in  favor  of  the  marble, — we  are 
confronted  with  grave  difficulties — much  graver  ones,  in  fact, 
than  are  presented  by  the  assumption  that  the  eruptive  con- 
tributed the  necessary  materials. 

Still  again,  if  we  recall  the  fact  that  the  garnet-rock  is  on  the 
whole  a  fairly  dense  and  solid  variety,  which  might  be  pro- 


COPPER-DEPOSITS    AT    SAN    JOSE,    TAMAULIPAS,    MEXICO.       581 

duced  from  limestone  by  new  contributions  of  silica,  alumina, 
and  iron,  able  to  take  the  place  of  the  eliminated  carbon  diox- 
ide ;  whereas,  the  recrystallization  of  an  impure  limestone  re- 
quires the  production  of  cavities,  theoretically  more  than  40 
per  cent,  of  the  original  volume  ;  we  shall  find  for  the  San  Jose 
case  that  the  addition  of  new  material  involves  fewer  difficulties 
and  is,  in  fact,  the  only  reasonable  explanation.  The  cavities, 
which  are  observable  and  which  are  filled  in  part  by  the  sul- 
phides, are  probably  due  to  the  rearrangements  brought  about 
by  the  combination  of  the  4  or  5  per  cent,  of  insolubles  with 
the  lime  of  the  calcite  and  the  attendant  loss  of  carbonic  acid 
involved. 

The  bodies  of  magnetite  were  doubtless  formed  by  direct  re- 
placement of  the  limestone  with  the  iron  oxides  and  seem  to 
indicate  a  local  richness  in  iron  for  the  emissions  from  the 
eruptive  where  they  are  found.  There  is  slight,  if  any,  reason 
to  regard  them  as  other  than  purely  contact-products.  One  or 
two  little  pockets  of  specularite  were  observed,  but  this  mineral 
does  not  exhibit  the  abundance  shown  elsewhere,  as,  for  instance, 
in  the  zones  at  the  Seven  Devils,  Idaho. 

The  introduction  of  the  sulphides  seems  to  have  been  in 
largest  part  one  of  the  later  phases  of  the  contact-metamor- 
phism  and  to  have  followed  the  production  of  the  silicates,  at 
least  in  part.  We  infer  this  from  the  relations  described  under 
the  sulphides  that,  besides  forming  inclusions  in  the  silicates, 
they  mold  around  the  garnets,  and  follow  crevices  in  the  mag- 
netite. Where  they  constitute  large  masses  they  doubtless  re- 
placed the  limestone,  although  in  the  midst  of  the  contact- 
zones. 

4.   Oxidized  Ores. 

The  production  of  the  oxidized  minerals  has  been  favored  in 
at  least  one  or  two  cases  by  faults.  It  is  possible  to  show  the 
existence  of  the  latter  by  the  heaved  condition  of  the  tinguaite 
dikes,  and  near  the  natural  conduit  thus  afforded  for  the  de- 
scending meteoric  waters  the  formation  of  oxidized  minerals 
has  been  recognizable. 

As  is  often  the  experience  with  copper-ores  in  deposits  of 
this  type,  a  small  amount  of  gold  is  shown  by  the  assays.  Other 
metals  are  practically  lacking  and  the  matte  is  very  clean. 


582  MAGMATIC    ORIGIN    OF   VEIN-FORMING   WATERS. 


No.  21. 


The  Magmatic  Origin  of  Vein-Forming  Waters  in 
Southeastern  Alaska.* 

BY  ARTHUR  C.  SPENCER,  WASHINGTON,  D.  C. 
(Washington  Meeting,  May,  1905.    Trans.,  xxxvi.,  364.) 

HAVING  suggested  magmatic  waters  as  the  probable  agents 
of  vein-  and  ore-deposition  in  southeastern  Alaska  in  a  paper  en- 
titled, The  Geology  of  the  Treadwell  Ore-Deposits,1  it  is  with 
particular  interest  that  I  note  W.  Lindgren's  application  of  the 
hypothesis  of  igneous  emanations  to  the  gold-quartz  veins  of 
Victoria  and  of  California.2 

Mr.  Lindgren  says  : 

"  In  the  above  paragraphs  I  have  repeatedly  called  attention  to  remarkable 
similarities  in  vein-filling  and  metasomatic  action  between  the  Victorian  quartz 
veins  and  those  of  Sierra  Nevada.  Another  striking  similarity  is  that  in  both  of 
these  regions  the  veins  were  formed  just  after  the  intrusions  of  vast  masses  of 
granite  or  dioritic  magma  into  crumpled  and  compressed  sediments.  I  am  con- 
vinced that  these  similarities  are  due  to  closely  similar  modes  of  formation.  With 
some  confidence,  I  would  formulate  the  hypothesis  that  the  gold  and  the  quartz  in 
this  type  of  veins  have  been  deposited  chiefly  by  '  eruptive  after-effects  /  in  other 
words,  chiefly  by  hot  ascending  waters  originally  contained  in  the  granitic  magma 
and  released  from  it  by  decreasing  pressure,  due  to  its  eruption  into  the  upper  parts 
of  the  lithosphere.  It  is  quite  possible  that  atmospheric  waters  may  have  played 
a  certain  part  by  aiding  the  precipitation  and  by  effecting  certain  forms  of  concen- 
tration in  the  deposits." 

There  are  many  reasons  for  extending  this  hypothesis  to 
southeastern  Alaska.  This  region  and  the  Sierra  Nevada  belt 
of  California  are  undoubtedly  parts  of  one  geologic  province, 
throughout  which  the  main  events  of  geologic  time  are  evi- 
denced by  identical  or  closely  similar  records  in  the  rocks. 
Our  knowledge  of  the  former  region  is  still  fragmentary,  to  be 
sure,  but  the  origin-dates  of  the  most  prominent  features  of 

*  Published  by  permission  of  the  Director  of  the  U   S.  Geological  Survey. 

1  Trans.,  xxxv.,  473  (1904). 

2  Characteristics  of  the  Gold-Quartz  Veins  of  Victoria,  Engineering  and  Mining 
Journal,  vol.  Ixxix.,  No.  10,  p.  460  (Mar.  9,  1905). 


MAGMATIC    ORIGIN    OF    VEIN-FORMING   WATERS.  583 

geology  have  been  located  in  the  time-scale,  and  found  to  cor- 
respond completely  with  the  red-letter  dates  in  the  California 
record.  In  both  regions,  viz. :  (1)  intense  folding  and  meta- 
morphism  followed  the  deposition  of  strata  which  palaeontolo- 
gists agree  are  either  uppermost  Jurassic  or  lowest  Cretaceous 
(Mariposa  beds  of  California) ;  (2)  intrusion  of  granitic  rocks 
(mainly  granodiorite  and  diorite)  accompanied  the  later  stages 
of  folding  or  closely  followed  the  plication  and  metamorphism ; 
(3)  after  the  intruded  rocks  had  solidified  both  they  and  the 
inclosing  formations  were  fractured ;  (4)  the  multitude  of 
wounds  were  healed  by  the  deposition  of  vein-fillings,  the  min- 
eralogy of  which  corresponds  in  almost  every  respect  in  the 
two  fields ;  and  finally,  (5)  erosion  ensued  and  was  followed  by 
the  deposition  of  formations  of  Tertiary  age. 

Reasoning  from  the  above  outline  alone,  is  it  not  to  be  ex- 
pected that  the  origin  of  the  veins  in  the  two  regions  must  be 
identical,  and  does  it  not  add  strength  to  the  suggested  hypo- 
thesis that  it  has  been  developed  and  applied  independently 
in  two  regions  geologically  so  similar  ? 

Students  of  ore-deposition  will  wait  with  keen  anticipation  a 
complete  exposition  by  Mr.  Lindgren  of  the  data  on  which  his 
hypothesis  is  based.  My  own  suggestions  concerning  the  veins 
of  southeastern  Alaska  are  necessarily  founded  on  a  very  in- 
complete knowledge  of  the  facts  involved,  since  all  of  the  ob- 
servations upon  which  they  rest  were  made  during  a  single 
summer.  •  The  hypothesis  here  presented,  therefore,  undoubt- 
edly borders  too  closely  on  pure  speculation  to  carry  much 
weight  by  itself.  Nevertheless,  none  of  the  data  at  hand  seem 
to  be  antagonistic  to  it,  and  it  is  hoped  that  by  stimulating 
the  collection  of  data  having  a  definite  bearing  pro  or  con  its 
prematureness  may  be  in  a  measure  compensated. 

The  most  striking  feature  of  geology  in  the  Alaska  Panhan- 
dle region  is  the  great  dioritic  core  of  the  Coast  range,  a  com- 
plex of  coarsely-granular  intrusive  rocks  which  is  known  to  be 
continuous  from  near  the  northern  boundary  of  Washington 
State  to  beyond  the  head  of  Lynn  canal.  Outside  of  this  band, 
many  masses  of  similar  rock  occur  throughout  the  Alexander 
archipelago,  and  likewise  in  the  region  back  of  the  coastal  bar- 
rier in  British  Columbia. 

The  wide  occurrence  of  this  invading  rock  has  led  to  the 


584  MAGMATIC    ORIGIN    OF    VEIN-FORMING   WATERS. 

conception  that  it  may  exiet  as  an  underlying  mass  throughout 
a  very  extensive  region,  in  which  the  surface-formations  are 
mainly  metamorphosed  sedimentary  rocks  comprising  repre- 
sentatives of  the  different  geologic  periods  from  Silurian  to 
Lower  Cretaceous. 

Metalliferous  quartz  veins  are  found  in  all  parts  of  the  re- 
gion, though  in  general  they  occur  less  frequently  in  large 
intrusions  than  in  small  masses  of  diorite,  and  are  most  numer- 
ous in  the  metamorphosed  formations  which  inclose  the  intru- 
sive rocks.  They  are  quite  as  numerous  away  from  the  bodies 
of  diorite  as  near  them  and,  in  fact,  show  no  distribution  rela- 
tion to  the  masses  of  intrusive  rock.  From  the  structural  fea- 
tures of  the  veins  there  can  be  little  doubt  that  most  of  them 
were  formed  during  a  single  period  of  water-circulation  which 
followed  not  only  the  invasion  of  the  diorite,  but,  in  fact,  the 
complete  solidification  of  those  parts  of  the  intrusive  masses 
now  exposed  to  view. 

Seeking  to  explain  the  relations  observed  and  to  determine 
the  source  of  the  vein-forming  waters,  it  may  be  assumed  that 
the  deep-seated  portion  of  the  magma  which  furnished  the 
Coast  range  diorite  remained  in  an  unconsolidated  condition 
long  after  the  complete  crystallization  of  the  masses  observable 
at  the  present  surface.  Under  certain  conditions  the  existence 
of  a  deep-seated  and  widely-distributed  magma  in  any  region 
might  be  favorable  to  the  production  of  general  fracturing  in 
the  solid  rocks  above  it,  and  the  magma  itself  might  well  be 
the  principal  source  of  the  vein-waters.  Leaving  the  origin  of 
the  vein-openings  for  separate  consideration,  let  us  turn  to  the 
question  of  the  magma  as  a  source  of  vein-forming  solutions. 

If,  during  and  subsequent  to  the  fracturing  of  the  rocks,  the 
abyssal  portion  of  the  magma  was  gradually  consolidating,  it 
must  have  given  off  large  amounts  of  water,  for  it  is  now  gen- 
erally agreed  by  petrologists  that  the  order  of  crystallization 
exhibited  by  the  minerals  of  the  granular  rocks  can  be  best 
explained  by  admitting  the  existence  of  more  water  in  the 
magma  before  and  during  its  consolidation  than  is  shown  by 
analysis  of  the  resulting  rock.  Accepting  this,  crystallization 
would  be  the  sine  qua  non  for  a  continuous  and  sufficient  supply 
of  water,  which  can  be  properly  conceived  of  as  containing 
in  solution  all  the  elements  necessary  to  form  the  observed 


MAGMATIC    ORIGIN    OF    VEIN-FORMING    WATERS.  585 

veins.  Deposition  from  such  magmatic  or  original  waters 
would  be  controlled  by  any  or  all  of  such  circumstances  as  de- 
crease of  pressure  or  temperature,  metasomatic  action  on  the 
country-rocks,  and  mingling  with  solutions  which  might  bring 
about  chemical  reaction. 

The  applicability  of  the  hypothesis  depends  upon  (1)  the 
existence  of  the  supposed  extensive  bed  of  diorite  beneath  the 
area  in  which  the  veins  occur,  (2)  the  possibility  that  such  a 
mass  could  rid  itself  of  water  freed  during  the  process  of  crys- 
tallization, and  (3)  the  competence  of  solutions  of  magmatic 
origin  to  produce  the  results  observed. 

The  first  requirement  may  be  assumed  to  exist  in  the  region 
under  discussion  on  the  ground  of  probability,  while  the  second 
and  third,  which  are  inherent  in  all  problems  of  ore-deposition 
where  the  instrumentality  of  magmatic  solutions  is  suspected, 
can  be  reasonably  inferred  from  well-known  observations.  The 
manner  in  which  water  has  escaped  from  masses  of  rock  dur- 
ing deep-seated  solidification  is  not  readily  arrived  at,  but,  that 
most  magmas  must  have  contained  more  water  than  is  to  be 
found  in  their  crystallized  products,  that  is  to  say,  in  the  rocks, 
is  reasonably  well  established,  and  is  accepted  by  such  recent 
writers  as  J.  H.  Vogt,  J.  F.  Kemp,  A.  C.  Lane,  and  C.  R.  Van 
Hise.  The  fact  that  water  must  have  escaped  is  patent  from  a 
comparison  of  the  dryness  of  the  rock  with  the  fairly-presumed 
wetness  of  the  magma. 

As  to  the  ability  of  magmatic  solutions  to  produce  quartz 
veins  carrying  gold  and  metallic  sulphides,  sometimes,  as  in 
Australia,  California,  and  Alaska,  with  albite  and  rutile,  or 
with  tourmaline,  there  can  be  little  doubt.  During  deep-seated 
solidification,  the  material  dissolved  in  the  magma-water  will 
vary  with  the  progress  of  fractional  crystallization,  and  as 
crystallization  proceeds  the  mother  liquor,  that  is  to  say,  the 
remaining  magma,  becomes  more  and  more  siliceous.  For 
granitic  and  dioritic  magmas,  this  follows  from  the  fact  that 
the  minerals  separate  essentially  in  the  order  of  their  relative 
basicity,  apatite  and  magnetite  being  followed  by  mica  and 
hornblende,  and  these  by  the  less  siliceous  feldspars,  and  finally 
by  the  siliceous  feldspars  and  by  quartz,  if  there  be  an  excess 
of  silica.  During  the  later  stages  of  consolidation,  silica  and 
'salts  of  the  alkalies  and  of  lime  come  to  be  the  main  constitu- 

37 


586  MAGMATIC    ORIGIN    OF    VEIN-FORMING   WATERS. 

ents  of  the  solutions.  This  may  be  inferred,  so  far  as  silica 
and  the  silicates  are  concerned,  from  the  position  of  quartz  and 
the  siliceous  feldspars,  orthoclase  and  oligoclase  or  albite,  in 
the  scheme  of  crystallization  given  above. 

In  general,  the  solutions  escaping  from  a  mass  of  crystalliz- 
ing rock  would  carry  with  them  the  greater  part  of  all  the 
highly-soluble  constituents  of  the  original  magma,  among  which 
chlorides,  fluorides,  carbonates,  and  sulphates  may  have  been 
present  in  important  amounts,  and,  if  present,  certain  of  these 
salts  would  increase  the  dissolving  power  of  the  waters  in  re- 
spect to  silica,  the  metallic  sulphides,  and  gold,  so  that  the  mag- 
matic  solutions  could  readily  have  produced  the  veins  referred 
to  them  by  the  hypothesis.  The  quotation  from  Arrhenius 
given  by  Vogt3  bears  directly  upon  this  point,  as  does  Brogger's 
statement4  of  the  order  of  formation  of  the  minerals  in  the 
pegmatites  of  southern  Norway,  where  the  so-called  mineraliz- 
ing-agents,  fluorine,  chlorine,  and  boron,  do  not  enter,  to  any 
great  extent,  into  the  constitution  of  the  minerals  formed  dur- 
ing the  first  stages  of  solidification,  but  are  found  in  consider- 
able amounts  in  the  minerals  formed  after  the  principal  mass 
of  the  magma  has  crystallized. 

The  list  of  vein-minerals  found  in  southeastern  Alaska  in- 
cludes most  of  those  recorded  from  the  California  mines,  but 
the  occurrence  of  tourmaline  is  frequent  rather  than  rare,  and 
considerable  amounts  of  rutile  are  present  in  a  certain  set  of 
veins  near  Juneau  and  in  the  Treadwell  ores.  In  both  in- 
stances the  rutile  is  associated  with  albite  and  carbonates  of 
lime,  magnesia,  and  iron.  The  bearing  which  the  presence  of 
tourmaline  and  rutile  may  have  upon  the  hypothesis  of  mag- 
matic  waters  will  be  considered  in  some  detail.  (For  a  recent 
list  of  localities  where  ores  are  accompanied  by  tourmaline  see 
Zeitschrift  fur  praktische  Geologic,  vol.  xii.,  1904,  p.  66). 

When,  in  1895,  Mr.  Lindgren5  assigned  the  vein-forming 
waters  of  the  Nevada  City  and  Grass  Valley  districts  to  surface- 
waters  penetrating  the  dioritic  rocks  and  dissolving  from  them 

3  Genesis  of  Ore-Deposits,  by  Posepny  and  others,  p.  644  (1902). 

*  Die  Mineralien  der  Syenitepegmatitegdnge  der  Sildnorwegischen  Augit-  und  Nephe- 
linsyenite,  pp.  148  to  181  (1890). 

5  Bulletin  of  the  Geological  Society  of  America,  vol.  vi.,  pp.  221  to  224  (1894)  ; 
also  Seventeenth  Annual  Report,  U.  S.  Geological  Survey,  Pt.  II.,  p.  176  (1895-96;. 


MAGMATIC    ORIGIN    OF    VEIN-FORMING    WATERS.  587 

metallic  elements  afterwards  deposited  during  the  return  jour- 
ney towards  the  surface,  a  difficult  point  to  explain  was  "  the 
absence  of  fluorine  and  boron-compounds  which  so  often  occur 
in  ore-deposits  in  granitic  rocks."  The  occurrence,  in  the  Ju- 
neau  region,  of  tourmaline  which  contains  these  elements  may 
be  regarded  as  favoring  a  source  in  igneous  rocks,  and  in  my 
belief  their  presence  lends  weight  to  the  magmatic  hypothesis. 

Titanium  oxide  and  albite  occurring  as  original  vein-miner- 
als may  point  in  the  same  direction,  in  the  light  of  Daubree's 
conclusions  concerning  the  genesis  of  the  titaniferous  albite 
veins  of  the  Alps.  This  distinguished  synthesist  produced 
crystals  of  titanium  oxide  by  submitting  titanium  chloride 
vapor  to  the  action  of  steam,6  a  procedure  which  was  supposed 
to  imitate  natural  conditions  of  deposition,  indicated  by  the 
paragenesis  of  the  three  oxides  of  titanium — rutile,  anataser 
and  brookite — in  the  Alpine  veins.  Daubree  therefore  had  no 
hesitation  in  suggesting  "  sublimations  "  as  the  active  agents 
in  forming  the  veins  marked  by  the  peculiar  association  of  the 
minerals  named  with  titaniferous  hematite,  quartz,  albite,  adu- 
laria,  calcite,  dolomite  and  siderite,  mica,  fluorite,  tourmaline, 
etc.  In  this  connection,  he  refers  to  the  discussion  by  filie  de 
Beaumont  of  the  relation  between  metalliferous  veins  and  vol- 
canic emanations,  showing  that  in  his  own  mind  Daubree  re- 
garded the  sublimations  as  related  to  igneous  activity. 

Both  Vog't  and  Lindgren 7  suggest  that  chloride  or  fluoride 
solutions,  or  vapors,  have  been  important  factors  in  the  forma- 
tion of  topaz-cassiterite,  scapolite-apatite,  and  tourmalinic  gold- 
copper  veins,  the  importance  of  which  in  the  present  connec- 
tion is,  that  rutile  is  a  common  accessory  mineral  in  the  types 
of  veins  enumerated. 

Bischof  has  shown  the  efficiency  of  sodium  chloride  solu- 
tions in  transforming  potassium  feldspar  to  albite,8  a  fact  which 
suggests  the  possibility  that  the  metasomatic  change  of  micro- 
perthite  to  albite  which  has  taken  place  in  the  Treadwell  de- 
posit9 may  have  been  produced  by  the  action  of  waters  carry- 
ing common  salt. 

6  Annaks  des  Mines,  Fourth  Series,  vol.  xvi. ,  p.  130  (1849). 

7  Genesis  of  Ore-Deposits,  Posepny,  pp.  540  to  564  and  643  to  648  (1902). 

8  Chemical  Geology,  vol.  ii.,  p.  410. 

9  Spencer,  Trans.,  xxxv.,  505  (1904). 


588  MAGMATIC    ORIGIN    OF    VEIN-FORMING    WATERS. 

In  the  Juneau  district  the  formation  of  albite  as  a  vein-min- 
eral, and  as  a  metasomatic  replacement  in  the  wall-rock,  is 
natural  if  the  depositing  waters  were  of  magmatic  origin,  be- 
cause the  diorites  of  the  region  from  which  such  waters  would 
have  been  derived  are  essentially  soda  rocks.  Likewise,  the 
presence  of  rutile  in  some  of  the  ore-deposits  corresponds  with 
unusual  amounts  of  titanite  in  the  intrusive  rocks.  That  chlo- 
rine and  possibly  fluorine  were  also  present  in  the  parent 
magma  may  be  properly  assumed  from  the  presence  of  abun- 
dant apatite  in  the  diorites.  On  the  magmatic  hypothesis, 
•either  fluorine  or  chlorine  may,  therefore,  well  have  taken  part 
in  the  formation  of  the  quartz-albite-rutile  veins.  In  conform- 
ity with  the  ideas  of  de  Beaumont  and  Daubree,  which  have 
been  especially  elaborated  along  original  lines  by  Vogt  and 
Arrhenius,  these  and  several  other  elements  may  play  an  im- 
portant role  in  vein-deposition  without  entering  into  the  con- 
stitution of  any  of  the  vein-minerals,  and  it  is  strongly  sus- 
pected that  sodium  chloride  may  have  been  an  essential  com- 
ponent in  the  vein-forming  solutions  of  this  region. 

In  the  veins  of  the  Juneau  district  which  have  not  yielded 
rutile  or  albite,  boron  and  fluorine  are  present  in  the  mineral 
tourmaline,  and  it  is  possible  that  chemical  tests  may  reveal 
chlorides  mechanically  inclosed  in  some  of  the  vein-quartz,  as 
in  the  case  of  certain  California  veins  investigated  by  Mr. 
Lindgren.  Unfortunately,  proper  material  for  this  determina- 
tion is  not  at  hand,  but  research  along  this  line  will  undoubt- 
edly be  undertaken  in  connection  with  future  studies  of  ore- 
genesis  in  southeastern  Alaska. 

The  existence  near  each  other  of  tourmaline-bearing  veins, 
which,  so  far  as  observation  shows,  contain  no  albite  and  rutile, 
and  others  containing  the  latter  minerals,  without  the  former, 
is  a  feature  the  bearing  of  which  is  still  unrecognized.  "No 
difference  in  relative  age  of  the  two  types  can  be  suggested,  all 
the  information  at  hand  going  to  show  the  practical  contempo- 
raneity of  the  fractures  in  which  they  occur,  so  that  it  seems 
not  at  all  improbable  that  the  depositing  solutions  were  of  prac- 
tically the  same  nature,  the  difference  in  the  mineral  aggregates 
in  the  two  sorts  of  veins  depending  upon  unlike  conditions  con- 
trolling deposition.  An  indication  that  this  explanation  may 
be  true  is  the  fact  that  the  veins  containing  albite  are  in  general 


MAGMATIC    ORIGIN    OF    VEIN-FORMING    WATERS.  589 

those  inclosed  by  igneous  rocks  which  have  suffered  consider- 
able metasomatic  changes,  due  to  the  vein-forming  waters, 
while  the  albite-free  veins  occur  typically  in  metamorphic  sed- 
iments, or  in  igneous  masses  practically  unaltered  by  the  de- 
positing solutions. 

The  above  considerations  seem  to  me  sufficient  to  show  that 
the  magmatic  hypothesis  is  adequate  to  account  for  the  facts 
in  southeastern  Alaska.  It  remains,  however,  to  show  the  in- 
adequacy of  the  meteoric  hypothesis  before  the  suggestion  of 
magmatic  waters  can  be  raised  to  the  dignity  of  a  theory.  For 
the  great  metalliferous  region  bordering  the  Pacific  coast  it 
seems  that  the  true  theory  of  vein-genesis  can  be  fully  developed 
only  by  establishing  with  the  greatest  possible  degree  of  accu- 
racy the  position  which  ore-deposition  occupies  in  the  geological 
history  of  the  region.  When  this  has  been  done  I  foresee  the 
probability  that  a  point  of  fatal  weakness,  in  any  attempt  to 
explain  the  ore-deposits  by  waters  derived  from  the  surface  of 
the  earth,  will  be  the  impossibility  of  attributing  to  the  action 
of  downward-percolating  waters  any  changes  observable  in  the 
rocks,  though  such  changes  should  be  recognizable  if  the  as- 
cending waters  by  which  the  veins  were  undoubtedly  deposited 
had  been  thus  derived. 


590   GENETIC  RELATIONS  OP  THE  WESTERN  NEVADA  ORES. 


No.  22. 


Genetic  Relations  of  the  Western  Nevada  Ores.* 

BY  J.    E.    SPURR,    WASHINGTON,   D.    C. 

(British  Columbia  Meeting,  July,  1905,    Trans,,  xxxvi.,  372. 

CONTENTS. 

PAGE 

I.   Introduction,          .         .         .         ...         ...         .         ...  590 

II.  Tonopah,      .         .         .         .         .    /  .         .         .         .         .         .         .  591 

1.  General  Geology,  .         ,        .         .         .-'.'.         .         .  591 

2.  Mineral  Veins, .         .         .         .593 

(a)  Veins  of  the  Earlier  Andesite,     .....         .         .  593 

(b)  Vems  of  the  Tonopah  Rhyolite-Dacite  Period,     .         .         .  594 

(c)  Veins  Dependent  upon  the  Oddie  Khyolite,          .  .  594 

(d)  Alteration  of  Wall-Rocks,    .         .      *.         .         .         .         .595 

(e)  Source  of  Mineralizing  Solutions,          .        ...         .         .         .  596 

(f)  Summary  of  Genesis  of  Tonopah  Ores,          ....  598 

III.  .Districts  near  Tonopah  and  Similar  to  It,     .         .         .         .         .         .  599 

1.  Gold  Mountain,    .         ....        .         .         .        .         .        .599 

2.  Goldfield,      .         .         .      ,4         .     •    ...        .  ..         .  599 

3.  Bullfrog  and  Kawich,    .         .         .         .  .         .         .         .600 

IV.  Comparison  of  the  Tertiary  Tonopah  Ores  with  those  of  Other  Regions,   601 
V.  Characteristics  and  Significance  of  the  Vein-Group,       ....  602 

VI.  Silver  Peak  Quadrangle,       .-         . 603 

1.  General  Geology,  .         .         .         .        .         .         .         .         .         .603 

(a)  Stratified  Rocks,  .         .         .        .        ..  i      .        .         .603 

(b)  Granitic  and  Aplitic  Rocks,         .         .         .         .         .         .604 

(c)  Dioritic  Rocks, .         .         .606 

(d)  Tertiary  and  Quaternary  Lavas,  .         .         .       '.         .         .  606 

2.  Mineral  Veins, 607 

(a)  Genetic  Relations  of  the  Ores  of  Mineral  Ridge,  .         .  607 

(b)  Genetic  Relations  of  the  Great  Gulch  Ores,          .       ".'         .612 

(c)  Genetic  Relations  of  the  Silver-Ores  of  Mineral  Ridge,         .  613 

(d)  Genetic  Relations  of  the  Ores  of  Lone  Mountain,         .         .  614 

(e)  Genesis  of  the  Ores  of  the  Southern  Part  of  the  Quadrangle,  615 
(f  )  General  Conclusions  as  to  the  Origin  of  the  Metalliferous 

Ores, .         .616 

VII.  Comparison  of  Silver  Peak  with  Other  Ore-Deposits,     .         .         .     ,    .617 
VIII.  Conclusions  Concerning  the  Silver  Peak  Type  of  Ores,  .....         .619 

IX.  Magmatic  Origin  of  Ores  of  Both  Provinces,       .  .         .  r     ,         .         .   620 

I.  INTRODUCTION. 

The  region  here  discussed  is  that  part  of  western  Nevada  in 
which,  during  the  last  few  years,  discoveries  of  rich  gold-  anti 

*  Published  by  permission  of  the  Director  of  the  U.  Geological  Survey. 


GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES.   591 

silver-ores  have  been  made  at  Tonopah,  Goldfield,  and  other 
camps.  The  special  studies  which  have  been  made  of  the  ore- 
deposits  have  chiefly  to  do  with  Tonopah  and  the  older  camp, 
Silver  Peak,  about  25  miles  southwest  of  Tonopah.  Other 
camps  in  the  same  region  have  also  been  visited.1 

II.  TONOPAH. 
1.   General  Geology. 

Only  those  features  of  the  general  geology  which  are  essen- 
tial to  the  understanding  of  the  ore-deposition  will  here  be  dis- 
cussed. Tonopah  is  situated  in  a  region  of  Tertiary  volcanics, 
and  the  study  of  the  general  geology  has  chiefly  to  do  with  the 
nature,  period,  and  effects  of  the  different  volcanic  eruptions. 
The  volcanic  rocks  comprise  andesites,  rhyolites,  dacites  (la- 
tites),  and  basalt.  There  are  also  present  Tertiary  lake-beds, 
mostly  stratified  tuffs  derived  from  the  volcanic  outbursts. 
The  structure  and  succession  of  these  lavas  indicate  a  varied 
history,  comprising  many  volcanic  eruptions,  which  brought 
forth  showers  of  ash  and  pumice,  or  streams  of  lava.  The  vol- 
canic activity  was  accompanied  by  movements  in  the  crust,  which 
produced  tilting  of  the  rocks  and  a  very  intense  and  complex 
faulting. 

There  are  grounds  for  believing  that  beneath  the  Tertiary 
volcanics  of  Tonopah  there  is  an  older  formation  of  Palaeozoic 
limestone  and  intrusive  granite.  Such  formations  outcrop  both 
to  the  south  and  to  the  north  at  frequent  intervals.  At  Tono- 
pah fragments  of  limestone  and  granite  are  among  the  blocks 
which  were  hurled  out  from  the  volcanoes  at  the  time  of  some 
of  the  dacitic  eruptions. 

The  oldest  of  the  Tertiary  volcanic  rocks  is  an  andesite  which 
I  have  called  the  earlier  andesite,  to  distinguish  it  from  a  sub- 
sequently erupted  rock  of  similar  composition.  This  earlier 
andesite,  wherever  found,  is  decomposed  to  a  variable  extent. 
From  microscopic  study  it  appears  that  the  original  fresh  rock 
was  a  hornblende-biotite-andesite,  the  feldspar  being  typically 
andesine-oligoclase.  In  the  present  altered  condition,  no  actual 
biotite  or  hornblende  has  been  found,  these  minerals  being 
represented  by  their  decomposition-products, — quartz,  sericite, 

1  I  have  described  these  camps  in  Professional  Papers  of  the  U.  S.  Geological 
Survey,  soon  to  be  issued. 


592   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

pyrite,  siderite,  and  hematite,  sometimes  chlorite  and  calcite. 
The  feldspar  is  usually  altered  to  quartz  and  sericite  or  quartz 
and  adularia.  As  a  result  of  the  alteration-processes  the  whole 
rock  is  usually  more  or  less  completely  altered  to  an  aggregate 
which  is  composed  of  quartz  and  sericite,  with  usually  some 
pyrite  and  siderite,  and  frequently  adularia,  kaolin,  and  iron 
oxides.  Chlorite  and  calcite  are  not  so  common,  but  may  be 
abundant.  They  indicate  a  process  of  decomposition  different 
from  the  ordinary.  As  a  rule  the  rocks  may  be  divided  accord- 
ing to  their  processes  of  decomposition  into  two  classes :  (1) 
quartz-sericite-adularia-pyrite-siderite  rocks, — most  abundant 
and  most  closely  associated  with  the  metalliferous  veins;  and 
(2)  chlorite-calcite  rocks, — not  associated  with  the  ores. 

The  next  oldest  rock  is  the  later  andesite.  This  is  much 
like  the  earlier  andesite,  but  is  slightly  less  siliceous.  It  is 
often  nearly  fresh,  and  is  in  other  places  largely  decomposed. 
The  general  process  of  decomposition  is  usually  different  from 
that  of  the  earlier  andesite.  The  phenocrysts  are  larger  and 
more  abundant  than  in  the  earlier  andesite,  and  consist  of  bio- 
tite,  augite,  hornblende,  and  feldspar  which  is  predominantly 
andesine-labradorite.  In  general  the  decomposition-products 
are  quartz,  chlorite,  calcite,  pyrite,  and  siderite.  The  later  an- 
desite overlies  the  earlier  andesite  and  covers  up  the  metallifer- 
ous veins  which  occur  in  the  latter  rock. 

Younger  than  the  andesites  are  a  series  of  rhyolitic  rocks 
(rhyolite-dacites  or  latites).  These  lavas  differ  slightly  in  com- 
position among  themselves  and  were  erupted  at  different  times 
during  a  single  general  period  of  volcanic  activity.  In  the  com- 
plete report  upon  this  district,2  several  of  these  eruptions  have 
been  distinguished  and  separately  mapped,  but  only  three  of 
these  need  here  be  mentioned.  One  of  these,  which  I  have 
called  the  Tonopah  rhyolite-dacite,  is  a  dense,  glassy  rock, 
occurring  in  intrusive  masses  and  thin  sheets.  This  rock  con- 
tains porphyritic  crystals  of  biotite,  feldspar,  and  quartz  in  a 
glassy  ground-mass.  The  most  common  feldspars  are  orthoclase 
and  andesine-oligoclase.  Near  its  intrusive  contacts,  this  rock 
is  often  greatly  silicified,  the  alteration  having  evidently  been 
accomplished  by  hot-spring  action  succeeding  the  intrusion. 

2  Geology  of  the  Tonopah  Mining  District,  Nevada,  Professional  Paper  No.  42, 
U.  S.  Geological  Survey  (1905). 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       593 

Secondary  quartz,  pyrite,  and  sometimes  siderite,  are  the  chief 
results. 

A  dacite  of  later  age  and  of  somewhat  different  character  is 
the  rock  which  forms  the  hills  around  Tonopah.  These  emi- 
nences represent  the  columns  of  lava  which  rose  from  the 
abysmal  regions  to  the  surface.  Near  the  contacts  of  these 
necks  the  intruded  rocks  are  usually  hardened  and  silicified 
and  the  cracks  are  coated  with  chalcedony. 

A  few  of  the  volcanic  necks  consist  of  white  siliceous  rhyo- 
lite  (Oddie  rhyolite)  of  nearly  the  same  age  as  the  dacite  necks. 
This  rhyolite  has  a  micro-granular  ground-mass  of  quartz  and 
feldspar,  with  porphyritic  crystals  of  coarse  quartz,  orthoclase, 
and  occasional  plagioclase  and  biotite. 

2.  Mineral  Veins. 

(a)  Veins  of  the  Earlier  Andesite. — The  most  important  veins 
of  the  Tonopah  district  are  in  the  early  andesite  and  do  not 
extend  into  the  overlying  rocks.  Where  the  early  andesite  is 
not  exposed  at  the  surface  the  later  rocks  form  a  capping  to 
the  veins.  This  fact  shows  plainly  that  the  veins  were  de- 
posited before  the  eruption  of  the  later  andesite  and  imme- 
diately after  that  of  the  earlier  andesite ;  indeed,  there  is  every 
evidence  that  they  were  formed  by  ascending  hot  waters  suc- 
ceeding and  connected  with  the  earlier  andesite  intrusion,  and 
that  these  waters  had  become  inactive  by  the  time  of  the  later 
andesite.  The  openings  which  afforded  channels  for  these  as- 
cending waters  were  sheeted  zones  in  the  rock.  The  rock  was 
complexly  fractured,  apparently  soon  after  cooling,  and  certain 
zones  of  maximum  fracturing  became  the  chief  circulation- 
channels.  These  fractured  zones  have  become  veins,  largely 
by  a  process  of  replacement  of  the  rock.  That  the  mineraliz- 
ing agency  was  water  is  evident  from  the  character  of  the  vein 
and  the  nature  of  the  alteration  of  the  wall-rock ;  that  its  action 
was  probably  connected  with  the  earlier  andesite  eruption  is 
shown  by  the  fact  that  it  followed  this,  and,  at  least  so  far  as 
mineralizing  activity  was  concerned,  was  of  limited  duration, 
for  its  effects  have  not  been  discovered  in  the  succeeding  later 
andesite.  It  appears  probable,  therefore,  that  the  mineralizing 
agents  were  volcanic  waters,  such  as  are  usual  among  the  after- 
effects of  volcanic  outbursts,  and  that  they  were  hot  and  as- 
cending. 


594   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

In  the  primary  sulphide  ores,  lying  below  the  oxidized  zone, 
the  principal  gangue-minerals  are  quartz,  adularia,  and  some 
sericite,  with  occasional  carbonates  of  lime,  magnesia,  iron,  and 
manganese.  The  ore-minerals  consist  of  sulphides  of  silver, 
antimony,  copper,  iron,  lead,  and  zinc,  in  the  form  of  stephanite, 
polybasite,  argentite,  chalcopyrite,  pyrite,  galena,  and  blende. 
A  considerable  quantity  of  silver  selenide  is  also  present,  and 
gold  in  a  yet-undetermined  form.  The  remarkable  thing  about 
the  metallic  contents  is  the  relative  scarcity  of  the  common 
elements  and  the  abundance  of  the  rarer  ones. 

The  depth  of  oxidation  in  these  veins  is  very  irregular,  de- 
pendent upon  the  relative  perviousness  of  the  overlying  rocks. 
In  the  oxidized  zone,  horn-silver  is  abundant,  with  some  bro- 
mides and  iodides.  Free  gold  has  been  deposited.  The  pres- 
ence of  limonite  and  black  oxide  of  manganese  is  characteristic. 

Pyrargyrite  or  ruby-silver  and  argentite  frequently  occur, 
coating  crevices  in  primary  ore,  and  in  such  cases  are  evidently 
6f  secondary  deposition. 

(b)  Veins  of  the  Tonopah  Ehyolite-Dacite  Period. — The  veins 
connected  with  the  earlier  andesite   constitute  the  principal 
class  at  Tonopah,  but  veins  belonging  to  a  later  period  are  fre- 
quently found.     These  veins  are  associated  with  the  Tonopah 
rhyolite-dacite  intrusions  and  are  dependent  upon  them,  in  the 
same  way  as  the  earlier  andesite  veins  depend  upon  the  earlier 
andesite.     The  veins  of  the  Tonopah  rhyolite-dacite  period  are 
characterized  by  irregularity  and  the  lack  of  persistence,  though 
their  size  may  locally  be  considerable.    The  veins  are  barren  or 
contain  small  quantities  of  gold  and  silver,  except  locally,  where 
rich  bunches  of  ore  may  occur.     A  characteristic  of  the  rhyo- 
lite-dacite veins,  to  which  there  are,  however,  numerous  excep- 
tions, is  the  greater  ratio  of  gold  and  silver  in  them  as  com- 
pared to  that  in  the   earlier  andesite  veins.     These  rhyolite- 
dacite  veins  are  also  plainly  the  result  of  ascending  hot  waters. 
The  lack  of  definition  and  persistence  as  compared  with  the 
veins  in  the  earlier  andesite  shows  that  at  the  time  they  were 
formed  no  definite  fracture-zones  were  available  as  channels. 

(c)  Veins  Dependent  Upon  the  Oddie  Rhyolite. — In  one  of  the 
rhyolite  volcanic  necks  (Mount  Ararat)  veins  of  a  different 
character  from  those  previously  described  have  been  formed. 
Near  the  contact  of  the  rhyolite  plug  with  the  older  rocks,  the 


GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES.   595 

rhy elite  is  peculiarly  brecciated,  showing  great  blocks  jumbled 
together,  with,  however,  rhyolitic  matrix  between.  The  dim 
outlines  of  these  blocks  and  the  nature  of  the  matrix  show  that 
the  breccia  was  formed  when  the  lava  was  only  partly  rigid  and 
in  the  process  of  cooling.  This  brecciation  is  confined  to  the 
zone  near  the  contact.  Many  sharp  fractures,  chiefly  parallel 
to  the  contact,  are  present  in  the  rhyolite.  These  have  been 
filled  with  vein-material,  consisting  of  quartz,  with  ferruginous 
calcite  containing  some  manganese  carbonate.  This  gangue- 
material  contains  a  little  gold.  These  fissures  and  fractures 
plainly  resulted  from  the  continuation  of  the  driving  upward 
of  the  plug  after  consolidation  was  practically  complete.  The 
vein-fillings  are  the  result  of  ascending  hot  waters  which  fol- 
lowed the  channels  thus  opened  and  cemented  them. 

A  consideration  of  these  veins  and  their  wall-rocks  does  not 
afford  evidence  of  the  mineralizing  waters  having  contained 
anything  beyond  silica,  lime  and  magnesian  carbonates,  and  a 
trace  of  gold.  The  presence  of  iron  is  contrasted  with  the 
probable  absence  of  iron  in  the  waters  which  produced  the 
veins  in  the  earlier  andesite. 

(d)  Alteration  of  Wall-Hocks. — In  the  altered'  phases  of  the 
earlier  andesite  there  are  all  transitions  between  the  typical 
quartz-sericite  phase,  in  which  calcite  and  chlorite  are  not  abun- 
dant, and  the  typical  calcite-chlorite  phase,  in  which  quartz  and 
especially  sericite  are  decidedly  subordinate.  Hence  it  has  been 
concluded  that  these  different  phases  are  due  to  the  chemical 
effects  of  the  same  mineralizing  waters,  which  differed  in  na- 
ture as  they  penetrated  to  a  greater  and  greater  distance  from 
the  circulation-channels.  Along  these  channels,  which  became 
veins,  the  rock  was  transformed  by  the  deposition  of  silica, 
sulphides  of  silver,  antimony,  etc.,  gold,  and  selenides.  The 
soda  and  magnesia,  and  part  of  the  lime  and  iron,  were  re- 
moved. In  the  wall-rock  near  the  vein,  lime,  iron,  magnesium, 
and  soda  have  been  replaced  by  silica  and  potash.  In  the  rocks 
more  remote  from  the  vein-channels,  though  the  alteration  has 
been  complete,  there  has  been  no  very  great  increase  or  de- 
crease in  the  original  elements. 

From  a  study  of  these  different  effects  of  the  mineralizing 
waters,  it  has  been  concluded  that  they  were  charged  with  an 
excess  of  silica  and  potash,  together  with  silver,  gold,  antimony, 


596   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

arsenic,  copper,  lead,  zinc,  selenium,  etc.  They  were  notably 
deficient  in  iron,  but  contained  carbonic  acid  and  sulphur,  as 
well  as  some  chlorine  and  fluorine.  The  presence  of  the  two 
last-named  gases  is  shown  by  some  probably  original  silver 
chloride  and  by  the  presence  of  muscovite  in  the  gangue,  a 
mineral  which  is  believed  to  crystallize  almost  invariably  in 
the  presence  of  fluorine.3 

The  later  andesite  is  not  altered  as  much  as  the  earlier  an- 
desite,  but  is,  however,  locally  greatly  decomposed.  From  a 
study  of  the  nature  of  this  alteration,  the  conclusion  has  been 
drawn  that  the  waters  which  produced  it  were  highly  charged 
with  carbonic  acid  and  sulphur,  and  that  they  contained  mag- 
nesia and  iron,  and  also  probably  lime,  in  considerable  quan- 
tity. They  were  clearly  hot-spring  waters,  as  shown  by  the 
excessive  carbonation  and  sulphuration,  as  well  as  the  for- 
mation of  sericite  and  talcose  materials,  uralite,  chlorite,  ser- 
pentine, zeolites,  etc.  Their  chemical  composition  was  quite 
different  from  that  of  those  waters  which  altered  the  earlier 
andesite.  From  a  study  of  the  localization  of  the  decomposi- 
tion of  the  later  andesite,  it  seems  likely  that  it  was  due  to  the 
influence  of  solutions  following  the  contacts  of  later  intrusive 
rhyolitic  rock. 

(e)  Source  of  Mineralizing  Solutions. — The  waters  which  pro- 
duced the  veins  and  the  rock-decomposition  in  the  early 
andesite  were  rich  in  silica  and  potash  and  poor  in  the  other 
common  rock-forming  elements.  They  seem  to  have  directly 
followed  the  earlier  andesite  eruption.  Those  that  altered  the 
later  andesite  were  rich  in  magnesia,  lime,  and  iron,  and  low 
in  silica  and  the  alkalies,  and  seem  to  have  followed  the 
eruption  of  rhyolitic  rocks,  especially  the  Oddie  rhyolite.  Both 
were  hot-spring  waters,  which  differed  in  their  composition  as 
much  as  the  rocks  which  they  accompanied.  There  is  an 
apparent  antithesis  in  each  case  between  the  composition  of 
the  erupted  rock  and  the  accompanying  hot  solutions.  The 
earlier  andesite,  a  rock  of  intermediate  composition,  was  fol- 
lowed by  the  advent  of  waters  rich  in  the  elements  character- 
istic of  extremely  acid  rocks.  The  eruption  of  the  Oddie 
rhyolite,  a  very  siliceous  rock,  was  followed  by  the  advent  of 

3  Doelter,  Chemische  Mineralogie,  p.  161 ;  and  Brauns,  Chemische  Mineraloyie,  p. 
247  (1896). 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       597 

waters  rich  in  elements  characteristic  of  basic  rocks  and  poor 
in  the  elements  represented  in  the  rhyolite.  The  exact  expla- 
nation of  this  antithesis  is  a  matter  for  future  study. 

There  are  two  possible  explanations  of  hot  springs  :  one  is 
that  they  a?e  due  to  atmospheric  water  which  has  sunk  down 
from  the  surface  to  such  a  depth  that  it  becomes  highly  heated 
and  then  rises  again ;  the  other  is  that  they  are  due  to  water 
which  forms  a  part  of  the  molten  material  in  the  earth's  inte- 
rior and  which  is  concentrated  and  separated  from  the  magma 
upon  the  cooling  of  a  molten  mass.  Lavas  which  cool  at  the 
surface  give  off  vast  quantities  of  water-vapor,  and  the  phe- 
nomena of  contact-metamorphism,  especially  that  connected 
with  siliceous  rocks,  show  that  in  depth  similar  water-vapor  is 
expelled  from  cooling  rock.  It  seems  therefore  impossible  to 
escape  the  conclusion  that  at  least  some  hot  springs,  the  after- 
phenomena  of  volcanic  activity,  are  due  to  magmatic  water. 

In  the  arid  Nevada  region  there  are,  as  a  rule,  no  flowing 
surface-waters,  the  whole  supply  emerging  from  the  ground  as 
springs.  These  springs  may  be  either  warm  or  cold.  The  cold 
springs  usually  show  two  characteristics  which  indicate  that 
they  are  of  vadose  or  atmospheric  origin  :  (1)  they  fluctuate 
with  the  season,  and  (2)  they  become  more  numerous  in  regions 
of  greater  precipitation  and  rarer  in  the  more  arid  portions. 
The  hot  springs,  however,  so  far  as  the  writer  knows,  do  not 
show  these  characteristics.  They  are  notably  associated  with 
areas  of  volcanic  rocks  and  they  are  often  very  vigorous  in  the 
heart  of  an  arid  region. 

Volcanic  activity  has  lasted  in  this  province  from  the  begin- 
ning of  the  Tertiary  to  within  a  few  hundred  years  ago,  but 
many  of  the  hot  springs  which  accompanied  or  followed  the 
different  manifestations  of  volcanic  activity  are  now  extinct. 
At  Tonopah,  waters  ascending  after  several  of  the  volcanic 
eruptions,  mineralized  and  altered  the  formations  through 
which  they  passed,  and  became  extinct  in  a  relatively  short 
space  of  geologic  time.  It  is  difficult  to  explain  the  totally 
different  composition  of  the  waters  of  the  different  periods  on 
the  hypothesis  that  they  were  of  atmospheric  origin,  and  the 
antithesis  pointed  out  between  the  contents  of  waters  of  differ- 
ent periods  and  the  composition  of  lavas  which  they  followed 
is  equally  difficult  to  account  for  on  this  hypothesis.  A  third 


598       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

consideration  is  the  peculiar  combination  of  materials  in  the 
waters  which  produced  the  veins  of  the  earlier  andesite,  espe- 
cially the  presence  of  unusually  large  quantities  of  the  rare 
metals  silver  and  gold,  and  unusually  small  ones  of  the  com- 
moner ones,  copper,  lead,  zinc,  and  iron.  Plainly  some  process 
of  separation  and  concentration  has  furnished  the  noble  ele- 
ments contained  in  the  mineralizing  waters,  separating  them 
from  the  baser  metals.  A  view  concerning  this  same  problem 
at  the  Comstock,  expressed  by  von  Richthofen,4  appeals  to  me 
as  an  explanation  of  the  Tonopah  ores  also.  Von  Richthofen 
pointed  out  that  the  volatile  materials,  chiefly  fluorine,  chlorine, 
and  sulphur,  given  off  during  solfataric  action,  would  extract 
from  the  cooling  rock  metallic  substances  of  much  the  same 
character  and  proportion  as  those  present  in  the  Comstock  loder 
while  ordinary  waters  would  furnish  primarily  the  more  abun- 
dant metals,  such  as  iron  and  manganese,  and  only  small 
amounts  of  silver  and  gold. 

(f)  Summary  of  Genesis   of   Tonopah   Ores. — The   considera- 
tions pointed  out  appear  to  indicate  the  following  conclusions. 

The  Tonopah  district  was  during  most  of  Tertiary  time  a 
region  of  active  vulcanism,  and  probably  after  each  eruption,, 
certainly  after  some  of  them,  solfataras  and  fumaroles,  suc- 
ceeded by  hot  springs,  thoroughly  altered  the  rocks  in  many 
parts  of  the  district.  At  the  surface,,  during  these  periods, 
the  phenomena  of  fumarolic,  solfataric,  and  hot-spring  action 
were  similar  to  those  witnessed  to-day  in  volcanic  regions; 
but  the  rocks  now  exposed  were  at  that  time  below  the  sur- 
face. The  veins  have  cemented  the  conduits  which  were 
formed  by  the  fractures  due  to  the  heavings  of  the  surging 
volcanic  forces  below,  and  along  which  gases,  steam,  and  finally 
hot  waters,  growing  gradually  cooler,  were  expelled,  relieving 
the  explosive  energies  of  the  subsiding  volcanism.  The  water 
and  other  vapors,  largely  given  off  by  the  congealing  lavas  be- 
low, carried  with  them,  separated  and  concentrated  from  the 
magma,  metals  of  such  kind  and  of  such  quantity  as  are  pres- 
ent in  the  veins,  together  with  silica  and  other  materials.  The 
nature  of  the  metallic  minerals  in  the  veins  is  believed  to  have 
depended  largely  upon  the  particular  magma  whence  the  ema- 
nations proceeded. 

4  Cited  in  Monograph  IIL,   U.  S.  Geological  Survey,  pp.  19  to  20  (1882). 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       599 

III.  DISTRICTS  J^EAR  TONOPAH  AND  SIMILAR  TO  IT. 
1.    Gold  Mountain. 

The  mining-district  of  Gold  mountain,  4  miles  south  of 
Tonopah,  has  been  prospected  for  several  years,  but  has  not 
developed  into  a  camp  of  any  importance.  The  rocks  here  are 
rhyolite,  rhyolite-breccia,  and  tuffs,  in  which  fracture-  or  brec- 
cia-zones have  been  formed,  and  have  been  transformed  into 
veins  by  circulating  waters.  The  vein-material  is  quartz,  often 
chalcedonic,  and  the  metallic  mineral  chiefly  pyrite,  which 
sometimes  contains  gold  and  sometimes  silver.  In  some  cases 
the  veins  contain  gold  only,  while  in  others  considerable  silver 
is  also  present.  Some  of  the  richest  ore  is  oxidized  and  occurs 
in  pockets  near  the  surface.  From  such  ore,  shipments  have 
been  made,  but  most  of  the  veins  are  of  low  grade. 

The  rocks  at  Gold  mountain  are  similar  to  the  Tonopah 
rhyolite-dacite  series  of  lava,  breccias,  and  associated  tuifs  at 
Tonopah,  and  the  characteristics  of  the  Gold  mountain  veins 
are  similar  to  those  of  the  rhyolite-dacite  veins  at  Tonopah. 
In  both  cases  the  veins,  while  they  are  locally  strong,  have  not 
the  regularity  or  persistence  of  the  earlier  andesite  veins. 

2.   Goldfield. 

I  have  visited  Goldfield,  about  24  miles  south  of  Gold  moun- 
tain, but  I  have  not  yet  studied  the  geology  thoroughly.  The 
rocks,  chiefly  volcanic,  consist  of  rhyolites,  rhyolite  tuffs,  ande- 
sites,  and  basalts,  all  probably  of  Tertiary  age.  One  andesite 
examined  microscopically  resembles  the  earlier  andesite  at  To- 
nopah, and  a  specimen  of  basalt  resembles  the  basalt  of  that 
district.  The  rhyolite  also  resembles  the  rhyolite  of  Gold 
mountain.  The  ores  occur  in  both  rhyolites  and  andesites, 
showing  that  the  mineralization  occurred  subsequent  to  the 
eruption  of  both  lavas.  It  is  therefore  possible  that  the  Gold- 
field  deposits  are  identical  in  origin  with  the  later  series  of 
veins  at  Tonopah,  which  accompany  the  Tonopah  rhyolite- 
dacite,  although  at  Goldfield  these  veins  are  of  vastly  greater 
economic  importance. 

There  is  also  a  resemblance  in  the  physical  characteristics  of 
the  later  Tonopah  veins  and  the  ore-bodies  at  Goldfield ;  in  the 
latter,  however,  the  quartz  masses  are  still  more  irregular;  the 


600       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

outcrops  may  be  roughly  elongated,  nearly  circular  or  crescen- 
tic.  The  quartz  is  gray  and  jaspery  and  is  due  to  the  silicifi- 
cation  of  the  volcanic  rock,  which  is  undoubtedly  the  work  of 
hot  springs.  Had  the  rocks  been  strongly  fractured  we  should 
have  had  more  definite  veins  like  those  of  the  earlier  andesite 
at  Tonopah. 

The  greater  part  of  one  of  these  quartz  reefs  at  Goldfield 
contains  little  or  no  gold,  although  pyrite  is  disseminated 
throughout.  Frequently,  however,  ore-shoots  of  relatively 
small  size  occur,  which  are  difficult  to  distinguish,  except  by 
assaying,  from  the  barren  portion.  It  seems  probable  that 
these  pay-shoots  represent  the  main  channels  of  circulation, 
while  the  siliceous  casings  are  the  result  of  water  soaking 
through  the  adjacent  rock.  The  values  of  the  ores  are  chiefly, 
sometimes  entirely,  in  gold,  but  in  some  cases  considerable 
silver  has  lately  been  found. 

The  sulphide  ores  lying  beneath  the  oxidized  surface-ores 
contain  tetrahedrite  which  is  highly  auriferous.  Tellurium  is 
present,  probably  in  the  form  of  gold  telluride.  Bismuth  sul- 
phide is  not  uncommon.  Free  gold  also  occurs  in  these  sul- 
phide ores.  In  the  gangue,  barite  is  common,  but  not  abundant. 

3.  Bullfrog  and  Kawich. 

Since  the  opening  up  of  Goldfield,  more  than  a  year  ago,  a 
number  of  promising  new  camps  have  been  discovered  in  the 
neighborhood,  especially  to  the  south  and  east.  Chief  among 
these  are  perhaps  the  Bullfrog  and  the  Kawich  districts,  the 
former  of  which  lies  60  miles  southeast  of  G-oldfield ;  the  latter 
72  miles  east.  I  have  not  yet  visited  these  camps,  but  from 
personal  correspondence  I  have  obtained  some  idea  of  their 
nature.  Oscar  Rohn  has  sent  photographs,  samples  and  de- 
scriptions of  the  Kawich  district,  which  indicate  for  this  camp 
a  close  analogy  to  Goldfield,  the  ore-bodies  occurring  in  similar 
rocks  and  being  of  the  same  character.  Mr.  Rohn  reports 
that  one  of  the  principal  formations  at  Bullfrog  is  rhyolite  and 
rhyolite-breccia,  which  he  regards  as  equivalent  to  lavas  of  the 
Tonopah  district.  The  veins  occur  in  part  at  least  along  fault- 
or  fracture-zones  in  the  volcanic  rock.  The  gangue  is  chiefly 
quartz,  and  the  values  are  gold  and  silver. 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       601 

IV.  COMPARISON  OF  THE  TERTIARY  NEVADA  ORES  WITH 
THOSE  OF  OTHER  REGIONS. 

Among  the  nearest  analogies  to  Tonopah  yet  described  else- 
where are  the  contiguous  mining-districts  of  Pachuca  and  Real 
del  Monte,  in  Mexico.5  These  districts  are  similar  to  Tonopah 
in  character  and  age  of  the  wall-rocks  (Miocene  andesites) ;  in 
the  nature  of  the  alteration  of  the  rock  near  the  veins  (silicifi- 
cation  near  the  veins,  propylitic  alteration  farther  away) ;  in 
the  structural  character  of  the  veins  (splitting  and  reuniting) ; 
the  general  character  of  the  ores  (both  oxide  and  sulphide), 
and  of  gangue  (though  adularia  as  a  gangue-material  and 
selenides  as  ores  have  not  been  recognized  at  Pachuca);  and  in 
the  occurrence  of  the  rich  ores  in  bonanzas,  which  seem  to  be 
due  to  the  intersection  of  transverse  fractures  with  the  main 
vein-zone. 

Many  other  deposits  in  Mexico  which  have  not  been  fully 
described  seem,  from  their  recorded  characteristics,  to  be 
closely  similar  to  Tonopah.6 

Pachuca  is  about  2,000  miles  southwest  of  Tonopah,  but  an 
analogous  deposit  lies  150  miles  to  the  northwest, — the  Corn- 
stock.  The  Comstock  is  similar  to  Tonopah  in  respect  to  the 
character  and  age  of  the  rocks  in  which  the  lode  lies  (Tertiary 
andesite)  and  their  "  propylitic "  alteration ;  in  the  nature  of 
the  gangue  and  ore ;  and  in  the  occurrence  of  the  rich  ore  in 
irregular  "  bonanzas."  The  chief  distinction  is  that  the  Com- 
stock consists  of  a  single  very  strong  lode,  while  at  Tonopah 
there  are  a  number  of  small  ones. 

Another  region  having  many  striking  peculiarities  in  com- 
mon with  Tonopah  lies  about  400  miles  due  north  of  it, — the 
districts  of  Silver  City  and  Delamar  in  southwestern  Idaho.7 
These  districts  are  similar  to  Tonopah  in  that  the  ores  occur 
in  Tertiary  volcanics  and  are  probably  in  both  cases  post-Mio- 
cene in  age ;  to  a  striking  degree  in  the  character  of  the  ores 
and  gangue-materials ;  in  the  structural  characteristics  of  the 
veins,  which  form  a  group  knit  together  by  branches ;  in  the 

6  Aguilera  and  Ordonez,  Boletin  del  Institute  Geologico  de  Mexico,  Nos.  7,  8  and 
9  (1897). 

6  J.  G.  Aguilera,  Trans.,  xxxii.,.513  (1901). 

7  Lindgren,  Waldemar,  Twentieth  Annual  Report,  U.S.  Geological  Survey,  Pt.IIL, 
pp.  107  to  189  (1898-99). 

38 


602       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

general  character  of  the  alteration  of  the  wall-rock ;  and  in  the 
occurrence  of  the  rich  ores  in  irregular  "  bonanzas."  The 
chief  difference  is  that,  in  these  Idaho  districts,  the  wall-rocks 
are  mainly  rhyolite,  and  not  andesite. 

V.  CHARACTERISTICS  AND  SIGNIFICANCE  OF  THE  VEIN-GROUP. 

The  different  mineral  districts,  mentioned  above,  exhibit  a 
definite  group  of  veins,  characterized  by  the  following  features  : 
They  occur  in  Tertiary  volcanic  rocks  of  similar  character 
in  the  different  localities,  being  chiefly  Miocene  andesites  or 
rhyolites.  They  constitute  strong  masses  or  veins  which  have 
as  gangue  essentially  quartz  with  frequently  a  little  calcite, 
while  adularia,  barite,  rhodochrosite,  or  rhodonite  may  also 
be  present  in  limited  quantity.  The  ore  is  characteristically  a 
silver-gold  one,  silver  being  usually  predominant  in  the  values 
in  varying  proportions,  though  the  relative  value  may  be  re- 
versed, and  in  some  extreme  cases  either  metal  may  occur  with 
little  admixture  of  the  other.  In  any  case  the  abundance  of 
silver  or  gold,  or  both,  in  reference  to  lead,  zinc,  iron,  etc.,  is 
characteristic.  Silver  sulphides,  especially  argentite,  also  ste- 
phanite  and  polybasite  (together  with  ruby-silver),  and  gold, 
probably  largely  in  a  free  state,  are  a  distinguishing  feature  in 
the  great  majority  of  cases.  Tellurides  and  selenides  may  also 
be  present.  Pyrite,  blende,  chalcopyrite,  and  galena  are  usu- 
ally present  in  varying  quantity.  Where  they  become  pre- 
dominant the  vein  becomes  relatively  low-grade.  Tetrahedrite, 
stibnite,  and  bismuthinite  are  also  known  to  occur.  The  wall- 
rocks  are  much  altered  to  quartz,  sericite,  chlorite,  calcite,  epi- 
dote,  pyrite,  etc.,  and  sometimes  to  adularia.  Frequently  the 
rocks  nearest  the  veins  are  chiefly  altered  to  quartz  and  seri- 
cite ;  those  farther  away  to  the  softer  "  propylitic  "  alteration, 
consisting  of  calcite,  chlorite,  pyrite,  epidote,  etc.  The  rich 
ores  occur  in  irregularly  outlined  portions  of  the  lode  called 
"  bonanzas,"  which  are  of  limited  extent,  both  horizontally  and 
vertically,  and  are  believed  to  have  arisen  as  a  consequence  of 
the  irregular  intersection  of  transverse  fractures  or  fissures  with 
the  main  vein-channels. 

Unquestionably  the  close  relation  between  the  different  min- 
eral districts  mentioned  shows  a  metallographic  province,  which 
in  this  case  coincides  with  a  portion  of  a  petrographic  prov- 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       603 

ince.8  It  is  probable  indeed  that  the  co-extension  of  the  metal- 
lographic  and  petrographic  provinces  is  greater  than  thus  es- 
tablished. At  many  points  along  the  belt  of  the  petrographic 
province  in  the  Andes  of  South  America, — for  example,  in  Peru9 
— veins  are  reported  to  have,  so  far  as  can  be  made  out,  a  mode 
of  occurrence,  age,  and  composition  similar  to  those  of  Mexico. 
In  that  better-established  portion  of  the  metallographic  prov- 
ince which  comprises  Mexico  and  Nevada,  the  ores  occur  in 
Miocene  andesites  in  a  great  majority  of  cases.  In  occasionally 
recurring  cases  they  appear  in  Miocene-Pliocene  rhyolites  which 
succeeded  the  andesites.  The  ores  are  believed  to  be  due  to 
the  after-actions  of  the  eruptions,  in  the  shape  of  fumaroles, 
solfataras,  and  hot  springs.  Moreover,  since  these  manifesta- 
tions follow  all  volcanic  eruptions,  it  is  probable  that  the  metals 
deposited  by  the  after-processes  owe  their  nature  and  amount 
to  an  unusual  proportion  of  them  in  the  magma  with  which, 
they  are  genetically  connected. 

VI.  SILVER  PEAK  QUADRANGLE. 

Of  quite  a  different  class  of  ore-deposits  from  that  described 
in  the  preceding  pages  are  those  of  the  Silver  Peak  quadrangle, 
whose  northeastern  corner  is  only  about  10  miles  west  of  To- 
nopah.  The  deposits  of  this  quadrangle  have  been  made  the 
subject  of  a  Professional  Paper,  to  be  published  by  the  U.  S. 
Geological  Survey. 

1.   General  Geology. 

(a)  Stratified  Eocks. — Palaeozoic  limestones  with  slates  and 
some  quartzites  are  well  represented  in  the  area  of  the  Silver 
Peak  quadrangle.  They  belong  entirely  within  the  Cambrian 
and  Ordovician  eras.  Most  of  our  knowledge  of  the  Palaeozoic 
strata  is  due  to  the  work  of  Messrs.  Turner,  Walcott,  and  Weeks, 
of  the  U.  S.  Geological  Survey.  The  known  fossils  show  the 
presence  of  strata  belonging  to  the  lower  Cambrian,  the  upper 
Cambrian,  and  the  Ordovician.  The  rocks,  however,  are  char- 
acteristically considerably  folded  and  faulted  and  frequently 
metamorphosed,  and  the  series,  which  is  several  thousand  feet 

8  Spurr,  J.  E.,  Trans.,  xxxiii.,  332  to  333  (1902)  ;  p.  295,  this  volume. 

9  Fuchs  et  de  Launay,  Traite  des  Gites  Mineraux  et  Metalliftres,  vol.  ii.,  p.  829 

(1893). 


604   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

thick,  presents  no  very  striking  and  constant  lithologic  differ- 
ences. The  detailed  stratigraphy  and  structure,  therefore,  are 
still  in  some  doubt. 

In  the  district  where  the  principal  gold-mines  are  situated, 
near  Silver  Peak  village,  there  is,  below  the  fossiliferous  Cam- 
brian, a  series  of  considerable  thickness  consisting  of  limestones 
and  slates,  with  some  dolomitic  marble  beds.  This  series  has 
been  intruded  by  numerous  alaskitic  sheets  and  by  quartz 
veins.  (Alaskite  is  a  granitic  rock  composed  essentially  of 
quartz  and  alkali  feldspar.)  It  has  become  largely  schistose 
find  gneissic. 

No  sedimentary  rocks  intermediate  in  age  between  the  Ordo- 
vician  and  the  probable  Eocene  have  been  found  within  the 
area  of  the  quadrangle,  but  there  are  extensive  and  thick  de- 
posits belonging  to  the  Tertiary.  These  Tertiary  deposits  flank 
the  edges  of  the  mountains  and  underlie  in  part  at  least  the 
Pleistocene  veneer  of  the  valleys.  They  consist  of  soft  shales, 
sandstones,  marls,  tuffs,  volcanic  breccias,  etc.,  with  interbedded 
layers  of  andesitic  and  rhyolitic  lava.  The  thickness  of  the 
whole  accumulation  is  very  likely  several  thousand  feet. 

(b)  Granitic  and  Aplitic  Rocks. — Granitic  rocks,  intrusive  into 
the  Palaeozoic  strata,  are  well  represented  in  the  quadrangle, 
especially  in  three  chief  areas — in  the  northeast  corner  near 
Lone  mountain,  on  Mineral  ridge  near  Silver  Peak  village,  and 
in  a  long  belt  running  northwesterly  across  the  southern  part 
of  the  quadrangle.  In  the  first-named  region,  near  Lone 
mountain,  H.  W.  Turner  has  found  that  the  granitic  rocks 
are  chiefly  true  granites,  composed  of  alkali  feldspar  and  quartz, 
with  some  biotite  and  muscovite.  The  feldspar  includes  ortho- 
clase,  micrpcline,  and  albite. 

In  Mineral  ridge,  the  interbedded  slates  and  thin  limestones 
have  been  thoroughly  injected  by  siliceous  granitic  rock,  mostly 
along  the  stratification,  forming  chiefly  interbedded,  more  or 
less  lenticular  bodies,  and  often  penetrating  the  intruded  rock 
thoroughly  and  altering  it  to  a  schistose  or  gneissic  condition. 
The  prevalent  phase  of  the  intrusive  rock  is  alaskite  or  quartz 
alkali-feldspar  rock,  having  a  granular  texture  like  that  typi- 
cal of  granite,  which  very  frequently  becomes  coarser  or  finer 
(pegmatitic  or  aplitic).  A  frequent,  but  not  common,  facies  of 
this  alaskite  is  a  siliceous  biotite-granite  like  that  at  Lone 
mountain.  On  the  other  hand,  the  alaskite  passes  by  gradual 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       605 

transitions,  by  a  diminution  of  the  feldspar,  into  pure  quartz 
veins  (dikes),  which  have  very  much  the  same  chemical  and 
genetic  relation  to  the  alaskite  that  the  alaskite  has  to  the 
granite.  The  alaskite  consists  almost  wholly  of  quartz  and 
feldspar,  the  chief  species  of  the  latter  having  heen  determined 
as  orthoclase,  microcline,  and  oligoclase-albite. 

The  granite  masses  studied  by  Mr.  Turner  in  the  southern 
part  of  the  quadrangle  show  a  variety  of  different  phases.  In 
composition  the  rock  varies  from  normal  granite  to  alaskite  on 
the  one  hand,  and  to  quartz-monzonite  or  granodiorite  on  the 
other,  the  proportions  of  lime,  soda,  and  potash  being  variable. 

In  connection  with  the  granitic  areas  near  Lone  mountain 
and  in  the  southern  part  of  the  quadrangle  there  are  numerous 
aplitic  dikes  which  clearly  represent  the  later  facies  of  the  in- 
trusions. They  are  mostly  quartz-feldspar  rocks  or  alaskites, 
more  siliceous  than  the  related  granites.  At  Mineral  ridge 
this  rock  is  the  predominant  type,  but  in  the  other  regions  is 
subordinate  to  the  granite  proper.  In  many  phases  of  these 
alaskitic  rocks  a  tendency  is  seen  under  the  microscope  for  the 
feldspar  and  quartz  to  segregate  in  bunches,  which  are  irregu- 
lar or  more  frequently  elongated.  These  segregations  increase 
in  size  until  they  are  conspicuous  to  the  naked  eye,  and  by 
further  enlargements  quartz  masses  (veins),  often  feldspathic, 
are  formed.  Such  granitic  and  magmatic  quartz  is  found  in 
all  the  granite  areas,  but  in  the  siliceous  alaskitic  area  of  Min- 
eral ridge  occurs  in  great  quantities,  in  thick  veins  or  lenses. 
The  various  closely  related  phases  of  the  granitic  intrusions 
are  regarded  as  variations  from  a  single  general  granitic  magma. 

It  is  probable  also  that  the  different  bodies  present  represent 
essentially  a  single  period  of  intrusion.  In  the  Silver  Peak 
quadrangle  the  granitic  rocks  were  intruded  subsequent  to  the 
deposition  of  the  Palaeozoic  strata  and  previous  to  the  Tertiary 
sediments  and  lavas.  The  date  of  their  intrusion  is  therefore 
post-Ordovician  and  pre-Tertiary.  A  short  distance  north  of 
the  Silver  Peak  quadrangle  granitic  rocks  similar  to  those  at 
Silver  Peak  are  probably  intrusive  into  Triassic  and  Jurassic 
strata  at  several  points  in  the  Pilot,  Excelsior,  Ellsworth,  and 
Star  Peak  ranges.10 

10  J.  E.  Spnrr,  Bulletin  No.  208,  U.  S.  Geological  Survey,  2d  ed.,  pp.  102, 103, 109 
(1903)  ;  and  G.  D.  Louderback,  Bulletin  of  the  Geological  Society  of  America,  vol. 
xv.,  pp.  317,  336  (1903). 


606       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

The  work  of  Mr.  Turner  has  shown  that  the  granitic  rocks 
in  the  southern  part  of  the  Silver  Peak  range  cross  Fish  Lake 
valley,  which  lies  west  of  the  range,  and  are  represented  in  the 
White  Mountain  range,  which  is  separated  from  the  Sierra 
Nevada  only  by  Owen's  Valley.  This  adjacent  portion  of  the 
Sierra  Nevada  is  made  up  almost  wholly  of  granitic  rocks,  con- 
sisting mainly  of  granodiorite  and  granite,  and  the  date  of 
their  intrusion  has  been  fixed  as  in  the  epoch  known  as  post- 
Jurassic. 

It  appears  probable,  therefore,  that  the  granitic  rocks  of  the 
Silver  Peak  quadrangle  and  of  various  other  ranges  of  western 
Nevada  are  similar  in  general  nature,  age,  and  origin  to  the 
granitic  rocks  of  the  Sierra  Nevada,  and  are  late  Jurassic  or 
early  Cretaceous  in  age. 

(c)  Dioritic  Rocks. — Small  dikes  of  diorite  are  abundant  in 
the  Silver  Peak  region.     They  are  almost  always  more  or  less 
altered,  sometimes  completely.     In  their  fresh  form  they  con- 
sisted essentially  of  feldspar  and  hornblende  in  varying  propor- 
tions, but  by  alteration  they  have  become  a  mass  of  secondary 
products.     They  are  thus  conveniently  designated  by  the  field- 
name of  greenstones.    The  alteration-products  include  chlorite, 
quartz,  calcite,  zeolites,  epidote,  zoisite,  kaolin,  talc,  biotite,  etc. 

These  dioritic  rocks  appear,  from  Mr.  Turner's  mapping,  to 
be  associated  with  the  areas  of  associated  granitic  rocks.  In 
point  of  age  the  dioritic  rocks  are  always  younger  than  the 
granitic  rocks,  which  they  frequently  cut.  When  they  occur 
associated  with  the  aplitic  rocks  (alaskites)  they  are  also  younger 
than  these,  and,  as  Mr.  Turner  has  found,  they  are  younger 
than  the  quartz  veins  of  Mineral  ridge,  which  I  have  determined 
to  be  the  siliceous  extreme  of  the  alaskitic  injection.  These 
greenstone  dikes  are  older  than  the  Tertiary  rocks,  since  they 
are  not  found  in  them.  Therefore,  the  only  direct  evidence  of 
their  age  is  that  they  are  post-0 r do vician  and  pre-Tertiary. 
The  apparent  association  with  the  granitic  areas  and  the  limited 
quantities  of  the  diorite,  whose  habit  and  amount  approximate 
those  of  the  alaskites,  suggest,  however,  that  the  dioritic  rocks 
may  be  a  later  manifestation  of  the  granitic  intrusions. 

(d)  Tertiary  and  Quaternary  Lavas. — In  the  area  under  con- 
sideration, lavas  were  erupted  in  large  quantity  during  most  of 
the  Tertiary,  and  the  volcanic  activity  continued  into  the  Qua- 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.        607 

ternary.  The  knowledge  of  the  Tertiary  lavas  of  the  Silver 
Peak  region  is  entirely  the  result  of  the  work  of  Mr.  Turner, 
who  has  mapped  the  different  rocks  separately  and  has  distin- 
guished and  studied  rhyolites,  andesites,  basalts,  and  some 
dacites.  These  lavas  seem  to  have  been  repeated  at  different 
periods. 

2.  Mineral  Veins. 

(a)  Genetic  Relations  of  the  Ores  of  Mineral  Ridge. — The  au- 
riferous quartz-ores  of  Mineral  ridge  are  economically  the  most 
important  in  the  quadrangle,  and  some  of  the  mines  here  have 
had  a  considerable  production.  The  Drinkwater  mine  and 
some  adjacent  mines  make  up  the  most  important  group. 

The  typical  auriferous  quartz  of  Mineral  ridge  is  white  and 
crystalline  and  is  seen  under  the  microscope  to  be  crowded  with 
liquid  inclusions.  Its  appearance  is  that  of  the  characteristic 
gold-quartz  found  in  so  many  districts  in  the  world.  Occasion- 
ally this  quartz  contains  original  muscovite  and,  rarely,  original 
chlorite  crystals.  Contemporaneous  sulphides  are  sparsely  dis- 
seminated, principally  pyrite,  more  rarely  galena.  Occasionally 
copper  pyrite  has  been  observed.  The  quartz  throughout  con- 
tains gold  and  a  little  silver,  the  proportion  of  the  latter  to  the 
former  being  about  1  to  100.  The  gold  is  finely  disseminated 
in  a  free  state  through  the  quartz  and  is  also  contained  in  the 
scattered  sulphides.  It  is  estimated  that  about  87  per  cent,  is 
in  the  free  disseminated  form  and  the  remainder  in  sulphides. 
The  gold-values  are  irregularly  concentrated  into  certain  groups 
of  quartz  lenses  and  certain  lenses  within  these  groups.  Thus, 
in  certain  portions,  it  is  high-grade,  while  in  others  it  is  low- 
grade  or  nearly  barren. 

The  quartz  lenses  are  intimately  associated  with  alaskite  in- 
trusions, one  not  occurring  without  the  other.  Petrographi- 
cally,  typical  quartz  and  typical  alaskite  form  two  ends  of  a 
rock  series,  between  which  every  gradation  is  abundantly 
represented.  The  alaskite  becomes  quartzose  and  passes  to 
a  state  where  it  contains  quartz  blotches  and  veinlets  and  so 
gradually  passes  over  into  typical  vein-quartz.  Nearly  every 
quartz  lens  which  has  been  mined  or  prospected  shows  in 
places  considerable  feldspar  mixed  with  the  quartz.  As  a 
rule,  the  gold-content  grows  rapidly  less  with  increasing  feld- 


608       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

spar,  although  occasionally  feldspar-bearing  rock  carries  good 
values.  In  one  place  primary  free  gold  has  been  found  in 
pegmatite. 

It  was  long  ago  recognized  that  granite  rocks  (which  family 
includes  the  alaskites)  had  originated  from  magmas  essentially 
different  in  nature  from  those  which  form  the  more  basic 
plutonic  rocks  and  from  those  which  produce  surface-lavas. 
This  recognition  was  due  to  the  discovery  of  many  minerals 
in  granite  which  cannot  be  formed  from  dry  melts.  Moreover, 
the  relative  order  of  crystallization  of  the  chief  granitic  min- 
erals is  not  the  order  of  their  relative  fusibility,  showing  that 
the  different  materials  were  not  held  in  the  fluid  state  by  the 
power  of  heat  alone.  All  the  granitic  minerals  have  been  arti- 
ficially formed  in  the  presence  of  mineralizers,  such  as  water, 
fluorides,  boron  compounds,  tungstic  acid,  etc.,  at  a  relatively 
moderate  heat,  but  most  of  them  cannot  be  formed  by  cooling 
from  a  dry  melted  mass.  The  contact-metamorphism  which 
intrusive  granitic  rocks  exert  upon  the  rocks  which  they  cut 
is  of  such  a  character  as  to  show  the  presence  of  mineralizers. 
Minerals  like  tourmaline,  scapolite,  muscovite,  etc.,  frequent  in 
the  contact-metamorphic  aureoles  of  granites,  testify  to  the 
emanation  of  boron,  chlorine,  fluorine,  acid,  water,  etc.,  from  the 
consolidating  granitic  magma.  From  these  and  other  consid- 
erations it  is  probable  that  granite  has  crystallized  at  a  rela- 
tively low  temperature  (compared  with  that  of  less  siliceous 
igneous  rocks),  and  that  it  has  remained  mobile  below  the 
fusing-point  of  most  of  the  granitic  constituents  on  account  of 
the  intermixture  of  water  and  other  mineralizers.  It  is  likely 
that  water  was  one  of  the  most  abundant  and  efficient  factors 
in  these  processes.  The  quantity  of  water  in  a  magma  has 
never  been  even  approximately  determined.  Scheerer u  esti- 
mated it  as  between  1  and  50  per  cent.,  but  believed  that  the 
actual  quantity  approached  much  nearer  the  minimum  than 
the  maximum  of  these  figures. 

Microscopic  study  of  thin  sections  of  the  alaskite  of  Mineral 
ridge  shows  that  the  crystallization  of  the  rock  was  slow  and 
interrupted.  Two  distinct  periods  or  generations  of  crystals 
are  always  represented.  In  different  sections  the  nature  and 

11  Bulletin  de  la  Societe  Geologique  de  France,  Second    Series,  vol.   iv.,   p.  490 
(1846-47). 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       609 

relative  amounts  of  the  minerals  belonging  to  each  genera- 
tion vary  greatly,  but  the  following  observations  apply  to  all 
cases : 

1.  Quartz'  is  usually  absent  from  the  first  generation,  or  if 
present  is  subordinate.     In  the  second  generation  it  is  always 
predominant.     In  some  cases  the  first  generation  is  made  up 
entirely  of  feldspar  and  the  second  entirely  of  quartz ;  but  the 
separation  is  usually  not  so  marked,  some  of  the  feldspar  crys- 
tallizing with  the.  second  generation  together  with  the  predomi- 
nating quartz. 

2.  Microcline  is  almost  always  of  the  second  generation. 

3.  Albite  and  oligoclase-albite  occur  generally  in  both  the 
first  and  second  generations. 

4.  Zircon  and  pyrite  have  been  noted  included  in  the  min- 
erals of  the  second  generation,  but  not  in  those  of  the  first. 

In  some  cases  the  rock  is  almost  entirely  made  up  of  crystals 
of  the  first  generation,  with  the  second  generation  represented 
in  a  very  subordinate  way.  Other  sections  show  the  first  gen- 
eration only  as  scattering  idiomorphic  crystals,  with  the  second 
generation  making  up  the  general  area.  In  most  cases,  how- 
ever, the  division  is  fairly  equable. 

The  chief  lesson  taught  is  that  the  quartz  is  slightly,  but  dis- 
tinctly, younger  than  the  feldspar.  It  is  frequently  segregated 
into  irregular  chains  of  grains,  which  lie  between  bands  of 
more  feldspathic  material. 

In  nearly  every  section  muscovite  is  present,  generally  in 
fine  fibers.  This  muscovite  in  many  cases  is  plainly  an  altera- 
tion-product which  has  formed  at  the  expense  of  feldspar.  It 
is,  however,  only  the  feldspars  of  the  first  generation  which 
have  been  thus  altered,  while  those  of  the  second  generation 
are  clear.  From  study  of  numerous  'sections,  three  general 
points  in  regard  to  the  muscovite  are  learned: 

1.  The  microcline  is  almost  always  clear  and  subsequent  to 
the  muscovitization. 

2.  The  quartz  is  almost  always  clear  and  subsequent  to  the 
muscovitization,  but  sometimes  incloses  fibers  and  blades  of 
muscovite.  , 

3.  The  orthoclase  and  striated  feldspars  (chiefly  albite  and 
oligoclase-albite)  are  in  part  muscovitized  and  in  part  clear,  as 
is  natural  from  their  belonging  to  both  generations. 


610   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

From  this  it  appears  that  a  partial  alteration  of  the  feldspar 
to  muscovite  took  place  when  the  magma  was  partly  con- 
solidated, and  before  the  deposition  of  the  remainder  of  the 
magma,  which  formed  the  second  generation. 

These  observations  show  that  the  crystallization  process  of 
the  alaskite  was  slow,  so  that  in  many  cases  the  magma  became 
filled  with  contiguous  idiom orphic  feldspar  crystals  of  the  first 
generation,  the  interstices  between  which  were  filled  with  resid- 
ual fluid.  The  mass  composed  of  the  first  generation  of  crys- 
tals was  sometimes  rigid  enough  to  be  partly  cracked  and 
fissured.  In  these  cracks  and  fissures,  as  well  as  in  the  inter- 
stitial spaces  between  the  crystals,  the  residual  fluid  solidified. 
Study  indicates  that  many  of  the  fissures  were  formed  by  con- 
traction consequent  upon  partial  consolidation ;  others  seem  to 
have  been  due  to  movements  brought  about  by  pressure.  Thus 
the  quartz  (which  makes  up  always  the  chief  part  of  the  second 
generation),  besides  forming  as  intergranular  quartz  within  the 
unbroken  alaskitic  fabric,  filled  the  small  fissures,  and  collect- 
ing in  larger  masses  formed  by  itself  on  a  small  scale  an  inde- 
pendent intrusive  in  nearly  the  same  sense  as  the  alaskitic 
magma  had  done.  We  may  logically  conclude  that  this  quartz 
left,  upon  consolidation,  a  residue  which  was  still  finer  grained 
and  more  aqueous. 

The  ore-deposits  are  lenses  of  such  magmatie  quartz,  which 
have  various  dimensions,  as  seen  both  on  horizontal  and  verti- 
cal planes.  These  lenses  are  most  abundant  along  certain 
zones  in  the  intruded  formation  and  overlap  on  one  another. 
They  disappear  by  wedging  or  by  forking  and  by  splitting  into 
two  or  more  branches.  These  lenses  are  original,  and  not  frag- 
ments of  larger  dike-like  bodies  which  have  attained  their  form 
as  a  consequence  of  shearing.  The  wedging-out  of  the  lenses 
is  not  attended  by  evidence  of  unusual  movement;  moreover, 
the  phenomena  of  splitting  and  uniting  forbid  the  assumption 
that  the  form  is  not  primary. 

In  the  chief  mines  of  the  district  the  formation  of  ore-min- 
erals subsequent  to  the  primary  consolidation  of  the  quartz 
lenses  has  taken  place  on  an  unimportant  scale.  Occasionally, 
however,  some  later  precipitation  has  taken  place.  Along 
cracks  in  the  quartz,  frequently  near  the  contact  of  the  quartz 
with  decomposed  greenstone  (altered  diorite)  dikes,  subsequent 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       611 

vein-material  has  formed,  having  a  gangue  of  quartz  with  some 
calcite  and  chlorite,  and  carrying  pyrite  and  galena.  The  in- 
ference is  that  subsequent  to  the  first  or  primary  deposition  of 
minerals,  and  subsequent  to  the  intrusion  of  the  diorite,  min- 
erals were  again  deposited  along  cracks  in  the  original  quartz. 
These  minerals  are  the  same  as  those  first  deposited,  and  might 
be  thought  to  be  due  to  subsequent  concentration,  the  material 
being  derived  from  the  first-formed  minerals,  and  simply  con- 
centrated by  subsequent  circulating  waters.  This  perhaps  has 
sometimes  been  the  case,  but  in  one  mine  where  the  subse- 
quent ore  is  economically  important  (the  Mary  mine),  the 
amount  of  the  subsequent  deposition  is  so  large  as  to  suggest 
a  fresh  and  independent  supply  of  material.  The  phenomena 
in  the  Mary  mine  indicate  the  work  of  ascending  waters,  and 
these  new  solutions  must  have  had  a  composition  much  like 
that  of  the  solutions  from  which  the  primary  ore  was  deposited. 

The  close  association  of  the  diorite  dikes  with  the  quartz- 
alaskite  bodies,  and  frequently  with  the  subsequent  ores,  easily 
leads  one  to  the  hypothesis  that  this  subsequent  mineralization 
was  dependent  on  the  diorite;  but  most  of  the  diorite  dikes 
have  no  later  ores  in  their  vicinity,  and  in  the  mine  where  the 
largest  deposit  of  subsequent  ore  was  noted  (the  Mary)  there 
is  no  diorite. 

The  general  conclusion  is  that  in  this  district  a  series  of 
shaly  limestones  have  been  intruded  by  a  highly  siliceous  alka- 
line magma.  From  this  magma  crystallized  principally  feld- 
spar and  quartz,  the  consolidation  of  the  feldspar  in  general 
preceding  that  of  the  quartz.  The  local  phenomena  indicate 
that  the  crystallization  was  practically  all  accomplished  subse- 
quent to  the  injection.  This  crystallization,  however,  was 
slow,  so  that  the  residual  quartz  was,  before  its  final  consolida- 
tion, in  part  drawn  off  into  large  and  small  reservoirs,  and  so 
could  play  the  role  of  an  independent  intrusion.  A  process  of 
magmatic  differentiation  by  partial  crystallization  is  here 
proved. 

That  the  lenses  are  the  fillings  of  cavities  which  were  present 
in  the  schist  is  out  of  the  question.  The  parallelism  of  the 
schistosity  with  the  curving  walls  of  the  lenses  shows  that  the 
intrusion  filled  spaces  which  it  itself  created.  The  lentic- 
ular form  of  these  alaskite  and  quartz  masses  (including  the 


612       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

ore-bodies)  is  like  that  of  the  masses  of  pegmatite  and  pegma- 
titic  quartz  which  have  been  observed  in  many  places  in  schists 
near  intrusive  granitic  contacts.  I  believe  that  this  form  is 
the  normal  one  for  attenuated,  aqueous,  but  still  viscous,  gran- 
itic material,  injected  into  schists.  The  fact  that  the  same 
characterizations  apply  as  a  rule  to  the  alaskite  lenses  and  the 
quartz  lenses,  indicates  that  the  alaskitic  fluid  must  have  been 
much  the  same  as  that  of  the  quartz,  both  being  less  viscous 
than  that  which  has  formed  the  true  granite,  which  neither  in 
this  quadrangle  nor  in  similar  provinces  is  accustomed  to  form 
lenticular  intrusions,  but  rather  bold  and  well-defined  dikes 
and  sheets  of  which  all  the  ramifications  are  easily  traceable. 

After  the  last  crystallization  of  the  intrusive  alaskite  and 
quartz,  diorite  dikes  were  injected,  and,  probably  directly  after- 
ward, relatively  thin  aqueous  solutions  circulated  along  cracks 
and  produced  a  subsequent  mineralization,  not  approaching, 
however,  in  commercial  importance  (in  this  especial  district), 
the  primary  mineralization.  The  brittle  quartz  of  the  lenses 
having  been  cracked  offered  the  best  channels,  and  here  the 
subsequent  mineralization  took  place,  generally  under  the  rela- 
tively impervious  schist  hanging-walls,  indicating  ascending 
waters. 

For  various  reasons  it  is  believed  that  these  subsequent  min- 
eralizing solutions  represented  a  residue  from  the  granitic  erup- 
tions, more  aqueous  than  that  from  which  the  primary  quartz 
crystallized. 

(b)  Genetic  Relations  of  the  Great  Gulch  Ores. — One  of  the 
gold-mines  of  Mineral  ridge  displays,  at  first  examination,  a 
different  character  from  the  general  type  which  has  just  been 
discussed.  At  the  Great  Gulch  mine  the  general  geology  is, 
for  the  most  part,  like  that  of  most  of  the  typical  gold-ores  of 
the  district.  The  country-rock  is  a  thiri-bedded  limestone- 
slate,  considerably  altered  and  schistose.  Alaskite  and  quartz, 
frequently  feldspathic,  occur  in  interbedded  lenses  in  the  schist. 
The  ore  is  auriferous  arsenopyrite,  which  occurs  in  solid 
streaks  of  all  thicknesses  up  to  1  or  2  ft.  It  is  distinctly  later 
than  the  quartz,  but  the  larger  streaks  are  noticeably  associated 
with  the  alaskite  and  quartz  lenses,  especially  with  the  latter. 
The  hanging-wall  of  quartz  lenses  is  an  especially  favorable 
locality. 


GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES.   613 

Here,  fracturing  has  occurred  subsequent  to  the  intrusion  of 
the  primary  alaskite  and  quartz.  Along  the  channels  thus 
formed  ascending  waters  arose  and  deposited  sulphur,  iron, 
arsenic,  and  gold.  The  period  of  this  mineralization  is  uncer- 
tain from  the  local  data,  but  from  the  resemblance  of  the  phe- 
nomena here  to  those  of  the  subsequent  mineralization  in  the 
Mary  mine  of  the  Drinkwater  group,  it  is  probable  that  the  ore 
in  the  two  cases  has  a  similar  origin. 

(c)  Genetic  Relations  of  the  Silver- Ores  of  Mineral  Ridge. — On 
the  periphery  of  the  gold-quartz  district  of  Mineral  ridge  there 
are  at  several  points  ores  which  contain  more  silver  than  gold. 
The  chief  of  these  are  at  the  Pocatello  and  Vanderbilt  mines. 
The  general  geology  here  is  like  that  of  the  Great  Gulch  mine. 
Alaskite  and  quartz  lenses  are  intrusive  into  a  schist  which 
represents  an  altered  shaly  limestone.  Greenstone  dikes  and 
sheets  are  present,  following  especially  a  zone  of  quartz  lenses. 
Near  the  greenstone  the  quartz  is  frequently  cracked,  broken, 
and  mineralized,  and  in  these  cracks  the  silver-bearing  ore  has 
been  deposited.  The  most  characteristic  mineral  is  a  mixed 
sulphide  and  oxide  containing  copper,  antimony,  silver,  and 
gold. 

Here  the  schists  were  first  injected  by  a  siliceous  magma 
which  crystallized  as  alaskite  and  quartz.  Basic  dikes  were 
subsequently  injected,  which  followed  along  the  zone  of  quartz 
and  alaskite  lenses,  because  here  fracturing  was  more  easy  on 
account  of  the  greater  brittleness  of  the  materials.  The  intru- 
sion of  the  diorite  produced  considerable  additional  fracturing 
in  the  quartz.  Along  the  cracks  thus  produced  mineralizing 
solutions  circulated  and  deposited  the  ore.  The  whole  history 
indicated  is  analogous  to  those  cases  of  mines  of  the  typical 
gold-quartz  type  which  show  notable  subsequent  mineraliza- 
tion, although  the  character  of  the  ore  is  somewhat  different  in 
that  more  silver  and  copper  in  proportion  to  gold  are  present. 

In  other  deposits  on  the  periphery  of  the  Mineral  ridge  aurif- 
erous quartz  district  there  are  ores  which  have  the  same  type 
of  metallic  minerals  as  in  the  Pocatello  and  Vanderbilt  group, 
but  which  have  formed  by  replacement  of  a  dolomitic  marble 
which  overlies  the  schist  formation  in  which  the  gold-bearing 
veins  lie.  In  these  cases  the  inclosing  quartz  of  the  vein  is 
contemporaneous  with  the  metallic  minerals,  instead  of  being 
antecedent  to  them  as  in  the  above-described  silver-mines. 


614   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

The  mineralization  in  all  these  silver-mines  seems  to  differ 
from  the  subsequent  mineralization  described  in  the  case  of  the 
gold-mines  and  prospects,  in  the  presence  of  more  silver  and 
copper;  otherwise  the  facts  are  not  unfavorable  for  regarding 
all  of  this  subsequent  mineralization  as  belonging  to  the  same 
period.  I  desire  to  put  forth  here,  as  a  plain  hypothesis,  an 
idea  which  has  been  arrived  at  by  considering  and  reasoning 
from  the  distribution  and  character  of  ore-deposits  throughout 
the  quadrangle,  The  hypothesis  is,  that  solutions  of  granitic 
origin  have  deposited  predominantly  gold  in  the  granite  or  in 
rocks  silicified  by  the  metamorphic  effect  of  the  granite,  and 
that  in  or  near  calcareous  or  dolomitic  rocks  more  silver  and 
copper  were  deposited  from  the  same  solutions,  the  difference 
being  due  to  the  different  precipitative  influence  of  the  wall- 
rocks. 

(d)  Genetic  Relations  of  the  Ores  of  Lone  Mountain. — The  Lone 
Mountain  group  of  mines  are  all  situated  in  Palaeozoic  lime- 
stones, dolomites,  and  shales  which  have  been  more  or  less  meta- 
morphosed by  intrusion  of  granitic  masses.  Metamorphism  is 
most  intense  near  the  contact,  and  fades  away  gradually  as  the 
distance  increases.  The  limestones  and  dolomites  are  changed 
into  marble,  the  shales  into  hornstones  and  schists,  with  the 
development  of  typical  metamorphic  minerals.  The  veins 
characteristically  follow  the  stratification  of  the  sedimentary 
rocks.  Where  they  thus  occur  along  bedding-planes  these 
planes  have  evidently  been  the  sites  of  differential  movement, 
producing  crushing  and  greater  openness.  More  rarely  the 
veins  occur  in  cross-cutting  shear-  or  fault-zones.  In  one  type 
of  ores,  the  black  mineral  containing  copper  and  antimony,  de- 
scribed in  the  case  of  the  silver-mines  of  Mineral  ridge,  occurs, 
together  with  galena  and  pyrite.  This  mineral  is  similar  to  that 
which  has  been  described  under  the  name  stetefeldtite,  and  will 
be  referred  to  under  this  name  in  the  present  article.  Copper, 
silver,  and  gold  are  present  in  these  ores.  The  ores  of  another 
type  are  characterized  by  typical  contaci>metamorphic  minerals 
as  gangue,  chiefly  epidote  and  garnet.  In  this  type  the  metallic 
minerals  are  magnetite,  specular  iron,  pyrite,  chalcopyrite,  ga- 
lena, gold,  and  silver.  In  another  type  a  quartz  gangue  con- 
tains a  small  amount  of  stetefeldtite,  with  galena,  free  gold, 
and  a  little  copper.  In  another  type  the  primary  ore  is  galena, 


GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES.   615 

now  largely  altered  to  carbonate.  In  general  there  is  a  strong 
likeness  among  the  different  ores  of  this  district. 

From  their  location  and  the  nature  of  their  gangue  the  ore- 
deposits  in  the  Lone  Mountain  district  are  plainly  connected 
with  the  metamorphism  of  the  sediments  produced  by  the 
granite.  At  the  time  of  the  granite  intrusion  siliceous  solu- 
tions emanated  from  the  hardening  mass  and  penetrated  the 
surrounding  sediments,  which  were  thus  recrystallized  and 
metamorphosed.  Such  solutions  circulated  most  vigorously 
along  openings  which  had  been  formed  by  the  intrusion. 
These  openings  were  chiefly  along  bedding-planes,  sometimes 
along  cross-cutting  shear-zones.  Along  them  circulating  gran- 
itic waters  deposited  quartz  and  metallic  minerals,  forming  the 
veins. 

(e)  Genesis  of  the  Ores  in  the  Southern  Part  of  the  Quadrangle. 
— In  the  southern  part  of  the  quadrangle  the  ore-deposits  are 
all  prospects,  no  paying  deposit  having  yet  been  discovered. 
One  type  of  deposits  consists  of  quartz  veins  of  granitic  origin, 
similar  to  the  primary  quartz  of  the  Mineral  Ridge  district. 
These  quartz  segregations,  however,  are  small  in  quantity  and 
unimportant  economically.  As  in  the  Mineral  Ridge  type,  they 
contain  some  gold  and  very  little  silver.  Other  quartz  veins  of 
a  different  type  follow  shear-zones  in  granite.  The  quartz  con- 
tains pyrite  and  gold,  and  the  wall-rocks  are  altered.  The  re- 
semblance of  these  veins  in  composition  to  the  magmatic  quartz 
veins  of  the  first  type  leads  to  the  belief  that  this  second  type 
also  is  due  to  siliceous  residual  solutions  derived  from  the  con- 
solidation of  the  granite,  which  have  circulated  along  available 
channels  in  portions  of  the  granite  which  had  already  consoli- 
dated. Another  type  of  veins  occurs  in  calcareous  and  argilla- 
ceous sediments  near  the  contact  of  the  granite.  The  gangue 
is  chiefly  quartz,  the  metallic  minerals  chiefly  stetefeldtite,  ga- 
lena, copper,  pyrite,  etc.  The  values  are  chiefly  in  silver  with 
some  gold.  The  country-rock  consists  of  metamorphosed  sedi- 
ments containing  typical  contaci>metamorphic  minerals.  Veins 
of  this  type  follow  fracture-zones,  and  along  such  a  zone  vein- 
formations  may  outcrop  at  intervals  for  short  distances.  In  one 
case  veins  of  this  type  in  calcareous  strata  lie  apparently  along 
the  same  fracture-zone  as  auriferous  quartz  veins,  of  the  second 
type  above  described,  which  lie  in  granite,  the  fracture-zone 


616       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

crossing  from  the  granite  into  the  intruded  rock.  The  fact  that 
along  what  seems  to  be  the  same  great  fracture-zone  the  ores 
are  of  different  types  in  the  granite  and  in  the  intruded  sedi- 
ments, suggests  that  they  were  probably  formed  by  the  same 
solutions,  and  the  different  character  of  the  veins  is  assumed  to 
be  due  to  the  different  character  of  the  wall-rock. 

(f)  General  Conclusions  as  to  the  Origin  of  the  Metalliferous  Ores. 

An  intimate  inter-relation  has  been  recognized  for  all-  the 
metalliferous  ores  of  the  quadrangle,  and  all  have  been  traced 
to  the  consequences  of  one  event,  namely,  the  intrusion  of  gran- 
itic rocks  into  Palaeozoic  sediments  in  probably  pos1>Jurassic 
time.  This  district  is  favorable  for  such  determinations  as 
have  been  made,  since  the  granitic  masses  are  small  and  the 
grouping  of  the  ore-deposits  around  them  is  therefore  more 
evident  than  in  a  region,  like  the  Sierra  Nevada,  where  the 
masses  of  granite  are  vastly  larger. 

The  ore-deposits  may  be  divided  into  the  two  chief  groups : 

1.  Bodies  of  auriferous  quartz,  probably  separated  out  in 
gelatinous  form  from  alaskite,  during  the  process  of  crystalliza- 
tion, and  of  the  same  age  and  nature   as  the    intergranular 
quartz  of  granite  and  alaskite.     In  such  quartz  bodies  gold  is 
in  places  segregated  in  commercial  quantities. 

2.  Quartz  veins    due  to  replacement    or    impregnation  of 
crushed  material   along  fracture-zones  by  siliceous    solutions 
more  attenuated  than  those  described  above  and  residual  from 
the   crystallization  of  the   magmatic  quartz  of  the  first  type. 
These  solutions  were  probably  in  various  degrees  of  dilution 
by  magmatic  water.     Such  deposits  were  formed  chiefly  along 
movement-zones   following    bedding-planes    in    the   intruded 
strata;  also  in  cross-cutting  movement-zones  in  the  strata,  and 
to  a  less  degree  in  the  granites.     They  were  formed  contempo- 
raneously with  the  recrystallization  and  contact-metamorphism 
of  the  sediments  under  the  influence  of  the  granite  intrusion. 
They  are  more  or  less  typical  quartz  veins  in  the  pure  carbonate 
rocks  and  in  the  granites,  but  in  the  argillaceous  rocks  the 
quartz  is  often  intermixed  in  various  degrees  with  metamorphic 
silicate  minerals,  such  as  garnet,  epidote,  etc.    The  metallic  ele- 
ments present  are  principally  silver,  gold,  lead,  arsenic,  anti- 
mony, copper,  iron,  etc.,  in  various   combinations.     There  is 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       617 

more  gold  in  the  granite,  more  silver  and  lead  in  the  intruded 
strata.  In  the  granite  the  metallic  mineral  is  mostly  pyrite, 
sometimes  arsenical.  In  the  sedimentary  strata  the  charac- 
teristic metallic  minerals  are  the  altered  sulphide  containing 
silver,  copper,  and  antimony,  which  we  may  provisionally  call 
stetefeldtite,  and  galena.  The  different  character  of  the  metallic 
minerals  is  believed  to  be  largely  due  to  the  wall-rocks,  which 
have  precipitated  certain  things  from  solution.  Aside  from 
the  quartz  the  nature  of  the  gangue  is  also  believed  to  be 
chiefly  due  to  the  nature  of  the  walls. 

In  all  the  types  of  ore-deposits  studied,  the  character  of  the 
solutions  is  believed  to  have  been  highly  siliceous  and  alkaline, 
with  mineralizers,  such  as  fluorine,  boron,  etc.,  present,  but  in 
a  limited  amount.  The  presence  of  gold  and  silver  and  other 
metals  is  sufficiently  explained  by  the  composition  of  solutions 
such  as  described,  in  which  the  necessary  solvents  are  present. 

VII.  COMPARISON  OP  SILVER  PEAK  WITH  OTHER  ORE-DEPOSITS. 

Fifty  miles  northeast  of  the  northeast  corner  of  the  Silver 
Peak  quadrangle  is  the  Belmont  district,  at  one  time  produc- 
tive, but  long  since  abandoned.  The  ore-deposits  consist  of 
quartz  veins  which  occur  in  the  immediate  vicinity  of  an  intru- 
sive mass  of  granite.  From  some  microscopic  work  done  by 
me 12  on  this  granite,  it  appears  that  magmatic  solutions  have 
been  active,  producing  quartz  and  muscovite  at  the  expense  of 
the  orthoclase  in  the  intrusive  rock,  and  altering  the  siliceous 
limestone  of  the  wall-rock  to  jasperoid  and  mica-schist.  The 
mineral-bearing  quartz  veins,  it  was  suggested,  were  probably 
contemporaneous  with  those  which  were  found  to  occur  in 
irregular  form  within  the  intrusive  rock,  and  which  were  held 
to  represent  the  final  product  of  the  magma.  In  these  quartz 
veins  the  metallic  minerals  are  chiefly  stetefeldtite  and  some 
lead,  copper,  and  iron. 

In  the  Toyabe  range  there  are  numerous  ore-deposits,  of 
which  the  chief  ones  lie  near  Austin,  about  65  miles  north  of 
Belmont.  S.  F.  Emmons  has  described  many  of  the  deposits, 
which  in  nearly  every  case  consist  of  white  quartz  veins  carry- 
ing metallic  sulphides.  In  the  vicinity  of  Austin  the  veins  are 

12  American  Journal  of  Science,  Fourth  Series,  vol.  x.,  No.  59,  p.  355  (Nov., 
1900). 

39 


618   GENETIC  RELATIONS  OF  THE  WESTERN  NEVADA  ORES. 

mainly  in  granite.  In  other  parts  of  the  district,  however,  the 
veins  occur  in  the  stratified  rocks.  In  some  of  the  veins  the 
chief  silver-bearing  mineral  is  a  mixed  sulphide  of  antimony, 
as  is  the  case  in  the  neighborhood  of  Belmont.  There  is  prob- 
ably here  an  intimate  connection  between  the  metalliferous 
quartz  veins  and  intrusive  rocks. 

About  15  miles  east  of  the  eastern  edge  of  the  Silver  Peak 
quadrangle  is  the  Southern  Klondike  district,  which  I  have 
visited  and  studied  briefly.  At  this  camp  the  main  country- 
rock  is  Palaeozoic  limestone,  which  is  intruded  by  a  long,  dike- 
like  mass  of  siliceous  granitic  rock,  of  a  composition  similar  to 
alaskite.  The  rock  as  a  whole  is  closely  related  to  that  which 
I  described  from  Belmont,  and  also  to  the  alaskite  of  Mineral 
ridge  at  Silver  Peak.  Occasionally  there  are  in  the  igneous 
mass  small  segregated  portions  of  pure  quartz,  in  which  bunches 
of  pyrite  and,  more  rarely,  galena  occur.  The  limestone  near 
the  contact  has  been  altered  to  hornstone  containing  epidote, 
zoisite  and  other  characteristic  products  of  contact-metamor- 
phism.  Not  many  yards  from  the  contact,  in  the  altered  lime- 
stone, is  a  quartz  vein  which  follows  parallel  to  the  contact 
closely  for  a  mile  or  more,  and  carries  scattered  values  of  silver 
and  gold.  The  minerals  contained  are  chiefly  galena  and  py- 
rite, with  small  bunches  of  the  rich  black  copper-silver  sulphide 
or  stetefeldtite,  which  has  been  described  as  characteristic  of 
those  veins  in  the  Silver  Peak  quadrangle  which  are  near  the 
contact  of  the  intrusive  granite,  but  not  in  the  granite  itself. 

All  these  mineral  districts  are  closely  similar.  All  the  ores- 
have  evidently  originated  as  the  result  of  the  intrusion  of  gran- 
itic bodies  into  Palaeozoic  sediments,  and  in  all  cases  the  ore- 
deposition  was  associated  with  contact-metamorphism.  The 
granitic  and  alaskitic  rocks  which  make  up  these  intrusive- 
bodies  are  similar  in  those  districts  which  I  have  examined, 
namely,  Silver  Peak,  Southern  Klondike  and  Belmont,  and, 
from  Mr.  Emmons's  description,  in  the  Toyabe  range.13 

In  the  three  districts  which  I  have  examined  there  are  simi- 
lar peculiarities  of  the  intrusive  rocks,  notably  the  segregation 
of  small  contemporaneous  quartz  masses  within  the  rock,  and 
the  alteration  of  the  feldspar  to  muscovite  by  magmatic  pro- 
cesses. 

13  Geological  Exploration  of  the  Fortieth  Parallel,  vol.  iii.,  p.  324  (1870). 


GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES.       619 

In  the  Sierra  Nevada,  associated  with  the  granitic  intrusions, 
are  auriferous  quartz  veins  whose  formation  immediately  suc- 
ceeded the  granitic  eruption.  The  relation  between  these 
quartz  veins  and  the  granite  has  long  been  noted.14  Recently 
Mr.  Lindgren  has  adopted  the  hypothesis  that  the  solutions 
which  deposited  the  veins  were  of  magmatic  origin.  These 
California  gold-quartz  veins  are  characterized  by  the  common 
occurrence  of  albite  as  a  gangue-mineral.15 

YIII.  CONCLUSIONS  CONCERNING  THE  SILVER  PEAK  TYPE  OF 

ORES. 

The  general  conclusion  is  that  the  Silver  Peak  deposits  are 
part  of  a  larger  province,  which  is  represented  more  abun- 
dantly in  the  Sierra  Nevada  of  California,  with  only  outlying 
smaller  areas  in  adjacent  portions  in  Nevada.  All  the  ore-de- 
posits of  this  province  seem  to  owe  their  existence  to  the  intru- 
sion of  the  post-Jurassic  granite.  The  ores  of  this  province 
have  been  concluded  to  be  due  to  siliceous  solutions,  which 
were  due  to  the  crystallization  of  the  granitic  rocks.  These 
solutions  deposited  the  minerals  they  contained  (silver,  gold, 
etc.)  along  fractures  or  shear-zones  or  other  channels,  thus 
forming  the  typical  gold-quartz  veins  of  the  region.  In  Ne- 
vada these  solutions  formed,  where  the  wall-rock  consisted  of 
the  calcareous  strata  intruded  by  the  granite,  a  type  of  noble 
silver-gold  veins  (that  is,  veins  often  containing  a  comparatively 
small  proportion  of  the  baser  metals)  characteristic  of  this 
period. 

This  metallographic  province  appears  to  be  most  typically 
developed  in  California,  for  which  reason  we  may  call  it  the 
California  province,  while  the  province  characterized  by  the 
ores  in  Neocene  lavas  is  best  represented  east  of  the  Sierra 
Nevada  in  the  State  of  Nevada,  and  may  therefore  be  called 
the  Nevada  province.  In  western  Nevada  the  Nevada  province 

14  Whitney,  J.  D.,  The  Auriferous  Gravels  of  the  Sierra  Nevada,  p.  353   (1880). 
Kemp,  J.  F.,  Ore-Deposits  of  the  United  States  and  Canada,  3d  ed.,  p  370  (1900). 
Lindgren,  W.,  Gold-Quartz  Veins  of  Nevada  City  and  Grass  Valley,  Seventeenth 
Annual  Report,  U.  S.  Geological  Survey,  Pt.  II.,  pp.  175  to  176  (1895-96). 

15  American  Journal  of  Science,  Second  Series,  vol.  xxviii.,  No.  83,  p.  249  (Sept., 
1859)  ;   and  Eansome,  F.  L.,  Mother  Lode  Folio,  No.  63,  U.  S.  Geological  Survey, 
p.  8  (1900). 


620       GENETIC    RELATIONS    OF    THE    WESTERN    NEVADA    ORES. 

overlaps  upon  the  California  province,  and  along  this  overlap 
the  ore-deposits  belonging  to  one  group  are  superimposed  upon 
the  other.  The  Nevada  province  is  coextensive  with  the  .ap- 
pearance of  Neocene  andesites  and  rhyolites  at  the  surface,  the 
California  province  with  the  appearance  at  the  surface  of  post- 
Jurassic  granitic  rocks.  Where,  as  in  western  Nevada,  these 
granitic  rocks  and  the  strata  which  they  intrude  are  exposed  by 
erosion  in  patches  lying  in  the  midst  of  Tertiary  volcanics,  we 
may  have  veins  belonging  to  the  different  periods  very  close 
together. 

IX.  MAGMATIC  ORIGIN  OF  ORES  OF  BOTH  PROVINCES. 
According  to  the  previously  expressed  conclusions,  all  the 
ore-deposits  of  this  rich  region  of  Nevada  can  be  referred  to 
two  chief  periods  of  intrusive  igneous  activity.  The  various 
ore-deposits  discussed  appear  to  be  genetically  connected  with 
one  or  the  other  of  these  two  great  periods.  In  both  cases  the 
mineralization  has  been  ascribed,  as  the  result  of  close  study, 
to  the  final  processes  of  rock-solidification  subsequent  to  intru- 
sion, the  residual  solutions  and  gases  resulting  from  consolida- 
tion having  been  the  agents  which  produced  the  mineraliza- 
tion. The  metals  also  are  in  all  cases  considered  to  have  been 
derived,  together  with  the  mineralizing  solutions,  from  the 
respective  magmas.  In  this  whole  district,  therefore,  the  effect 
of  the  concentrating  action  of  ordinary  circulating  ground- 
water  does  not  enter  perceptibly  into  our  conclusions,  and  so 
far  as  we  yet  know  it  is  negligible,  except  for  some  minor 
effects  in  rearranging  the  ores  of  the  oxidized  zone. 


QUARTZrVEINS    OF    SILVER    PEAK,    NEVADA.  621 


No.  23. 


Are  the  Quartz- Veins  of  Silver  Peak,  Nevada,  the   Result 
of  Magmatic   Segregation  ? 

BY  JOHN   B.  HASTINGS,    DENVER,*  COLO. 
(British  Columbia  Meeting,  July,  1995.     Trans.,  xxxvi.,  647). 

CHIEF  among  the  varied  problems  facing  the  mine-manager 
is  that  of  vein-structure  and  origin,  which  is  highly  important 
as  a  guide  to  successful  discovery  and  development.  If  metal- 
liferous deposits  can  be  traced  to  the  intrusion  of  waters  along 
definite  lines,  then  is  there  something  tangible  for  him  to  study. 
But  when  he  is  told  by  a  geologist  that  metalliferous  deposits 
are  due  to  some  other  cause,  like  magmatic  differentiation, 
while  not  perhaps  discouraged,  he  is  impressed  with  a  vague 
sense  of  new  worlds  to  be  conquered. 

In  1897,  while  manager  of  the  War  Eagle  mine  at  Rossland, 
B.  C.,  where,  previously,  the  ore-bodies  had  not  been  supposed 
to  occur  as  veins,  I  suggested  to  visiting  members  of  the  Cana- 
dian Geological  Survey  that,  perhaps,  the  structure  of  the  pyr- 
rhotite-bodies  of  that  mine,  which  had  been  proved  to  occur 
along  well-defined  fractures,  might  throw  some  light  on  the 
similar  deposits  of  Sudbury,  then  held  to  be  basic  aggregations 
from  the  original  magma.  Later  investigation  has  at  least  pro- 
voked discussion  of  this  last  deduction,  questioning  its  correct- 
ness and  suggesting  that,  perhaps,  the  deposits  are  actual  veins. 

The  following  extract  from  a  paper  by  J.  E.  Spurr l  is  quoted, 
because  it  sets  forth  Mr.  Spurr's  theory  of  the  quartz-occurrences 
of  the  Silver  Peak  mines,  which  will  be  discussed  in  this  article. 
It  also  graphically  describes  the  attendant  geological  features. 

"  The  Drinkwater  group  of  mines,  which  is  the  most  important  part  of  the 
Blair  gold  properties,  and  which  has  produced  practically  all  of  the  million 
dollars'  worth  of  ore,  as  above  stated,  may  be  taken  as  typical  of  the  gold- veins 
which,  though  widespread  and  numerous,  show  a  wonderful  similarity  of  character. 
On  the  surface  two  adjacent  veins  outcrop,  the  Crowning  Glory  and  the  Drink  - 

1  Ore  Deposits  of  Silver  Peak  Quadrangle,  Bulletin  No.  225,  U.  S.  Geological 
Survey  (1904). 


622  QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA. 

water,  the  former  the  larger,  the  latter  containing  the  greater  quantity  of  good 
ore.  The  quality  of  the  ore  still  left  standing  (only  the  richer  portions  having 
been  removed  for  milling)  has  been  more  or  less  carefully  determined  a  number 
of  times 

"  Geologically,  the  veins  of  the  Blair  mine  are  interesting.  Properly  speaking, 
they  are  hardly  veins,  but  flattened  lenses  of  quartz  occurring  in  a  definite  zone 
100  ft.  or  more  in  thickness.  The  lenses  wedge  out  and  disappear  both  horizontally 
and  vertically,  and  their  place  is  taken  by  overlapping  lenses.  The  wall-rock  is  a 
schist,  derived  chiefly  from  the  metamorphism  of  an  original  limy  shale  or  lime- 
stone. Frequently,  also,  the  wall- rock  is  a  very  siliceous  granitic  rock  (alaskite), 
made  up  essentially  of  quartz  and  feldspar.  This  alaskite  occurs  in  the  schist  in 
lenses  similar  to  the  quartz.  There  is,  moreover,  every  transition  between  the 
alaskite  and  the  quartz ;  and  the  schist  has  been,  so  to  speak,  saturated  with  this 
siliceous  material,  which  forms  seams  and  thin  lenses  in  it.  The  auriferous  quartz- 
lenses  in  the  mine  in  many  places  run  laterally  into  quartz-feldspar  rock  (alaskite) . 
As  a  rule,  the  values  grow  insignificant  with  the  coming-in  of  the  feldspar,  but 
occasionally  high  values  may  still  be  found. 

"The  general  conclusion  is,  that  here  a  series  of  fissile  shales  and  thin-bedded 
limestones  has  been  invaded  by  a  very  siliceous  granitic  intrusion  which  has  meta- 
morphosed the  sediments  to  schists.  The  quartz  has  plainly  the  same  origin  and 
nature  as  th&  alaskite,  both  being  siliceous  phases  of  a  granitic  magma  [the  italics  are 
mine. — J.  B.  H.].  The  gold  in  the  quartz  is  usually  free,  sometimes  associated 
with  scattered  galena  [and  pyrite.— J.  B.  H.].  Greenstone  or  diorite  dikes  cut 
the  veins  or  follow  along  them,  but  are  of  later  age.  Along  the  dikes  there  has 
been  water-circulation,  resulting  sometimes  in  impoverishment,  sometimes  in  rela- 
tive concentration  of  the  original  values. 

"This  zone  of  veins  outcrops  for  a  mile  along  the  mountain  side.  At  one  point, 
some  distance  below  the  vein-zone,  free  gold  in  fresh  alaskite-pegmatite  country- 
rock  was  found. 

' '  In  the  main,  the  other  gold-mines  or  prospects  of  the  district  have  exactly  the 
same  geological  relations." 

At  my  first  examination  of  the  Blair  properties,  in  December, 
1900,  having,  to  guide  me,  the  thorough  reports  of  James  D. 
Hague  and  George  "W.  Maynard,  I  spent  only  one  day  on  the 
hill;  at  my  second  visit,  in  May,  1905,  I  was  half  a  day  at  the 
Blair  mines  and  three  days  at  the  adjoining  Valcalde  group. 

The  mines  are  on  ridges  north  from  the  Silver  Peak,  not  on 
that  mountain  proper,  which  rises  1,500  ft.  higher  (to  9,000  ft.). 
It  is  volcanic;  the  various  flows  extend  for  miles  easterly,  and 
the  successive  stages  of  its  growth  are  marked.  It  is  reported 
that  there  is  on  the  top  an  oblong  depression,  2,000  ft.  long, 
filled  with  water  from  melting  snow. 

Many  mining  engineers,  who  have  examined  veins  in  schists, 
will  recognize  the  accuracy  of  Mr.  Spurr's  description  of  the 
formation  in  lenses,  the  disappearance  both  horizontally  and 
vertically,  and  the  replacement  by  overlapping  ones.  They  also 


QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA.  623 

have  sampled  veins  in  granite  which  have  passed  gradually  from 
quartz  to  granite,  and  have  noted  the  usual  disappearance  of 
metallic  values  with  the  appearance  of  the  feldspars. 

At  my  first  visit,  having  no  idea  of  the  quartz  ever  being 
considered  a  phase  of  the  granite,  and  at  my  last,  being  busily 
engaged  with  the  economic  features  of  the  Yalcalde  group,  I 
did  not  closely  study  the  occurrence  of  alas  kite  within  the  gran- 
itic area ;  but  it  was  seen  in  proximity  to  the  great  cuts  on  the 
Drinkwater  mine,  especially  on  the  northeasterly  or  hanging- 
wall  ;  and  large  masses  in  front  of  the  vein  presented  a  gneis- 
soid  appearance  and  were  extremely  silicified.  In  the  south 
westerly  or  foot-wall  of  the  veins,  the  rock  appeared  to  be  nor- 
mal granite,  with  muscovite  and  biotite ;  occasionally  it  looked 
as  if  the  muscovite  might  be  an  alteration-product,  but  usually 
the  rock  was  in  normal  condition,  except  that  in  all  the  pieces 
found  the  biotites  were  in  the  last  stages  of  alteration.  Alas- 
kite  was  observed  in  other  places  among  the  mines,  and  away 
from  the  veins;  and  it  seemed  as  if  the  absence  of  the  micas 
was  due,  in  part,  to  their  elimination  near  the  veins  and  other 
zones  of  movement,  and  sometimes  to  differentiation  of  the 
magma.  The  lenses  in  the  schists  are  usually  alaskite,  but  as 
most  of  these  areas  have  been  subjected  to  solfatarisni,  I  could 
not  decide  whether  the  absence  of  the  mica  was  primary  or  sec- 
ondary. At  the  Drinkwater  group  the  outer  area  bordering 
the  limy  shales  is  alaskite,  and  at  the  Yalcalde  group  the  gran- 
ite adjoins  the  same  rocks.  The  whole  granitic  mass  of  the 
mines  is  one  magma.  There  has  been  fissuring  of  the  normal 
granite,  attended  with  injection  of  dikes  and  formation -of  veins, 
but  sometimes  without  either.  The  micas  adjacent  to  the  move- 
ment have  been  more  or  less  destroyed  (as  in  the  Boise  basin) 
and  aplite  has  been  formed ;  and  again  aplite  occurs  as  a  phase 
of  the  original  magma. 

The  whole  granitic  area  is  slightly  fractured,  the  cracks 
cemented  with  the  usual  quartz  as  seen  in  granite,  sometimes 
auriferous,  usually  not.  These  quartz  seams  are  white  and  solid, 
glassy,  chalcedonic  or  crystalline,  and  contain  cavities,  which 
are  sometimes  filled  in  with  chalcedonic  quartz. 

Mr.  Spurr  speaks  of  finding  gold  in  fresh  alaskite-pegmatite 
country-rock  below  the  veins.  I  found  coarse  gold  at  a  point 
in  the  gulch  below  the  Frank  ~No.  2  mine,  possibly  on  the  Co- 


624  QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA. 

lumbus,  and  south  of  the  New  York,  from  200  to  500  ft.  from 
the  veins.  The  gulch  follows  a  line  of  movement  occupied  more 
or  less  by  a  greenstone  dike,  from  6  to  8  in.  wide,  dipping  flatly 
to  the  west.  At  this  particular  place  the  dike  is  not  seen. 
Along  the  denuded  foot-wall  the  alaskite  is  unaltered,  except 
for  small  deposits  of  quartz  and  iron  in  masses  an  inch  or  so  in 
diameter  where  the  gold  occurred,  and  which  I  take  to  have 
been  connected  with  a  small  quartz  vein  6  in.  or  less  wide, 
intermittently  accompanying  the  dike,  which  is  also  the  foot, 
wall.  This  vein  outcrops  at  the  bottom  of  the  gulch,  and  the 
quartz  is  clearly  different  from  the  component  quartz  of  the 
alaskite.  Its  strike  is  £TE.  and  dip  NW. ;  the  Blair  veins  strike 
NW.  and  dip  NE. ;  and  the  Valcalde  veins  in  this  neighbor- 
hood strike  north  and  dip  east. 

The  following  characteristics  of  the  Blair  veins  were  noted : 
Beginning  at  the  workings  farthest  south,  a  50-ft.  tunnel  is  run 
in  the  foot-wall,  and  two  cross-cuts  made  to  the  vein ;  the  first 
one  is  20  ft.  in  the  solid  white  vein-quartz,  and  not  through  it; 
the  quartz  comes  in  on  well-defined  fissuring,  course  N.  30°  W., 
with  regular  dip  20°  NE.  The  second  cross-cut  just  enters,  at 
the  roof,  the  same  white  quartz ;  there  is  strong  fissuring  on  the 
contact;  the  course  is  more  westerly  and  the  dip  is  the  same  as 
in  No.  1.  The  foot-wall  is  alaskite,  containing  a  few  quartz 
seams ;  the  vein,  as  specified,  is  hard  white  quartz,  separated 
from  the  fooi>wall  by  uniform  and  distinct  fissuring.  The 
workings  on  the  south  side  of  the  gulch  expose  the  vein  with 
the  same  quartz  and  the  same  flat  dip,  which  follows  a  well- 
defined  fissuring  of  the  alaskite,  and  a  thin  greenstone  dike, 
also  fissured.  A  projected  cross-section,  showing  the  uniform 
dip  of  the  Crowning  Glory  and  Drinkwater  veins  for  1,000  ft. 
in  depth,  is  given  in  Fig.  1. 

The  main  Blair  deposits,  as  Mr.  Spurr  says,  occur  in  two 
separate  veins ;  and  it  may  be  added  that  these  are  parallel  and 
100  ft.  apart. 

This  outcrop  of  sheared  country-rock  and  quartz,  from  75 
to  100  ft.  wide,  striking  about  1ST.  35°  W.,  and  dipping  from 
15°  to  50°  NE.,  can  be  traced  for  6,000  ft.  across  a  deep  gulch, 
from  the  Crowning  Glory  to  the  New  York.  Throughout  the 
whole  distance,  it  is  attended  with  fissuring.  At  the  New 
York  there  is  a  belt  of  the  limy  shale,  with  possibly  a  fissured 


QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA. 


625 


dike  which  the  vein  follows,  being  always  parallel  to  the  fissur- 
ing.  The  quartz  outcrop  is  very  prominent  for  500  ft.  over 
the  New  York  hill,  and  extends  some  distance  beyond.  The 
belt  of  foreign  rock  (limy  shale,  etc.),  included  in  the  granite, 
is  about  100  ft.  wide,  but  is  local;  another  inclusion  joins  it  on 
the  north,  more  evidently  the  limy  shale  country-rock;  here 
both  the  shale  and  granite  are  sheared,  but  more  nearly  north 
and  south  than  at  the  vein,  and  with  some  silicification.  Along- 
side the  vein  the  granite  is  not  sheared  on  the  NQW  York 
(as  it  is  further  south), — as  if  there  had  been  enough  of  the 
shale  to  take  up  the  movement. 


HIGHEST  POINT 

STORED  ON 
CROWNING  GLORY  VEIN 


FIG.  1. — PROJECTED  CROSS-SECTION  OF  CROWNING  GLORY  AND 
DRINKWATER  VEINS. 

There  are,  perhaps,  three  ages  of  greenstone  dikes, — a  diorite 
quite  recent,  running  ISTW-SE. ;  a  greenstone  later  than  the 
veins  and  sometimes  faulting  them ;  and  a  greenstone  older 
than  the  veins,  which,  to  a  great  extent,  the  latter  have  followed. 

Mr.  Spurr  thinks  that  all  the  dikes  are  later  than  the  veins ; 
but  those  followed  by  the  veins  sometimes  inclose  them,  and 
the  quartz  is  not  sheared  or  broken,  while  the  dike,  espe- 
cially that  portion  occupied  by  the  vein,  is  sheared  to  schis- 
tosity.  The  quartz,  both  in  the  dikes  and  granite,  is  usually 
remarkably  clean.  Distinct  silicifi  cation  of  the  dikes  is  seen, 
which,  however,  might  be  secondary. 


626  QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA. 

The  Sentinel  mine  is  on  the  divide  between  the  New  York 
and  the  Drinkwater,  in  the  limy  shale.  The  only  ore-body  and 
occurrence  of  quartz  of  consequence  is  at  the  open-cut  alongside 
the  road.  This  lens  is  about  30  ft.  long,  20  ft.  at  the  widest, 
strikes  K  20°  W.,  and  dips  from  20°  to  25°  E.,  conformably 
with  the  schists.  It  is  near  the  granite  contact.  The  fissuring 
differs  from  that  of  the  Blair  mines,  and  agrees  with  the  regu- 
lar foliation  of  the  limy  shales ;  it  continues  down  hill  to  the 
north,  and  is  accentuated  by  lenticular  streaks  of  alaskite  in- 
trusions. There  has  evidently  been  solfataric  action  along  it, 
resulting  in  alteration  on  a  small  scale  of  the  schists,  and  some- 
times of  the  alaskite,  and  the  formation  of  compact,  crystalline 
and  chalcedonic  seams  of  quartz.  On  the  whole,  the  silicifica- 
tion  seems  to  have  affected  the  schists  more  than  the  alaskite. 

The  Valcalde  group,  adjoining  the  Blair,  exhibits  much  nar- 
rower veins.  It  comprises  in  one  vein-system  the  Columbus, 
Lincoln,  Frank  No.  2,  Washington,  and  Porto,  to  which  might 
be  added  the  Lucky  Sam,  owned  by  other  parties.  It  seems 
as  if  all  these  claims  were  on  one  vein.  At  least,  their 
characteristics  are  so  uniform,  and  the  portions  developed 
occupy  such  relative  positions,  that  they  may  be  considered 
'as  belonging  together.  The  vein-fissuring  and  deposition  of 
quartz  has  followed  a  pre-existing  flat  dike,  sometimes  horizon- 
tal, and  again  dipping  as  much  as  15°  easterly  or  westerly;  the 
dike  as  seen  is  from  a  few  inches  to  5  ft.  thick,  and  the  quartz 
from  a  few  inches  to  6  ft.  The  dike  is  distinctly  sheared,  as 
is  also  the  granite  near  the  contact,  and,  in  some  places,  for  a 
foot  or  two  away,  the  quartz  is  not  broken  in  the  least.  The 
quartz,  which  is  sometimes  lenticular  in  the  sheared  dike,  also 
occurs  in  continuous  streaks  several  feet  wide  within  the  dike, 
and  also  on  top  of  it,  with  the  granite  for  a  distinct  hanging- 
wall.  In  some  places  the  dike  is  not  seen  at  all,  the  quartz 
occurring  as  a  regular  streak  in  the  granite,  from  4  to  6  ft. 
wide,  with  a  remarkably  smooth  and  well-defined  hanging- 
wall  ;  the  fooi>wall  is  not  exposed. 

This  flat  fissure,  extending  from  the  New  York  2,000  ft. 
southerly,  outcrops  along  both  sides  of  a  north-and-south  gulch 
(the  central  portion  having  been  eroded  away),  and  terminates, 
so  far  as  known,  in  the  basin  at  the  head  of  it.  Laterally,  it 
may  be  1,500  ft.  wide ;  this  width  is  only  indicated  by  the  Porto 


QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA.  627 

mine.  It  has  been  disturbed  by  north-and-south  movements, 
with  and  without  dikes. 

The  area  is  either  granite  or  alaskite,  the  latter  in  small 
patches.  The  quartz  is  entirely  similar  to  that  of  the  Blair 
mines,  carrying  a  little  galena  and  iron  sulphides  in  the 
best  ore. 

The  Soda  mine  lies  south  of  the  flat  vein  above  described. 
The  vein  strikes  north  and  dips  50°  westerly.  The  hard,  white 
vein-quartz  is  similar  to  that  of  the  other  mines,  the  best  con- 
taining galena  arid  pyrite.  At  the  working  farthest  south  it  is 
found  on  the  hanging-wall  of  a  lenticular  mass  of  an  alaskite 
dike  in  limy  shale.  About  30  in.  of  the  alaskite  has  been 
silicified.  The  east  or  hanging-wall  of  the  quartz  is  limy  shale 
and -a  greenstone  dike,  the  relations  of  which  could  not  be  as- 
certained. The  wall  is  fissured  parallel  to  the  vein.  The  foot- 
wall  is  alaskite ;  and  the  quartz  merges  into  it.  The  alaskite 
lens,  as  developed,  is  25  ft.  long,  10  ft.  wide  at  the  middle,  and 
of  unknown  extent,  the  northern  half  only  being  exposed. 
Beyond  this  northern  half  no  more  alaskite  is  found ;  but  the 
vein,  composed  of  quartz  stringers  and  lenses  parallel  to  the 
foliation  of  the  schists,  has  been  developed,  with  a  width  of 
from  6  to  10  ft.,  for  300  ft.  further. 

The  Salisbury  mine  is  in  granite,  a  quarter  of  a  mile  from  the 
end  of  the  flat  vein.  It  strikes  IS".  18°  E.  and  dips  55°  east- 
erly. The  foo1>wall  is  well  defined  by  2  ft.  of  strong  fissuring, 
with  a  small  dike.  The  vein  is  40  in.  wide  and  merges  into 
the  granite,  having  no  defined  hanging-wall ;  but  the  width 
of  the  vein,  developed  for  55  ft.,  is  uniform.  It  is  cut  off  on 
the  strike  by  a  !N"W.  fault  and  dike,  dipping  northeasterly, 
which  carries  quartz  without  values,  as  the  result  of  a  second- 
ary silicification.  The  vein-quartz  is,  like  that  of  the  other 
mines,  hard  and  white,  and  carrying  galena  and  pyrite. 

The  Paris  mine  has  about  the  same  character  as  the  Soda, 
but  without  an  alaskite  dike;  the  inclosing  walls  are  schists, 
within  a  granite  area;  the  veins  are  lenticular  and  small,  from 
2  to  4  ft.  wide,  and  contain  the  same  white  quartz,  with  galena 
and  pyrite  in  the  best  ore.  The  course  is  north  and  south,  and 
the  dip  35°  east. 

A  few  specimens  from  the  Yalcalde  group  exhibited :  (1) 
wire  gold  in  soft  crystalline  quartz  (called  "  decomposed  "  by 


628  QUARTZ-VEINS    OF    SILVER    PEAK,    NEVADA. 

the  miners) ;  (2)  crystalline  gold  in  a  dog-tooth  quartz  lining 
of  a  cavity,  which  was  afterwards  filled  with  chalcedony ;  (3) 
sheets  of  gold  from  cracks  in  chalcedony;  and  (4)  particles  of 
gold  in  the  ordinary  vein-quartz,  that  has  been  freed  by  oxida- 
tion of  the  sulphides. 

From  the  above  it  appears  to  me :  (1)  That  this  district  pre- 
sents bodies  of  quartz  of  uniform  type,  following  a  well-defined 
fracture-zone  with  regular  course  and  dip,  each  great  fissure  hav- 
ing its  own  direction,  varying  from  IsTW.  in  the  Blair  mines  to 
N.  18°  E.  in  the  Salisbury  mine,  and  a  dip  from  horizontal  to 
15°  westerly  and  55°  easterly,  the  easterly  dip  prevailing. 

(2)  That  the  values  are  in  the  quartz,  which  is  confined  to 
narrow  lateral  limits,  being  well-defined  walls,  which  may  be 
granite,  schist,  or,  in  a  subsidiary  way,  greenstone  dikes.     The 
passing  of  the  quartz  into  the  granite  occurs  in  the  usual  man- 
ner of  veins  in  a  granitoid  rock;  and  the  relative  amount  of 
accompanying  silicified  or  mineralized  granite  is  not  more  than 
usual. 

(3)  That,  consequently,  the  veins  are  not  siliceous  segrega- 
tions from  the  granite,  but  have  been  formed  in  the  usual  man- 
ner by  ascending  waters  along  lines  of  fracturing. 


OCCURRENCE    OF    STIBNITE    AT    STEAMBOAT    SPRINGS,  NEVADA.       629 

• 

No.  24. 

The  Occurrence  of  Stibnite  at  Steamboat  Springs, 
Nevada. 

BY  WALDEMAR  LINDGREN,  WASHINGTON,  D.   C.* 

(Washington  Meeting,  May,  1905.     Trans.,  xxxvi.,  27.) 

THE  important  investigations  of  Dr.  G.  F.  Becker  at  Steam- 
boat Springs,  Nev.,  in  1885,  aided  by  the  analytical  work  of 
W.  H.  Melville,  established  the  fact  that  sulphides  were  being 
deposited  at  the  surface  by  hot  ascending  waters.1  Steamboat 
Springs  is  situated  near  the  eastern  base  of  the  escarpment  of 
the  Sierra  Nevada,  six  miles  distant  from  the  Comstock  lode. 
In  a  region  of  former  volcanic  activity,  hot  springs  with  a  tem- 
perature of  about  80°  C.  break  forth  through  a  fissure  in  gran- 
odiorite,  and  at  the  base  of  a  basaltic  bluif  the  waters  have 
deposited  a  large  amount  of  siliceous  and  calcareous  sinter, 
some  of  which  is  colored  red  by  antimony  sulphide.  The  sin- 
ter from  one  of  the  springs  was  analyzed  by  Mr.  Melville,2  and 
his  results,  re-calculated  to  grams  per  kilogram,  showed : 


Grams  per  Kilogram. 

Ferric  oxide, 1.0263 

Antimonious  and  arsenious  sulphides,         ....  22.9298 

Mercuric  sulphide,     ........  0.0021 

Cupric  sulphide,         .         .......  0.0124 

Lead, 0.0211 

Gold 0.0010 

Silver, 0.0003 


The  relative  quantities  of  antimonious  and  arsenious  sul- 
phides are  not  given  in  the  above  analysis,  but  I  believe  that 
the  former  greatly  predominated. 

The  water  of  one  of  the  springs  was  also  analyzed  by  Mel- 
ville and  the  re-calculation  of  this  analysis  to  salts  that  were 
possibly  present  is  given  in  Table  I. 

*  Published  by  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 

1  Monograph  XIII. ,  U.  S.  Geological  Survey,  pp.  331-353. 

2  Op.  cit.,  p.  344  (Sample  II.). 


630       OCCURRENCE    OF    STIBNITE    AT    STEAMBOAT    SPRINGS,   NEVADA. 

TABLE  I. — Possible  Composition  of  the  Water  of  Steamboat 
Springs,  Prior  to  Oxidation? 

Grams  per  1 0  Liters. 

Ferrous  carbonate,  FeCO3,          .         .         .         .         .         .  0.0029 

Magnesium  carbonate,  MgCO3, 0.0099 

Calcic  carbonate,  CaCO3, 0. 1577 

Calcic  phosphate,  Ca3P2O8, 0.0137 

Potassic  chloride,  KC1, 1.9735 

Lithic  sulphate,  Li2SO4,      .        , 0.5650 

Sodic  chloride,  NaCl, 14.1475 

Sodic  sulphydrate,  NaHS, 0.0358 

Sodic  sulphate,  Na2SO4, .1.1147 

Sodic  bicarbonate,  NaHCO3, 2.9023 

Sodic  monocarbonate,  Na2CO3,  ......  0.4314 

Sodic  biborate,  Na2B4O7, 3.1368 

Sodic  tetrasilicate,  Na^Si^g,       , 8.9090 

Sodic  sulphantiraonide,  Na^SbSg, 0.0100 

Sodic  sulpharsenide,  Na2AsS3,   ......  0.0866 

Alumina,  A12O3,          ..        .         .         *'..-•         .         ,         »  0.0025 

Sodium-mercury  sulphide,  HgS,  wNa2S,     .         .         .         .  trace 

The  recalculation  given  in  Table  I.  is,  of  course,  only  of  very 
approximate  value,  since  it  is  not  known  with  certainty  in  what 
condition  the  different  acids  and  bases  are  present.  Moreover, 
the  salts  are  partly  dissociated.  Attention  should  be  called  to 
the  fact  that  the  water  contains  far  more  arsenic  than  antimony, 
but  during  its  nitration  a  red  precipitate  formed,  consisting  of 
arsenic  and  antimony  sulphides, — in  what  relative  amounts  the 
report  does  not  state. 

Having  assisted  Dr.  Becker  in  his  examinations  in  1885,  I 
naturally  felt  a  strong  interest  in  this  locality;  and,  in  1901,  I 
revisited  the  place  for  a  few  hours,  making  a  few  observations 
which  are  here  recorded. 

The  flow  of  water  from  the  springs  was  found  to  be  greatly 
reduced,  probably  on  account  of  clogging  of  the  channel.  Sev- 
eral bore-holes  had  been  sunk  in  order  to  obtain  a  better  flow, 
and  from  these  holes  fragments  of  quartz  had  been  brought  up 
which  were  said  to  assay  high  in  gold  and  silver.  Of  this  I 
know  nothing  except  from  hearsay;  but,  at  any  rate, these  results 
seern  to  have  stimulated  prospecting  activity,  for  a  shaft  had  re- 
cently been  sunk  to  a  depth  of  30  ft.  near  the  railway-station, 
on  the  sinter-flat  a  few  hundred  feet  away  from,  and  about  20 

3  Op.  cit.,  p.  347. 


OCCURRENCE    OF    STIBNITE    AT    STEAMBOAT    SPRINGS,  NEVADA-       631 

ft.  above,  Steamboat  creek,  which  is  the  main  drainage-line  of 
the  valley.  After  sinking  25  ft.  through  sinter,  a  loose  sandy 
gravel  was  struck  containing  well-washed  pebbles  of  granite 
and  andesite,  which  carried  so  great  an  abundance  of  hot  water 
as  to  lead  to  the  suspension  of  mining  operations.  The  gravel 
was  said  to  contain  small  quantities  of  gold  and  silver,  but  I 
am  not  prepared  to  discuss  this  aspect  of  the  case ;  moreover,  the 
assays  or  the  material  would  have  no  great  value  regarding  the 
derivation  of  the  gold  and  silver  if  found,  for  they  might  have 
been  introduced  in  different  ways.  A  sample  of  the  same  or 
similar  material,  transmitted  to  me  in  the  summer  of  1904  by 
Mr.  W.  H.  Weed,  was  assayed  and  yielded  a  trace  of  gold. 

Upon  examining  the  dump,  I  found  that  the  gravel  through- 
out contained  small  shining  prisms  and  particles  of  metallic 
luster.  A  generous  sample  of  the  material  was  collected,  but 
further  work  was  delayed,  until  1903,  when  an  examination  of 
the  sandy  part  of  the  gravel  showed  it  to  contain  a  consider- 
able quantity  of  stibnite,  in  the  form  of  loose  slender  prisms  of 
the  usual  type,  up  to  about  1mm.  in  length,  and  usually  with- 
out terminal  faces.  The  prisms  are  sometimes  bent  and  often 
combined  in  radiating  groups,  and  may  be  observed  adhering 
to  the  surface  of  nearly  every  pebble  of  the  gravel,  both  large 
and  small.  Some  of  the  larger  granite-cobbles,  which  usually 
are  soft  and  decomposed,  contain  bunches  of  stibnite  crystals 
in  cracks  and  crevices.  With  the  exception  of  clastic  magne- 
tite, the  only  other  metallic  mineral  found  in  the  gravel  is 
pyrite,  which  forms  loose  or  intergrown  crystals  of  octahedral 
form,  sometimes  combined  with  the  cube.  In  many  cases  both 
pyrite  and  stibnite  have  crystallized  on  the  surface  of  pebbles, 
the  former  often  being  tarnished  to  a  black  color.  Grains  of 
quartz  occur  with  the  pyrite,  but  they  are  not  clearly  crystallized 
and  may  be  clastic.  A  black  opaline  material  containing  about 
1  per  cent,  of  carbon,  according  to  Dr.  E.  T.  Allen,  of  the 
U.  S.  Geological  Survey,  sometimes  adheres  to  the  andesite 
pebbles. 

In  order  to  obtain  an  idea  of  quantitative  relationships,  the 
sandy  part  of  the  gravel  was  further  examined  by  Dr.  E.  T. 
Allen,  who  found  that  lead,  copper,  zinc  and  mercury  were 
absent,  and  that  the  material  contained  antimony,  0.4,  arsenic, 
0.067,  and  sulphur,  1.88  per  cent.,  which  corresponds  to  stib- 


632       OCCURRENCE    OF    STIBNITE    AT    STEAMBOAT    SPRINGS,  NEVADA. 

nite  (Sb2S3),  0.56;  orpiment,  (As2S3),  0.107;  and  pyrite  (FeS2), 
3.13  per  cent. 

It  is  not  certain  in  what  form  the  arsenic  is  present.  Stib- 
nite  does  not  usually  contain  arsenic,  and,  on  the  other  hand, 
no  separate  arsenical  mineral  could  be  recognized. 

That  stibnite  and  pyrite  could  be  of  clastic  origin  is  entirely 
out  of  the  question,  and  I  believe  it  absolutely  certain  that  they 
have  been  deposited  by  the  hot  waters  which  permeate  the 
gravel.  Considering  that  the  waters  have  been  shown  to  con- 
tain a  considerable  quantity  of  antimony,  the  occurrence  seems 
of  great  interest. 

No  metallic  sulphides,  corresponding  in  appearance  to  the 
normal  minerals,  were  found  by  Dr.  Becker  in  the  sinters,  but 
cinnabar  occurs  disseminated  in  the  decomposed  granite,  some 
distance  away  from  the  present  springs.  The  antimonious  sul- 
phide, which  colors  parts  of  the  sinter  and  always  appears  red 
and  amorphous,  was  called  metastibnite  by  Dr.  Becker.  The 
absence  of  ordinary  minerals  of  metallic  luster  indicated,  in  a 
way,  a  missing  link  in  the  chain  of  evidence  to  prove  the  dep- 
osition of  ores  from  hot  ascending  waters ;  and  this  link  is  now 
supplied  by  the  observations  recorded  above. 

Physical  conditions  differing  very  slightly  from  those  at  the 
actual  surface  will  evidently  produce  crystallized  minerals  of 
normal  habit  and  form.  Many  years  ago  Senarmont  succeeded 
in  forming  crystals  of  stibnite  from  the  amorphous  sulphide  by 
heating  it  to  250°  C.  in  a  closed  tube  with  a  solution  of  sodium 
carbonate. 

During  the  investigation  of  the  quicksilver-deposits  of  the 
Pacific  slope,  Messrs.  Becker  and  Melville  found  that  stibnite  is 
easily  crystallized  from  solutions  similar  to  the  waters  of  Steam- 
boat Springs  in  sealed  tubes  heated  to  about  150°  C.  This 
renders  it  probable  that  a  moderate  pressure,  such  as  exists  at 
a  small  distance  below  the  surface,  is  sufficient  to  induce  the 
formation  of  the  crystals  described  in  this  paper.  Very  likely, 
also,  the  presence  of  organic  matter  in  the  gravel  is  one  of  the 
conditions  favoring  such  deposition. 

Many  important  deposits  of  stibnite  occur  in  sedimentary 
rocks  in  a  manner  which  renders  very  probable  a  genesis  some- 
what similar  to  that  of  the  occurrence  here  described. 


GEOLOGY    OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.         633 


No.  25. 


A  Summary  of  Lake  Superior  Geology  with  Special  Refer- 
ence to  Recent  Studies  of  the  Iron-Bearing  Series.* 

BY  C.  K.  LEITH,  MADISON,  WIS. 
(Lake  Superior  Meeting,  September,  1904.     Trans.,  xxxvi.,  101.) 

GENERAL  GEOLOGY  OF  THE  LAKE  SUPERIOR  IRON-BEARING  AND 
COPPER-BEARING  SERIES. 

********** 

The  ores  of  the  region  are  contained  in  rocks  of  pre-Cam- 
brian  age,  which,  for  most  of  the  country  up  to  recent  years, 
have  usually  been  referred  to  as  "  crystalline  schists  "  or  "  crys- 
talline complex;"  and  regarded  principally  as  a  metamorphosed 
basement-unit  upon  which  the  sedimentary  rocks,  beginning 
with  the  Paleozoic,  were  laid  down.  In  the  Lake  Superior  re- 
gion this  pre-Cambrian  complex  presents  an  unusual  variety  of 
rocks  with  determinate  relations.  It  has  been  possible,  with 
the  large  expenditures  which  the  magnitude  of  the  iron-mining 
industry  warrants,  to  work  out  their  stratigraphy  to  a  larger 
degree  than  has  been  possible  in  almost  any  other  area  of  pre- 
Cambrian  rocks. 

********** 

[The  portion  here  omitted  contains  descriptions  of  the  Archean,  Algonkian,  and 
Keweenawan  rocks  of  the  several  districts,  their  structure,  distribution,  correlation, 
and  succession.  Table  I.  and  the  geological  map  of  the  Lake  Superior  region  be- 
long to  this  portion,  but  are  here  reproduced  on  account  of  their  value  as  guides 
to  the  readers  of  the  rest  of  the  paper.] 

The  simplest  and  clearest  conception  of  the  pre-Cambrian 
succession  for  the  Lake  Superior  region  may  perhaps  be  ob- 
tained by  thinking  of  it  as  primarily  divided  into  six  series — 
Keweenawan,  Upper  Huronian,  Middle  Huronian,  Lower  Hu- 
ronian,  Keewatin,  and  Laurentian — all  but  the  last  two  sepa- 
rated by  unconformities  of  varying  and  disputed  relative  im- 

*  Published  by  permission  of  the  Director  of  the  United  States  Geological 
Survey.  Reprinted  here  in  part  only. 

40 


634  GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

TABLE  I. — Correlation  of  Pre-  Cambrian 


Mesabi  District. 

Penokee-Gogebic 
District. 

Vermilion 
District. 

Marquette 
District. 

KEWEENAWAN. 
(Copper  -bear- 
ing.) 

Great  basal  gab- 
bro  and  gran- 
ite. 

Gabbros,       dia- 
bases, etc. 

Great  gabbro. 

Upper  Marquette  : 
Michiga  m  m  e 

formation 

(slate)  (local- 

ly   replaced 

by      Clarks- 

ALGONKIAN. 

UPPER   HURON- 
IAN. 
(Iron-bearing.) 

Mesabi  Series  : 
Virginia     for- 
mation   (up- 
per slate). 
Biwabik      for- 
mation (iron- 
bearing  and 
productive). 
Pok  egam  a 
formation 
(quartzite 
and    quartz- 
slate). 

Penokee-  Gogebic 
Series: 
Tyler      forma- 
tion    (upper 
slate). 
Iron  wood  for- 
mation (iron- 
bearing  and 
productive}. 
Palms    forma- 
tion (quartz- 
slate). 

A  nimikie  Series  : 
Upper  slate 
formation. 
Gunflint      for- 
mation (iron- 
bearing,  but 
non  -  produc- 
tive). 

burg    v  o  1- 
canic  forma- 
tion).     Con- 
tains produc- 
tive iron-ores 
near  base. 
Ishpeming  for- 
mation, con- 
sisting of  two 
memb  ers: 
Bijiki  schist 
(in    western 
part   of  dis- 
trict) and  the 

Goo  drich 

quartzite 

containing 

productive 

detrital  ores 

at  its  base. 

Middle  Marquette: 

Negaunee  for- 

MIDDLE HURON- 

mation  (iron- 
bearing  and 

(Iron-bearing.) 

productive). 
Siamo  slate. 

Ajibik  quartz- 

ite. 

Intrusives. 

Granite     intru- 

Knife slate. 

LOWER  HURON- 
IAN. 

sive  in  lower 
formations. 
Slate-  gray- 
wacke-con- 

Bad  River  lime- 
stone    forma- 
tion (cherty 
limestone)  . 

Agawa     forma-  Lower  Marqnette  : 
tion   (iron-      We  we  slate, 
bearing,     but  j    Kona  dolomite, 
non  -  produc-      Mesnard 

glomerate  for- 
mation. 

Quartzite. 

tive).                               quartzite.  , 
Ogishke  con- 

glomerate. 

LAURENTIAN. 
(Intrusive    into 
Keewatin.) 

Granites      and 
porphyries. 

Granite    and 
gra  nito  i  d 
gneiss. 

Intrusive  gran- 
ites,   porphy- 
ries and  green- 
stones. 

Granite,  sye- 
nite. 
Palmer  gneiss. 

Kit  chi  schist 

ARCHEAN  or 
BASEMENT 
COMPLEX. 

KEEWATIN. 
(Iron-bearing.) 

Greenstones, 
hornblende- 
schists     and 
porphyries. 

Green      schists 
and     f  i  n  e- 
grained  gneiss. 

Soudan    forma- 
t  i  o  n   (i  r  o  n- 
bearing     and 
productive). 
Ely  greenstone, 
an     ellipsoid- 
ally-parted 
basic  igneous 
and  largely 
volcanic  rock. 

and    M  o  n  a 
schist,  the  lat- 
ter banded, 
and  in  a  few 
places    con- 
taining    nar- 
row bands  of 
non  -  produc- 
t  i  v  e   i  r  o  n- 
bearing      for- 
mation. 

Peridotite. 

GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          635 

Series  of  the  Lake  Superior  Region. 


Other   Parts   of 

Crystal  Falls 
District. 

Menominee 
District. 

Keweenaw 
Point. 

Michipicoten. 

Ontario  North 
of  Lake  Supe- 
rior. 

Lower,    Middle 

and  Upper 
Keweenawan. 
Interbedded 
lavas  and  sed- 
iments grad- 
ing up  into 

Interbedded 
sediments  and 
traps   along 
Lake  Superior 
•     shore. 

sandstones. 

Upper  Menominee: 

Hanbury      forma- 

tion,   mainly 

slate,  bearing  in 

Michigamme 
formation.con- 
taining  a  pro- 
ductive iron- 
bearing  hori- 
zon not  sepa- 
rated in  map- 
ping for  much 
of  the  district. 

lower      portions 
calcareous 
slates,  etc.,  con- 
taining   siderite 
and  iron  oxide. 
Vulcan  formation, 
consisting    of 
three  members  : 
Curry    member 
(iron  -  bearing), 

Animikie  series 
of   northwest 
shore  compris- 
ing    iron  -for- 
mation   over- 
lain by  slate. 

Brier  slate   and 

Traders  mem- 

ber    (iron-bear- 

ing). 

Hemlock  forma- 
tion (basic  vol- 
canic). 
Negaunee     for- 
mation   (iron- 
bearing). 

Negaunee      forma- 
tion     doubtfully 
present. 

1 

Undivided  pre- 
Animikie 
sediments, 

mainly  gray- 

^    w  a  c  k  e  s, 
r     slates  and 

conglomer- 

Randville  dolo- 
mite. 
Sturgeon  quartz- 
ite. 

Lower  Menominee  : 
Randville  dolo- 
mite. 
Sturgeon    quartz- 
ite. 

Basic  eruptives. 
Acid  eruptives. 
Don*    conglom- 
erate. 

ates,  much 
m  e  t  a  m  o  r- 
phosed. 

Granite. 

Granites    and 
gneisses. 

Granites      and 
gneisses. 

Granites      and 
gneisses. 

Eleanor  slates. 

Helen  forma- 

Greenstone and 

tion      (i  r  o  n- 

Iron  formation, 

Quinnesec  schist.  (?) 

bearing     and 
productive). 
Wawa  tuffs. 

similar  10  that 
of   Vermilion 
district     of 

Gros  Cap  green- 

Minnesota. 

stones. 

636 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 


This  sketch-map  of  the  geology  of  the  Lake  Superior  region  is  generalized  and 
modified  from  a  general  geological  map  of  the  Lake  Superior  region,  on  a  scale 
of  ten  inches  to  the  mile,  compiled  by  C.  E.  Van  Hise  and  C.  K.  Leith  for  publi- 
cation in  a  final  general  monograph  on  Lake  Superior  geology  in  preparation  for 
the  IT,  S.  Geological  Survey. 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.         637 

portance,  and  with  age-values  not  yet  decided.  These  series 
may  then  be  grouped  under  the  two  terms,  Algonkian  and 
Archean,  thereby  expressing  our  opinion  that  the  unconformity 
at  the  base  of  the  Huronian,  in  connection  with  difference  in 
lithological  characters  above  and  below  this  horizon,  should  be 
singled  out  for  special  emphasis.  If  we  believe,  as  Lawson  does, 
that  the  essential  break  is  at  the  base  of  the  Upper  Huronian 
series,  his  "  Eparchean  interval,"  then  we  should  express  our 
view,  as  he  has  done,  by  grouping  all  of  the  rocks  beneath  this 
unconformity  under  one  major  heading. 

Since  the  manuscript  of  this  paper  was  written,  the  joint 
committee  of  the  Canadian  and  United  States  Geological  Sur- 
veys, appointed  to  reach  an  agreement  on  disputed  points  of 
correlation  and  nomenclature,  has  completed  its  report,  and 
recommends  this  nomenclature,  without  expressing  opinion  as 
to  the  desirability  of  a  major  grouping  of  the  series  under 
Archean  and  Algonkian.  It  is  agreed  further,  in  recognition 
of  the  difficulties  of  mapping  broad  granitic  and  gneissic  areas 
in  Canada,  that  the  term  Laurentiaii  may  sometimes  be  applied 
to  areas  of  such  rocks  which  locally  may  be  known  to  be  pre- 
Huronian,  but  which  for  the  most  part  may  be  of  unknown  age. 

THE  IRON-ORES. 
Nature,  Occurrence,  Relations  to  Adjacent  Rocks,  Origin. 

A  general  summary  of  the  work  of  the  U.  S.  Geological 
Survey  on  the  iron-ores  of  the  Lake  Superior  region  is  given 
by  Van  Hise.11  The  present  summary  covers  much  of  the  same 
ground,  but  includes  also  developments  subsequent  to  the  pub- 
lication of  his  report. 

The  iron-ores  of  the  Lake  Superior  region  occur  as  concen- 
trations in  "  iron-formations,"  ranging  from  a  few  hundred  to 
1,000  ft.  or  more  in  thickness.  These  formations,  in  their  pres- 
ent form,  represent  the  alterations  of  chemically  deposited  sedi- 
ments, for  the  most  part  interbedded  with  normal  clastic  sedi- 
ments, such  as  slate  and  quartzite. 

Because  of  the  definite  stratigraphical  position  of  the  iron- 
ores,  in  contrast  to  many  vein-deposits,  the  mapping  and  inter- 
pretation of  the  general  geology  of  the  region  has  been  found 
to  be  of  direct  and  practical  value  to  the  mining-industry,  thus 

11  21st  Annual  Report  of  the  U.  S.  Geological  Survey. 


638         GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

explaining  the  large  expenditures  by  mining-interests  on  geo- 
logical work. 

In  the  Vermilion  and  Michipicoten  districts  the  productive 
iron-formation  is  in  the  Keewatin  division  of  the  Archean.  In 
the  Mesabi  and  Gogebic  districts  the  iron-formation  is  a  part  of 
the  Upper  Huronian  series.  In  the  Marquette  district  two  pro- 
ductive iron-formations  are  present,  one  in  the  Middle  Huro- 
nian and  another  in  the  Upper  Huronian,  the  former  being  the 
more  important.  In  the  Crystal  Falls  district  the  iron-forma- 
tion is  in  both  Upper  Huronian  and  Lower  Huronian  series, 
the  former  being  the  principal  producer.  In  the  Menominee 
district  the  formation  is  of  Upper  Huronian  age. 

The  iron-formations  of  the  different  districts  and  ages  are 
surprisingly  similar  in  their  general  characters.  Indeed,  it  was 
long  assumed,  erroneously,  that  because  of  their  similarity  they 
must  be  of  the  same  age  and  origin.  A  single  description  will 
therefore  suffice  for  them  all. 

The  iron-formation  consists  mainly  of  chert  or  quartz,  and 
ferric  oxide,  segregated  in  bands  or  shots,  or  mingled  irregu- 
larly. Where  in  bands,  with  the  quartz  bands  colored  red  and 
the  rock  highly  crystalline,  it  is  called  jasper.  Where  less  crys- 
talline and  either  in  bands  or  irregularly  intermingled,  the  rock 
is  known  as  ferruginous  chert.  In  the  Mesabi  district  the  local 
name  "  taconite  "  is  applied  to  the  ferruginous  chert.  Other 
phases  of  the  iron-formation  subordinate  in  quantity  are,  (1)  or- 
dinary clay  slates,  showing  every  possible  gradation  through 
ferruginous  slate  into  ferruginous  chert;  (2)  paint-rocks,  altered 
equivalents  of  the  slates;  (3)  amphibole-magnetite  schists;  (4) 
cherty  iron  carbonate  (siderite)  and  hydrous  ferrous  silicate 
(greenalite) ;  (5)  the  iron-ores  themselves. 

It  may  be  emphasized  that  almost  the  entire  bulk  of  the  iron- 
formation  now  consists  of  iron  oxide  and  silica,  with  carbonates 
and  alumina  present  in  subordinate  quantity.  The  varying 
combination  of  part  or  all  of  these  constituents,  mechanically, 
or  chemically,  or  both,  gives  all  of  the  rock-types  above  listed. 

A  series  of  cross-sections,  Figs.  1,  2,  3  and  4,  summarizes 
better  than  a  description  the  structural  relations  of  the  ores  to 
the  adjacent  rocks  in  the  different  districts  and  formations. 

It  has  been  shown  that  the  ferruginous  cherts,  jaspers,  am- 
phibole-magnetite schists,  and  iron-ores  of  the  iron-formation 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 


639 


result  from  the  alteration  either  of  the  cherty  iron  carbonate  or 
of  ferrous  silicate  (greenalite),  or,  to  a  minute  extent,  from  iron 
sulphide.  The  small  amounts  of  iron  carbonate  or  ferrous  sili- 
cate now  found  in  the  formations  represent  mere  remnants  left 


FIG.  1. — GENERALIZED  VERTICAL  SECTION  IN  MARQUETTE  DISTRICT,  MICHIGAN, 
SHOWING  KELATION  OF  DIFFERENT  CLASSES  OF  ORE-DEPOSITS  TO  ASSO- 
CIATED FORMATIONS. 

unaltered  where  so  protected  by  other  rocks  as  not  to  have  been 
affected  by  altering  agents.  The  steps  of  the  alteration  may  be 
observed,  and,  in  the  end-products,  the  structures  and  textures 


FIG.  2. — GENERALIZED  VERTICAL  SECTION  THROUGH  PENOKEE-GOGEBIC  ORE- 
DEPOSIT  AND  ADJACENT  ROCKS  ;  COLBY  MINE,  BESSEMER,  MICH. 

of  the  original  rocks  are  often  preserved  to  a  remarkable  de- 
gree. The  chemistry  of  the  change  is  summarized  in  Table  II. 
Let  it  be  emphasized  that  the  ores  and  ferruginous  cherts  or 
jaspers  and  the  amphibole-schists  represent  alterations  from  the 


640          GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

sam  e  original  types.    There  is  a  prevailing  notion  that  the  orig- 
nal  source  of  the  ores  is  the  jaspers  or  ferruginous  cherts  them- 


FIG.  3. — GENERALIZED  VERTICAL  SECTION  THROUGH  MESABI  ORE-DEPOSIT 
AND  ADJACENT  ROCKS. 

selves,  in  their  present  form.     While  the  leaching  out  of  silica 
from  such  rocks  does  yield  ore  in  many  cases,  it  is  believed  that 


SHAFT  NO.  2 

Jg^/M 

mm 


FIG.  4.— VERTICAL  SECTION  THROUGH  ORE-DEPOSIT  AND  ADJACENT  ROCKS 
OF  VERMILION  IRON  RANGE  ;  CHANDLER  MINE,  ELY,  MINN. 

ores  and  jaspers,  often  of  the  largest  deposits,  develop  side  by 
side  contemporaneously  from  the  alteration  of  iron  carbonates, 
or  iron  silicates. 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          641 

The  agent  of  the  alteration  is  water,  coming  more  or  less 
directly  from  the  surface,  carrying  oxygen  and  carbon  dioxide. 
The  concentration  of  the  ores  has  been  found  to  occur  where 
such  waters  have  been  converged.  Various  factors  have  de- 
termined this  convergence — fracturing  and  brecciation  of  the 
iron-formation,  existence  of  impervious  layers  in  such  attitudes 
as  either  to  converge  waters  coming  from  above  or  to  impound 
the  waters  and  deflect  their  course  between  two  layers.  The 
presence  of  an  impervious  layer,  forming  a  pitching-trough,  is 
perhaps  the  most  conspicuous  structural  feature  determining 
the  convergence  of  waters  concentrating  the  ores.  The  imper- 
vious troughs  consist,  in  the  Mesabi  district,  of  slate  or  paint- 
rock  layers  writhin  the  formation  itself;  in  the  Vermilion  dis- 
trict, of  greenstone  with  which  the  iron-formation  is  infolded 
or  interbedded ;  in  the  Penokee-Gogebic  district,  of  the  inter- 
section of  diorite  dikes  with  a  foot-wall  quartzite;  in  the  Mar- 
quette  district,  of  a  greenstone  intrusive  into  the  iron-formation, 
or  of  a  slate  underlying  the  iron-formation ;  in  the  Menominee 
district,  of  dolomite  underlying  the  iron-formation  or  of  slate 
layers  within  the  formation  itself.  In  all  these  districts,  except 
the  Mesabi,  the  presence  of  this  impervious  basement  seems  to 
be  clearly  the  controlling  factor  in  the  convergence  of  waters 
which  have  concentrated  the  ores. 

In  the  Mesabi  district,  also,  impervious  troughs  may  be  im- 
portant, but  they  probably  are  subordinate  to,  or,  at  least,  not 
more  important  than,  other  factors.  The  iron-formation  and 
its  associated  rocks  lie  in  beds  on  the  south  slope  of  the  Giant's 
range,  and  dip  off  gently  to  the  south  at  angles  averaging  from 
8°  to  10°.  In  addition  to  the  general  southward  tilting  of  the 
beds,  they  are  gently  flexed  into  folds  with  axes  transverse  to 
the  trend  of  the  range.  Waters  falling  on  the  south  slope  of 
the  Giant's  range,  and  flowing  to  the  south,  enter  the  eroded 
edges  of  the  iron-formation  and  continue  their  way  down  along 
its  layers,  some  of  which  are  pervious  and  some  of  which  are 
slaty  and  comparatively  impervious  to  water.  The  flow  thus 
tends  to  become  concentrated  along  the  axes  of  the  synclines 
which  pitch  gently  to  the  southward.  Such  synclines  are  not 
necessarily  surface-troughs.  They  are  evidenced  by  the  atti- 
tude of  the  layers  of  the  iron-formation,  and  may  not  be  ap- 
parent in  the  unequally-eroded  rock-surface  or  at  the  surface 


642        GEOLOGY    OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 


ORIGINAL  ROCKS 


TABLE  II. —  Origin  and  Development  of  the 

(Prepared  for  the  St.  Louis  Exposition  by  C.  R. 
CHEMICAL  ALTERATIONS 


/Th 


rThe  original  rocke  from  which  the  Iron  orfs  have 
I  developed  wen  deposited  ID  sedimentary  "iron  fc 
/  aliens"  (in  general  In  rather  massive  beds,  bat  In 
/  part  slaty),  the  Iron  of  which  was  probably  derived 
/  largely  from  the  more  ancient  ba*lc  volcanic  rocki 
j  of  the  Lake  Superior  region.  The  iron  formation* 

are  underlain  and  overlain  by  sedimentary  formation* 
I      which  are  relatively  Impcrriong  to 
\      qnartzite  and  slate;  also  in  part  by  Keweenawan 
\    gabbro.    They  are  cat  by  intrusive  rocks  of  varton* 
\  kinds,  and  cbaracterUtlcally  folded  and  metamor- 

V 


CO,  liberated. 

FeO  uniting  with  310,,  and  prodneing- 
Oranerite  (FeO.  3iO,) 
Fayallte   (2FeO.  SIO,) 

Fe,  Mg,  Ca,  etc.,  uniting  with  SiO,,  and  producing- 
Cnmmlngtonite    (FeMg)SiO, 
Chrysolite  (MgFe),SiO, 

Hornblende 
Actinolite  (CaMgFe)SiO 

FeO  partially  oxidized,  and  producing- 

Magnetite  (FeO.  Fe,O,)  (This  occurs  exten- 
sively where  Iron  formation  has  been  affect- 
ed by  Keweenawan  gabbro  intrusion). 

Where  FeS,  (pyrite)  is  originally  present  in  aband- 
pyrite  is  found  In  resulting  rocks. 


•CHEKTT  IRON  CARBONATE.    (FeCO,,  with  CaCO,.  and  SIO,) 


Locality 

Age 

Vermilion       District,  Minn. 
Michiplcoten         ••       Ontario 
Marqnette             "       Mich. 
Penokee-Qogebic  "        Wle.  and  Mich. 
Menominee            "       Mich. 
Crystal  Fall  

Archean 

Algonkian  —  Lower  Huron 
Upper       " 

FERROUS  SILICATE  ROCK. 

(FeSiO,nH,0,  with  Mg  and  other  impurities. 


ilesabi  Diotrict,  Ml! 


Ugonsian-Cpper 


PYRITIC  CARBONATE  ROCK. 

(FeS,  disseminated  through  carbonate  Iron  formation 
of  very  subordinate  importance). 


1  Vermilion  District,   Minn. 
Mlcbiplcoren  District,  Ontario 

Archean 

Partial  oxidation 


formation  of  silicates; 
and  removal  of  / 

carbon  dioxide.  / 


'Oxidation  of  ferrons\ 
iron;  separation  \ 

t  silica;  and  removal  ) 
of  carbon  diox 


«"/ 


I.    CHERTY   IRON  CARBONATE. 

(1)  3FeOO,  4- SiO,  4- O  4- nH,0  = 
Fe,0,nH,0  +  SiO,  +  2CO, 

(8)  2FeCO,  4- SiO,  4- O  4- nH,0  = 
Fe,03  4-  SiO,  4-  2CO,  -r  nH,O 
SFeOO,  4-  SIO,  4-  2O  4-  nH.O  = 
Fe,O,  4-  Fe,04  4-  SiO,  4-  SCO,  +  uH,0 

II.     FERROUS  SILICATE  ROCK. 

Fe8iO,nH,0  +  CO,  +  nH,O  = 
FeCO,  +  H48iO.  +  nH,O 

2FeC03  4-  O  4-  nH,O  = 
Fe,O,nH,0  4-  SCO, 

Also  reactions  analogous  to  (8)  and  (8) 

above. 

III.    PYRITIC  CARBONATE  ROCKS. 

FeCO,  4-  FeS,  +  SiO,  4-  6O  4-  »H,O  = 

Fe,O, .  nH,O  4-  SiO,  4-  2SO,  4-  CO, 
Also  reactions  analogous  to  (2)  and  (3) 
above. 


GEOLOGY  OF  LAKE  SUPERIOR  IRON-BEARING  SERIES. 


643 


Iron-  Ores  of  the  Lake  Superior  Region. 

Van  Hise,  C.  K.  Leith  and  W.  N.  Smith.) 

RESULTING    PRODUCTS 


.MPHIBOLITIC  -  MAGNETITIC  BOCKS. 
•YROXENIC  -  CHRTSOLITIC  -  MAGNETITIC  ROCKS, 


d 


JASPrLITE-"  Hard  Ore  Jasper." 


(Produced  by  dehydration  and  rccrystalllzatlon  ] 
of  ferruginous  cherts  and  ferruginous  elites 
probably  under  conditions  of  deep  burial, 
Igneous  Intrusion.) 


/  rn?*Ti 


FERRUGINOUS  CHERTS. 

(Produced  by  alteration  of  more  massive 
bedded  phases  of  iron  formation.) 

I   From  Cherty  Iron  Carbonate.    ("  Soft  Ore  Jasper.") 
II    From  Ferrous  Silicate  Rock.    ("Taconlte.") 

FERRUGINOUS  SLATES. 

(Produced  by  alteration  of  slaty 
phases  of  Iron  formation.) 


'IRON  ORES,  HARD. 

Produced  by  farther  metamorphism 
of  the  soft  on 

cherts  by  processes  which  include 
dehydration,  derillclficBtion,  and 
enrichment  by  lofllitratlon,   prob- 
ably nnder  conditions  of  deep 
burial,  dynamic  action,  or  ig- 
neous Intrusion,  or  any  combina- 
tion of  them. 

Blue  non-bydrated  hematite. 
Red  non-hydrated  hematite. 
Micaceous  or  specnlar  non- 

hydrated  hematite. 
Magnetite.. 

• 

Produced    nnder  weathering  conditions 
by  oxidation  of  magnetite  to  hematite. 


f  IRON  ORES,   SOFT. 

Soft  Hydrated  Hematite  or  Liraonite. 
Hard  Hydrated  HeraaUw. 


DETRITAL  IRON  ORES. 

(Formed  by  breaking  up  through  wavt 
action  of  pre-existing  ores  or 
ferruginous  cherts  and  jaspers.  In 
the  latter  case  often  Involving 
concentration  by  assorting,  by 
leaching  oat  of  silica,  and  by 
subsequent  enrichment.) 
Detrltal  ore  (conglomerate  ore)  from 

base  of  Upper  Huronian.    Sediment 
formed  from  pre-existing  ferrug- 
inous chert  or  jasper  which  bas 
been  subsequently  deeilicified  and 
enriched. 

Oetrital  ore  from  Menominee  district. 

Mich.,  from  base  of  Upper  Huronian. 
Sediment  formed  directly  from  pre- 
existing ores. 

Detrital  ore  from  Menominee  district. 

Mich.,  from  base  of  Cambrian. 
Produced  by  breaking  up  of  pre- 


644          GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

of  the  irregular  covering  of  glacial  drift.  The  concentration  of 
the  flow  along  the  synclines  in  the  layers  of  the  iron-formation 
seems  so  simple  and  evident  that  there  is  a  temptation  to  gen- 
eralize and  say  that  the  underground  circulation  has  prohably 
concentrated  the  ores  along  these  broad  synclines.  When  the 
district  was  first  examined  by  the  U.  S.  Geological  Survey  this 
simple  explanation  was  applied.  But  further  study  shows  that 
other  factors  modify  the  circulation  of  water  and  the  localiza- 
tion of  the  ore,  and  that  these  secondary  factors  may  be  locally 
dominant. 

The  most  important  of  these  modifying  factors  is  the  fractur- 
ing of  the  iron-formation,  which  has  furnished  numerous  trunk- 
channels  for  the  circulation  of  underground-waters.  The  water 
has  been  confined  to  narrow,  irregular  and  most  devious  trunk- 
channels  formed  by  the  fracturing  of  the  iron-formation,  and, 
while  it  has  probably  followed  the  fracture-openings  along  syn- 
clines to  a  greater  extent  than  along  anticlines,  it  has  not  filled 
the  entire  syncline  formed  by  the  folding  of  the  iron-formation. 
The  result  is  that  the  ores  have  developed  along  limited  and 
irregular  areas  within  the  synclines.  They  may  occupy  a  con- 
siderable part  of  the  syncline,  in  which  case  the  synclinal  struc- 
ture of  the  iron-formation  may  be  observed  in  the  layers  of 
wall-rock  adjacent  to  the  ores.  In  other  cases,  they  occupy 
so  small  a  proportion  of  the  syncline  that  the  layers  of  the 
iron-formation  in  the  adjacent  wall-rock  give  no  indication  of 
synclinal  dips.  Not  infrequently,  several  more  or  less  inde- 
pendent deposits  may  have  developed  in  the  same  general 
syncline,  as,  for  instance,  in  the  area  adjacent  to  the  town  of 
Virginia.  To  put  it  briefly,  the  ores  show  such  position,  irreg- 
ularity, extent,  and  relations  to  wall-rocks  as  to  make  applica- 
ble the  expression  sometimes  heard  in  the  district  that  the  ores 
have  developed  through  the  "  rotting "  of  the  iron-formation 
along  fractures,  usually,  but  not  always,  in  broad  synclinal 
areas. 

Other  factors  modifying  the  general  underground-flow  ot 
water  in  the  Mesabi  iron-formation  are  the  numerous  impervi- 
ous slaty  layers  within  the  iron-formation,  and  the  Virginia 
slate  capping  the  iron-formation  of  the  south ;  all  of  which  have 
considerable  effect.  So  far  as  the  water  is  free  to  flowT  south- 
ward through  the  iron-formation,  the  impervious  layers  serve 


GEOLOGY  OF    LAKE    SUPERIOR    IROX-BEARING    SERIES.          645 

only  to  limit  the  flow  below.  But  the  continuous  south  dip 
of  the  impervious  strata  carries  the  waters  down  to  a  point 
when  the  ground  is  saturated  and  the  waters  are  ponded  be- 
tween impervious  layers  above  and  below.  That  ponding  actu- 
ally occurs  is  shown  by  the  fact  that  drill-holes  penetrating 
the  slates  and  entering  the  iron-formation  frequently  meet 
water  under  pressure,  indicating  artesian  conditions.  When 
ponded,  the  water  seeks  the  lowest  point  of  escape,  which 
is  likely  to  be  found  near  the  north  margin  of  the  slate-layers. 
The  movement  of  the  water  towards  the  lowest  point  of  escape 
causes  a  considerable  lateral  movement  in  the  circulation,  and 
this  lateral  movement  has  probably,  at  least  in  part,  controlled 
the  shape  of  certain  deposits  on  the  range,  which  have  their 
longer  dimensions  parallel  to  the  strike  of  the  layers  of  the 
iron-formation. 

The  ponding  of  the  water  and  consequent  overflow  has  still 
another  effect.  Where  ponded  the  flow  is  governed  by  the 
point  of  lowest  escape  rather  than  by  the  shape  of  the  impervi- 
ous basement.  When  water  is  drawn  off  at  the  edge  of  a  basin, 
the  flow  is  greatest  near  the  point  of  escape  and  diminishes  in 
all  directions  away  from  that  point.  This  statement  is  true, 
whether  the  bottom  of  the  basin  is  flat  or  fluted ;  hence,  in  the 
Mesabi  iron-formation,  where  the  water  is  ponded,  the  flow  is 
concentrated  near  the  point  of  lowest  escape  regardless  of 
whether  this  be  over  a  syncline  or  anticline  provided  both  are 
below  water-level.  The  lowest  point  of  escape  is  likely  to  be 
over  synclines,  but  the  surface  erosion,  both  by  glacial'  and  me- 
teoric agencies,  has  been  such  that  this  is  not  always  the  case. 
For  this  reason  it  is  not  certain  that  iron-ore  deposits  near  the 
edge  of  the  Virginia  slate  or  near  the  edge  of  interstratified 
slate-layers  may  not  have  developed  along  arches  as  well  as  in 
synclines  of  the  iron-formation. 

The  above  facts  are  intimately  related  to  the  problem  of 
finding  ore  under  the  solid  black  Virginia  slate.  The  ques- 
tion is  frequently  asked,  is  there  any  reason  why  ore  shall  not 
be  found  under  the  black  slate?  The  absence  of  ore  under 
the  slate  has  not  been  demonstrated  by  actual  drilling;  only  a 
comparatively  few  holes  have  penetrated  any  considerable 
thickness  of  the  Virginia  slate  and  entered  the  iron-formation 
below.  Yet  such  holes  as  have  been  put  down  have  revealed 


646          GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

ore  only  near  the  slate-margin  and  frequently  of  low-grade. 
In  several  cases,  the  iron-formation  beneath  the  slate  has  been 
shown  to  be  of  a  green,  unaltered  variety,  indicating  that  the 
alteration  necessary  for  the  development  of  ore-deposits  has  not 
gone  far.  If  the  development  of  the  ore  is  dependent  upon  a 
vigorous  circulation,  and  this  vigorous  circulation  is  lacking 
under  the  Virginia  slate  because  of  the  ponding,  we  have  here 
an  adequate  cause  for  the  non-existence  of  ore-deposits  under 
the  black  slate.  Yet,  further  work  may  show  that  other  factors 
have  entered;  and,  considering  the  extent  and  value  of  the 
new  iron-bearing  territory,  which  would  be  thrown  open  were 
ore  found  under  the  Virginia  slate,  additional  actual  drilling 
seems  to  be  advisable. 

In  the  Gogebic  district,  while  the  impervious  basement  has 
been  the  controlling  factor  in  the  concentration  of  waters,  and 
consequently  of  the  ores,  faulting  through  the  dikes  has  afforded 
free  passages  for  waters  which  have  been  taken  advantage  of, 
with  the  result  that  the  ores  follow  such  faulting-planes  and  are 
not  uniformly  confined  to  positions  on  the  impervious  troughs. 

In  Figs.  1,  2,  3  and  4,  it  will  be  noted  that,  for  all  of  the  dis- 
tricts except  the  Mesabi,  the  vertical  element  in  the  distribution 
of  the  ores  is  an  important  one.  In  the  Mesabi  district  the 
horizontal  element  is  the  greatest  one  in  most  cases.  Here,  a 
single  ore-body  or  a  group  of  ore-deposits  may  give  practically 
a  continuous  surface  of  iron-ore  for  several  miles,  with  a  depth 
ranging  from  a  few  feet  to  400  ft.  or  more.  In  the  other  ranges 
a  depth  of  ore  of  1,000  ft.  is  common  and  2,000  ft.  has  been 
exceptionally  reached.  It  is  not  unlikely  that  in  some  places, 
particularly  the  Gogebic  district,  the  ores  will  be  found  to 
greater  depth,  although  the  lower  limit  is  well  determined  for 
the  most  part.  Theoretically,  the  lower  limit  of  the  ore-bodies 
ought  to  be  the  lower  limit  of  the  active  circulation  of  oxidiz- 
ing waters  from  the  surface.  In  the  Mesabi  district  the  pro- 
portion of  the  area  of  the  ore-bodies  appearing  at  the  rock- 
surface,  to  that  of  the  iron-formation  as  a  whole,  is  about  8  per 
cent,  for  the  productive  part  of  the  district,  and  5  per  cent,  for 
the  entire  district.  For  the  other  districts  of  the  Lake  Supe- 
rior region,  the  area  of  the  iron-ore  deposits  is  far  less  than  this 
percentage  of  the  area  of  the  iron-formation  as  a  whole.  In  bulk, 
the  percentage  of  ores  to  the  iron-formation  is  much  smaller 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          647 

throughout  the  Lake  Superior  country,  for  it  will  be  remem- 
bered that  the  ores  are  essentially  surface-alterations  and  are 
therefore  well  represented  at  the  surface. 

The  alteration  of  the  iron-formation,  resulting  in  the  concen- 
tration of  the  iron-ores  or  in  the  development  of  ferruginous 
cherts  and  jaspers  and  amphibole-schists,  has  taken  place  in 
different  geological  periods  under  various  conditions,  with  a 
result  that  the  ores  of  each  of  the  districts,  as  well  as  of  differ- 
ent parts  of  the  same  district,  show  considerable  lithological 
variety.  The  same  ingredients — iron  oxide  and  silica — appear 
here  mechanically  combined  as  highly  crystalline  jasper,  there 
in  the  hydration  as  a  soft  ferruginous  chert,  or  both  mechani- 
cally and  chemically  combined  as  an  amphibole-magnetite 
schist.  The  iron-oxide  may  appear  here  as  a  brilliant  specular 
hematite  or  magnetite,  and  there  as  a  soft  granular  hematite  or 
limonite.  The  ores  of  the  Mesabi  district  are  soft  and  granu- 
lar and  associated  with  ferruginous  cherts.  At  the  east  end 
they  become  amphibolitic,  magnetitic  and  non-productive.  The 
ores  of  the  Gogebic  district  are  of  a  similar  nature  and  become 
amphibolitic,  magnetitic  and  non-productive  at  both  the  east 
and  west  ends  of  the  district.  The  ores  of  the  Vermilion  dis- 
trict are  hard,  blue  and  red  ores,  at  Ely,  brecciated,  associated 
with  jaspers.  The  ores  of  the  Marquette  district  comprise 
hard  blue  ores  and  brilliant  specular  ores  associated  with  jas- 
pers, called  "  hard-ore  jaspers,"  soft  ores  associated  with  fer- 
ruginous cherts,  or  "  soft-ore  jaspers,"  and  with  underlying 
slates,  and  at  the  west  end  of  the  district,  magnetite  and  specu- 
lar hematite  ores  associated  with  jaspers  and  with  amphibole- 
magnetite  rocks. 

Without  going  into  the  variable  conditions  in  the  several 
districts  and  the  varying  geological  history  of  the  different  ores 
and  rocks,  it  may  be  said  that,  so  far  as  the  alteration  of  the 
iron-formation  has  proceeded  continuously  under  the  influence 
of  surface-waters  without  interruption  by  igneous  activity  or 
Orogenic  movements,  the  soft  ores  and  ferruginous  cherts  have 
resulted.  So  far  as  these  have  been  subsequently  under  deep- 
seated  conditions  of  alteration,  they  have  become  dehydrated 
into  hard  red  and  blue  specular  ores  and  brilliant  jaspers.  This 
phase  of  the  alteration  did  not  require  the  agency  of  surface  oxi- 
dizing-waters.  So  far  as  the  alteration  of  the  original  iron-forma- 


648          GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

tion  took  place  within  the  sphere  of  influence  of  great  intrusive 
masses  where  the  waters  were  heated  and  oxygen  was  not  abun- 
dant, or  under  similar  conditions  developed  by  deep  burial  and 
orogenic  movement,  the  iron  oxide  and  silica  of  the  formation 
combined  with  small  amounts  of  other  substances  to  form  fer- 
rous silicates,  and  the  ferrous  iron  was  oxidized  to  magnetite, 
making  one  of  the  variety  of  rocks  usually  described  as  amphi- 
bole-magnetite  schists. 

In  the  discussion  of  the  development  of  the  ores,  we  have 
begun  with  the  original  rocks  of  the  iron-formation,  namely, 
the  iron  carbonates  and  greenalite  rocks,  containing  minute 
amounts  of  sulphide,  which  constituted  the  formation  when  it 
was  first  deposited.  The  origin  of  these  rocks  themselves  is  a 
subject  of  absorbing  interest,  but  it  is  a  subject  in  which  direct 
evidence,  such  as  we  have  been  dealing  with,  is  lacking;  and 
a  subject,  furthermore,  of  less  practical  importance  and  less 
direct  bearing  upon  the  study  of  the  ores  themselves.  Certain 
facts  are  well  known.  Both  the  iron  carbonates  and  the  green- 
alites  (and  their  altered  equivalents)  constitute  a  conformable 
part  of  a  continuous  sedimentary  succession,  being  interbedded, 
overlain  and  underlain  by  fragmental  rocks,  such  as  quartzite 
and  slate.  They  are  themselves  bedded.  It  is  impossible  to 
escape  the  conclusion  that  they  are  water-deposited  sediments. 
It  is,  further,  clear  that  they  are  not  water-deposited  sediments 
of  an  ordinary  nature.  They  are  not  fragmental ;  their  nearest 
analogues  are  chemical  sediments,  such  as  limestones. 

From  here  on  in  our  explanation  we  must  depend  rather 
upon  analogy  with  chemical  sediments,  such  as  limestone,  and 
with  iron  compounds  now  being  precipitated  in  bogs  and  lakes 
and  elsewhere,  than  upon  direct  evidence  in  the  formation 
itself.  On  this  basis,  the  history  of  the  development  of  these 
rocks,  as  outlined  by  Van  Hise,12  is  as  follows : 

.  .  .  ' '  It  is,  however,  my  belief  that  the  iron  for  the  iron-bearing  formations 
was  largely  derived  from  the  more  ancient  basic  volcanic  rocks  of  the  Lake  Supe- 
rior region.  When  the  individual  districts  are  taken  up  it  will  be  seen  that  a  green- 
stone, often  ellipsoidal,  in  many  places  porous  and  amygdaloidal,  in  many  places 

12  The  Iron-Ore  Deposits  of  the  Lake  Superior  Kegion,  by  C.  R.  Van  Hise,  21st 
Annual  Report,  U.  S.  Geological  Survey,  Pt.  III.,  pp.  319,  320. 
See  also  : 
Monograph  XLIIL,  U.  S.  Geological  Survey,  by  C.  K.  Leith. 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          649 

schistose,  and  rich  in  iron,  is  the  most  characteristic  rock  of  the  Archean,  and 
that  similar  rocks  occur  abundantly  in  the  Huronian.  Where  these  igneous 
rocks  were  adjacent  to  the  seas  they  would  be  leached  by  the  underground  water 
and  the  iron  transported  to  the  adjacent  seas.  It  is  probable  that  to  some  extent 
this  leaching  process  also  went  on  below  the  waters  cf  the  sea.  The  iron  was 
probably  transported  to  the  water  mainly  as  carbonate,  but  to  some  extent  as 
sulphate.  The  carbonate  would  there  be  thrown  down  by  oxidation  and  hydra- 
tion  as  limonite,  and  the  sulphate  in  part  as  basic  ferric  sulphate.  Much  of  the 
sulphate  was  probably  directly  precipitated  as  sulphide  by  the  organic  material. 
The  limonite  would  be  mingled  with  the  organic  matter  which  was  undoubtedly 
present,  as  shown  by  the  associated  carbonaceous  and  graphitic  shales  and  slates. 
When  deeply  buried  the  organic  matter  would  reduce  the  iron  sesquioxide  to 
iron  protoxide.  By  the  simultaneous  decomposition  of  the  organic  matter  carbon 
dioxide  would  be  produced,  which  would  unite  with  much  of  the  protoxide  of 
iron,  producing  iron  carbonate.  The  sulphate  of  the  basic  ferrous  sulphate 
would  be  reduced  to  the  sulphide  by  the  organic  material,  thus  producing  the 
pyritic  carbonates.  Where  the  iron  was  brought  to  the  water  mainly  as  sulphate 
the  direct  reduction  of  this  salt  by  organic  matter  would  form  iron  sulphide  with 
little  or  no  carbonate.  Simultaneously  with  the  production  of  these  substances 
chert  was  formed,  probably  through  the  influence  of  organisms.13 

"Some  of  this  silica  would  unite  with  a  part  of  the  protoxide,  producing  fer- 
rous silicate.  More  or  less  mechanical  sediment  would  also  be  laid  down.  Thus 
the  original  rocks — the  cherty  iron  carbonates,  the  ferrous  silicate  rocks,  and  the 
pyritic  cherts — would  be  produced. 

"  It  has  chanced  that  at  three  different  periods  in  the  history  of  the  Lake 
Superior  region,  these  processes  of  the  development  of  the  original  rocks  of  the 
iron-bearing  formations  have  occurred  extensively.  While  this  might  at  first  be 
thought  remarkable,  there  is  no  good  reason  for  thus  regarding  it.  At  some  time 
during  each  of  the  Archean,  Lower  Huronian  and  Upper  Huronian  periods  the 
quiescent  conditions  of  chemical  and  organic  sedimentation  have  occurred,  and 
since  the  iron-bearing  volcanic  rocks  were  each  time  available  for  the  work  of 
underground  waters  and  sea- waters,  naturally  iron  carbonate  and  the  other  origi- 
nal rocks  have  been  produced.  In  each  period  the  source  of  the  material  and 
the  process  of  its  formation  were  essentially  the  same." 

Time  of  Concentration. 

The  concentration  of  the  ores  of  the  Lake  Superior  region 
was  far  advanced  before  Cambrian  time,  as  shown  by  the  ex- 
istence of  ore  and  other  iron-formation  boulders,  derived  from 
the  pre-Cambrian,  in  Cambrian  conglomerates.  For  each  of 
the  districts  the  particular  time  of  concentration  has  been  more 
closely  calculated,  but  this  is  a  subject  which  would  require  a 
longer  discussion  than  the  scope  of  this  paper  warrants,  and 

13  The  Penokee  Iron-Bearing  Series  of  Michigan  and  Wisconsin,  by  E.  D. 
Irving  and  C.  R.  Van  Hise :  Monograph,  U.  S.  Geological  Survey,  vol.  xix.,  1892, 
pp.  246-253. 

Fossil  Medusae,  by  C.  D.  Walcott:  Monograph,  U.  S.  Geological  Survey,  vol. 
xxx.,  1898,  pp.  17-21. 

41 


650         GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

the  reader  is  referred  to  Van  Hise's  general  paper  already 
cited. 

Topographic  Relations  of  the  Ores. 

With  very  few  exceptions,  the  ore-deposits  of  the  Lake  Su- 
perior region  lie  either  on  the  slopes  or  at  the  foot  of  conspicu- 
ous ranges  or  hills.  This  has  been  explained  by  Van  Hise  as 
due  to  the  concentration  of  ores  through  the  circulation  of 
ground-waters.  Topographic  elevations  have  given  the  waters 
sufficient  head  to  search  the  ground  on  their  slopes  and  per- 
haps at  the  base  of  the  slopes.  On  the  slopes  the  movement  of 
the  water  is  largely  downward  and  more  or  less  direct  from  the 
surface,  thus  carrying  an  abundance  of  altering  agents,  particu- 
larly oxygen  and  carbon  dioxide ;  while  in  intervening  low-lying 
areas,  the  waters  escape  with  a  lateral  and  upward  movement 
after  a  longer  underground  journey,  during  which  they  have 
lost  considerable  proportions  of  the  agents  which  alter  the  iron- 
formation  to  ores.  Van  Hise  holds  that,  in  the  latter  positions, 
the  ores  have  not  developed  so  abundantly  as  on  the  slopes. 
The  present  topography  is,  in  many  places,  not  the  same  in  de- 
tail as  the  topography  which  existed  at  the  time  the  ores  were 
concentrated ;  and  accordingly  it  is  not  safe,  in  discussing  the 
relations  of  the  ores  to  the  topography,  to  consider  too  small 
topographic  units.  Believing  that  the  present  major  topo- 
graphic conditions  represent,  at  least  in  part,  the  past  condi- 
tions, Van  Hise  has  discussed  in  some  detail  the  relations  of 
the  Lake  Superior  ores  to  the  particular  topographic  features 
of  the  different  districts.  In  one  or  two  cases,  and  especially 
in  the  Glogebic  district,  the  topographic  units  selected  for  dis- 
cussion may  have  been  too  small,  and  this  has  resulted  in  criti- 
cism of  the  entire  theory.  It  is  believed  that  his  main  conclu- 
sions as  to  the  relations  of  the  ores  to  the  major  topographic 
features  have  been  confirmed,  rather  than  disproved,  by  recent 
work. 

Present  Studies  of  the  Origin  of  the  Ores. 

The  ores  of  the  Lake  Superior  region  have  been  shown,  in 
certain  districts,  to  have  been  developed  from  the  alteration  of 
iron  carbonate,  in  other  districts  from  the  alteration  of  iron 
silicate,  and  in  others,  from  both.  In  the  Marquette,  Gogebic, 
Vermilion,  and  Crystal  Falls  districts,  the  original  rock  has 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          651 

been  described  as  iron  carbonate.  In  the  Mesabi  district,  tbe 
original  rock  bas  been  described  as  consisting  of  ferrous  sili- 
cate or  "  greenalite  "  granules  principally,  but  witb  subordinate 
amounts  of  iron  carbonate.  In  tbe  Felch  Mountain  and  Re- 
public areas,  the  presence  of  granules  similar  to  the  Mesabi 
granules  has  been  noted.  In  the  Menominee  district,  both  iron 
carbonate  and  silicate  granules  have  been  supposed  to  yield 
the  ore. 

The  vast  scale  on  which  the  alteration  of  ferrous  silicate 
granules  has  occurred  in  the  Mesabi  district,  together  with 
the  evidence  of  the  somewhat  wide-spread  distribution  of  such 
granules  in  unknown  but  small  quantity,  has  led  to  a  re-exami- 
nation of  the  ores  and  rock  of  the  remaining  districts,  with  the 
result  that  evidence  of  the  prior  existence  of  granules  has  been 
found  also  in  both  the  Gogebic  and  Crystal  Falls  districts.  So- 
far  as  the  re-examination  has  gone,  however,  it  tends  to  confirm 
the  essential  correctness  of  the  determination  of  iron  carbonate 
as  the  original  iron-formation  rock  for  these  districts. 

In  the  new  Animikie  iron-range,  on  the  northwest  coast  of 
Lake  Superior,  the  eastern  continuation  of  the  Mesabi  range, 
original  and  secondary  iron  carbonate  and  pseudomorphs  after 
greenalite  are  found  so  well  exposed  and  so  closely  associated 
that  it  is  hoped  that  the  study  of  this  district  now  in  progress 
will  furnish  decisive  evidence  of  the  real  relations  of  these  two 
substances. 

In  the  new  Baraboo  iron-range  of  Wisconsin,  which  is  of 
pre-Cambrian  age  and  similar  in  many  respects  to  the  Lake 
Superior  deposits,  Weidman  has  attempted  to  show  that  the 
ores  are  original  bog-deposits,  which  have  become  dehydrated. 
His  conclusion  does  not  necessarily  affect  the  remaining  Lake 
Superior  ores,  but  the  similarity  in  geology  is  so  close  that, 
until  the  contrary  is  proved,  it  is  believed  that  the  explanation 
applied  to  one  region  will  apply  substantially  to  others.  Rea- 
sons are  given  on  a  subsequent  page  for  believing  that  his  ex- 
planation is  not  a  true  one. 

Experimental  work  in  the  laboratories  of  the  University  of 
Wisconsin  shows  the  great  ease  of  the  alteration  of  the  iron  car- 
bonates through  the  agency  of  water.  In  a  few  hours  this  sub- 
stance becomes  coated  with  hydrous  iron  oxide  when  treated 
with  warm  water  containing  only  small  amounts  of  oxygen  de- 


652         GEOLOGY    OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

rived  from  contact  with  the  air.  Iron  silicate  has  been  found 
to  be  much  more  refractory,  but  still  has  yielded  slightly  to  the 
action  of  ordinary  water.  Quantitative  results  are  looked  for 
at  an  early  date.  Analysis  of  mine-waters  from  the  Lake  Supe- 
rior region  as  a  whole,  it  is  hoped,  will  yield  results  indicating 
the  manner  in  which  the  ores  and  rocks  of  the  iron-formation 
have  been  altered. 

The  form  in  which  the  phosphorus  occurs  is  not  definitely 
settled.  Some  of  it  is  certainly  in  the  form  of  apatite.  But 
many  ores,  and  especially  Mesabi  ores  containing  phosphorus, 
apparently  do  not  contain  apatite.  The  association  of  phos- 
phorus with  aluminum,  both  in  ores  and  in  other  phases  of  the 
iron-formation,  suggests  the  possibility  that  the  phosphorus  is 
chemically  combined  with  aluminum.  The  solubility  of  the 
phosphorus  compounds  in  the  ores  is  still  a  mooted  question. 
Incidents  may  be  cited  of  the  remarkable  change  of  phospho- 
rus-content in  stock-piles  and  mines,  because  of  the  washing  of 
surface-waters;  and  in  drilling, allowances  are  frequently  made 
for  changes  in  phosphorus-content  in  washing.  Whether  this  is 
mechanical  or  chemical,  its  extent  and  its  commercial  impor- 
tance are  yet  to  be  decided.  ,It  is  hoped  that  investigations 
now  in  progress  will  settle  these  questions. 

Iron-Ranges  of  Recent  Discovery. 

********** 

[The  portion  here  omitted  contains  a  description  of  the  Baraboo  range,  of  south 
central  Wisconsin,  where,  associated  with  pre-Cambrian  quartzites,  beneath  the 
Paleozoic  rocks,  slate,  dolomite,  and  iron-ore  occur.  The  district  has  been  described 
in  Bulletin  xiii.  of  the  Wis.  Geol.  and  Nat.  Hist.  Survey  (1904),  by  Dr.  Samuel 
Weidman.  The  iron-ore  is  low-grade  (below  55  per  cent.)  Bessemer  hematite  ? 
with  a  little  limonite,  associated  with  and  grading  into  "dolomite,  cherty 
ferruginous  dolomite,  ferruginous  chert,  ferruginous  slate,  and  ferruginous  dolo- 
mitic  slate."  It  is  stratified  conformably  with  the  rocks  below  and  above  it.  For 
the  following  reasons,  Dr.  Weidman  thinks  the  Baraboo  ores  are  bog-deposits, 
subsequently  dehydrated.] 

"1.  The  iron-ore  deposits  are  bedded  and,  to  all  appearances,  stratified  like 
other  sedimentary  deposits. 

"  2.  The  stratified  iron-ore  deposits  are  not  set  off  sharply  from  the  surrounding 
associated  stratified  rocks,  such  as  slate,  chert  and  dolomite,  but  grade  into  them 
through  all  possible  gradations.  The  iron-ore  is  not  especially  associated  with 
any  particular  kind  of  the  various  rocks  adjacent,  and  the  stratification  of  these 
various  kinds  of  rocks  is  always  conformable  to  that  of  the  iron-ore.  Since  the 
slate,  dolomite  and  chert  are  original  sedimentary  deposits,  and  since  the  iron- 
ore  grades  into  them  and  is  conformable  to  them,  it  is  believed  that  the  iron-ore 
has  the  same  origin  as  these  conformable  interstratified  deposits  of  related  rock. 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          653 

"  3.  That  the  physical  conditions  in  the  district  at  the  time  the  iron-formation 
was  deposited  were  favorable  for  the  formation  of  such  shallow-water  deposits  as 
iron-ore  is  indicated  by  the  presence  of  sun-cracks  in  the  rocks  of  the  iron-forma- 
tion immediately  adjacent  to  the  iron-ore  and  also  by  the  presence  of  carbona- 
ceous material,  probably  decayed  vegetable  matter  in  the  iron-ore  and  associated 
ferruginous  rocks.  Furthermore,  the  rapid  alternation  in  the  various  strata  of 
the  iron-formation  indicates  changing  conditions  of  sedimentation, — a  common 
characteristic  of  shallow-water  deposits,  and  the  composition  of  the  iron-bearing 
formation  itself,  with  its  chert,  carbonate  rock  and  slate,  is  identical  with  the 
composition  of  shallow- water  deposits  being  formed  to-day. 

"  4.  That  the  iron-ore  deposits  originated  long  antecedent  to  the  folding  and 
fracturing  of  the  iron-formation  and  the  deposition  of  the  mineral  veins  is 
shown  by  the  fact  that  the  strata  of  iron-ore  are  generally  folded,  crumpled  and 
fractured,  and  that  the  mineral  veins  cut  across  the  stratification  and  also  across 
the  folds  of  the  iron-ore  and  associated  rocks.  The  folding  of  the  ore-deposits 
appears  to  conform  in  all  respects  to  the  folding  of  the  associated  rocks,  and  the 
ore-deposits  appear  to  have  the  position  and  distribution  which  they  should  have 
if  formed  before  the  general  folding  of  the  pre-Cambrian  formations  into  their 
present  position  took  place. 

"5.  The  change  in  the  ore  subsequent  to  its  original  deposition  as  limonite, 
as  shown  by  the  microscopic  and  chemical  study  of  the  rocks,  is  believed  to  be 
mainly  a  change  to  hematite  by  dehydration  of  the  limonite  under  deep-seated 
conditions  of  metamorphism.  This  change  is  exactly  parallel  to  the  dehydration 
of  the  original  clay-minerals  of  the  gray  Seeley  slate-formation  and  of  the  clay- 
minerals  in  the  slate-phases  of  the  iron-formation,  which  now  contain  very  little 
water  of  constitution,  only  2  or  3  per  cent. ,  but  which  originally  must  have  con- 
tained from  10  to  25  per  cent.  This  change  of  limonite  by  dehydration  is  also 
analogous  to  the  probable  dehydration  of  the  original  siliceous  deposits  now  con- 
stituting the  chert  layers. 

"  The  geological  data  which  led  the  writer  to  believe  that  the  Baraboo  iron-ore 
was  very  probably  deposited  as  limonite  under  conditions  similar  to  those  under 
which  bog-  and  lake-ore  are  formed  to-day,  and  later  merely  partially  dehydrated 
to  form  hematite,  have  just  been  briefly  outlined.  The  principal  evidence  be- 
lieved to  be  directly  opposed  to  the  theory  of  the  secondary  development  of  the 
iron-ore  as  replacement-  and  alteration-deposits  by  work  of  the  underground  water 
is  mainly  furnished  by  the  character  of  the  work  of  the  underground  water  at 
present,  as  indicated  by  its  chemical  composition,  and  by  the  work  of  the  ground- 
water  of  the  past,  as  indicated  by  the  character  and  composition  of  the  mineral 
veins  in  the  ore  and  associated  rocks. 

"From  the  study  of  the  composition  of  the  ground-water  now  circulating 
through  the  iron-bearing  rock  and  associated  formations  in  the  district,  and  its 
comparison  with  that  of  ground-water  outside  the  district  and  with  river-waters 
and  with  chalybeate  mineral  waters,  it  has  been  concluded  that  very  probably  the 
present  work  of  the  ground-water  in  the  iron-formation  is  not  that  of  depositing 
iron-ore.  It  is  quite  generally  accepted  that  mineral  veins  are  deposited  from 
underground  water  circulating  through  fractures  in  rocks  ;  and  the  fact  that  the 
mineral  veins  in  the  iron-ore  and  associated  rocks  are  largely  quartz  and  not  iron- 
ore  is  interpreted  as  evidence  that  the  work  of  the  ground-water  of  the  past  was 
very  probably  not  that  of  depositing  iron-ore.  If  the  work  of  circulating  ground- 
water  of  the  past  could  have  or  did  develop  the  iron-ore  deposits,  why  should  not 
the  work  be  now  in  progress,  since  ground-water  is  now  circulating  through  the 
ore-deposits  and  associated  rocks  as  it  has  in  the  past ;  and  if  the  iron-ore  could 
have  been  or  was  developed  by  the  work  or  agency  of  ground-water,  why  should 


654         GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

not  the  mineral  veins  that  ramify  through  the  ore-deposits  and  associated  iron- 
bearing  rocks  be  composed  largely  of  iron-ore  instead  of  quartz?" 

As  the  Baraboo  district  is  related  geographically  and  strati- 
graphically  with  Lake  Superior  ore-bearing  districts,  Weidman's 
conclusion  that  the  ores  are  original  deposits  immediately 
suggests  that  the  same  origin  may  hold  for  the  ores  elsewhere 
in  the  Lake  Superior  region,  or,  vice  versa ;  and  that  explana- 
tions of  the  secondary  origin  of  the  Lake  Superior  ores  may 
really  apply  in  the  Baraboo  district.  It  is  believed  that  Weid- 
man  has  not  proved  the  Baraboo  ores  lo  be  an  original  deposit, 
for  the  following  reasons : 

His  arguments  1,  2  and  3,  without  change,  may  be  used  equally 
well  in  support  of  a  theory  of  secondary  concentration  from  an 
originally  deposited  chemical  sediment — iron  carbonate  or  iron 
silicate — described  as  laid  down  in  shallow  waters. 

~No  evidence  is  presented  in  support  of  argument  4.  The 
secondary  alteration  of  previously  folded  and  contorted  iron- 
formations  to  iron-ore,  with  the  retention  of  all  the  folded  and 
contorted  structures,  is  the  common  feature  for  the  Lake  Supe- 
rior country.  Accompanying  and  following  this  change,  there 
has  been  some  additional  folding,  followed  in  some  cases  by  an 
introduction  of  normal  mineral  veins,  but  usually  it  has  been  a 
minor  phenomenon.  The  fact  of  the  folding  and  contortion  of 
iron-formation  layers  could  not  be  accepted  elsewhere  in  the 
Lake  Superior  country  as  evidence  of  the  subsequent  occur- 
rence of  the  major  folding. 

The  argument  that  the  presence  of  quartz-veins  shows  that 
quartz  only,  and  not  iron-ore,  has  been  introduced  or  concen- 
trated subsequent  to  the  deformation,  it  is  believed,  will  not 
stand  analysis.  In  the  Lake  Superior  region,  abundant  evi- 
dence may  be  presented  to  show  that  quartz-veins  have  devel- 
oped both  before  and  after  the  concentration  of  the  iron-ore, 
and  I  know  of  no  criteria  that  will  enable  one  to  say  that  the 
presence  of  quartz,  rather  than  iron-ore,  in  particular  fractures  or 
veins,  proves  or  disproves  the  secondary  origin  of  the  ore.  In 
the  Vermilion  district,  minute  veins  of  ore  may  be  seen  cross- 
ing both  quartz-veins  and  an  earlier  concentration  of  the  ore, 
and  in  turn  are  crossed  by  later  quartz-veins. 

The  dehydration  of  limonite  (5)  has  probably  occurred,  but  it 
would  make  little  difference  whether  the  limonite  were  an 
original  deposit  or  were  itself  a  secondary  alteration. 


GEOLOGY  OF    LAKE    SUPERIOR    IRON-BEARING    SERIES.          655 

The  argument  that  the  composition  of  the  waters  seems  to 
show  that  ore-concentration  is  not  at  present  occurring  is  beside 
the  mark  when  we  remember  that  for  the  Lake  Superior  region 
as  a  whole,  and  hence  for  the  Baraboo  district  itself  until  the 
contrary  is  proven,  the  concentration  of  the  ores  was  largely 
finished  before  Cambrian  time.  The  conditions  at  that  time 
doubtless  differed  widely  from  present  conditions,  but  even  ad- 
mitting that  they  are  similar,  the  fact  that  waters  from  the  iron- 
formation,  which  have  been  analyzed,  contain  no  ingredients 
different  from  the  surface-waters  of  the  region,  does  not  show 
that  they  may  not  still  be  doing  work.  Van  Hise  has  empha- 
sized the  fact  that  the  ordinary  surface-waters  are  the  ones  that 
do  the  work,  and  that  the  development  of  iron  oxides  from  iron 
carbonates  and  iron  silicates  is  the  normal  work  of  percolating- 
waters  for  the  belt  of  weathering  in  general.  The  presence  of 
silica  in  the  Baraboo  waters  shows  that  silica  is  being  carried 
away  from  this  general  zone  or  region,  and  there  is  every  reason 
to  believe  that  it  may  be  carried  as  well  from  the  ore  as  from 
the  overlying  sandstone.  Certainly  it  could  not  be  assumed 
that  the  silica  contained  in  the  water,  notwithstanding  the  fact 
that  it  is  no  more  abundant  in  mine-waters  than  elsewhere, 
might  not  be  coming  from  the  ores  themselves,  thus  enriching 
them.  It  is  believed,  also,  that  the  process  of  alteration  has 
gone  so  far  in  the  mines  from  which  the  waters  were  secured, 
that  the  waters  now  circulating  there  are,  for  the  most  part,  in 
contact  with  oxidized  products — the  end-products  of  alteration 
under  such  conditions — and  that  they  could  scarcely  be  expected 
to  contain  any  considerable  amounts  of  ferrous  compounds.  It 
is  not  at  all  certain  that  waters,  working  through  less-altered 
parts  of  the  formation,  either  in  the  past  or  elsewhere  in  this 
district,  might  not  show  a  different  composition. 

Finally,  Weidman's  theory  would  require  that,  after  straight- 
ening out  the  secondary  folds  and  contortions,  the  iron-ore 
should  lie  in  a  continuous  even  bed  or  layer,  having  only  such 
irregularities  as  would  result  from  uneven  deposition  in  shal- 
low waters.  If,  in  the  Lake  Superior  region  as  a  whole,  the 
iron-formation  layers  should  be  straightened  out,  the  resulting 
bed  or  layer  would  have  strange  shapes  indeed,  and  would  here 
and  there  end  abruptly  along  the  strike  or  dip,  against  other 
phases  of  the  iron-formation  or  even  against  a  dike  or  boss 
of  greenstone.  (See  Fig.  1.)  Indeed,  Weidman's  theory  is 


656         GEOLOGY    OF    LAKE    SUPERIOR    IRON-BEARING    SERIES. 

squarely  opposed  to  nearly  all  conceptions  of  the  structural 
relations  of  the  ores  to  the  adjacent  rocks,  worked  out  inde- 
pendently for  each  of  the  Lake  Superior  districts,  where  ex- 
ploitation has  gone  far  enough  to  allow  of  satisfactory  study. 
It  is  believed  that  these  structural  facts,  worked  out  for  the  re- 
gion as  a  whole,  will  apply  in  the  Baraboo  district  itself,  so  far 
as  the  facts  are  known  in  the  present  state  of  exploration. 

The  ores  thus  far  found  have  been  along  the  eroded  edges 
of  the  iron-formation.  Attempts  to  locate  the  ore  in  the  center 
of  the  great  Baraboo  valley  beneath  the  dolomite  have  met 
with  failure.  Straightening  out  the  folds  in  the  iron-ore  bodies, 
and  reproducing  the  original  attitude  and  distribution,  the  iron- 
ore  deposits  would  appear,  so  far  as  is  now  known,  as  a  series 
of  lenses,  limited  by  dolomite  or  feathering-out  beneath  it, 
down  the  dip,  in  the  direction  of  what  is  now  the  center  of  the 
valley.  On  Weidman's  theory,  the  ore  might  be  found  any- 
where beneath  the  dolomite,  and  its  truncation  by  an  erosion- 
surface  would  be  purely  a  matter  of  accident.  It  must  be  ad- 
mitted that  drilling  has  not  gone  sufficiently  far  to  prove  that 
the  iron-ore  lenses  uniformly  reach  the  pre-Cambrian  erosion- 
surface  at  some  point;  but  sufficient  drilling  has  been  done  to 
lead  certain  mining  engineers  of  the  district  and  me  to  conclude 
that  the  evidence  is  strongly  in  favor  of  this  view  and  that  the 
normal  Lake  Superior  conditions  here  prevail. 

While  it  is  believed,  for  the  above  reasons,  that  Weidman's 
conclusion  as  to  the  origin  of  the  Baraboo  ores  is  not  supported 
by  the  evidence  he  has  presented,  the  fact  that  the  ore  grades 
into,  and  is  overlain  by,  dolomite — a  unique  occurrence  for  the 
Lake  Superior  region — would  make  it  easy  to  accept  an  ex- 
planation of  the  origin  of  the  Baraboo  ores  different  from  that 
applied  to  the  remaining  Lake  Superior  ores,  if  sufficient  evi- 
dence be  presented ;  and  such  acceptance  would  not  necessarily 
imply  a  revision  of  views  of  the  secondary  origin  of  the  remain- 
ing Lake  Superior  ores. 

****5)«*5iC*** 

[The  portion  here  omitted  gives  brief  accounts  of  the  Guyana  range  in  Crow 
Wing  county,  Minn,  ("containing  ore  of  possible  commercial  value,"  and  possi- 
bly of  Archean,  Middle  Huronian  or  Upper  Huronian  age) ,  and  the  Animikie 
range,  extending  NE.  from  Gunflint  lake  along  the  international  boundary  to  the 
east  end  of  Thunder  bay,  and  regarded  as  an  eastward  continuation  of  the 
Mesabi.  The  paper  ends  with  a  statement  of  the  work  which  must  still  be  done, 
before  the  complex  problems  of  the  general  and  the  economic  geology  of  the 
Lake  Superior  region  can  be  regarded  as  completely  solved.] 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       657 


No.  26. 
The  Geological  Relations  of  the  Scandinavian  Iron-Ores. 

BY   PROF.    HJALMAR   SJOGREN,    PH.D.,*   STOCKHOLM,    SWEDEN. 

(Toronto  Meeting,  July,  1907.     Trans.,  xxxviii.,  766.) 
********** 

AMONG  the  feldspar-rocks  there  are  certain  types  which  occur 
constantly  in  different  areas — viz.,  the  amphibolitic  plagioclase- 
rocks  and  the  granulitic  rocks  composed  of  quartz  and  alkaline 
feldspars.  Among  the  latter  soda-granulites  as  well  as  potash- 
granulites  are  met  with ;  also  the  corresponding  gneisses  occur. 

********** 
GROUP  I. — THE  ORES  OF  THE  ARCH.EAN  CRYSTALLINE  SCHISTS. 

********** 

The  Rocks. 

The  ore-bearing  rocks  of  the  ore-province  of  central  Sweden 
are  chemically  and  petrographically  unlike  the  more  monoto- 
nous gneiss-  and  granite-areas  which  surround  them.  On  the 
whole,  they  constitute  a  quartz-feldspar  formation  in  which 
purer  quartzitic  rocks,  limestones,  "  skarn "  rocks  and  ore- 
bodies  are  very  subordinate  members.  (Skarn  is  the  Swedish 
name  for  rocks  of  varying  composition,  mostly  consisting  of 
lime,  magnesia,  iron,  and  alumina  silicates  of  the  pyroxene, 
amphibole,  and  garnet  groups ;  as  secondary  minerals,  epidote, 
chlorite,  biotite,  and  talc  occur.  The  skarn  is  scarcely  an  inde- 
pendent rock  but  is  connected  with  the  ore-deposits.  It  is 
formed  through  an  interchange  between  the  silica  of  the  quartz- 
feldspar  rocks  and  the  basic  constituents  of  the  ore-formation.) 


[ABRIDGED  SUMMARY. — The  amphibolites  must  be  considered  as  stretched  and 
dynamo-metamorphosed  dioritic*  rocks.  The  granulites  are  divided  into  two 
groups,  one  showing  predominant  plagioclase,  the  other  equal  or  predominant 
orthoclase.  Evidently,  the  iron-ore  deposits  are  connected  in  some  way  with  the 

*  Director  of  the  Mineralogical  Department  of  the  State  Natural  History 
Museum,  Stockholm,  Sweden. 


658       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 


rocks  of  granulitic  structure.  This  structure  is  most  probably  due,  in  general, 
to  a  recrystallization,  under  stress  and  movement,  within  the  anamorphic  zone  of 
depth.  "Simultaneously  with  the  mechanical  deformation  of  the  rock-masses 


there  has  been  also  a  supply  of  iron-bearing  ma^matic  material  by  solutions, 
imparting  to  the  ore-deposits  their  present  peculiar  epigenetic  characters." 
Numerous  pegmatitic  dikes,  penetrating  both  ore  and  rock,  are  to  be  considered 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       659 

as  crystallized  from  aqueo-igneous  solutions  in  contraction-fissures,  during  the 
cooling  of  the  rock.  Stripes,  stratification,  contortion,  and  even  brecciation  of  the 
country-rock  near  the  ore-body,  indicate  the  metasomatic  deposition  of  the  latter 
in  shear-zones,  or  in  portions  of  the  original  rock  contracted  in  volume  by  the 
chemical  changes  involved,  as  well  as  fractured  by  movement.  There  is  also  a 
linear  or  stretched  structure,  sometimes  conformable  to  the  pitch  of  the  ore-bodies. 
The  arnphibolites  and  a  great  part  of  the  granulites  seem  to  be  igneous  rocks  of 
deep-seated  origin. 

The  ores  are  of  five  types  :  (A)  Ores  carrying  apatite,  disseminated  or  in  stripes, 
with  low  percentage  of  silica  and  feldspar.  These  were  originally  magnetite,  but 
have  been  altered  in  many  places  to  specular  hematite  by  a  process  which  simul- 
taneously reduced  the  proportion  of  apatite.  They  are  products  either  of  mag- 
matic  differentiation  in  the  granulite  or  of  metasomatic  replacement  of  feldspar- 
rock  by  iron-bearing  solutions  in  the  anamorphic  zone.  The  constant  large  amount 
of  apatite  favors  the  former  hypothesis.  (B)  Mixed  hematites  and  magnetites, 
nearly  related  to  the  preceding,  and  evidently  formed  through  injection  of 
iron-bearing  solutions  and  partial  replacement — the  ore  being  therefore  much 
younger  than  the  country-rock.  (C)  Quartz-banded  ores,  chiefly  specular  hema- 
tites. The  alternation  of  ore  and  gangue  is  often,  but  not  always,  as  definite  as  in 
the  jasper-banded  ores  of  Lake  Superior.  This  structure  has  been  generally  re- 
garded as  due  to  a  primary  stratification,  on  which  hypothesis  the  ores  must  have 
formed  by  the  alteration  of  stratified  rocks.  But  it  seems  more  probable  that  the 
structure  is  a  secondary  feature,  produced  during  the  replacement  process.  (D) 
The  tl  skarn1'  ores,  rich  magnetites,  accompanied  and  connected  by  beds  of 
tl  skarn"  minerals  (see  definition  of  "skarn,"  on  a  preceding  page).  They  have 
often  been  formed  by  metasomatic  replacement  of  limestone  and  dolomite,  ore  and 
gangue-minerals  being  thus  younger  than  the  country-rock.  (E)  Limestone-ores, 
occurring  in  or  with  limestone  and  dolomite,  of  which  they  are  metasomatic  re- 
placements. ] 

The  Origin  rf  the  Ore-Deposits. 

During  the  last  century  the  ores  of  this  group  were  regarded 
by  Swedish  geologists  as  sedimentary  deposits,  laid  down  to- 
gether with  the  over-  and  underlying  granulite  formation.  Such 
opinions  were  advocated  by  A.  Erdmann,  Anton  Sjogren,  A. 
E.  Tornebohm,  B.  Santesson,  and  others ;  among  the  Norwe- 
gian geologists  Yogt  has  with  eagerness  developed  this  theory.3 
Only  with  respect  to  the  Gellivare  ores,  opinions  were  much 
divided,  and  several  geologists — e.g.,  Lundbohm,  v.  Post  and 
L  of  strand — believed  them  to  be  of  igneous  origin. 

3  See,  for  instance,  J.  H.  L.  Vogt,  De  lagformigt  optraedende  jernmalmfore- 
komster,  Geologiska  Foreningen  Forhandlingar,  vol.  xvi.,  p.  275  (1894)  ;  Dunder- 
landsdalens  jernmalmfelt,  Norges  Geologiska  Under  so  g  else,  No.  15,  pp.  56  to  63 
(1894)  ;  Om  de  lagrade  jernmalmsfyn-digheternas  bildningssatt,  Werml.  Bergsman- 
nafor  Ann.  (1896). 

The  same  opinion  has  also  been  expressed  by  several  foreign  geologists,  for  in- 
stance, De  Launay,  Annales  des  Mines,  Tenth  Series,  vol.  iv.,  pp.  49  to  209  (1903), 
as  well  as  in  the  German  treatises  on  Ore-Deposits  by  Beck  (1901),  and  Stelzner- 
Bergeat  (1906). 


660       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

Since  1890,  the  present  writer  has  in  several  papers  argued 
that  metasomatic  processes  undoubtedly  played  a  prominent 
part  in  the  formation  of  these  ores,  and  has  been  able  to  point 
out  several  analogies  with  the  iron-ores  of  the  Lake  Superior 
region. 

In  this  paper  I  shall  attempt  to  show  that  the  metasomatic 
processes  must  have  taken  place,  not  in  the  surface-zone  but  in 
the  anamorphic  zone,  and  that  the  ores  bear  fully,  in  their  min- 
eralogical  features  and  association,  characters  of  formations  of 
the  deep-seated  zone. 

In  several  cases,  it  may  not  be  possible  to  determine  whether 
the  original  iron-bearing  material  was  the  product  of  primary 
magmatic  differentiation,  as  in  the  apatite-ores,  or  iron-bearing 
magmatic  solutions  producing  metasomatic  deposits,  as  in  the 
lime-  and  s&arn-ores,  or  possibly  altered  chemical  sediments,  as 
in  the  quartz-banded-ore  type. 

The  iron-bearing  solutions  may  frequently  have  been  of  mag- 
matic origin,  thus  carrying  iron-bearing  material  from  below; 
or  it  may  be  that  the  very  small  amount  of  water  contained  in 
the  rocks  was  sufficient,  under  the  condition  of  dynamic  meta- 
morphism  in  the  anamorphic  zone,  to  collect  and  concentrate  the 
iron  particles.  The  occurrence  of  ore-deposits  in  connection 
with  surface-rocks,  above  pointed  out,  and  their  absence  in  the 
greater  granite  laccolites  seems  to  prove  that  the  deposits  are 
formed  in  a  depth  less  than  that  in  which  the  granite  consoli- 
dated, but  still  in  the  anamorphic  zone. 

Arguments  Against  the  Sedimentation  Theory. — That  these  de- 
posits are  not  sedimentary  is  indicated  by  the  fact  that  the 
surrounding  rocks  are  igneous.  So  long  as  the  granulite  of 
Grangesberg  and  Gellivare  was  considered  a  sedimentary  rock, 
it  was  possible  to  ascribe  the  same  nature  to  the  ore-deposits. 
But  this  foundation  of  the  sedimentary  theory  seems  more  and 
more  to  give  way. 

Again,  the  form  of  these  ore-deposits  differs  as  widely  as  pos- 
sible from  that  of  stratified  bodies.  They  have  been  termed 
lenses,  stocks,  lineals,  etc.  In  general,  they  are  much  more 
irregular  than  is  consistent  with  a  sedimentary  formation.  Some- 
times these  ores  divide  or  branch  into  the  surrounding  rock  (see 
Fig.  2,  showing  the  central  part  of  Dannemora),  a  feature  which 
does  not  agree  with  any  known  form  of  primary  sedimentation,. 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       661 

but  must  be  interpreted  as  secondary.  At  other  places,  the  ore 
incloses  portions  of  the  surrounding  rock,  which  sometimes 
take  the  form  of  irregular  sinuous  bands,  cutting  obliquely 
through  the  ore  from  the  hanging-wall  to  the  foot-wall.  (See 
Fig.  3,  showing  the  central  part  of  Grangesberg.)  In  such 
cases  it  appears  that  the  overlying  and  the  underlying  rock, 
together  with  the  narrow  partition-walls  between  the  ore-lenses, 
form  "  a  continuous  whole,  pre-existing  to  the  ore."  This 
mode  of  occurrence  also  is  incompatible  with  sedimentary  de- 
position. 


Diorite 


Gangue 

FIG.  2. — DANNEMORA  MINE,  CENTRAL  PART. 

In  a  few  cases  only,  a  structure  resembling  primitive  stratifi- 
cation is  met  with;  e.g.,  in  the  banded  quartziferous  ores  (type 
C),  which  for  this  reason  possess  special  interest.  The  ores 
rich  in  silica  and  alumina  (type  B)  sometimes  present  a  schis- 
tose structure ;  but  this  is  without  any  doubt  a  foliation  caused 
by  pressure. 

Even  where  the  stratified  structure  is  present,  we  are  not 
justified  in  concluding  that  the  material  is  primitive;  for  in 
this  case  also,  though  retaining  the  original  structure,  it  may 
have  been  subjected  to  subsequent  metasomatic  transformation. 
Thus  the  banded  quartziferous  ores  may  have  originally  con- 
sisted of  alternating  bands  of  a  carbonate  and  of  amorphous 
silica,  since  altered  or  replaced  in  situ. 


662       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 


lUi'JW.I  O 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       663 

Concentration  and  Transformation  Within  the  Deep-Seated  Ana- 
morphic  Zone. — To  this  zone  the  rocks  were  transferred  during 
the  period  of  the  plication,  by  which  evidently  a  part  were 
folded  to  a  considerable  depth,  being  at  the  same  time  sub- 
jected to  dynamo-metamorphic  alterations,  which  in  many 
cases  determined  their  present  characters. 

During  this  period  the  ores  and  the  gangue  were  formed  by 
thermal  iron-bearing  solutions  acting  under  high  pressure.  To 
what  degree  these  solutions  were  magmatic,  carrying  ore-sub- 
stance from  below,  or  to  what  degree  the  small  amount  of 
water  contained  in  the  rock  was  active,  it  is  not  possible  to 
determine.  In  either  case,  the  process  was  different  from  the 
action  of  solutions  circulating  in  open  channels.  It  consisted 
in  a  solution  of  the  rock-substance,  which  was  intensified  by 
the  stress  and  friction,  according  to  the  principle  of  Riecke, 
and  also  in  an  accumulation  and  concentration  of  the  ore,  the 
surface-tension  operating  to  unite  particles  of  the  same  sub- 
stance. 

The  ore-material,  participating  in  the  plication  process,  with 
its  upheavals,  folding  and  dislocations  of  the  strata,  has  suf- 
fered some  mechanical  changes.  One  of  the  effects  which,  in 
many  cases  at  least,"  may  be  ascribed  to  the  mechanical  fold- 
ing is  the  peculiar  overlapping  which  many  ore-bodies  pre- 
sent. This  may  be  a  primitive  form  of  metasomatic  deposi- 
tion, but  may  also  be  considered  as  a  result  of  the  mechanical 
displacement  of  an  ore-layer.  Through  a  number  of  inclined 
or  even  vertical  planes  of  dislocation,  the  deposit  has  been  cut 
into  pieces,  which  have  then  been  somewhat  displaced  in  rela- 
tion to  one  another.  Often  these  dislocations  can  be  pointed 
out  only  with  difficulty,  or  not  at  all ;  they  are  more  obvious 
when  the  iron-ore  occurs  associated  with  a  limestone  bed.  (See 
Fig.  4,  showing  the  plan  of  Stallberget.)  The  whole  limestone 
horizon,  with  its  accompanying  iron-ore,  is  here  fractured  into 
several  lenses,  oblique  to  one  another.  The  planes  of  disloca- 
tion have  been  effaced  by  the  recrystallization  of  the  granulite, 
and  the  schistose  structure  thereby  developed,  with  its  lamina- 
tion running  obliquely  to  the  different  lenses,  which  gives  the 
appearance  of  being  situated  on  different  levels  of  the  strati- 
graphical  series. 

Another  mechanical  effect  of  the  rock-plication  is  the  stretch- 


664      GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.  ' 

ing  of  the  surrounding  rock,  by  which  it  has  assumed  a  linear 
structure,  a  system  of  smaller  folds,  with  the  axis  of  folding 
parallel  to  the  stretching,  having  often  been  formed  at  the  same 
time.  In  many  cases  (e.  g.,  the  Lekomberga  mine  in  the  parish 
of  Ludvika,  and  the  Smedje  and  Mossaberg  mines  in  Striberg), 
a  connection  between  the  stretching  of  the  rocks  and  the  pitch 
of  the  ore-bodies  is  observable,  the  axis  of  the  stretching  coin- 
ciding with  the  direction  of  the  pitch.  Yet  it  cannot  be  as- 
sumed as  beyond  dispute  that  this  connection  is  in  every  case 


-Itroithinaqrufy 


Magnetite.  Limestone.  Granulite.  Diorite. 

FIG.  4. — STALLBERG  MINES'. 

due  to  a  stretching  of  the  ores  themselves ;  it  may  also  be  ex- 
plained as  produced  by  the  ferriferous  solutions,  chiefly  follow- 
ing the  directions  indicated  by  the  folds,  formed  simultane- 
ously with  the  stretching  of  the  rocks. 

The  stretching  of  the  rocks  has  given  rise  to  the  character- 
istic form  presented  by  the  Swedish  ores  of  this  type,  which 
form  is  evidently  due  to  a  factor  acting  in  a  vertical  direction. 
This  form  is  represented  in  Fig.  5,  which  is  a  longitudinal  sec- 
tion of  part  of  the  Svartvik  mines,  according  to  B.  Santesson. 
Sometimes  this  form  will  be  developed  into  such  an  extreme 
type  as  that  of  the  mine  of  Stora  Malmsjoberg,  in  which  the 
ore  mined  in  1898  had,  according  to  H.  Sundholm,  a  length  of 
15  m.,  a  breadth  of  12  m.,  and  a  depth  of  150  meters. 

The  Chemical  Changes. — These  have  been  much  increased,  not 
only  by  the  high  temperature  in  the  anamorphic  zone,  but  also 
by  the  stress  and  mechanical  deformation,  which  tends  to  in- 
crease the  solubility  of  the  ore-material,  as  well  as  of  the  rocks. 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       665 

The  more  easily  soluble  limestones  were  especially  adapted 
to  take  up  the  ore-deposition ;  and  generally  great  changes  and 
transfers  of  the  ores  to  secondary  places  of  deposition  have 
taken  place  in  them,  depending  on  water-courses,  impermeable 
sub-strata,  etc.  The  concentration  has  occurred  especially  along 
folds,  fracture-zones,  fissure-systems,  and  contacts.  Thus  the 
ores  assume  the  irregular,  secondary  forms  characteristic  of 
metasomatic  deposits,  as  shown  in  Fig.  2,  representing  the  cen- 
tral part  of  Dannemora. 


.  Q METER 


O40 


GranuRte 

FIG.  5. — LONGITUDINAL  SECTION  OF  THE  SVARTVIK  MINES. 

Other  instances  of  concentration  by  solutions  are  offered  by 
the  fairly  numerous  cases  in  which  the  ore  proves  to  be  younger 
than  dikes  which  traverse  it.  Such  an  instance  is  the  Timans- 
berg,  a  deposit  of  type  D,  which  is  traversed  by  minor  dioritic 
dikes.  Of  these,  C.  H.  Vrang  writes  that  "  in  their  vicinity 
the  ore  increases  considerably  in  thickness."  4  In  the  Kran- 
grufva,  in  the  Persberg  district,  the  rich  and  pure  ore  is  chiefly 
found  on  one  side  of  a  large  diorite  dike;  a  dislocation  is  out 
of  the  question,  for  the  ore-bearing  layer  is  also  found  on  the 
other  side  of  the  diorite,  but  without  equally  distinct  ore-con- 
centration. H.  V.  Tiberg  has  described  how,  in  the  Qustavus 
mine  of  the  Langban  district,  a  deposit  consisting  of  specular 
iron-ore  and  magnetite,  with  gangue,  continues  from  the  sur- 
face to  a  flat  system  of  diabase  apophyses  occurring  at  a  depth 

4  Geologiska  Foreningen  Forhandlingar,  Stockholm,  vol.  ix.,  p.  244  (1887). 

42 


666       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

of  from  54  to  60  m.,  on  which  the  ore  spreads  like  a  cake, 
while  below  the  diabase  dikes  the  rock  is  dolomite  only.  In 
such  cases  the  intrusive  dikes  have  evidently  preserved  the 
underlying  rock  from  transformation.  A  similar  instance  from 
Dannemora  is  mentioned  by  A.  E.  Fahlcrantz,5  who  says  that 
over  a  dike  of  halleflinta  (felsite-porphyry)  a  band  of  iron-ore 
a  few  inches  in  thickness  was  met  with,  accompanying  the  hal- 
leflinta. In  this  case,  however,  it  is  probable  that  the  ore  is  a 
more  recent  formation;  for  the  majority  of  the  Dannemora 
ores  are  certainly  older  than  the  felsite-porphyries. 

Many  limestone  beds  have  been  largely,  or  even  wholly,  trans- 
formed into  ores,  especially  of  type  D,  the  gangues  of  which, 
consisting  of  calcium  and  magnesium  silicates,  clearly  indicate 
their  origin. 

At  Uto  it  is  questionable  whether  the  concentration  of  the 
most  prominent  ore-deposit  is  not  connected  with  the  two  trav- 
ersing pegmatite  dikes.  The  largest  and  deepest  mines,  which 
have  followed  the  deposit  down  to  a  vertical  depth  of  more  than 
200  m.,  are  situated  between  these  two  pegmatite  dikes;  more- 
over, on  the  outer  sides  of  the  pegmatites  there  is  a  continuous 
ore-mass,  which  has  been  followed  down  to  a  comparatively  great 
depth.  At  some  distance  from  these  dikes  the  ore  has  every- 
where been  less  thick  and  less  concentrated,  and  has,  therefore, 
been  mined  on  a  small  scale  only.  While  the  pegmatite  dikes 
evidently  originated  at  a  great  depth,  it  follows  that  the  ore-con- 
centration could  not  have  been  accomplished  earlier  than  the 
submersion  in  the  deep-seated  zone. 

The  numerous  mines  of  the  Grangesberg,  Blotberg,  Fred- 
muiidsberg,  and  Grasberg  districts  offer  good  opportunities  to 
observe  the  relation  between  the  pegmatites  and  the  ores.  The 
former  occur  here  as  dikes,  partly  traversing  the  ores,  and 
partly  parallel  to  the  stratification,  but  in  a  manner  which  indi- 
cates that  they  are  of  later  formation  than  the  ores.  Coarsely 
crystalline  magnetite  is  often  found  in  the  pegmatite  veins,  in- 
dicating that  the  aqueo-igneous  solutions  giving  rise  to  the  peg- 
matite originated  from  the  same  source  as  the  iron-ore. 

In  this  connection  attention  may  be  called  to  the  not  uncom- 
mon fact  that  the  ores  of  this  type  occur  along  contacts,  gener- 

5  Bihang  till  Handlingar  Kongliga  Svenska  Vetanskaps- Akademie,  Stockholm,  4 
(1876). 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN   IRON-ORES.       667 

ally  between  limestone  and  granulite,  but  also  along  the  contact 
with  intrusive  rocks.  A  marked  instance  of  the  former  mode 
of  occurrence  is  seen  at  Persberg  (Fig.  6),  where  the  upper  ore- 
bearing  horizon  occupies  a  basin  with  granulite  in  the  foot- wall 
and  dolomized  limestone  in  the  hanging-wall.  Similar  instances 


SCALE   1  :  10,000 


Limestone 


Pron-ore 


GTamilite 


FIG.  6. — PERSBERG. 


are  found  in  several  other  ore-deposits  of  type  D ;  e.g.,  the 
grufve  mine  and  the  Nordmark  mines  in  Vermland,  and  Sten- 
ring  and  Ramhall  in  Upland.  In  such  cases  the  situation  of  the 
ores  along  the  contact  can  hardly  be  explained  by  assuming 
them  to  be  of  primary  origin ;  the  only  explanation  possible  is 


668       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 


that  the  ores  have  been  precipitated  along  the  contact  from  fer- 
riferous solutions. 

The  same  explanation  presents  itself  in  such  a  case  as  that  of 
the  Hogborn  district  in  Orebro,  where  the  most  important  de- 
posits occur  on  a  certain  level  between  a  diorite  mass  and  the 
granulite  (Fig.  7).  If  the  ores  were  assumed  to  have  been  laid 
down  as  a  sedimentary  deposition  on  a  certain  level  within  the 
granulite,  it  would  be  necessary  to  explain  the  fact  that  the 
diorite  had  been  injected  on  this  very  level  and  formed  a  lac- 
colite  there.  The  assumption  that  the  ores  are  younger  than 


rJur£en  *,*\  *„  V  %  **  *JuSf?***t'**  **  V*  '*  *«  V  *  *[****•* '  *" 

**^*l^a™^'ldJSSF^*  *  *  *  « ^*  xx *'  *•  * *«**  *" *  **«  "* «  « 

^J-;/;^:;«^L>.':^--- 


Wankagrna 


SCALE  1  : 10,000 


Granulite  K*xVV»|  Diorite  j 

FIG.  7. — HOGBORN  MINES. 


Diabase 


the  dioritic  laccolite,  and  that  they  have  been  precipitated  from 
ferriferous  solutions,  removes  this  difficulty.  The  most  satisfac- 
tory view,  therefore,  is  that  the  ores  along  such  contacts  are 
epigenetic  formations. 

To  this  period  also  belongs  the  formation  of  the  gangues, 
which  are  the  result  of  the  silicification  that  takes  place  in  the 
deep-seated  zone.  Whole  layers  of  limestone  have,  through 
the  interchange  of  constituents,  been  transformed  into  lime- 
magnesia-iron  silicates  (sto-ft-deposits).  If  the  limestone  has 
already  undergone  a  dolomitizing  process,  or  if  Mg  is  added 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       669 

by  the  solution,  the  chief  alteration-products  will  be  amphi- 
boles,  which  are  rich  in  magnesia;  if  the  limestones  are  com- 
paratively pure,  pyroxenes  are  formed.  Though  the  garnet  of 
the  gangues  may  often  be  an  alteration-product  of  pyroxene 
or  amphibole  minerals,  it  may,  however,  frequently  be  of  pri- 
mary formation,  depending  on  the  chemical  composition  of  the 
solutions  and  the  transformed  material. 

Transformations  in  the  Surface-Zone. — When  the  erosion  and 
removal  of  the  overlying  Cambro-Silurian  strata  exposed  the 
Archaean  rocks,  the  ore-deposits  were  subjected  to  the  influence 
of  catamorphic  agencies. 

Among  the  transformations  of  this  period  we  have  to  note 
the  formation  of  many  skolar  of  chlorite  and  talc  (soapstone) 
by  the  decomposition  of  the  pyroxene  and  amphibole  of  the 
gangues  or  the  granulite  of  the  wall-rock.  Many  skolar ',  too, 
owe  their  origin  to  the  decomposition  of  intrusive  greenstone 
veins. 

Indeed,  the  wl  ole  mass  of  the  gangues  may,  under  certain 
circumstances,  be  changed,  quite  new  ore-types  being  the  re- 
sult of  the  transformation.  A  common  phase  of  this  transfor- 
mation is  the  occurrence  of  epidote,  quartz,  and  calcite  in  the 
gangue ;  if  the  alteration  proceeds  to  a  certain  degree,  hydrated 
minerals  of  the  talc  and  chlorite  groups  are  formed.  As  has 
been  shown  by  H.  V.  Tiberg,6  the  gangue  in  the  Taberg  mines 
in  Vermland,  the  ore  of  which  is,  in  its  upper  part,  markedly 
talcose,  has  been  formed  by  metasomatic  transformation  of 
augite  and  amphibole.  This  transformation  reaches  only  as 
far  down  as  320  m.,  at  which  depth  the  ore  is  cut  nearly  hori- 
zontally by  a  fissure  which  yields  plenty  of  water.  The  same 
author  adduces,  also,  the  Alabama  mine  in  the  Persberg  dis- 
trict as  an  instance  of  similar  transformation ;  in  its  southern 
part  the  ore  is  talcose,  but  in  the  northern  part  the  original 
gangues,  pyroxene  and  amphibole,  are  still  found.  No  doubt 
the  ores  of  Dalkarlsberget,  as  well  as  all  the  ores  belonging  to 
the  so-called  "  Rosberg  type  "  of  B.  Santesson,  ought  to  be  in- 
terpreted in  the  same  way,  as  being  derived  from  type  D 
through  alteration. 

Several  other  transformations   may  be  viewed  as  compara- 

6   Werml.  Bergsmannafor.  Ann.  (1908). 


670       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

lively  recent  and,  consequently,  belonging  to  this  period.  The 
ores  of  the  Striberg  type  are  often  found  to  lose  their  charac- 
teristic bandedness  in  the  direction  of  the  strike,  the  quartz 
being  replaced  by  a  somewhat  porous  magnetite,  sometimes 
also  by  calcite.  Concentrations  of  richer  magnetite  often  occur 
among  the  ores  of  this  type ;  they  are  generally  accompanied 
by  quartzose  segregations  or  chloritic  skolar. 

Simultaneously  with  this,  a  concentration  of  the  iron  may 
take  place,  Si02  being  dissolved  by  means  of  alkaline  car- 
bonates and  the  silica  replaced  by  ferric  oxides.  It  is  by  such 
concentration,  for  instance,  the  rich  ore  deposits  have  been 
formed  which  are  often  met  with  in  folds;  e.  g.,  in  Nordmark 
and  in  the  Hogborn  mines  in  Vermland.  In  localities  where 
very  thick  deposits  of  ore  not  enriched,  and  retaining  the  prim- 
itive structure,  occur  in  folds,  as  at  the  Stripa  mine,  the  abnor- 
mal thickness  must  be  ascribed  to  mechanical  deformation. 

Among  the  Grasberg  mines,  which  are  worked  on  a  folded 
layer  in  the  form  of  a  trough  sloping  NNW.9  there  occurs  in  the 
Bolag  mine  a  highly  concentrated  magnetite  in  the  fold,  the 
rest  of  the  ore  being  a  poor  hematite  with  quartz  bands.7  That 
a  concentration  process  has  taken  place  here  is  beyond  doubt, 
though  it  is  not  possible  to  determine  to  what  period  it  should 
be  assigned. 

On  a  still  larger  scale,  a  similar  transformation  has  taken 
place  in  the  Bispberg  mine,  producing  a  rich,  pure  magnetite, 
mined  in  the  deeper  levels  of  this  mine,  while  in  the  upper 
parts  the  ore  was  a  typical  low-grade  quartz-banded  hematite. 

Such  transformation  on  a  large  scale  of  specular  hematite 
into  magnetite  has  long  been  known  from  several  ore-deposits ; 
e.  g.,  Korberg,  Striberg,  Gellivare.  In  the  ends  of  the  ore- 
bodies  and  in  the  sides  contiguous  to  the  surrounding  rocks 
the  transformation  is  most  advanced,  but  also  the  interior  por- 
tions of  the  ores  consist  of  a  mixture  of  specular  hematite  and 
magnetite.  The  cause  of  this  transformation  is  not  fully  un- 
derstood; but  it  is  evidently  a  reaction,  depending  on  mass- 
action,  and  continuing  to  a  certain  limit,  where  equilibrium 
ensues.  It  looks  as  if  the  reaction  proceeded  from  the  sur- 
rounding or  traversing  silicate-rocks;  and  it  has  been  conjec- 

7  H.  Sundholm,  Jern-Kontorets  Annaler,  vol.  liii.,  p.  162  (1898). 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       671 

tared  that  the  alteration  has  been  produced  by  organic  sub- 
stances (humic  acids)  contained  in  the  surface-waters  descending 
along  the  walls  of  these  rocks.  Even  though  it  might  be  sup- 
posed that ;  these  organic  substances  had  the  power  of  reduc- 
ing specular  hematite  into  magnetite,  this  explanation  is  not 
very  satisfactory;  for  the  transformation  that  has  taken  place 
is  not  a  reduction  of  hematite  into  magnetite  with  retention  of 
the  structure  of  the  former,  but  a  solution  and  recrystallization 
of  the  iron-ore.  One  might  rather  suggest  the  action  of  alka- 
line solutions  proceeding  from  the  silicate-rocks,  or  some  other 
reagent. 

The  change  from  hematite  to  magnetite  is  reversible;  and 
in  some  places  we  meet  with  transformations  on  a  large  scale 
of  magnetite  into  hematite.  Of  the  anhydrous  iron  oxides, 
magnetite  is  more  stable  in  the  deep-seated  zone,  hematite  in 
the  surface-zone ;  and  it  seems  safe  to  assume  that  the  last- 
mentioned  alteration  belongs  to  the  surface-zone.  Such  a 
transformation  is  found  in  the  Grangesberg  mines,  where  the 
ore  close  to  the  foot-wall  consists  of  a  scaly  hematite  low  in 
phosphorus. 

The  Grangesberg  and  Norrbotten  Deposits. 

A  separate  position  should  be  assigned  to  those  ores  of  the 
type  which  are  chiefly  represented  by  the  large  deposits  of 
Grangesberg,  in  central  Sweden,  and  Gellivare,  in  Norrbotten. 
They  diverge  in  some  points  from  the  majority  of  the  ores  of 
the  Archaean  schists;  and  their  characteristic  properties  seem 
to  be  most  satisfactorily  explained  by  assuming  them  to  be 
transformed  basic  segregations  in  gneiss  -  granites  (ortho- 
gneisses). 


Analogous  Deposits. 

The  ores  of  this  group  are  well  represented  within  the  Ar- 
chaean series  of  the  United  States  and  Canada ;  indeed,  all.  the 
different  types  mentioned  above  are  found  there.  This  feature, 
that  the  same  ore-types  may  be  recognized  in  areas  so  far  apart 
as  North  America  and  the  Scandinavian  peninsula,  strongly 
indicates  that  these  types  correspond  to  certain  genetic  con- 
ditions. 


672       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 


[ABRIDGED  SUMMARY. — Ores  of  type  A  are  found  at  Mineville,  Lake  Cham- 
plain,  N.  Y.,  corresponding  to  the  Swedish  ores  in  appearance,  composition,  form 
of  ore-bodies,  etc.  Type  B,  rich  in  silica  and  alumina,  represents  in  part  the  Ar- 
chaean deposits  of  New  York  and  New  Jersey.  Type  C  recalls  at  many  points  the 
siliceous  banded  ores  of  Lake  Superior,  especially  the  Archaean  ores  of  the  Ver- 
milion range,  but  also,  in  some  respects,  the  Huronian  ores  of  Marquette  and 
Crystal  Falls.  Type  D  (the  "  Skarn"-ores)  has  also  its  representatives  among 
the  Archaean  deposits  of  New  York,  New  Jersey,  and  Pennsylvania,  and  in  the 
Cranberry  range  of  North  Carolina  and  Tennessee,  and  some  deposits  in  Eastern 
Ontario,  Can.  The  Tilly  Foster  mine,  in  Putnam  county,  N.  Y.,  is  a  striking 
instance.  Type  E  seems  to  be  comparatively  rare  in  the  United  States,  but  the 
iron-ore  of  Franklin,  N.  J. ,  and  some  other  places  in  the  United  States  and  Onta- 
rio, occurs  in  limestone. 

GROUP  II. — THE  ORES  OF  THE  PORPHYRIES  (KERATOPHYRES). 

The  province  of  Norrbotten  contains  many  times  as  much  iron 
as  all  the  rest  of  Sweden.  Some  of  the  deposits  in  this  province 
may  be  reckoned  among  the  largest  in  the  world.  The  export 
from  Kiirunavaara  commenced  as  late  as  1902,  when  the  rail- 
way to  Narvik  on  the  fjord  of  Ofoten  was  opened ;  in  the  fol- 
lowing year  the  exploitation  of  the  less  considerable  neighbor- 
ing deposit  of  Tuollavaara  also  began. 

Geologically,  the  iron-ore  deposits  of  Norrbotten  are  of  three 
kinds :  (1)  the  ores  of  the  crystalline  schists,  which  embrace  the 
deposits  of  Gellivare  and  Svappavare,  treated  in  the  preceding 
section ;  (2)  the  ores  of  the  Kiiruna  type,  connected  with  sye- 
nitic  porphyries;  and  (3)  ores  connected  with  basic  igneous 
rocks.  These  ores  will  be  treated  in  the  next  section.  (See  Fig.  8.) 

Topographically,  the  more  important  deposits  may  be  divided 
into  four  groups :  (1)  Gellivare,  embracing  Malmberget  and 
Koskulls  Kulle  and  a  few  copper  ore-deposits  north  of  the  Lina- 
elf;  (2)  Svappavare,  Leveaniemi  and  Mertainen,  situated  be- 
tween the  Kalix  and  the  Tornea  rivers;  (3)  a  group  in  the 
vicinity  of  Lake  Luossajarvi,  embracing  Kiirunavaara,  Luossa- 
vaara,  and  Tuollavaara ;  (4)  Ekstromberg,  which  belongs  to  the 
basin  of  the  Kalix  river.  Besides  these,  minor  deposits,  for  the 
most  part  only  imperfectly  known,  are  scattered  all  over  the 
wide  area. 

Kiirunavaara,  Luossavaara,  and  Tuollavaara. 

The  iron-ore  deposit  of  Kiirunavaara  is  undoubtedly  the  largest 
deposit  of  ore  found  in  Europe.  The  neighboring  deposits  of 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       673 


Luossavaara  and  Tuollavaara  are  geologically  of  the  same  nature, 
though  smaller.  The  first  two  of  these  deposits  have  been 
known  for  more  than  two  centuries.  Luossavaara  is  mentioned 
as  early  as  about  the  year  1690,  Kiiruna  not  before  1736 ;  a  de- 
scription of  both  is  given  in  the  Report  of  the  Government  Min- 
ing Inspector  for  1751.  The  first  survey  was  made  shortly  be- 
fore 1760.  Tuollavaara,  being  concealed  under  a  thick  moraine, 
was  not  discovered  until  1897.  (See  Fig.  9.) 


Basic  Eruptives,    Older     Cambrian     Pre-Cambrian.  Silurian' 
Silurian  or  younger.  Basic 

Eruptives. 


Gneissic  Rocks. 


Granite         Granulite    Porphyritic 

and  and  Rocks. 

Syenite.  Archaean  Schist. 


FIG.  8. — ORE-PROVINCE  OF  NORBOTTEN. 

The  ores  in  question  prove  to  be  genetically  connected  with 
a  group  of  eruptive  rocks  of  syenitic  composition,  and  charac- 
terized by  their  high  percentage  of  soda.  These  rocks  show 
the  structures  of  deep-seated  as  well  as  of  vein-rocks.  They 
are  intruded  in  a  sedimentary,  partly  clastic,  complex  of  strata, 
including  conglomerates  and  semi-crystalline  schists. 


674      GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

The  porphyritic  rocks  were,  for  a  long  time,  regarded  by  the 
Swedish  geologists,  Hummel,  Gumselius,  Fredholm,  and  others 
(in  analogy  with  the  case  of  central  Sweden),  as  a  sedimentary 
halleflinta,  and  the  stratified  rock-complex  in  which  they  occur 
was  called  hdlleflinta-schist.  In  1889,  however,  Tornebohm 
pointed  out  the  porphyritic  nature  of  the  so-called  hdtteflinta, 
and  afterwards  the  hatteflwto-Bchista  were  found  to  consist  of 
partly  clastic  rocks. 

The  ores  of  the  three  deposits  form  stratiform  masses  of  con- 
siderably greater  length  than  breadth — the  length  of  the  Kiiru- 
navaara  deposits  is  about  2.8  kilometers. 


FIG.  9. — PART  OF  ORE-DEPOSIT  OF  KIIRUNAVAARA  (LOOKING  NORTH). 

The  ores  are  immediately  surrounded  by  intrusive  rocks  of 
porphyritic  development  which,  on  account  of  their  composi- 
tion, are  to  be  referred  to  the  soda-syenite-porphyries.  They 
have  also  been  called  keratophyres  (H.  Backstrom) ;  however, 
as  this  name  is  applied  to  effusive  rocks,  and  the  effusive  nature 
of  the  Kiiruna  porphyries  seems  to  me  at  least  questionable,  I 
prefer,  for  the  present,  the  name  porphyries.  Two  kinds  of 
porphyry  may  be  distinguished :  one  more  basic,  occurring 
chiefly  in  the  foot-wall,  but  partly  also  in  the  hanging- wall  of 
the  ore,  and  one  more  acid,  often  developed  as  quartz -porphyry 
and  occurring  in  the  hanging-wall  of  the  ores  of  Kiirunavaara 
and  Luossavaara,  around  Tuollavaara,  etc.  The  basic  porphyry 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       675 

is  closely  connected  with  the  syenitic  rock  which  accompa- 
nies it. 

The  Syenite. — This  is  a  soda-syenite,  the  chief  mass  of  which 
is  a  soda-feldspar.  Secondary  basic  minerals  are  present  in 
abundance.  The  structure  is  eugranitic.  This  soda-syenite 
shows  gradations  into  the  porphyry  of  the  foot-wall,  with 
whidh  it  is  closely  allied  in  composition. 

The  Porphyry  of  the  Foot-  Wall. — This  rock  presents,  micro- 
scopically as  well  as  macroscopically,  a  fluidic  structure  with  a 
trachytoidal  arrangement  of  the  feldspar  of  the  ground-mass ; 
sometimes,  also,  spherulitic  structures  are  observable.  The 
primary  structures  are,  however,  frequently  difficult  to  distin- 
guish, being  in  part  totally  obliterated  by  the  alteration  of  the 
rock.  The  basic  constituents  are  almost  wholly  altered  into 
amphibole,  epidote,  and  chlorite.  Magnetite  seems  to  occur  in 
two  generations :  one  primary,  the  other  of  later  immigration. 
As  fissure-minerals,  indicating  a  secondary  action  of  pneuma- 
tolytic  nature,  occur  amphibole,  titanite,  apatite,  and  magnetite. 
In  the  contact-zone  the  fissures  sometimes  form  cavities  a  deci- 
meter in  diameter,  filled  with  the  said  mineral  combination. 

The  Porphyry  of  the  Hanging-Wall. — This  is  considerably 
more  acid  (containing  10  per  cent,  more  of  Si00)  than  the  syen- 
ite and  the  porphyry  of  the  foot- wall,  which  circumstance  places 
it  among  the  quartz-porphyries.  Quartz  occurs  in  the  ground- 
mass  partly  as  so-called  "  quartz  globulaire"  but  in  larger  quan- 
tities where  the  ground-mass  has  undergone  a  recrystallization. 
Here,  too,  a  secondary  generation  of  magnetite  can  be  observed. 
The  primary  basic  mineral  constituents  are  completely  altered, 
having  produced  amphibole,  epidote,  and  chlorite.  The  rock 
shows,  even  macroscopically,  a  distinct  fluidic  structure. 

Segregations  of  pure  magnetite,  mostly  in  rounded  pieces,  are 
worthy  of  notice ;  these  segregations  sometimes  show  a  concen- 
tric structure  and  at  times  inclose  grains  of  the  feldspar  of  the 
porphyry.  When  the  fragmentary  character  is  more  distinct, 
they  are  probably  portions  of  segregations,  solidified  in  depth 
at  an  earlier  date,  which  have  been  partly  rounded  by  resorp- 
tion.  These  segregations  have  also  been  interpreted  as  fragments 
of  the  great  ore-body ;  and  from  this  it  has  been  concluded  that 
the  porphyry  of  the  hanging-wall  should  be  younger  than  the 
mass  of  ore. 


676       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

The  unmistakable  "  consanguinity  "  between  the  soda-syenite 
and  the  porphyries  is  manifested  by  the  high  percentage  of  Na, 
which  varies  between  5.5  and  7.5  per  cent.;  apatite,  titanite, 
and  magnetite  are,  besides,  minerals  common  to  the  syenite,  the 
porphyries,  and  the  ore-deposits. 

The  Ores. — (In  the  following  exposition  of  the  Kiirunavaara 
and  Luossavaara  ore-deposits,  I  follow  chiefly  the  official  report 
made  by  Hj.  Lundbohm  in  1898.)  The  iron-ore  occurring 
among  the  porphyry  masses  forms,  on  the  whole,  pure,  nearly 
homogeneous  ore-deposits;  other  minerals  found  in  it  are  of 
comparatively  subordinate  significance. 

A  property  characteristic  of  the  ore  of  Kiiruna-,  Luossa-,  and 
Tuollavaara  is  its  general  extremely  fine-grained  texture,  which 
proves  that  it  has  been  subject  to  a  slight  degree  only  to  the 
action  of  recrystallizing  agents.  By  this  structure,  which  is 
also  found  in  a  few  other  ores  in  Norbotten,  this  ore-type  is  dis- 
tinguished from  the  rest  of  the  Scandinavian  ores. 

The  only  mineral  that  occurs  in  the  ore  with  undoubtedly 
primary  characters  is  apatite,  the  distribution  of  which  is  ex- 
ceedingly irregular,  so  that  the  percentage  of  phosphorus  in 
the  ore  varies  greatly. 

In  Kiirunavaara,  chiefly  close  to  the  foot-wall,  but  also  here 
and  there  in  the  interior  of  the  ore,  occurs  an  ore-type  with 
mostly  grayish-black  and  dull,  compact  fracture  (Lundbohm's 
type  5).  When  examined  with  the  microscope  it  proves  to  be 
interlarded  with  apatite  individuals  idiomorphically  developed ; 
its  phosphorus-percentage  is  from  3  to  6  per  cent.  This  ore 
frequently  presents  a  stratiform  structure. 

The  ore-type  which  quantitatively  predominates  contains  the 
apatite  in  nodules  and  irregular  lenses  (Lundbohm's  type  4). 
Here,  too,  the  apatite  seems  to  be,  at  least  in  part,  of  primary 
origin,  since  it  occurs  partly  as  a  minute  impregnation  of  the 
ore,  partly  in  irregular  nests  and  veins,  giving  rise  to  a  structure 
which  bears  some  resemblance  to  a  largely  developed  flow- 
structure  (Fig.  10). 

Primary  structural  forms  which  may  be  referred  to  flow- 
structure  may  also  be  observed  in  the  relations  between  different 
ore-types,  when,  e.g.,  one  type  contains  fragments  or  "  schlieren  " 
of  another  type,  or  when  one  ore-type  occurs  as  intruding  dikes 
in  another  (Fig.  11).  Especially  on  weathered  ore-surfaces 
these  structures  are  easily  observable. 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       677 

It  is  likely  that  the  highly  phosphoric  ores,  though  embracing 
several  types,  must  in  general  be  regarded  as  primary,  and  those 
poorer  in  apatite  as  secondary,  leached,  and  in  part  recrystal- 
lized.  The  latter  also  contain  martite  and  specular  hematite, 
the  occurrence  of  which  is  here  evidently  secondary. 


FIG.  10. — IRREGULAR  VEINS   OF  APATITE  IN  MAGNETITE,  KIIRUNAVAARA 

(Lundbohm). 

In  the  low-phosphorus  ores  occur  also  calcite  (formed  at  the 
expense  of  the  apatite),  secondary  quartz  in  fissures,  and  second- 
ary silicates  as  amphibole,  talc,  and  chlorite  minerals.  The 
secondary  ore-types  are  sometimes  porous,  the  more  soluble 
minerals  having  been  leached  out. 


FIG.  11. — FLOW-STRUCTURE  IN  MAGNETITE,  KIIRUNAVAARA  (Lundbohm). 

From  a  practical  point  of  view,  the  ores  in  question  have 
been  divided  into  several  classes  according  to  their  percentage 
of  phosphorus.  Those  classes  which  range  above  1  per  cent, 
constitute  the  principal  mass  of  the  ores  of  Kiirunavaara.  As 
a  fairly  certain  result  of  the  examinations  of  the  ores  with  regard 
to  their  percentage  of  phosphorus,  it  may  be  said  that  ores  con- 


678       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

taining  less  than  0.05  per  cent.,  and  ores  with  from  0.05  to  0.1 
per  cent.,  of  phosphorus,  occur  separately  in  such  a  mode  that 
they  can  be  utilized,  but  that  both  kinds,  especially  the  former, 
are,  as  regards  quantity,  rather  subordinate  to  those  richer  in 
phosphorus. 


The  Genesis  of  the  Deposits. — The  genetic  connection  of  these 
ores  with  the  porphyry-rocks  is  so  manifest,  that  it  has  been 
admitted  by  all  who  have  expressed  their  opinion  on  the  sub- 
ject. Even  those  geologists  (Hummel  and  Gumselius  in  1875, 
Fredholm  in  1891),  who  regarded  the  porphyries  as  sedimen- 
tary katteflintor,  acknowledged  this  connection,  and  consequently 
considered  the  ores  as  sedimentary  formations.  Lofstrand,  in 
1891  and  1892,  in  describing  other  basic  segregations  and  vein- 
like  formations  of  iron-ore  in  acid  igneous  rocks,  pointed  out 
that  the  connection  of  the  ores  of  Kiiruna  with  the  porphyries 
ought  to  be  interpreted  in  the  same  way.  The  same  opinion 
was  expressed  more  positively  in  1898  by  Hogbom,17  who  laid 
special  stress  on  the  agreement  with  the  deposits  connected 
with  syenitic  rocks  in  the  eastern  Ural:  Wyssokaia  Gora,  Le- 
biajaia,  and  Gora  Blagodat.  A  similar  opinion  was  pronounced 
at  a  later  time  by  0.  Stutzer,  who  holds  that  the  ores  have 
been  formed  in  an  epigenetic-magmatic  way  as  "  eine  nach  oben 
gewanderte  magmatische  Ausscheidung " — i.  e.,  a  magmatic 
vein-formation. 

A  pneumatolytic  sedimentary  mode  of  formation  has  been 
maintained  by  Backstrom  and,  later,  by  De  Launay  (1903).  The 
latter  author,  who  gives  the  most  detailed  exposition  of  this 
view,  has  formed  the  following  conception  of  the  process :  The 
porphyry  of  the  foot-wall  is  an  effusive  rock,  on  which  the  iron- 
ore,  formed  through  the  decomposition  of  chloride  and  sulphide 
of  iron  in  contact  with  water,  has  been  deposited.  Later  on  a 
new  eruption  of  porphyry  followed,  by  which  the  porphyry  of 
the  hanging-wall  was  formed. 

This  interpretation  is  based  on  the  opinion  that  the  ore  is 
younger  than  the  porphyry  of  the  foot-wall  and  older  than  the 
porphyry  of  the  hanging-wall,  which,  however,  is  hardly  com- 

1T  Geologiska  Foreningen  Forhandlingar,  Stockholm,  vol.  xx.,  p.  115  (1898). 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       679 

patible  with  the  fact  that  the  magnetite  is,  in  places  completely 
surrounded  by  the  basic  porphyry. 

The  above-mentioned  fluidic  structures  in  the  magnetite  can 
be  accounted  for  only  by  assuming  that  the  magnetite,  together 
with  the  greater  part  of  the  apatite,  has  formed  a  segregation 
from  an  iron-alkali-silicate  magma,  intruded  as  a  vein  between 
the  porphyries.  After  this  intrusion  the  effects  of  pneumato- 
lytic  agencies,  which  are  especially  well-marked  at  the  contact 
with  the  basic  porphyry,  have  arisen.  Hogbom  has  given  a 
theoretical  exposition  of  the  formation  of  ores  of  this  kind.  He 
starts  from  an  iron-alkali-silicate  magma  composed,  approxi- 
mately, in  the  proportion  of  1  molecule  of  orthoclase,  1  mole- 
cule of  albite,  and  1  molecule  of  magnetite.  Such  a  magma 
differs  in  composition  from  known  and  common  magma-types 
only  by  containing  a  little  more  ferric  oxide  and  a  somewhat 
smaller  amount  of  lime  and  magnesia.  As,  at  the  solidification 
of  such  a  magma,  the  larger  part  of  the  iron  must  segregate  as 
magnetite,  because,  owing  to  the  absence  of  lime  and  magnesia, 
it  cannot  combine  with  the  silica,  the  differentiation  of  two  rocks, 
one  chiefly  consisting  of  magnetite,  the  other  of  feldspar,  is  easily 
accounted  for.  Hogbom,  therefore,  holds  that  the  alkali-silicate 
magmas  rich  in  iron,  to  which  petrography  has  as  yet  paid  but 
little  attention,  have  a  just  claim  to  a  place  in  the  system,  and 
that  their  most  typical  representatives  are  magnetite-bearing 
syenitic  rocks  of  this  kind. 


[ABRIDGED  SUMMARY. — At  Mertainen,  30  km.  southeast  of  Kiiruna,  the  ores 
are  connected  with  a  syenite-porphyry,  mainly  consisting  of  a  soda-feldspar.  At 
the  contact,  the  rock  has  undergone  pneumatolytic  transformation.  Its  original 
basic  constituents  have  disappeared  and  new  magnesia  silicates  appear  in  their  place. 
The  soda-feldspar  has,  in  part,  been  transformed  into  scapolite,  but  biotite  and 
titanite  also  have  been  produced.  The  magnetite  occurs  partly  finely  disseminated, 
partly  in  small  segregations,  from  the  size  of  an  almond  to  that  of  an  egg.  These 
have  been  interpreted  as  cavity-fillings  ;  but  the  deposit  is  properly  a  magnetite 
breccia.  A  fine-grained  magnetite  fills  the  corrosion-fissures  of  the  rock,  associated 
sometimes  with  amphibole,  less  frequently  with  apatite.  A  similar  deposit  occurs  at 
Painirova,  8  miles  to  the  south.  The  deposits  of  Mertainen  and  Painirova  are, 
like  those  of  Kiiruna,  genetically  connected  with  the  syenite-porphyries.  But  at 
Mertainen  the  pneumatolytic  characters  are  most  marked,  and  there  is  nothing  like 
the  pure  ore-masses  of  magmatic  origin  and  partly  of  fluidic  structure  which  form 
the  main  deposit  at  Kiiruna.  At  Ekstromberg,  about  30  km.  west  of  Kiiruna- 
vaara,  the  ore  is  connected  with  syenitic  porphyries  ;  and  many  other  deposits  of 
this  general  class  are  known  in  Norrbotten.] 


680       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

Analogous  Deposits. 

The  ores  in  Norrbotten  of  the  Kiiruna  type  belong  to  a 
particularly  well-defined  geological-petrographical  type,  which 
is  also  met  with  in  other  parts  of  the  world. 

Hogbom  has  already,  in  the  above-mentioned  paper,  pointed 
out  the  agreement  between  the  iron-ore  deposits  in  the  eastern 
Ural  and  the  Kiiruna  type.  In  the  iron-mountains  of  the  Ural 
a  secondary  epidotization  of  the  rocks  has  taken  place  on  a 
larger  scale  than  in  Norbotten,  especially  along  certain  planes 
of  dislocation.  On  the  other  hand,  the  pneumatolytic  charac- 
ters so  well  marked  in  the  Kiiruna  type  are  not  met  with  in  the 
deposits  of  the  Ural.  The  secondary  transformations,  such  as 
the  development  of  martite  and  specular  hematite,  the  leaching 
out  of  pyrite  and  apatite,  the  formation  of  porous  ore  or  ore 
containing  calcite,  and  the  accumulation  of  the  apatite  chiefly 
near  the  foot-wall,  are  common  to  the  two  districts. 

The  ores  of  the  (for  the  most  part  exhausted)  deposits  of 
Iron  Mountain  and  Pilot  Knob  in  Missouri,  which  also  occur 
in  association  with  porphyry-rocks,  have  been  compared  to  and 
classed  with  the  Kiiruna  type  by  several  authors.  At  Iron 
Mountain  the  ore  mined  occurred  as  veins  and  irregular  masses 
of  martite  and  specular  iron-ore  in  a  mostly  decomposed  por- 
phyry of  Archaean  age.  At  Shepherd  Mountain  similar  de- 
posits in  porphyry  were  worked.  The  deposits  of  Pilot  Knob, 
on  the  contrary,  are  secondary  redepositions  of  the  primary 
iron  of  the  porphyry ;  they  seem  to  bear  a  strong  resemblance 
to  the  deposit  of  specular  iron-ore  in  the  Hauki  schists  east  of 
Luossavaara. 

Also,  the  Mexican  deposits  at  Durango  and  Las  Truchas 
agree  in  some  respects  with  those  in  Norbotten;  but  their 
geological  conditions  have  not,  as  yet,  been  sufficiently  inves- 
tigated to  make  a  direct  comparison  possible. 

GROUP  III. — IRON-ORES  FORMED  BY  MAGMATIC  SEGREGATION  IN 
BASIC  ERUPTIVES. 

The  ores  of  this  kind  form  a  natural  and  well-defined  class 
encountered  in  all  parts  of  the  world.  That  they  are  geneti- 
cally connected  with  eruptive  rocks  has  long  been  admitted. 
The  nature  of  their  facies  of  differentiation  was  not  understood 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       681 

until  the  differentiation  of  rock-magmas  was  clearly  conceived. 
In  this  regard,  their  structural  characters,  which  are  the  same 
as  those  of  the  eruptive  rocks,  and  their  frequent  presentation 
of  all  degrees  of  transition  to  the  normal  rock,  are  evidential. 
(Fig.  13.) 

Magmatic  differentiations  of  this  kind  seem  to  be  connected 
only  with  intrusive  eruptives,  and  occur  in  laccolites  as  well  as 
in  vein-like  intrusions.  In  general,  a  distinction  can  he  made 
between  such  differentiations  as  have  taken  place  within  the 
mass  of  the  laccolite,  in  situ,  and  such  as  have  taken  place  in 
the  deep-seated  magma.  In  the  latter  case  the  product  of 
magmatic  segregation  has  been  carried  up  to  the  level  of  the 
laccolite  by  a  separate  act  of  eruption. 

Taberg  in  Smdland. 

As  far  as  a  hundred  years  back  Hausmann 18  expressed  the 
opinion  that  "  the  mass  of  Taberg  is  a  greenstone  bed  of  toler- 
ably great  thickness,  mixed  with  much  iron-ore  and  lying  in 
gneiss."  Through  the  investigations  of  A.  Sjogren19  and 
Tornebohm 20  it  was  established  that  the  ore-deposit  of  Taberg 
ought  to  be  considered  as  a  segregation  in  a  basic  eruptive,  the 
chief  constituents  of  which  are  olivine,  plagioclase,  a  rhombic 
pyroxene,  and  magnetite.  The  structure  is  that  of  a  deep-seated 
rock,  and  the  rock,  which  has  been  called  hyperite  by  the 
Swedish  geologists,  is  olivine-norite  according  to  the  nomen- 
clature of  Rosenbusch.  Taberg  was  the  first  iron-ore  deposit 
interpreted  as  a  phase  of  an  eruptive  rock.  Tornebohm 21  says 
that  the  Taberg  ore  "  may  be  regarded  as  a  variety  of  hyperite 
rich  in  iron."  As  the  ideas  of  magnetic  differentiation  were 
not  clearly  formulated  until  later,  the  nature  of  the  ore  could 
not  in  1881  be  expressed  in  plainer  terms.  The  whole  of  the 
eruptive  constitutes  an  intrusion  (laccolite)  in  the  surrounding 
gneiss,  above  which  it  now  rises,  by  reason  of  its  greater  power 
of  resistance  to  erosion.  (Fig.  14.) 

The  ore-deposit  occupies  the  central  portion  of  the  mountain. 
The  ore-segregation  consists  of  titaniferous  magnetite  and 

18  R&ise  durch  Skandinavien,  Pt.  I.,  pp.  158  to  167  (1806-07). 

19  Geologiska  Foreningen  Forhandlingar,  vol.  iii.,  p.  42  (1876). 

20  Idem,  vol.  v.,  p.  610  (1881). 

21  Loc.  cit. 

43 


682       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 


0  2          ¥  6          8         10         II         if         Itf         |ft         10        it,        i*t-      16        28 


FIG.  13. — DISTRIBUTION  OF  TITAN i FERGUS  IRON-ORES. 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       683 


J^rofil  of  Tdbcrg  from. 

Scale,   1:10,000 


a         ____/ — , . ,.,    L-  — r-*-  :•.-.'.- .•:::.•. 

^I^^v:^X^»?r^v^:^ 

•:••&    . 


The  surface  of 
-fhf  rividet:. 


I','/,'/!    Gneiss  and 
I .  .  n  «  iilgntMssir  granite 

jv:-'::^;v:.v'jj     Magnetite 
'•'•'•  '•'••''••'•'''      olivinite- 


.       L.,    ,. 
A  Amphibohte. 

''' 


-".'       Gabbro - 
diorite. 


FIG.  14.— TABEBQ  (Tornebohm). 


684      GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

olivine  and  has  received  the  petrographical  name  magnetite- 
olivinite.  Where  it  approaches  the  normal  rock,  it  first  takes 
up  plagioclase,  then  pyroxene,  so  that  there  is  a  transition  from 
the  ore  to  the  normal  rock,  which  also  contains  magnetite  and 
olivine.  The  ore-stock  thus  forming  the  kernel  of  the  moun- 
tain is  next  surrounded  by  a  shell  or  mantle  of  normal  gabbro, 
which,  in  its  turn,  towards  the  inclosing  gneiss,  passes  into  the 
schistose,  dynamo-metamorphic  border-facies,  the  gabbro-am- 
phibolite. 

The  ore  is  poor  throughout,  carrying  generally  from  20  to  30 
per  cent,  of  iron.  Vein-like  segregations  containing  up  to  60 
per  cent,  occur  as  rare  exceptions.  Titanic  acid  varies  between 
4  and  6  per  cent. ;  the  percentage  of  phosphorus  does  not  exceed 
0.1 ;  to  which  may  be  added  a  constant  percentage  of  vanadine. 


[ABRIDGED  SUMMARY. — Minor  deposits  in  central  and  southern  Sweden,  and 
several  in  Norway,  belong  to  this  class.  And  in  the  small  islands  along  the  coast 
of  Angumanland  occur  similar  segregations  in  a  diabase  younger  than  the  Dala 
sandstone,  forming,  between  stratified  quartzites,  bed-like  intrusions  which  have 
been  exposed  by  erosion.  The  darker  bands  of  this  rock  have  acquired,  in  some 
places,  through  a  concentration  of  titano-magnetite,  the  character  of  iron-ore. 
The  proportion  of  titanic  acid  may  amount  to  25  per  cent.  In  the  island  of  Alno 
concentrations  of  titano-magnetite  in  a  boss  of  nepheline-syenite  have  been  worked 
in  a  small  way  as  iron-mines.  At  Ekersund  and  Soggendal,  in  Norway,  deposits 
of  iron-ore  occur  in  a  colossal  laccolite  of  highly  differentiated  basic  rocks,  sup- 
posed to  be  of  post-Silurian  age.  They  have  been  worked  at  different  times,  but 
without  commercial  profit,  since  they  contain,  as  an  average,  only  40  per  cent,  of 
iron,  and  from  40  to  42  per  cent,  of  titanic  acid.  Deposits  of  this  class  are  nu- 
merous along  the  coast  of  Norway,  in  laccolites  laid  bare  by  the  fjords.  One  of 
the  largest  in  Scandinavia  is  that  of  Routivare  in  Norrbotten,  which  was  formed 
by  segregations  in  an  intrusive  rock,  occurring  as  a  laccolite  in  the  metamorphic 
Silurian  formations.] 

Summary. 

Though  the  rocks  which  inclose  the  deposits  of  this  class 
differ  in  composition  (as  real  gabbros,  norites,  diabases,  or  neph- 
eline-syenites),  as  well  as  in  age  (some  of  them  belonging  to 
the  oldest  Archaean  formation,  and  the  youngest  dating  from 
post-Silurian  time),  yet  a  marked  degree  of  basicity  seems  to 
be  a  necessary  condition  for  the  formation  of  such  concentra- 
tions. Yogt  puts  the  highest  acidity  at  57  per  cent,  of  Si02. 
The  majority  of  the  deposits  occur  in  rocks  with  a  silica-per- 
centage of  from  48  to  54  per  cent.  The  different  facies  of 
gabbro-rocks  inclose  deposits  of  different  character.  The  pure 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       685 

ilmenite-segregations  (Ekersund,  Soggendal,  Lofoten,  etc.), 
seem  to  be  confined  to  the  labradoritic  rock.  In  the  same  rock- 
series  we  also  find  the  ilmenite-norite.  In  the  olivine-gabbro, 
rich  in  magnesia,  which  incloses  the  deposit  of  Taberg,  the  seg- 
regation has  assumed  the  mineralogical  character  of  magne- 
tite-olivinite,  and  in  the  rocks  which  are  richer  in  alumina, 
magnetite-spinellite  has  been  segregated,  as  at  Routivare,  Ando- 
pen,  on  Stjerno  in  Finnrnarken,  and  elsewhere. 

A  remarkable  feature  of  the  ore-concentrations  in  question 
is  their  occurrence,  almost  without  exception,  in  the  central 
parts  of  the  eruptive  masses.  This  gives  them  a  character  dif- 
ferent from  that  of  those  concentrations  of  basic  constituents 
in  an  eruptive  rock  which  are  often  met  with  along  the  mar- 
gins of  rock-veins,  and  in  which  the  enrichment  has  not  pro- 
ceeded so  far  as  to  form  an  iron-ore. 

As  to  the  degree  of  concentration  of  the  iron,  the  ore-types 
differ  also  from  one  another.  The  concentrates  richest  in  iron 
are  the  magnetite-spinellites,  with  an  iron-percentage  exceed- 
ing 50  per  cent.  (Routivare,  50  to  54;  Solnor,  54;  Hellevig, 
51 ;  Andopen,  nearly  60).  Next  to  these  come  the  segrega- 
tions of  the  nepheline-syenites,  of  which  in  Alno  some  con- 
tain from  46  to  53  per  cent. ;  and  after  these  the  ilmenite-seg- 
regations in  the  labradoritic  rock  and  the  norite,  with  about 
40  per  cent,  of  iron,  and  nearly  as  high  a  percentage  of  titanic 
acid.  Poorer  still  are  the  ores  of  the  olivine-gabbros  of  the 
Taberg  type,  which  contain  little  more  than  30  per  cent,  of 
iron.  Comparable  to  them  are  the  ores  of  the  oli vine- diabase 
(the  Ulfo  type),  with  about  34  per  cent.  At  the  bottom  of  the 
scale  stands  the  ilmenite-norite,  the  Storgang  type,  with  about 
21  per  cent,  of  iron. 

Besides  the  iron,  it  is  chiefly  the  titanic  acid,  the  magnesia, 
and  the  alumina  that  have  been  concentrated.  The  percentage 
of  titanic  acid  is  highest  in  the  ilmenite-segregations  of  the 
labradorite  and  norite,  where  it  amounts  to  from  39  to  43  per 
cent.;  next  come  the  ilmenite-norites,  which  contain  18  per 
cent. ;  the  magnetite-spinellites  (type  Routivare)  vary  between 
10  and  18  per  cent.;  the  segregations  of  the  nepheline-syenite 
show  about  10  per  cent,  (the  Trygg  mine,  in  Alno,  from  9.10 
to  12.14);  in  the  Taberg  type,  the  magnetite-olivinite,  the  per- 
centage of  titanium,  like  that  of  iron,  is  the  lowest — viz.,  6.30 


686       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

in  the  Taberg  ore  and  8.50  in  the  ore  of  Langhult.  The  Ulfo 
type,  with  about  10  per  cent,  of  Ti02,  shows  the  greatest  agree- 
ment with  the  Taberg  type. 

The  concentration  of  magnesia  has  taken  place  not  so  much 
in  the  ore  as  in  the  concentration-facies  between  the  normal 
rock  and  the  segregations  richest  in  iron.  It  manifests  itself 
in  the  formation  of  Mg-Fe  silicates  of  the  olivine  and  pyroxene 
groups.  The  rock-facies,  which  have  received  the  names  mag- 
netite-olivinite,  ilmenite-norite,  and  ilmenite-enstatite,  have 
originated  in  this  way.  A  certain  percentage  of  Mg  is  found 
even  in  the  purest  segregations  of  ilmenite  in  the  labradoritic 
rock,  owing  to  a  mixture  with  MgTi02.  The  alumina  left  in 
the  final  concentrates  combines  particularly  with  the  magnesia, 
thus  forming  spinel,  the  formation  of  which  is  favored  by  the 
relation-deficiency  of  silica  in  the  magma.  This  mineral  occurs 
in  the  following  ore-types :  the  magnetite-olivinite  (Ransberg) ; 
the  ilmenite-norite  (Ekersund);  and  the  magnetite-spinellite 
(Routivare,  Hellevig,  Lofoten,  and  Stjerno).  Yogt  has  called 
attention  to  the  fact  that  the  Mg-percentage  increases  in  the 
first  stage  of  concentration  and  then  diminishes.  While  the 
original  magma  contains  more  A1203  than  MgO,  the  case  is 
quite  the  reverse  in  the  earlier  stages  of  concentration.  In  the 
final  product,  however,  the  amount  of  alumina  again  exceeds 
that  of  magnesia. 

Besides  the  aforesaid  substances,  chrome  and  vanadium, 
which  occur  in  small  quantities,  have  undergone  a  concentra- 
tion. The  phosphorus,  on  the  other  hand,  is  not  in  general 
concentrated  to  any  noteworthy  degree.  To  this,  however, 
there  are  exceptions,  such  as  the  segregations  of  ilmenite-norite 
traversing  the  labradoritic  rock  in  the  Soggendal-Ekersund 
field,  which  contain  a  fairly  high  percentage  of  phosphorus, 
while  the  surrounding  rock  carries  little,  and  the  above-men- 
tioned concentrations,  rich  in  apatite,  in  the  hypersthene-gab- 
bro  at  Krekling,  Norway,  and  also  in  the  nepheline-syenite  of 
Alno. 

That  silica,  lime,  and  alkalies  occur  in  smaller  quantities  in 
the  concentrates  than  in  the  rest  of  the  rock-mass  is  manifested 
mineralogically  by  the  total  absence  of  feldspar  from  these  con- 
centrations. 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       687 

Vogt  has  pointed  out 22  that  in  several  places  in  Lofoten  and 
Vesteraalen,  in  the  labradoritic  rock  containing  olivine  and 
hypersthene,  there  are  besides  segregations  of  magnetite-dial- 
agite,  also  schlieren-\ike  segregations  of  pure  olivine  rock  as 
well  as  of  hypersthenite.  This  shows  that  in  the  same  magma 
differentiation  processes  following  different  lines  have  taken 
place  nearly  contemporaneously.  As  extreme  basic  segrega- 
tions the  limestones  occurring  in  the  nepheline-syenite  may 
also  be  explained. 

Many  different  attempts  to  suggest  the  cause  of  these  differ- 
entiations have  been  made,  but  no  satisfactory  explanation  has 
as  yet  been  proposed.23  It  seems  as  if,  with  respect  to  this 
kind  of  segregations,  the  view  according  to  which  the  magma 
is  regarded  as  a  mixture  of  different  liquids,  partly  insoluble 
in  one  another,  were  decidedly  preferable  to  the  theory  which 
considers  the  laws  of  dilute  solutions  applicable  to  the  magma. 
The  principle  of  limited  solubility  must  be  considered  as  the 
physico-chemical  principle  governing  the  differentiation-phe- 
nomena of  silicate-magmas  in  general. 

Neither  "  Soret's  principle,"  nor  any  other  form  of  the  theory 
of  diffusion,  nor  "  connection  currents,"  nor  the  magnetic  at- 
traction of  the  "  liquid  molecules,"  nor  the  different  weight  of 
the  segregated  solid  constituents  can  afford  an  explanation  of 
differentiation-phenomena  of  this  kind.  The  geological  condi- 
tions also  seem  to  harmonize  better  with  the  view  which  con- 
nects the  differentiation  with  the  segregation  and  solidification 
of  liquids  insoluble  in  the  remaining  magma.  These  are  sepa- 
rated out  in  consequence  of  the  cooling  of  the  magma,  by 
which  the  conditions  of  solubility  are  changed,  or  of  the  escape 
of  water  or  other  mineralizers ;  the  segregation  takes  place  at 
first  in  the  form  of  drops  throughout  the  magma,  which  drops? 
on  account  of  the  surface-tension,  have  a  decided  tendency  to 
coalesce  and  flow  together  into  schlieren  and  larger  concen- 
trations. Which  of  the  liquids  is  attracted  to  the  side-walls 
and  solidifies  there,  and  which  of  them  solidifies  in  the  center, 
will  in  each  case  depend  on  the  relative  force  of  the  adhesion 
to  the  side-walls. 

22  Zeitschrift  fur  praktische  Geologic,  vol.  xiv.,  pp.  217  to  233  (1906). 

23  Vogt,  Zeitschrift  fur  praktische  Oeologie,  vol.  ix.,  pp.  327  to  340  (1901). 


688       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

Analogous  Deposits. 

Titaniferous  iron-ore  segregations  in  basic  eruptive  masses 
constitute  a  well-defined  class,  which  has  representatives  in  all 
parts  of  the  world.  Several  of  the  different  types  found  in 
Scandinavia  occur  in  other  countries  also. 

In  the  United  States  and  Canada  these  ores  have  long  been 
grouped  together  as  a  separate  class,  and  a  great  many  deposits 
of  this  kind  have  been  described. 

The  magnetite-olivinite  or  Taberg  type  is  analogous  to  the 
deposit  at  Iron-mine  Hill  in  Cumberland,  R.  L,  described  by 
Wadsworth,  though  the  latter  is  of  smaller  dimension.  The 
"  gabbro  titanic-iron-ores  "  of  the  Mesabi  range  in  Minnesota, 
described  by  N.  H.  and  H.  V.  Winchell,  also  seem  to  come 
very  near  to  the  type,  though  the  concentration  of  the  iron  and 
the  titanium  has  in  these  ores  proceeded  further.  Among  the 
segregations  occurring  in  large  masses  in  the  various  gabbro 
and  labradoritic  rocks  of  the  eastern  Adirondacks,  the  Taberg 
as  well  as  the  Ekersund  type  is  represented. 

Perfect  analogies  to  the  Ekersund  type  of  ilmenite-segrega- 
tions  in  labradoritic  rock  are  offered  by  the  Canadian  ilmenite- 
deposits  of  Quebec  and  Ontario,  which  frequently  contain  from 
30  to  40  per  cent,  of  titanic  acid  and,  in  consequence  thereof, 
a  low  percentage  of  iron.  Some  of  these  ores  seem  to  consist 
of  a  mixture  of  ilmenite  and  titano-magnetite  with  a  diminu- 
tion of  the  percentage  of  titanic  acid  and  an  increase  of  that  of 
iron.  The  inclosing  rocks  are  labradorite  and  norite. 

Deposits  analogous  to  the  magnetite-spinellites  of  the  Routi- 
vare  type  also  occur  in  the  United  States — namely,  the  chemi- 
cally closely  allied  magnetite-spinellite  deposits,  accompanied 
by  corundum,  in  the  norites  of  the  Cortlandt  series,  described 
by  G.  H.  Williams.24 

To  the  titanic  ores  of  the  nepheline-syenites  correspond 
segregations  of  quite  the  same  character  in  the  rock-series  of 
Magnet  Cove.25 

24  "  The  Iron-Ore  and  Emery  in  the  Cortlandt  Norite,"  in  Norites  of  the  "  Cort- 
landt Series,"  on  the  Hudson  Kiver  near  Peekskill,  N.  Y.,  American  Journal  of 
Science,  Third  Series,  vol.  xxxiii.,  No.  195,  p.  194  (Mar.,  1887). 

25  H.  S.  Washington.     Igneous  Complex  of  Magnet  Cove,  Arkansas,  Bulletin  of 
the  Geological  Society  of  America,  vol.  xi.,  pp.  389  to  416  (1900). 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       689 

Utilization. 

From  the  above  it  appears  that  the  Scandinavian  countries- 
inclose  very  large  supplies  of  iron-ores  of  this  kind,  and  that, 
in  reality,  some  of  these  deposits,  such  as  Taberg,  Routivare, 
Ekersund-Soggendal,  etc.,  are  among  the  largest  iron-ore  de- 
posits in  Sweden  and  Norway.  Numerous  attempts  at  exploit- 
ing them  have  been  made  in  different  parts  of  the  two  countries. 
Taberg  has  given  rise  to  a  local  iron  industry  on  a  small  scale 
carried  on  during  two  centuries.  The  ores  of  Ulfo  have  been 
used  in  several  blast-furnaces  in  Norrland;  from  Ekersund- 
Soggendal  during  a  succession  of  years  ore  was  exported  to 
England  and  smelted  there ;  numerous  minor  mines  scattered 
all  over  Sweden  and  Norway  bear  testimony  to  the  attention 
which  these  deposits  have  attracted.  However,  all  these 
attempts  have  been  given  up  because  of  the  unfitness  of  the 
ores  for  metallurgical  purposes,  which  is  also  the  cause  why 
all  or  nearly  all  other  titaniferous  iron-ores  all  over  the  world 
lie  unworked. 

GROUP  IV. — THE  IRON-ORE-?  OF  THE  METAMORPHOSED  CAMBRO- 
SILURIAN  SCHISTS. 

These  ores,  which  form  a  very  well-defined  geological  class, 
are  also  territorially  confined  to  a  certain  "  ore-province."  They 
occur  exclusively  within  the  area  of  more  or  less  metamorphosed 
schists  which  forms  the  greater  part  of  the  mountain-districts 
of  the  Scandinavian  peninsula  north  of  the  65th  degree  of  lati- 
tude. Through  the  abrasion  of  the  Atlantic  and  the  erosion  the 
ore-bearing  horizons  have  in  places  been  laid  bare ;  these  ores 
are  therefore  almost  exclusively  confined  to  the  Norwegian  coast 
and  the  valleys  penetrating  into  the  country  from  the  sea.  The 
fjord-valleys  deeply  indenting  the  coast,  as  well  as  the  nearest 
islands,  are  rich  in  deposits  of  this  kind. 

These  ores  have  long  been  known,  but,  in  spite  of  the  favor- 
able situation  of  several  of  the  larger  deposits  on  or  near  the 
Atlantic,  they  have  been  exploited,  either  not  at  all  or  to  very 
small  extent,  by  reason  of  their  low  percentage  of  iron.  Only 
since  the  introduction  of  magnetic  ore-concentration  have  at- 
tempts been  made  to  utilize  them  for  export  on  a  larger  scale. 

[A  discussion  of  the  geological  horizon  of  this  group,  and  descriptions  of  Dunder- 
land,  Naeverhaugen,  Salangen,  etc.,  follow.] 


690       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 


Summary. 

The  deposits  of  this  group  belong  to  a  ferriferous  formation 
of  vast  horizontal  extent,  occupying  nearly  the  same  geological 
horizon  in  the  series  as  the  mica-schist-marble  member  of  this 
sedimentary  series.  The  ferriferous  formation  occurs  regularly 
associated  with  limestones,  in  most  cases,  however,  in  the  schists 
underlying  the  limestone.  The  connection  with  the  limestone 
is  so  strongly  marked  that  in  certain  districts  nearly  every 
limestone  bed  is  accompanied  by  iron-ore;  some  observers 
have  even  been  inclined  to  assume  a  connection  between  the 
thickness  of  the  limestone  beds  and  the  size  of  the  iron-ore 
deposits. 

Mineralogically,  the  ores  are  characterized  as  mixtures  of 
magnetite  and  specular  hematites ;  and  further,  by  the  occur- 
rence of  iron-magnesia-lime  silicates  of  the  amphibole,  augite, 
epidote,  and  garnet  groups.  Quartz  is  always  present  in  large 
quantity.  Chemically,  these  ores  are  characterized  by  a  high 
percentage  of  silicic  acid,  low  percentages  of  CaO,  MgO,  and 
A12O3,  a  medium  percentage  of  phosphorus,  and  small  amounts 
of  sulphur  and  titanic  acid.  Whether  these  ores  are  primary 
sedimentary  deposits  or  secondary  concentrations  of  leaner  iron- 
bearing  formations  is  still  an  open  question  of  the  greatest  prac- 
tical importance. 

These  ores  have,  e.g.,  in  Dunderland,  an  extent  of  several 
kilometers  in  length  and,  at  the  same  time,  a  considerable  thick- 
ness. If,  taking  the  syngenetic  point  of  view,  we  regarded 
these  ores  as  ordinary  stratified  formations,  altered  only  by  re- 
gional metamorphism,  we  would  have  to  assume  an  extent  of 
several  kilometers  in  the  direction  of  the  dip.  Such  a  conclu- 
sion might  be  highly  misleading  writh  regard  to  the  ore-supply. 
As  to  the  depth  which  the  ores  of  this  kind  reach,  there  is  as 
yet  no  practical  experience,  as  neither  exploratory  work  nor  even 
any  borings  below  the  present  or  former  ground- water  level  have 
been  performed. 

A  comparison  with  the  Archaean  ores  of  Group  I.  shows,  it 
is  true,  some  points  of  agreement.  On  the  whole,  the  primary 
characters  of  chemical  sediments  are  much  more  evident  in  this 
class  of  ores  than  in  the  Archaean  ores.  Above  all,  the  trans- 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       691 

formations  in  the  anamorphic  zone  are  less  marked;  this  is 
shown  by  the  gangues  being  less  developed  and  the  alteration 
into  magnetite  less  advanced.  No  analogies  to  the  large  mag- 
netite-stocks among  the  Archaean  ores  are  found  here.  Although 
the  nearness  to  the  magnesian  limestone  has  offered  plenty  of 
material  for  the  formation  of  lime-magiiesian  silicates  of  the 
pyroxene,  amphibole,  and  garnet  groups,  these  silicates  never 
are  formed  in  such  abundance  as  to  compare  with  the  skarn 
gangue  of  the  Archaean  ores.  The  interchange  of  constituents 
between  the  schist,  the  iron-ore,  and  the  limestone,  lying  close 
to  one  another,  has  been  rather  limited.  Probably  also  the  sub- 
mersion in  the  anamorphic  zone  did  not  go  so  deep  as  to  reach 
a  temperature  high  enough  for  the  formation  of  anhydrous  sili- 
cates on  a  large  scale.  The  depth  and  the  temperature  under 
which  the  crystallization  of  these  ores  occurred  seem  to  have 
been  better  adapted  to  produce  the  slightly  hydrated  silicates  of 
the  epidote  group. 

The  transformations  in  the  catamorphic  zone  also  are  less 
marked ;  one  finds  no  concentrations  of  so  great  richness,'  no 
"  s&o/ "-formations,  and  no  accumulations  of  ores  in  pitching 
troughs  or  on  impervious  basements.  The  ores  are  of  more 
equal  leanness,  and  in  general  the  concentration  does  not 
exceed  40  per  cent,  of  iron. 

On  the  whole,  one  may  consider  these  deposits  as  the  roots 
or  the  deepest,  comparatively  unconcentrated  parts  of  regional 
metamorphosed  chemical  depositions,  laid  open  by  the  deeply 
penetrating  fjords  and  valleys  of  the  Norwegian  coast;  the 
upper,  probably  more  concentrated  and  richer  parts  of  the 
same  deposits,  having  been  destroyed  by  erosion. 

Analogous  Deposits. 

The  ores  of  this  class  are  in  many  respects  comparable  to 
those  of  the  lower  Silurian  formation  in  the  eastern  United 
States,  especially  to  those  occurring  in  a  belt  from  Vermont  to 
Alabama.  These  ores  occur  only  where  the  lower  Silurian 
limestone  and  the  Hudson  shales  meet,  as  the  Norwegian  ores 
always  occur  at  or  near  limestones,  sometimes  dolomitized. 
This  is,  indeed,  one  of  their  most  important  geological  char- 
acters. The  Norwegian  rock-strata  are,  of  course,  more  meta- 
morphosed, the  rocks  consisting  of  crystalline  schists  and  mar- 


692       GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

ble  or  magnesia-limestone,  and  the  ores  being  specular  hema- 
tite or  magnetite,  instead  of  red  and  brown  hematite.  The 
Clinton  ores  likewise  show,  with  regard  to  geological  condi- 
tions, great  agreement  with  the  Norwegian  Palaeozoic  ores. 

GROUP  V. — CONTACT-DEPOSITS  IN  THE  CHRISTIANIA  REGION. 

These  ores  were  considered  by  Keilhau,  Daubree,  and  Kjerulf 
as  genetically  connected  with  the  intrusion  of  granite  in  the 
same  region ;  and  this  opinion  was  afterwards  confirmed  by 
Vogt,  who  executed  a  minute  survey  of  the  deposits.27 

Classification  of  the  Rocks. 

According  to  Brogger,  the  igneous  rocks  of  the  Christiania 
region  may  be  divided  into  seven  groups  of  different  age ;  the 
oldest  three  are  more  basic,  and  consist  of  (1)  gabbro-diabases ; 
(2)  basic  augite-,  mica-  and  nepheline-syenites  (laurvikite  and 
laurdalite) ;  and  (3)  quartz-bearing  augite-syenite  (akerite). 
Of  later  age  is  the  following  syenitic  and  granitic  series,  com- 
prising (4)  red  quartz-syenites  (nordmarkite) ;  (5)  soda-granites 
(grorudite) ;  and  (6)  granitite.  As  the  youngest  members  occur 
dike-forming  diabase  and  diabase-porphyrite.  The  eruptives 
are  probably  of  Devonian,  surely  of  post-Silurian,  age.  They 
occupy  an  area  about  250  km.  long,  and  in  some  places  more 
than  100  km.  wide. 

The  intrusives  are  bordered  partly  by  Archaean  rocks,  partly 
by  the  Silurian  strata,  and  by  porphyry-outflows.  The  con- 
tact-deposits are  found  in  all  these  different  pre-granitic  rocks. 

Most  of  the  deposits  are  connected  with  the  red  quartz- 
syenite  (nordmarkite),  some  of  them  with  the  soda-granite 
(grorudite)  and  the  granitite. 

The  Ores. 

The  iron-ores  are,  as  a  rule,  mixed  with  true  contact-min- 
erals, such  as  different  species  of  the  garnet  and  vesuvian 
groups,  scapolite,  wollastonite  and  others.  This  is  especially 
the  case  with  the  deposits  occurring  in  the  limestone  and  marly 
slates.  In  the  clay-slate,  chiastolite  is  found  as  contact-mineral. 
The  percentage  of  iron  is  through  the  gangue  reduced  to  from 

27  Zeitschrift  fur  praktische  Geologic,  vol.  ii.,  pp.  177,  464  (1894),  vol.  iii.,  p.  154 
(1895). 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       693 

30  to  35,  and  only  exceptionally  exceeds  40.  The  ores  are 
generally  strongly  pyritic,  but  low  in  phosphorus  and  titanium. 
Frequently  they  occur  in  the  immediate  vicinity  of  the  intru- 
sive rock,  but  they  may  also  be  found  up  to  1  km.  from  the 
contact.  In  a  few  cases  the  distance  from  the  visible  contact 
is  more  than  1  km.,  but  the  ores  never  are  found  outside  of 
the  metamorphic  zone  of  the  contact.  The  majority  of  the 
deposits  occur  in  the  Silurian  strata,  partly  at  the  borders  of 
the  Silurian  rocks,  partly  in  big  metamorphosed  Silurian  rock- 
fragments,  completely  surrounded  by  the  igneous  rock.  The 
different  Silurian  horizons  are  equally  impregnated  with  ores ; 
and  the  clay-slates  as  frequently  contain  ore-deposits  as  do  the 
limestones  and  marly  slates.  Also,  the  Archaean  gneisses,  and 
sometimes  the  porphyries,  are  ore-bearing. 

The  ore-deposits  show  generally  a  stratiform  extension,  and 
may  be  followed  with  varying  thickness  along  the  same  bed 
for  several  hundred  meters. 

These  deposits,  though  numerous,  are  quantitatively  too  in- 
significant to  play  any  commercial  role.  In  earlier  times  sev- 
eral hundred  small  ore-bodies  were  worked.  The  ore  is  mainly 
magnetite,  but  also  specular  hematite.  Also,  sulphides  of  iron 
and  copper  occur  in  so  great  amount  that  the  ore  may  obtain 
the  character  of  a  copper-ore.  Exceptionally,  also,  galena  and 
blende  have  been  found  in  such  quantities  as  to  be  mined  as 
ores.  But  all  the  deposits  are  small.  From  the  seventeenth 
up  to  the  latter  part  of  the  nineteenth  century,  they  furnished 
a  group  of  small  blast-furnaces  with  iron-ores ;  and  an  insignifi- 
cant copper-  and  lead-production  was  in  early  times  based  on 
these  ores. 

Analogous  Deposits. 

The  ore-deposits  of  the  Christiania  territory  are  genetically 
most  similar  to  the  Pitkaranda  deposit  in  Finland,  and  the 
known  deposits  of  Schmiedeberg  in  Silesia  and  Berggiesshiibel 
in  Saxony. 

There  are  a  great  number  of  deposits  of  this  kind  in  the 
western  United  States,  chiefly  in  Colorado  and  California, 
where  they  occur  associated  with  the  younger  eruptives  of  the 
Rocky  mountains  and  the  Sierra  Nevada. 


694      GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES. 

GROUP  VI. — LAKE-  AND  BOG-ORES. 

These  ores  formed  the  raw-material  for  the  oldest  iron-in- 
dustry in  Scandinavia,  long  before  the  blast-furnace  process 
was  known.  For  this  reason,  Carl  Linnaeus  called  them  Tophus 
Tabalcaini,  after  Tubal  Cain,  the  first  blacksmith  (Gen.  iv,  22). 
The  lake-ores  occur  in  most  provinces  of  Sweden  and  in 
the  southern  part  of  Norway.  But  their  abundant  occurrence 
is  confined  to  regions  where  the  ground  consists  of  moraine 
and  glacial  gravel  and  sand,  especially  the  high  plateau  of 
Smaland,  the  northern  parts  of  Vermland,  Vestmanland  and 
Dalarne,  and  the  greater  portion  of  Norrland.  They  occur 
only  sparingly  in  the  regions  covered  by  glacial  and  post-gla- 
cial marine-deposits,  such  as  the  lower  coast-belt  of  southern 
Sweden,  and  the  plains  surrounding  the  great  lakes  of  Vanern, 
Yettern,  Hjelmaren  and  Malaren.  In  short,  the  lake-  and  bog- 
ores  are  most  frequent  above  the  marine  level  of  the  glacial 
period.  A  certain  connection  with  the  distribution  of  the 
peat-mosses  is  indicated.  On  the  other  hand,  the  bog-ores  are 
by  no  means  more  frequent  in  the  districts  rich  in  other  iron- 
ore  deposits.  In  some  places,  a  connection  with  the  greater 
pyrite-deposits  may  be  suggested. 

The  bog-ores  are  recent  formations,  produced  before  our 
eyes.  In  lakes,  where  the  ore  has  once  been  exploited,  it 
grows  and  may  be  utilized  again.  In  some  lakes  of  Smaland 
mining-operations  have  been  resumed  at  places  exhausted  25 
years  before. 

In  the  ore-bearing  lakes,  the  iron  is  precipitated  from  dilute 
solutions  chiefly  along  certain  zones,  parallel  to  the  shores,  at 
a  depth  of  from  2  to  4  m.,  and  the  ores  are  thus  distributed  in 
belts  on  the  bottom  of  the  lake,  to  a  thickness  of  at  most  0.5  m. 
Lakes  connected  by  a  water-course  frequently  all  contain  bog- 
ores.  In  the  upper  lakes  the  ore  is  more  tine-grained  ("  gun- 
powder-ore," "  pearl-ore "),  while  in  the  lower  lakes  the  ore 
has  grown  to  coarser  concretions  ("  money-ore,"  "  cake-ore  "). 

The  purer  lake-ores  generally  contain  from  50  to  60  per  cent, 
of  Fe203  and  from  10  to  15  per  cent,  of  water.  Silicic  acid  is 
frequently  mechanically  intermixed,  reducing  the  iron-percent- 
age. Sometimes  the  ores  contain  a  considerable  amount  of 
manganese  (up  to  20  per  cent.).  The  percentage  of  phosphorus, 
as  well  as  of  sulphur  is  generally  high. 


GEOLOGICAL    RELATIONS    OF    SCANDINAVIAN    IRON-ORES.       695 

Bog-ores  are  often  formed  in  lakes  as  lake-ores,  and  later,  by 
a  natural  draining,  brought  above  the  water-level.  But  fre- 
quently bog-ores  occur  in  a  manner  indicating  their  formation 
in  the  ground  close  to  the  surface ;  in  such  cases  they  are  often 
formed  in  connection  with  peat-mosses. 

The  utilization  of  the  lake-ores  has  in  later  years  much  de- 
creased, and  is  to-day  without  importance.  From  1860  to 
1875  the  annual  production  in  Sweden  was  about  10,000  tons. 
From  1900  to  1905,  it  was  only  about  1,000  tons,  varying  from 
300  up  to  1,500  tons,  according  to  the  severity  of  the  winters. 
The  whole  product  comes  from  Smaland  and  is  used  for  the 
fabrication  of  cast-iron. 


696       FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS. 


No.  27. 
The  Formation  and  Enrichment  of  Ore-Bearing  Veins. 

BY  GEORGE  J.  BANCROFT,  DENVER,  COLO. 

(New  York  Meeting,  April,  1907.    Trans.,  xxxviii.,  245). 

INTRODUCTION. 

IT  is  unnecessary  to  repeat  here  the  contents  of  many  valu- 
able contributions  to  this  subject  which  have  appeared  in  the 
Transactions  and  in  the  publications  of  the  U.  S.  Geological 
Survey.  As  a  basis  for  the  further  suggestions  of  this  paper, 
the  following  are  the  most  important : 

1.  The  investigation  of  J.  R.  Don,1  showing  the  gold  of  cer- 
tain Australasian  veins  to  have  been  deposited  by  ascending 
solutions,  and  not  by  lateral  secretion. 

2.  The  theory  of  Prof.  Posepny,2  distinguishing  the  vadose 
from  the  deep  circulation,  and  ascribing  the  origin  of  certain 
classes  of  ore-deposits  to  ascending  solutions  of  the  latter  class. 

3.  The  theory  of  Prof.  Van  Hise,3  as  to  the  underground 
circulation  and  the  primary  enrichment  of  veins  thereby. 

4.  The  paper  of  Prof.  J.  F.  Kemp,4  showing  that  ore-de- 
posits are  largely  the  products  of  "  expiring  vulcanism."    Many 
of  Prof.  Kemp's  ideas  have  been  widely  adopted  by  mining 
men. 

5.  The  theory  of  secondary  enrichment,  so  lucidly  expounded 
by  Mr.  S.  F.  Emmons.5     This  theory,  dealing  with  the  rear- 
rangement of  ore-bodies  after  primary  mineralization,  has  been 
generally  adopted,  and  seems  to  me  to  have  been  as  completely 
proved  as  the  nature  of  the  case  permits. 

There  are  two  facts  which  I  think  should  be  constantly 
borne  in  mind  in  formulating  a  theory  of  the  genesis  of  ore- 


1  The  Genesis  of  Certain  Auriferous  Lodes,  p.  162,  this  volume. 

2  Genesis  of  Ore-Deposits,  pp.  1  to  187,  and  Trans.,  xxiii.,  197  to  369  (1893). 

3  Some  Principles  Controlling  the  Deposition  of  Ores,    Genesis  of  Ore- Deposits, 
pp.  282  to  432  ;  also,  Trans.,  xxx.,  27' to  177  (1900). 

4  The  Hole  of  the  Igneous  Kocks  in  the  Formation  of  Veins,    Genesis  of  Ore- 
Deposits,  pp.  681  to  709  ;  also,  Trans.,  xxxi.,  169  to  198  (1901). 

6  Genesis  of  Ore- Deposits,  p.  462,  and  Trans.,  xxx.,  206  (1900). 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     697 

bodies.  The  first  is  that  commercially  valuable  mines  are  rela- 
tively few.  Countless  veins  present  all  the  characteristics  of 
good  mines,  except  the  values.  I  suppose  that  there  are  a 
hundred  barren  veins  for  every  enriched  one,  and  even  the  lat- 
ter are  rarely  enriched  to  the  extent  of  more  than  20  per  cent, 
of  their  volume.  The  stope-map  of  any  old  mine,  showing  the 
proportion  of  stopes  to  barren  ground,  will  very  seldom  indi- 
cate that  more  than  20  per  cent,  of  the  vein  has  been  removed. 

The  second  fact  is,  that  nearly  all  ore-bodies  are  found  in 
close  association  with  eruptive  rocks.  So  generally  is  this  fact 
recognized  that  an  old  mining  man  does  not  like  to  spend 
money  on  a  prospect  in  a  new  district  where  there  is  no  "  por- 
phyry "  ("  porphyry,"  in  the  broad  miners'  sense,  meaning  any 
kind  of  eruptive  rock). 

In  view  of  these  two  facts,  it  seems  to  me  that  any  theory 
which  does  not  recognize  that  only  exceptional  conditions 
could  produce  such  exceptional  results  of  enrichment,  which 
does  not  recognize  and  explain  the  relationship  between 
"  porphyry"  and  ore,  falls  short  of  the  mark. 

My  own  observations  as  a  mining  engineer  have  led  me  to 
the  following  tentative  views  :  (I.)  that  the  majority  of  mineral- 
ized veins  are  the  product  of  expiring  vulcanism;  (II.)  that 
most  of  these  veins  were  primarily  mineralized  by  compara- 
tively rich  solutions  in  comparatively  short  periods  of  time ; 
(III.)  that  the  solutions  derived  their  metal-values  from  a  com- 
paratively rich  source ;  (IV.)  that  there  is  a  barysphere  con- 
taining large  amounts  of  the  useful  metals ;  (Y.)  that  eruptions 
spring  from  various  depths  and  bring  various  kinds  of  magma 
towards  the  surface ;  and  (VI.)  that  only  those  eruptions  which 
disturb  the  barysphere,  and  bring  a  magma  rich  in  metals  suf- 
ficiently near  the  surface  to  be  leached  by  vein-making  solu- 
tions, are  productive  of  valuable  ore-deposits,  other  eruptions 
producing  barren  veins. 

Ore-bodies  due  to  magmatic  segregation  are  not  included  in 
this  general  survey. 

These  propositions  will  be  successively  considered  in  the 
present  paper. 


44 


698    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS. 

I.  THE  MAJORITY  OF  MINERALIZED  VEINS  ARE  THE  PRODUCTS 
OF  EXPIRING  VULCANISM. 

This  proposition  has  been  so  fully  demonstrated  by  Prof. 
Kemp  in  his  very  valuable  article  entitled  The  Role  of  the  Igne- 
ous Rocks  in  the  Formation  of  Veins,6  that  I  feel  it  would  be 
superfluous  to  add  much  to  it. 

There  is,  however,  one  small  matter  in  which  I  differ  with  * 
Prof.  Kemp — namely,  I  do  not  think  there  is  good  reason  to 
believe,  that  the  surface-water  does  not  sink  down  into  the 
rocks  to  very  considerable  depths.  Prof.  Kemp  notes  that 
many  mines  are  dry  to  the  point  of  being  "  dusty,"  at  depths 
below  1,000  ft.  This  is  true;  but  in  a  drift  which  is  being  rap- 
idly driven  the  freshly-broken  breast  will  always  be  found  to 
be  damp.  The  reason  the  lower  levels  of  so  many  mines  are 
dry  and  dusty  is  that  the  evaporation,  slow  as  it  is,  is  neverthe- 
less faster  than  the  very  torpid  movement  of  the  ground-water. 
This  torpidity  of  the  ground-water  in  depth  is  caused  by  the 
"  tightness  "  of  the  rocks.  It  is  a  familiar  experience  in  min- 
ing that  the  ground  gets  tighter  the  deeper  one  goes.  Of  course, 
in  individual  districts  there  may  be  other  obstacles,  such  as 
sills  of  impervious  rocks  or  clay,  preventing  the  ground-water 
from  sinking  into  the  lithosphere;  but,  in  almost  every  case 
known  to  me,  the  tightness  of  the  rocks  in  the  lower  levels  will 
account  for  any  observed  diminution  of  water-flow.  "Where  re- 
cent fissuring  has  occurred,  there  is  generally  no  diminution  of 
water-flow  with  depth.  Indeed  there  may  be,  as  at  Cripple 
Creek,  an  increase. 

It  is  often  overlooked,  in  discussing  the  saturation  of  the 
ground,  that  in  many  mining  districts  the  yearly  evaporation  is 
greater  than  the  yearly  rain-fall  less  the  run-off.  This  question 
has  been  very  extensively  studied  by  the  U.  S.  Hydrographic 
Survey.  One  of  its  publications,  entitled  The  Relation  of 
Rain-fall  to  Run-off,  sets  forth  data  on  this  subject  gathered 
in  many  places.  ~No  general  conclusions  are  drawn;  but  I  figure 
that  in  Colorado  the  run-off  is  about  one-third  the  rain-fall.  The  .* 
rain-fall  varies  from  12  to  24  in.,  or,  after  deducting  the  run-off, 
we  have  from  8  to  16  in.  per  year.  The  capacity  for  evaporation 
is  more  than  3  ft.  per  year ;  so  that,  except  in  those  channels 

6  Genesis  of  Ore-Deposits,  pp.  681  to  ^09,  and  Trans.,  xxxi.,  189  to  223  (1901). 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS.     699 

where  water  quickly  gathers  after  a  rain,  the  country  must  be  in 
a  state  of  continual  thirst,  and  only  such  water  will  remain  un- 
der ground  as  is  held  there  by  capillary  attraction.  As  depth 
is  gained  and  the  water-gathering  channels  become  less  fre- 
quent, we  find  the  rocks  to  be  moist  but  not  always  wet.  Simi- 
lar conditions  prevail  in  many  mining  regions. 

Prof.  Van  Hise  has  drawn  attention  to  what  he  calls  the  zone 
of  flowage,  which  begins  at  depths  of  from  5,000  to  12,000  m. 
To  my  mind  the  zone  of  flowage  is  more  a  matter  of  time,  and 
less  a  matter  of  depth,  than  he  considers  it.  I  think  a  chan- 
nel may  exist  at  much  greater  depth  than  his  limit  for  a  short 
time,  but  when  a  long  time  is  involved,  I  think  the  zone  of 
flowage  may  come  very  close  to  the  surface. 

It  seems  to  me  entirely  logical  to  suppose  that  a  channel  may 
remain  open  as  long  as  it  takes  a  laccolite  to  cool  and  yet  grad- 
ually close  till  it  is  tight,  except  where  quartz  or  other  vein- 
matter  has  formed  in  it.  A  channel  that  would  stay  open  when 
the  surrounding  rocks  were  quiet  would  have  a  strong  tendency 
to  close  gradually  if  those  rocks  were  subjected  to  forces  which 
cause  flexure  or  other  movement  in  the  earth's  crust.  If  this 
supposition  be  well  founded,  it  will  account  for  those  cases 
where  the  quartz  is  in  lenticular  masses  and  mere  tight  cracks 
in  the  rocks  represent  the  veins  beyond  the  limit  of  any  lenti- 
cles.  Such  cases  simply  indicate  that  the  channels  have  closed 
since  the  vein  was  formed.  It  is  noticeable  that  such  veins  are 
often  found  in  schist,  or  other  rocks  that  show  the  effect  of 
movement  and  pressure.  The  matter  of  open  channels  is  fur- 
ther discussed  under  my  third  proposition. 

In  districts  which  have  been  fissured  quite  recently,  like 
Cripple  Creek,  we  find  open  fissures  and  much  water  as  far  down 
(about  1,500  ft.)  as  the  deepest  shafts  have  gone.  But  even  in 
this  camp  the  deep  shafts  in  the  granite  are  nearly  dry  at  the 
bottom.  Whether  this  is  because  the  granite  was  fissured  less 
than  the  eruptive  rocks  in  the  first  place,  or  because  the  gran- 
ite is  more  mobile  under  pressure  and  has  closed  in  on  its  fis- 
sures, I  am  not  prepared  to  say.  At  all  events,  the  shafts  in 
the  granite  are  dry  at  horizons  where  shafts  in  the  eruptive 
rocks  are  troubled  with  a  great  deal  of  water ;  and  this  water 
has  been  conclusively  proved  to  be  simply  rain-water  stored  in 
the  vast  underground  reservoir  formed  by  the  countless  open 


700    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

fissures  in  the  eruptive  rocks.  There  are  no  volcanic  springs 
active  in  Cripple  Creek  to-day.  Hence,  I  think  Prof.  Kemp 
gives  a  wrong  impression,  and  one  which  he  probably  did  not 
intend,  when  he  says  that  many  mines  are  dry  to  the  point  of 
being  dusty  in  depth,  which  were  wet  near  the  surface.  I  be- 
lieve that  the  earth  is  very  generally  impregnated  with  mois- 
ture; but  I  quite  agree  with  Prof.  Kemp  that  this  "  sea  of  un- 
derground water  "  is  utterly  inadequate  to  account  for  ore- 
bodies.  In  most  formations,  there  is  practically  no  movement 
in  this  water  below  the  500-ft.  level.  In  many  cases  it  will  not 
run  into  a  mine  fast  enough  to  equal  the  slow  evaporation ; 
and  it  is  beyond  conception  that  such  a  torpid  agent  could  ac- 
complish anything  in  the  line  of  vein-making  before  a  fissure 
would  close  up,  even  at  moderate  depths. 

All  mining  men  have  met  with  "  swelling  ground,"  and  most 
of  them  have  known  of  swelling  ground  that  could  not  be  ac- 
counted for  by  the  action  of  the  air  admitted  by  the  mine-work- 
ings. This  kind  of  swelling  is,  of  course,  very  much  slower  than 
that  due  to  the  "  slacking  "  of  lime  or  other  rocks  influenced 
by  the  air;  but  it  shows  the  general  tendency  of  rocks  to  close 
up  any  opening  beneath  the  surface.  Yet  this  tendency  is 
always  a  function  of  time,  and  time  is  one  of  the  most  puzzling 
factors  in  any  geological  discussion. 

It  is  impossible  to  state  in  years  how  long  a  geological  oper- 
ation lasted.  The  most  that  can  be  done  is  to  compare  the 
duration  of  one  geological  operation  with  that  of  another.  To 
my  mind,  most  ore-deposits  show  that  the  time  consumed  in 
their  formation  was  very  short,  compared,  for  instance,  with  the 
time  necessary  to  carve  out  the  canyon  of  the  Colorado ;  hence, 
I  think  that  a  fissure  that  would  in  time  close  up  tight,  might 
nevertheless  stay  open  during  the  (geologically)  brief  interval 
required  to  cool  a  mass  of  eruptive  rocks. 

II.  MOST  OF  THESE  VEINS  WERE  PRIMARILY  MINERALIZED  BY 

COMPARATIVELY  RICH  SOLUTIONS  IN  COMPARATIVELY 

SHORT  PERIODS. 

That  considerable  mineralization  has  been  effected  where  the 
solutions  passed  through  very  small  channels,  leaving  those 
channels  very  little  altered,  is  evidenced  in  many  places.  The 
so-called  "  flats  "  of  the  Black  Hills  are  cases  in  point.  In  the 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS.      701 

Penobscot  mine,  for  instance,  several  flat  deposits  of  gold-ore 
in  the  sedimentary  rocks  have  been  extensively  worked.  The 
ore  occurs  in  shoots  averaging  perhaps  45  ft.  wide  and  4.5  ft. 
thick.  Each  ore-shoot  has  a  vertical  fissure  coming  up  through 
the  so-called  "  quartzite  "  beneath  it;  and  over  these  fissures 
the  richest  ore  is  found.  These  fissures  are  so  small  as  to  be 
easily  overlooked.  Those  that  I  saw  varied  from  0.125  to  0.675 
in.  in  thickness.  In  some  places  they  were  open,  while  in  other 
places,  where  the  width  was  about  the  same,  they  were  filled  with 
quartz,  a  circumstance  which  indicates  that  these  fissures  have 
not  closed  up  to  any  great  extent. 

That  such  extensive  ore-bodies  should  be  mineralized  through 
such  small  fissures  suggests  strongly  that  the  solutions  were 
comparatively  rich  and  that  they  flowed  for  a  comparatively 
short  time.  A  long-continued  flow,  I  think,  would  have  either 
enlarged  the  little  fissures  or  filled  them  completely  full  of 
quartz. 

The  Cortez  mine,  Nevada,  and  the  Lisbon  Valley  copper- 
fields  of  Utah  are  also  cases  in  point.  At  these  places  mineral- 
ized solutions  came  up  through  hard  strata  of  sedimentary  rocks 
and  spread  out  in  soft  porous  strata,  mineralizing  considerable 
areas.  In  both  localities  the  vertical  fissures  are  small,  and 
•  show  little  alteration  of  the  wall-rocks.  From  specimens  I  have 
seen  which  were  brought  from  Cobalt,  Ontario,  Can.,  I  would 
say  this  is  another  case  in  point.  The  specimens  show  solid 
sheets  of  silver  between  comparatively  unaltered  walls. 

That  the  lavas  issuing  from  volcanoes  contain  large  quantities 
of  steam  is  well  known.  During  the  early  stages  of  the  erup- 
tion of  Vesuvius,  in  1898, 1  observed  a  small  lava  stream  on  two 
occasions,  about  6  days  apart.  The  stream  was  about  half*  a  mile 
long,  and  was  moving  very  slowly.  I  presume  it  had  taken 
three  weeks  to  gain  this  length,  yet  it  was  spitting  steam  con- 
tinually from  every  pore  throughout  its  entire  length.  I  was 
much  impressed  with  two  things :  the  great  amount  of  steam 
escaping  from  a  stream  15  ft.  wide  and  4  ft.  deep;  and  the  fact 
that  the  lower  end  continued  to  advance  when  it  had  only  a 
very  dull  red  heat.  I  wondered  whether  the  escaping  steam 
did  not  account  for  its  mobility  in  some  way.  If  all  magmas 
have  stored  in  them  as  great  quantities  of  water  as  the  Vesuvius 
lavas  and  if  they  tend  to  discharge  it  when  brought  into  condi- 


702    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS. 

tions  of  lessened  pressure  we  have  here  a  source  of  water  of  no 
small  moment.  It  is  hardly  conceivable,  however,  that  this 
source  can  alone  supply  all  the  water  used  in  vein-making  in  all 
cases.  For  instance,  if  a  magma  contained  as  much  as  25  per 
cent,  of  water,  then  a  spring  running  10  miners'  inches  would 
in  200  years  exhaust  a  body  of  the  magma  40  ft.  thick  and  3,600 
acres  in  extent.  I  think  we  must  agree,  therefore,  that  in  some 
cases  the  volcanic  waters  are  serviceable  principally  in  starting 
and  maintaining  open  waterways  and  establishing  a  current. 
In  such  cases  they  are  probably  joined  by  other  waters,  and  the 
combined  flow  accounts  for  the  volume  of  water  which  we  find 
issuing  from  some  mineral  springs.  Thus  we  find  ore-deposits, 
such  as  the  immense  quartz-veins  of  the  San  Juan,  in  Colorado, 
or  the  big  quartz-lenses  of  the  Homestake,  in  S.  Dakota,  and  of 
the  Mother  Lode,  in  California,  that  seem  to  have  been  formed 
by  a  generous  supply  of  water ;  and  we  find  other  ore-bodies 
which  indicate  that  very  little  water  ever  circulated  through 
the  veins,  as,  for  instance,  the  ore-shoots  of  Goldfield,  Nev., 
which  occupy  single  cracks  or  net-works  of  cracks,  made  since 
the  big  quartz-reefs  were  formed,  and  in  which  angular  cor- 
ners of  the  walls  frequently  stick  out  into  the  solid  masses  of 
sulphide  ore.  As  the  ore-bodies  are  found  in  the  easily  altered 
country-rocks  as  well  as  in  the  quartz-ledges,  such  angular  cor- 
ners are  the  more  remarkable.  If  the  mineralized  solutions  had 
run  a  long  time,  these  corners  would  have  been  rounded  off. 
At  Cripple  Creek,  likewise,  we  find  areas  where  the  joints 
and  seams  of  the  country-rock  are  coated  with  sylvanite,  and 
where  there  is  no  other  evidence  of  vein-making  agencies.  In 
the  veins  themselves  silicification  is  very  slight.  Kalgoorlie, 
West  Australia,  where  a  great  deal  of  enrichment  has  taken 
place  with  very  little  silicification  or  other  alteration  of  the 
country-rock,  is  another  illustration.  Such  camps  are  irrecon- 
cilable, in  my  mind,  with  the  theory  that  veins  were  formed  by 
very  lean  solutions  acting  through  long  periods  of  time.  Even 
the  big  low-grade  quartz-veins  seem  to  indicate  an  agent  much 
more  active  than  is  generally  recognized.  To  my  mind,  the 
evidence  suggests  that  some  ore-bodies  were  formed  by  the 
magmatic  waters  or  vapors  alone,  while  others  were  formed  or 
rearranged  by  considerable  volumes  of  water.  There  is  some 
reason  to  believe  that  the  quartz  of  an  ore-body  is  not  always  a 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS.     703 

full-blooded  brother  to  the  mineral  contents  of  that  body ;  but 
I  will  not  discuss  that  matter  at  this  time. 

In  most  genetic  processes  nature  is  extremely  wasteful.  In 
the  formation  of  a  sand-bar  in  the  Mississippi  river,  hundreds 
of  tons  of  material  pass  down  the  river  every  day ;  but  it  is  only 
an  occasional  grain  that  lodges  on  the  sand-bar.  Or  in  the 
growth  of  mounds  around  mineral  springs,  the  water  that  flows 
over  them  is  all  charged  with  mineral  matter  but  it  is  only  an 
occasional  atom  that  lodges  on  the  mound.  In  view  of  this  con- 
sideration, it  seems  to  me  that  the  theory  that  ore-deposits  were 
formed  by  leaching  the  extremely  lean,  eruptive,  or  other  rocks 
known  to  us  on  the  surface,  involves  one  of  two  rather  unten- 
able suppositions.  Either  we  must  conclude  that  nature  has 
operated  with  a  degree  of  accuracy  which  is  almost  unattain- 
able in  the  laboratory ;  that  she  has  leached  absolutely  clean 
the  metal-contents  of  a  rock  which  had  the  merest  trace 
to  start  with,  and  that  she  has  precipitated  every  bit  of  the 
metal  so  gathered  in  an  ore-body,  leaving  the  solution  abso- 
lutely barren;  or  else,  in  case  it  is  admitted  that  nature  prob- 
ably operated  with  her  usual  prodigality,  we  must  assume  that  a 
tremendously  large  mass  has  been  subjected  to  leaching  action 
to  form  a  relatively  small  ore-body.  In  accounting  for  a  large 
ore-body,  such  as  those  of  our  leading  copper-camps,  it  is  diffi- 
cult to  understand  how  the  leachings  from  such  a  great  area  as 
this  hypothesis  necessitates  could  have  been  gathered  together 
into  one  underground  channel.  We  are  forced  to  assume  that 
veins  must  branch  out  downwardly  like  the  limbs  and  twigs  of 
a  giant  tree  inverted.  Such  conditions  are  contrary  to  ordi- 
nary observation.  Veins  not  infrequently  unite  as  depth  is 
gained,  but  very  seldom  branch  out  with  depth.  This  again 
leads  to  the  conclusion  that  the  solutions  that  formed  ore-bodies 
were  not  the  extremely  dilute  solutions  which  would  result  from 
leaching  lean  rocks. 

Another  reason  for  believing  that  ore-bodies  were  formed 
from  comparatively  rich  solutions  is  the  well-known  difficulty 
of  precipitating  the  last  trace  of  any  metal  in  solution.  Who- 
ever has  had  to  do  with  a  leaching  process,  such  as  cyanidation 
or  chlorination,  knows  how  difficult  it  is  to  get  into  solution  the 
last  trace  of  gold  in  the  ore,  and  to  precipitate  the  last  trace  of 
value  from  the  solution.  In  fact,  this  is  practically  impossible ; 


704    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

tailings  carrying  from  30  to  60  cents  per  ton  are  considered  in 
most  cases  to  indicate  good  work;  and  foul  solution  that  con- 
tains no  more  than  20  or  30  cents  of  value  per  ton  is  considered 
poor  enough  to  throw  away.  Yet  the  surface-rocks,  considered  by 
some  to  be  the  source  of  the  metals,  are  much  leaner  than  the 
poorest  tailings;  therefore,  solutions  picking  up  metals  from 
them  must  be  poorer  than  the  solutions  we  are  forced  to  dis- 
card as  worthless — in  fact,  not  less  dilute  than  the  sea-water, 
which  Don  found  to  contain  0.071  grain  of  gold  per  ton  of 
2,240  Ib.  Don  was  unable  to  precipitate  directly  from  this 
sea-water  any  gold  at  all,  although  he  used  the  best  precipitants 
under  the  most  favorable  conditions.  He  made  his  determina- 
tions by  slowly  evaporating  several  tons  of  sea-water  and  assay- 
ing the  residue. 

As  to  the  time  occupied  in  forming  veins,  it  seems  to  me  that 
most  of  the  work  has  been  done  during  the  period  that  Prof. 
Kemp  so  fittingly  calls  that  of  "expiring  vulcanism."  This  is 
a  relatively  short  period — so  short,  in  fact,  that  changes  in  its 
conditions  may  be  noticed  within  a  human  life-time.  Hot  springs 
are  very  generally  associated  with  expiring  vulcanism;  and 
nearly  all  the  hot  springs  that  I  know  of  are  noticeably  drying  up. 
At  Steamboat  springs,  Nevada,  at  least  two  borings  have  had 
to  be  made  to  bring  the  flow  up  to  its  original  capacity.  Old 
settlers  at  Glenwood  springs,  Colorado,  testify  that  hot  water 
used  to  issue  from  a  number  of  minor  vents  which  are  now  dry,, 
and  that  the  main  streams  are  slowly  decreasing  in  flow.  At 
Aguacaliente,  in  Sonora,  the  water  is  used  for  irrigation,  and 
the  abandoned  fields  farthest  down  the  gulch  bear  mute  testi- 
mony to  the  gradually  decreasing  flow.  This  spring  is  a  fine 
example  of  the  fact  that  hot  mineral  springs  have  some  source 
other  than  rain-water.  The  only  range  in  this  dry  country  that 
receives  any  rain-fall  to  speak  of  is  the  Sierra  Madre,  100  miles 
east  and  across  the  Yaqui  valley.  The  largest  cold  springs 
within  a  radius  of  20  miles  are  only  large  enough  to  supply 
water  for  domestic  use. 

In  discussing  mineral  springs,  it  must  be  borne  in  mind  that 
some  of  them  are  no  doubt  of  secondary  origin.  Thus,  Trimble 
springs,  Colorado,  gives  every  evidence  of  having  received  its 
heat  and  mineral  contents  from  the  oxidization  of  a  large  body 
of  iron  pyrites. 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS.    705 


inco 


CO  O  CN  rH  iO  CC 
1C        rH  r-( 


grHjOrH 


$£££$3 


GO  rH  rH  g)  I-  <N  O 

CO  "^  l>  O*  rH  CO  O 

g  d  r~  oi  c^i  • 


\        rH  T!<  <M_  rH  !>.  CO  C 

rH         I       d  rH  in  rH  GO  OS  O 
10        rH 


rH  ^OOOlNOOOrH 


00  £  rH  10  C<J  O 


0040t^00400O 


o       o     04 


O  rH  rH  rH  -5  lO  O  O  -C 


|S88 

iodd 


ioo«o- 


o»oi> 


j    :8SSSS 


icic 


c£'^ 


!  18 


8     " 


ricOCOOriij>faSo 


^"HcIfsJ^S"! 

Cllfiftfii 

w<uS."SaQo       i^;<u 

!|ill!^l  I 


706    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 


TABLE  II. — Analyses  of  Spring-  Waters. 

Parts  in  one  thousand. 


No. 

1 

2 

3 

4 

0.3040 
0.0094 
0.0121 
0.0004 

5 

6 

7 

8           9 

10 

11 

12 

0.0020 
0.0128 
0.0012 

Na  

0.1042 
tr. 
0.5060 

0.7743 
0.0669 
0.0305 
0.0010 

0.3554 
0.0191 
0.0367 
0.0034 

0.6116 
0.0630 
0.0589 
0.0604 

0.0310 
0.0372 

K  

0.1285 
1.0739 
0.2352 

Ca  

Me.... 



Ba 

tr 

Sr 

Li  

fr. 

!     0    6603 

Fe 

tr. 

0  O0'>7 

Mn  

tr, 

0  0009 

Cl  
Br 

tr. 

0.9697 

0.2396 

6.2070 

0.2272 

0.9524 



14.2730 
0  0095 

0.0480 



I                

tr. 

Fl 

CO2  
S03  
HPC>4 

0.0852 
0.1614 
tr 

0.3555 

tr. 
0.3901 

6.3492 

0.5787 
0.3131 

0.1776 
0.1039 

0.2624 

1.7513!  0.1792 
2.0318 
tr      |H  rwu 

6.0383 

0.0089 
0.0040 
0.0179 

6.0012 
0.0317 

B,O7 

6.  21741.8784 
0.0003!  
0,31060.0371 

2.4043;     tr. 
6.0418  "6"  2464 

tr, 

0.0022 
0.0080 
0  0030 

••""••• 

SK,:  :  

SiO9.... 

tr. 
tr. 

0.0010 
0.2788 

6.1136 

6.1310 

0.0018 
0.1220 

H 

tr 

0.0050 
6V6645' 

0  0076 

O  
H2S  
KHS  and  S 

0.0500 

0.0194 

6.0255 

6.0080 

0.0325 

0.0005 

0  0069 

6/6bo7  ";;;;;!;;; 







As«O 

0  0036 

SbO* 

0  0005 

p9o<T 

0  0006 

HgS  "  " 

tr 

FeO 

0.0002 

MgO 

0  0005 

NaoO 

0  9193 

CaO 

0  0005 

KoO 

0  1246 

FeCO3 

O.ob'lO      tr. 
1.039713.6226 
0.3809:  0  4768 

2.0398 

6.0154 

0.0109 
0.0243 

NaCl  
Alk  Carb 











1.1027 
2  0075 

KSC>4 

0  3005 

CaSO4         

0.0234 

1  1548 

NaSO4 

0  6890 

MffCl  ... 

0  1637 

KC1  
NaBr 







0.0470 

0.0747  

0  0704 

0.1149 

Total  0.9068 

2.5171 

1.1834 

1.0211  2.0692 

2.81945.3675 

6.3910  16.0352 

9.9814 

0.1699 

SPRINGS. 

No.  1,  Sulphur  springs,  Los  Angeles  ;  Annual  Report  U.  S.  Geological  Survey, 
p.  195,  1876.  No.  2,  Hot  spring  at  Hot  Spring  station,  C.  P.  K.  K.  ;  Chamberlin 
and  Salisbury's  Geology,  pp.  224-225.  No.  3,  Hot  springs  at  the  base  of  the 
Granite  mountains,  Nevada  ;  Chamberlin  and  Salisbury's  Geology,  pp.  224-225. 
No.  4,  Boiling  spring  at  Honey  Lake  valley,  California  ;  Chamberlin  and  Salisbury's 
Geology,  pp.  224-225.  No.  5,  Warm  spring,  Mono  basin,  California  ;  Bulletin  No. 
9,  U.  8.  Geological  Survey,  p.  27.  No.  6,  Steamboat  springs,  Nevada  ;  G.  F, 
Becker,  Geology  of  the  Quicksilver  Deposits  of  the  Pacific  Slope;  Monograph  xiii. 
U.  S.  Geological  Survey,  p.  347.  No.  7  and  No.  8,  two  different  shafts  at  Sulphur 
Bank,  California  ;  G.  F.  Becker,  Geology  of  the  Quicksilver  Deposits  of  the  Pacific 
Slope ;  Monograph  xiii,  U.  S.  Geological  Survey,  p.  259.  No.  9,  Glenwood  springs, 
Colorado  ;  Glenwood  Springs  Hotel  Pamphlet.  No.  10,  artesian  well  at  Sheboygan, 
Wisconsin  ;  C.  F.  Chandler,  American  Chemist,  p.  370, 1876.  No.  11,  the  Mississippi 
river  ;  W.  J.  Jones,  Report  Louisiana  State  Board  of  Health,  p.  370,  1882.  No.  12, 
the  Sacramento  river  ;  W.  J.  Jones,  Report  California  State  Board  of  Health,  1878. 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS.     707 

Table  I.  contains  analyses  of  23  eruptive  rocks,  and  Table  II. 
the  analyses  of  12  spring-waters,  the  first  nine  of  the  latter  be- 
ing hot  springs,  the  tenth  an  artesian  well,  and  the  eleventh 
and  twelfth  river-waters.  The  rock  analyses,  which  are  from 
representative  surface  eruptives,  show  that  these  rocks  must  be 
very  lean  indeed  in  the  useful  metals.  Mr.  Waldemar  Lind- 
gren7  mentions  the  finding  of  traces  of  pyrite,  chalcopyrite  and 
galena  in  the  gray  gneiss  of  Freiberg.  Prof.  Kemp  mentions  the 
finding  of  various  metals  in  various  eruptive  rocks,  but  does  not 
give  any  quantitative  analyses.8 

Don  was  unable  to  find  any  gold  at  all  in  the  rocks  he  ex- 
amined except  in  association  with  iron  pyrites,  which  latter 
gave  evidence  of  being  the  result  of  vein-making  agencies.  Of 
course,  it  may  be  said  that  all  the  analyses  of  the  eruptive  rocks 
are  made  after  they  have  been  leached  out.  If  it  could  be 
shown  that  the  surface  eruptive  rocks  have  a  tendency  to  throw 
off  metals,  as  they  do  steam  and  sulphur,  during  the  cooling 
process  this  would  remove  many  of  my  objections  to  considering 
them  the  source  of  the  metals  in  our  ore-bodies.  In  the  lack  of 
such  proof,  however,  we  must  recognize  that  they  are  extremely 
lean,  and  therefore  a  very  unlikely  source  of  mineral  wealth. 

Of  the  four  rocks  from  the  Telluride  quadrangle  only  one 
shows  manganese ;  yet  rhodonite  and  rhodocrosite  are  very  com- 
mon to  the  veins  of  this  district.  Of  the  six  analyses  from  the 
La  Plata  quadrangle,  every  one  shows  manganese ;  yet  it  has 
been  my  observation  that  manganese  is  a  rare  constituent  of  the 
veins  of  this  quadrangle.  In  the  13  analyses  of  rock  from  the 
Port  Orford  quadrangle  a  wide  range  of  minerals  is  seen,  which 
often  are  found  in  veins,  yet  the  veins  of  this  locality  contain 
little  but  quartz,  pyrite,  chalcopyrite  and  gold.9 

The  table  of  spring-waters  was  rather  surprising  to  me  in 
that  it  shows  that  an  artesian  well-water  may  contain  as  much 
mineral  matter  in  solution  as  the  average  hot  spring.  I  do  not 
see  that  a  comparison  of  the  minerals  found  in  hot  springs  with 
those  minerals  found  in  the  eruptive  rocks  is  very  instructive. 
Unfortunately,  I  have  no  complete  analyses  of  all  the  rocks  im- 

7  Metasomatic  Processes  in  Fissure- Veins,  Trans.,  xxx.,  659  et  seq.  (1900). 

8  The  R61e  of  the  Igneous  Rocks  in  the  Formation  of  Veins,  Genesis  of  Ore- 
Deposits,  pp.  681  to  709,  and  Trans.,  xxxi.,  169  to  198  (1901.^ 

9  Port  Orford  Folio,  U.  S.  Geological  Survey. 


708    FORMATION    AND    ENRICHMENT    OP    ORE-BEARING    VEINS. 

mediately  surrounding  a  hot  spring.  If  such  analyses  were 
available  they  would  be  very  instructive.  As  it  is,  the  only  dis- 
tinguishing characteristic  of  hot  springs  brought  out  by  the 
analyses  is  the  presence  of  sulphur  and  sulphur  gases  and  of 
chlorine  combinations.  Fresh  lava,  we  know,  gives  off  fumes 
of  sulphur  and  chlorine ;  hence  it  is  natural  to  connect  hot  sul- 
phur springs  with  fresh  eruptives. 

The  analyses  given  in  Table  I.  show  very  few  of  the  useful 
metals  in  solution,  but  Posepny  in  his  Genesis  of  Ore-Deposits 
mentions  that  lead  occurs  in  the  springs  of  Rippoldsau  (accord- 
ing to  Will,  1.6  to  3.7  mg.  per  ton),  and  in  the  Kissingen  spring 
(13  mg.  per  ton),  and  quotes  from  G.  Bischof,  as  follows,  the 
maxima  found  in  mineral  springs  up  to  1854,  in  milligrams  per 
ton  of  water:10  Arsenious  acid,  1.5;  antimony  oxide,  0.1;  zinc 
oxide  (sulphate),  13.3;  lead  oxide,  0.1;  copper  oxide,  6.4;  tin 
oxide,  0.1. 

It  is  not  mentioned  whether  or  not  any  of  these  may  have 
been  enriched  in  a  secondary  way.  It  would  not,  however,  be 
surprising  if  no  spring  among  those  analyzed  had  been  prima- 
rily enriched  with  useful  metals.  We  have  only  a  few  analy- 
ses ;  ore-bodies  are  very  rare  things,  and  give  evidence  of  hav- 
ing been  made  in  comparatively  short  periods,  while  veins  are 
very  common  things ;  so  that,  granted  the  hot  springs  are  mak- 
ing veins,  the  probabilities  are  that  they  are  nearly  all  making 
barren  veins  or  barren  parts  of  veins.  Posepny  found  that  the 
Sulphur  Bank  spring,  whose  enrichment  is  probably  primary, 
carried  small  quantities  of  mercurial  sulphide  in  suspension. 
At  least  he  found  this  material  on  his  filter-paper  after  filtering 
the  water,  but  he  found  only  a  trace  of  mercury  in  the  water. 
Unless  we  accept  this  case,  I  have  not  read  of  any  in  which  a 
mineral  spring  has  been  "  caught  in  the  act "  of  making  an 
ore-body,  and  this  only  emphasizes  my  belief  that  ore-bodies 
are  formed  in  relatively  short  periods  of  time.  Ore-bodies  seem 
to  have  been  formed  in  every  geological  age  since  early  Palaeo- 
zoic times ;  and  if  we  grant  that  each  mineralized  district  was 
enriched  in  a  relatively  short  period,  it  would  not  be  strange  if 
very  few  ore-bodies,  or  none  at  all,  were  in  process  of  formation 
at  the  present  moment. 

10  Genesis  of  Ore-Deposits,  p.  47. 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.      709 

We  know  that  many  veins  are  now  in  process  of  formation ; 
and  we  find  that  many  springs  carry  in  solution  the  materials 
found  in  veins,  showing  that  nature  is  prodigal  in  her  methods. 
Probably  a  small  part  only  of  the  vein-making  contents  of  any 
spring  is  deposited  in  the  underground  channel;  the  rest  "  goes 
down  the  creek."  If  we  should  find  a  mineral  spring  in  the 
process  of  forming  an  ore-body,  we  might  expect  most  of  the 
metallic  constituents  of  the  solution  to  have  remained  in  it  after 
it  issued  from  the  ground. 

It  is  true  that  we  analyze  spring-waters  after  they  have 
passed  through  the  zone  of  precipitation ;  and  it  is  conceivable 
that  a  water  showing  at  the  surface  no  trace  of  metal  may  have 
carried  material  quantities  of  metal  before  it  reached  the  zone 
of  precipitation.  But  in  that  case  the  water  must  have  been 
completely  robbed  of  metal-values  in  the  zone  of  precipitation ; 
and  it  is  hard  to  understand  how  such  a  clean  precipitation 
could  be  effected  by  such  precipitating-agents  as  we  attribute 
to  the  superficial  zone.  It  is  easier  to  believe  that  we  have 
not  as  yet  found  an  ore-body  forming  or  a  spring  engaged  in 
forming  one. 

It  has  been  asserted  lately  that  the  curative  effect  of  some 
mineral  springs  is  largely  due  to  radio-activity.  Nearly  all  the 
radio-active  metals  are  of  high  specific  gravity ;  so  that  the  as- 
sociation of  mineral  springs  with  ore-bodies  or  with  magmas 
rich  in  heavy  metals  is  further  indicated  in  this  way. 

Glenwood  springs,  Colorado,  and  Hot  springs,  Arkansas,  have 
both  been  found  to  be  slightly  radio-active.  But  the  springs 
most  remarkable  in  this  respect  hitherto  discovered  are  the 
Doughty  springs,  in  Delta  county,  Colo.  Dr.  Wm.  P.  Headden 
has  made  some  very  fine  radiographs  from  the  sinter  surround- 
ing these  springs.11 

There  are  several  springs,  and  the  analyses  differ  somewhat; 
but  the  principal  radio-active  spring  (called  the  Drinking  spring) 
has  the  following  analysis,  in  parts  per  1,000  :  ISTa,  0.045863; 
K,  0.001576;  Li,  0.000446;  KE4,  0.000068;  Ca,  0.005272; 
Ba,  0.000192;  Sr,  0.000150;  Mg,  0.003230;  Fe,  0.000026; 
Al,  0.000054;  Mn,  0.000060 ;  Zn,  trace;  Cl,  0.019762 ;  Br, 
0.000065;  I,  trace;  S04,  0.013022;  Si02,  0.000696;  B02, 
0.000174;  total,  0.090656. 

11  Proceedings  Colorado  Scientific  Society,  vol.  viii.,  pp.  1  to  30  (1905). 


710    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

These  are  not  hot  springs ;  and  whether  or  not  they  are 
springs  of  primary  enrichment  is  not  clearly  shown.  It  will  be 
noted  from  the  analysis  that  ETa,  Cl,  and  S04  are  the  principal 
substances  found  in  solution;  but  the  distinguishing  feature  of 
the  spring  is  the  barium  sulphate  which  the  water  is  actively 
precipitating  on  the  mound  around  the  spring.  Dr.  Headden 
says :  "  The  deposition  of  practically  pure  baric  sulphate  by  a 
mineral  spring  is,  so  far  as  I  have  been  able  to  find,  a  unique 
fact."12  The  radium  is  intimately  associated  with  the  barium 
sulphate. 

III.  THE  SOLUTIONS  DERIVED  THEIR  METAL-VALUES  FROM  A 
COMPARATIVELY  RICH  SOURCE. 

This  follows  necessarily,  if  it  be  admitted  that  ore-bodies 
give  unmistakable  evidence  that  they  were  formed  by  rich  solu- 
tions. If  we  believe  that  the  source  of  the  values  was  the  sur- 
face-rocks, but  admit  that  "  expiring  vulcanism  "  set  matters  in 
motion  for  vein-making,  we  should  expect  all  veins  to  show  a 
certain  amount  of  concentration  of  mineral  values ;  at  least  all 
of  the  veins  in  the  vicinity  of  eruptive  rocks.  But  the  com- 
plete barrenness  of  most  veins,  even  in  mining  districts,  is  one 
of  the  hard  facts  that  are  pressed  home  upon  every  experienced 
mining  man.  There  are  also,  of  course,  countless  absolutely 
barren  veins  and  dislocations  outside  the  mining  districts. 

Some  writers  suppose  that  the  surface  eruptive  rocks  carry 
appreciably  more  mineral  than  other  rocks,  and  that  they  are 
the  source  of  the  mineral  in  the  ore-deposits.  It  is,  however,  a 
common  observation  that  the  characteristic  eruptive  rocks  of 
a  mining  camp  are  not  confined  to  the  mineralized  area.  As 
examples,  I  will  mention  Cripple  Creek,  Colo.,  The  Homestake, 
S.  D.,  Kalgoorlie,  W.  A.,  Monte  Christo,  Wash.,  Goldfield, 
Nev.,  Arizona  King,  Ariz.,  and  El  Trinidad,  Sonora.  It  is  also 
common  that  these  rocks  carry  either  no  values  at  all  or  a 
metal  that  is  not  characteristic  of  the  camp.  In  the  analyses 
given  in  Table  I.  it  will  be  noticed  that  the  eruptives  of  the  La 
Plata  quadrangle  all  carry  manganese,  while  only  one  of  those 
in  the  Telluride  quadrangle  carries  manganese.  Rhodocrosite 
and  rhodonite  are  very  prevalent  in  the  Telluride  quadrangle, 
but  only  occasionally  met  with  in  the  La  Platas,  if  my  own 

12  Proceedings  Colorado  Scientific  Society,  vol.  viii.,  p.  26  (1905). 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.      711 

limited  observations  are  to  be  relied  upon.  I  think  that  all  this 
points  to  the  exceptional  and  unusual  sources  for  such  ore-bodies. 
The  principal  objection  to  a  deep-seated  and  rich  source  for 
the  mineralization  of  veins  which  I  have  read  is  that  of  Van 
Hise,  who,  calling  attention  to  the  limits  of  the  zone  of  frac- 
ture, says  :13 

**  On  the  assumptions  (a)  that  the  strength  of  the  rocks  is  the  same  as  at  the  sur- 
face, (b)  that  the  rocks  are  all  of  the  same  kind,  (c)  that  the  temperature  is  the 
same  as  at  the  surface,  (d)  that  the  water  present  does  not  make  any  difference  in 
the  character  of  deformation,  (e)  that  the  rocks  yield  as  readily  by  fracture  as  by 
flowage,  (f)  that  the  rocks  break  as  readily  by  fracture  when  the  deformation  is 
slow  as  when  it  is  rapid,  and  (g)  that  the  rocks  are  among  the  strongest,  I  have 
calculated  that  the  maximum  depth  of  the  upper  part  of  the  zone  of  flowage  under 
mass-static  conditions  can  not  be  greater  than  12,000  meters." 

He  concludes  that  the  practical  limit  in  depth  of  the  zone  of 
fracture  is  about  5,000  m.,  and  that  a  fissure  would  close  almost 
at  once  at  a  depth  of  12,000  meters. 

The  resistance  of  a  large  number  of  rocks  to  binding  and 
crushing  has  been  determined;  but  such  figures  give  us  no  sat- 
isfactory basis  for  the  calculation  here  involved.  It  is  necessary 
to  consider  also  the  "  arching  "  of  any  material,  even  of  crushed 
material.  Loose  coke  and  ore  have  no  strength  whatever  to  re- 
sist flexure,  yet  they  will  "  bridge  "  a  blast-furnace,  and  broken 
ore  will  often  arch  in  an  ore-chute  and  choke  it  up. 

If  Prof.  Van  Hise's  conclusion  is  correct,  why  does  not  rock- 
flowage  prevent  the  continued  existence  of  mountain-peaks  5,000 
m.  high,  and  of  springs  at  the  base  of  such  masses?14  If  a 
fissure  could  not  exist  at  a  given  depth,  how  can  a  peak  exist  to 
an  equal  height  ?  Such  a  peak  may  represent  the  foot-wall  of 
a  rather  flat  fissure,  the  opposite  side  of  which  has  been  re- 
moved. Would  the  absence  of  the  opposite  side  prevent  the 
action  of  rock-flowage  ?  Has  the  phenomenon  of  rock-flowage 
ever  been  observed,  bulging  out  the  solid  rock  at  the  base  of  a 
peak  or  precipice  ? 

If  a  spring  can  flow  from  under  a  mass  of  rock  20,000  ft.  high, 
why  could  not  a  fissure  exist  20,000  ft.  below  the  surface  ? 

13  A  Treatise  on  Metamorphism,  Monograph  xlvii.,  U.  S.  Geological  Survey,  p.  189 
(1904). 

14  According  to  Mr.  M.  W.  Con  way's  Climbing  and  Exploration  in  the  Karakoram- 
Himalayas  (vol.  i.,  p.  486,  1894),  Peak  K2  of  that  range  is  28,000  ft.  above  sea- 
level,  and  many  other  peaks  exceed  20,000  ft.     In  Bolivia  there  are  mountains 
rising  somewhat  abruptly  21,000  or  22,000  ft.  from  sea-level.  Many  other   in- 
stances could  be  cited,  from  British  Columbia  and  Alaska. 


712    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

Again,  the  effect  of  rock-flowage,  whatever  it  may  be,  is  ad- 
mittedly slow,  and  must  be  subject  to  arrest  or  diversion  by  the 
greater  force  of  rock-movements  in  mass.  Such  movements, 
indicated  in  innumerable  instances  by  their  geological  effects, 
are  continually  presented  for  our  observation  in  non-volcanic 
earthquakes,  like  those  at  Charleston,  San  Francisco,  Jamaica, 
etc.,  and  are  reported  daily  by  the  seismometers  of  the  world. 
Is  it  reasonable  to  believe  that  a  movement  felt  at  a  horizontal 
distance  of  10,000  miles  has  had  no  effect  below  the  depth  of 
5,000  or  12,000  m.  (3  or  7  miles)  ?  If  it  has  had  such  effect, 
it  must  have  counteracted  the  previous  work  of  rock-flowage, 
and  opened  new  fissures,  upon  which  that  slow  agency  must 
commence  operations  de  novo. 

Very  recent  seismometric  observations  (preceding  by  a  few 
weeks  the  Jamaica  earthquake  of  January,  1907)  reported  a 
submarine  earthquake  in  the  deepest  part  of  the  Pacific,  far  ex- 
ceeding in  intensity  and  energy  anything  hitherto  observed  on 
land.  Such  earthquakes  occur  under,  say,  24,000  ft.  of  sea- 
water  (the  maximum  depth  off  the  coast  of  Asia  is  greater  than 
that),  equivalent  in  weight  to  10,000  ft.  of  rock;  yet  they  not 
only  break  the  sea-bottom,  but  possess  surplus  energy  enough 
to  lift  the  sea  itself,  producing  enormous  tidal  waves.  May  we 
not  safely  conclude  that  they  might  still  occur  under  a  greater 
superincumbent  pressure,  and,  in  particular,  that  15,000  or 
20,000  ft.  of  rock,  the  pressure  of  which,  producing  rock-flowage, 
operates  much  more  slowly  than  an  equal  pressure  producing 
water-flowage,  would  not  necessarily  prevent  an  earthquake  suf- 
ficient to  make  and,  for  a  time  at  least,  maintain  fissures?15 

Again,  it  is  not  proved  that  the  pressure  which  would  close 
an  open  crack  by  rock-flowage  would  be  sufficient  to  change 
the  density  of  the  rock  itself,  and  close  all  pores  and  capillary 
passages  in  it.  On  the  contrary,  it  is  probable  that  the  slow  de- 
formation of  rocks  under  pressure  takes  place  without  fracture 
or  change  of  density.  This,  at  least,  is  indicated  by  the  early 
experiments  of  Sorby  and  others,  and  by  the  actual  observed 
conditions  of  limestone,  etc.,  which  have  been  thus  changed  in 
form,  yet  show  their  original  structure.  It  follows,  apparently, 
that  the  assumed  lower  limit  of  rock-flowage  is  not  necessarily 
the  limit  of  rock  permeability,  and  also  that  any  interruption 

15  This  consideration  was  suggested  to  me  in  a  private  communication  by  the 
Secretary  of  the  Institute. 


FORMATION    AND    ENRICHMENT    OP    ORE-BEARING    VEINS.     713 

of  the  closing  of  a  fissure  by  rock-flow  age  might  continue  for 
an  indefinite  period,  or  until  rock-flowage  in  new  directions,  or 
a  forced  change  in  the  density  of  the  rock,  had  completed  the 
process  thus  interrupted.  This  leaves  room  for  the  hypothesis 
here  advanced,  which  requires,  not  the  endless  persistence,  but 
only  the  existence  for  a  sufficient  period,  of  deep  channels  of 
circulation. 

Now,  there  is  here  no  question  of  an  absolutely  open  fissure, 
with  walls  nowhere  in  contact.  On  the  contrary,  fissures  are  al- 
most always  formed  by  movements  of  one  wall  relatively  to  the 
other,  and  are  almost  always  "  closed  "  to  a  certain  extent  by 
the  "  misfit "  contact  of  the  walls  in  their  new  relative  position. 
This  leaves  more  or  less  continuous  and  connected  channels  for 
underground  waters  and  gases,  the  further  closing  of  which  by 
the  pressure  of  the  inclosing  rocks  may  be  long  delayed  by  the 
fact  that  the  pressure  tending  to  close  the  openings  must  over- 
come the  resistance  of  the  solid  masses  which  are  keeping  them 
open  and  the  "  arching  "  of  the  material  around  such  openings. 
It  must  be  admitted  that  the  complete  "  squeezing  out "  of  all 
such  residual  and  interstitial  cavities  is  likely  to  be  a  much 
slower  process  than  the  closing  of  altogether  open  and  con- 
tinuous fissures.  - 

In  view  of  the  foregoing  considerations,  I  can  see  no  reason 
why  small  open  channels  may  not  exist  as  far  below  the  surface 
of  the  earth  as  mountain  peaks  extend  above  the  average  grav- 
ity-level; and,  moreover,  as  these  channels  would  doubtless  be 
filled  with  water,  a  practically  incompressible  liquid,  having 
material  weight  of  its  own,  I  think  we  may  conclude  that  they 
would  resist  closing  all  the  more  on  that  account,  and,  indeed, 
could  not  be  completely  closed,  unless  the  water  were  provided 
with  the  means  of  escape — in  other  words,  with  channels ! 

Prof.  Van  Hise  calls  attention  to  the  fact  that  at  a  certain 
depth  the  critical  temperature  of  water  (360°  C.)  would  be 
reached,  and  that  it  could  not  exist  as  water  below  that  depth. 
But  it  does  not  follow  that  the  form  in  which  it  could  exist 
would  not  possess  equal  density  and  solvent  power. 

According  to  the  rate  of  increase  assumed  by  many  writers — 
1°  C.  for  every  30  m.  of  added  depth — the  critical  temperature 
would  be  reached  at  10,350  m.,  if  15°  C.  be  taken  as  the  tem- 
perature of  the  surface.  But  we  are  scarcely  warranted  in  as- 

45 


714    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

suming  that  rate  as  uniform  to  great  depths.  M.  Walferdin, 
by  a  series  of  careful  observations  in  two  shafts  at  Creuzot, 
proved  that  down  to  a  depth  of  1,800  ft.  the  increase  in  temper- 
ature amounted  to  1°  F.  for  every  55  ft.  of  descent;  but  below 
the  depth  named  the  rate  of  increase  was  as  great  as  1°  F.  for 
every  44  ft.  On  the  other  hand,  in  the  great  boring  of  Gren- 
elle,  at  Paris,  the  increase  in  temperature  down  to  740  ft.  was 
1°  F.  for  every  50  ft. ;  but  from  740  to  1,600  ft.  it  diminished 
to  1°  F.  for  every  75  ft.  A  similar  remarkable  fact  was  shown 
in  the  Sperenberg  boring,  near  Berlin,  where  the  rate  of  in- 
crease for  1,900  ft.  was  1°  F.  for  every  55  ft.,  and  for  the  next 
2,000  ft.  only  1°  F.  for  every  62  ft.  In  the  deep  well  at  Buda 
Pesth  there  was  actually  found  a  decline  in  temperature  below 
the  depth  of  3,000  ft. 

A  list  of  164  wells,  from  400  to  2,220  ft.  deep,  bored  in  the 
United  States,16  shows  irregularities  of  temperature  not  to  be  re- 
ferred to  any  general  formula.  To  the  rule  mentioned  above — 
namely,  1°  C.  for  every  30  m.  of  added  depth — there  are  far  more 
exceptions  than  confirmations.  No  doubt  these  variations  are 
due  to  local  physical  or  chemical  causes ;  and,  in  like  manner, 
it  must  be  conceded  that  under  conditions  of  expiring  vulcan- 
ism  very  high  temperatures  may  prevail,  prob.ably  even  beyond 
the  critical  temperature  of  water.  But  it  seems  unsafe  to  reckon 
upon  a  transcendently  hot  interior  of  the  mass  of  the  earth. 

Finally,  it  is  not  safe  to  assume  that  this  mass  is  under  such 
pressure  as  to  be  precluded  from  all  movement  whatever  below 
a  few  thousand  feet  of  its  4,000  miles  of  radius;  and  a  move- 
ment causing  displacement  would  give  opportunity  for  the  rise 
of  a  heavy  magma  to  a  higher  level. 

In  view  of  the  above  considerations,  I  find  nothing  preclud- 
ing the  idea  that  the  solutions  which  have  formed  ore-bodies 
have  had  comparatively  rich  sources,  and  that  these  sources 
were  very  likely  laccolites  of  heavy  magmas,  brought  up  from 
the  barysphere  into  the  lower  part  of  the  zone  of  fracture. 

IV.  THERE  is  A  BARYSPHERE  CONTAINING  LARGE  AMOUNTS  OF' 

THE  USEFUL  METALS. 

This,  I  think,  has  never  been  seriously  questioned.  Physi- 
cists and  astronomers  have  weighed  the  earth  and  found  it  not 

16  Water  Supply  and  Irrigation  Paper  No.  149,  U.  S.  Geological  Survey  (1905). 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     715 

"  wanting,"  but  over-weight.  R.  von  Sternbeck  determined  the 
specific  gravity  of  the  earth  to  be  5.6,  while  the  average  density 
of  the  surface-rock  is  2.5.  Charaberlin  and  Salisbury  in  their 
treatise  on  geology  give  the  specific  gravity  of  the  earth  as  5.57, 
and  that  of  the  lithosphere  as  2.7.  There  is  a  theory  that  the 
greater  relative  weight  of  the  earth  is  caused  by  pressure  alone ; 
that  the  material  is  the  same  throughout,  but  that  the  pressure 
has  made  the  interior  rocks  more  dense.  I  believe  it  has  been 
demonstrated  that  rocks  do  yield  somewhat  to  such  pressure  as 
may  be  artificially  applied;  but  such  evidence  comes  far  short 
of  the  proof  here  required.  To  satisfy  this  theory  it  would  be 
necessary  for  the  rocks  to  be  compressed,  near  the  center  of  the 
earth,  to  one-fourth  their  volume  at  the  surface.  Against  this 
hypothesis,  we  have  the  facts  that  magmas  of  very  different 
specific  gravity  issue  from  the  interior  of  the  earth,  and  that 
eruptive  rocks,  as  a  class,  are  heavier  than  surface-rocks. 
Van  Hise  remarks  :17 

"It  is  noticeable  in  the  altered  rocks  that  in  proportion  as  deep-seated  meta- 
morphism  is  advanced  the  heavier  (of  the  above)  minerals  appear." 

Y.  ERUPTIONS  SPRING  FROM  VARIOUS  DEPTHS  AND  BRING 
VARIOUS  KINDS  OF  MAGMA  TOWARD  THE  SURFACE. 

This  seems  to  me  to  be  shown  by  what  is  known  of  eruptions. 
As  vents  filled  with  molten  material  would  not  be  subject  to  the 
causes  limiting  the  depths  of  water-channels  there  is  no  limit  to 
the  depths  to  which  we  may  expect  them  to  extend.  I  under- 
stand that  the  majority  of  both  astronomers  and  geologists  re- 
gard the  earth's  interior  as  solid  and  rigid  as  steel.  Eruptions 
are  generally  considered  to  be  the  result  of  local  stress  and 
friction.  Just  what  is  the  cause  of  the  stress  and  just  how  the 
force  is  applied  are  matters  of  discussion.  A  very  simple  ex- 
planation, but  one  which  does  not  seem  to  appeal  to  most 
writers,  is  that  the  axis  of  the  earth  is  gradually  shifting,  and 
the  earth  being  an  oblate  spheroid  has  to  keep  rearranging  its 
mass  to  suit  the  new  positions  of  the  axis. 

At  Cananea,  Sonora,  in  1902,  I  saw  an  illustration  of  a  vol- 
cano on  a  very  small  scale.  A  block  of  heavy  iron  gossan,  con- 
stituting, roughly,  a  cube  of  about  200  ft.  on  a  side,  or  8,000,- 

17  A  Treatise  on  Metamorphism,  Monograph  xlvii.,  U.  S.  Geological  Survey ,  p. 
183(1904). 


716     FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

000  cu.  ft.  in  volume,  had  been  undermined,  and  slipped  down 
6  ft.,  crushing  the  timbers.  The  heat  produced  underground, 
near  the  foot-wall,  was  intense,  and  on  the  surface  two  or  three 
small  jets  of  steam  appeared.  If  a  little  block  of  ground  like 
that,  slipping  6  ft.,  could  generate  sufficient  heat  to  produce 
such  jets  of  steam,  it  is  easy  to  understand  how  the  movements 
of  a  large  region  might  incidentally  produce  a  volcano  or  two. 
Suppose,  for  example,  that  an  eruption  is  caused  by  a  force 
which  produces  faulting  under  great  pressure.  The  first  ef- 
fect may  be  confined  to  the  lithosphere,  so  that  barren  magmas 
are  squeezed  out.  But,  as  the  force  gathers  intensity,  the  fault 
extends  into  the  bary sphere,  and  some  of  the  latter  is  forced 
upward,  crowding  out  the  lighter  lavas  above  it.  By  reason  of 
its  greater  specific  gravity  it  floats  the  lighter  rocks  above  it, 
and  forms,  within  the  reach  of  underground  waters,  a  laccolite, 
which  may  subsequently  become  the  source  of  valuable  mineral 
deposits. 

Chester  "Wells  Purington,  in  the  Telluride  Folio  of  the  U.  S. 
Geological  Survey,  says,  in  effect,  that  the  basic  parts  of  eruptive 
rocks,  such  as  hornblende,  augite,  biotite,  contain  more  of  the 
useful  metals  than  the  other  parts,  and  deems  it  probable  that 
the  mother  magma  had  a  basic  portion,  which  might  be  the 
source  of  the  metals  in  the  ore-deposits.  His  idea  and  mine  are 
not  widely  at  variance. 

VI.  ONLY  THOSE  ERUPTIONS  WHICH  DISTURB  THE  BARYSPHERE 
AND  BRING  A  MAGMA  RICH  IN  METALS  SUFFICIENTLY  NEAR 
THE  SURFACE  TO  BE  LEACHED  BY  VEIN-MAKING  SOLUTIONS 
ARE  PRODUCTIVE  OF  VALUABLE  ORE-DEPOSITS,  OTHER  ERUP- 
TIONS PRODUCING  BARREN  VEINS. 

In  support  of  this  proposition  there  are  many  indications  not 
mentioned  above.  In  many  mining  districts  there  have  been 
successive  eruptions,  but  the  ore-bodies  are  definitely  associated 
with  one  eruption  and  appear  to  have  no  relationship  with 
the  others.  Thus,  at  Butte,  Mont,  the  ore-bodies  are  associated 
with  a  quartz-porphyry  eruption,  while  the  acid  granite,  basic 
granite  and  rhyolite  eruptions  produced  no  ore-bodies.  At 
Cripple  Creek  we  have  a  whole  series  of  eruptions ;  but  the 
mineralization  of  the  veins  followed  on  the  heels  of  the  nephe- 
line-basalt  eruption. 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     717 

We  often  find  in  a  mining  district  several  series  of  veins, 
only  one  of  which,  bears  mineral  values.  At  Rico,  Colo.,  for 
instance,  there  is  a  series,  terminating  at  the  so-called  "  con- 
tact," which  has  been  enriched  with  silver  and  other  metals ; 
and  there  is  another  series  of  strong  quartz-veins  not  thus 
enriched.  These  facts  suggest  that,  among  the  eruptions,  one 
must  have  been  radically  different  from  the  others.  Yet  analy- 
ses of  the  surface-rocks  do  not  reveal  any  startling  differences. 
It  seems  evident  that  the  mineralized  series  of  veins  must  have 
been  formed  from  a  source  radically  different  from  that  of  the 
barren  ones.  My  explanation  is,  that  in  a  series  of  eruptions, 
one  may  have  been  sufficiently  deep-seated  to  disturb  the  bary- 
sphere  and  force  some  of  its  material  toward  the  surface.  It 
would  never  reach  the  surface,  because  its  specific  gravity 
would  cause  it  to  form,  sooner  or  later,  a  laccolite,  floating  the 
surface-rocks.  But,  in  exceptional  cases,  it  might  rise  far  enough 
to  become  subject  to  the  agencies  which  make  mineral-bearing 
veins. 

I  presume  that  the  barysphere  includes  different  kinds  of 
unsegregated  magmas.  It  may  be  built  up  concentrically,  or  it 
may  be  simply  spotted,  as  the  surface  is,  with  different  rocks. 
A  laccolite  of  magma  rich  in  copper  might  give  rise  to  a  sur- 
face region  yielding  copper ;  one  rich  in  gold  might  become 
the  origin  of  a  gold-bearing  district,  etc. 

I  do  not  mean  that  the  constituents  of  the  magma  would 
govern  entirely.  It  is  conceivable  that  conditions  of  the  solu- 
tion and  precipitation  of  the  metals  might  also  be  influential. 
But  this  general  hypothesis  suggests  an  explanation  of  those 
cases  in  which  totally  different  kinds  of  ore-deposits  occur  in 
the  same  surface-rocks,  close  together,  and  under  conditions 
apparently  similar,  except  as  to  age.  Butte,  Rico  and  Leadville 
are  cases  in  point.  At  Butte  there  is  a  great  mass  of  dark, 
basic  granite,  which  contains  two  vein-systems.  In  the  southern 
part  of  the  camp  are  the  famous  veins  of  copper,  containing 
sulphide  ore-bodies  with  more  or  less  quartz.  The  northern 
system  produces  ores  of  silver,  lead,  zinc  and  iron.  Prof.  Kemp 
has  called  attention  to  the  fact  that  the  northern  ores  are 
abundantly  associated  with  manganese  minerals,  especially  rho- 
donite; that  no  manganese  occurs  in  the  copper  belt  and  no 
copper  in  the  silver  belt;  and  infers  that  "such  results  could 
originate  only  in  different  deep-seated  sources." 


718    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS. 

This  hypothesis  offers  also  an  explanation  of  cases  in  which 
there  is  an  extensive  surface-area,  showing  similar  eruptive 
rocks  throughout,  yet  only  a  small  part  of  which  has  been  min- 
eralized. Thus,  in  areas  like  southern  Nevada  and  the  Yaqui 
River  country  of  Sonora,  there  are  vast  quantities  of  eruptive 
rocks  of  much  the  same  kinds,  but  only  in  isolated  localities 
have  paying  veins  been  found.  Sometimes  these  localities  are, 
and  sometimes  they  are  not,  characterized  by  a  trifling  ex- 
posure of  a  peculiar  eruptive  rock.  In  the  former  case,  the  tri- 
fling surface  manifestation  seems  utterly  inadequate  to  account 
for  the  very  exceptional  vein-contents  of  the  localities. 

Cripple  Creek  is  another  case  in  point.  The  whole  Arkansas 
plateau  is  prolific  of  all  the  rocks  characteristic  of  Cripple 
Creek  (unless,  it  may  be,  the  basalt  dikes).  The  largest  masses 
of  phonolite  I  know  of  are  found,  as  in  Grouse  mountain  and 
Little  Pisgah  peak,  outside  the  productive  area,  while  around 
Saddle  mountain  and  at  Bare  hills  there  are  large  masses  of 
andesitic  breccia,  yet  no  ore-deposits.  At  Globe,  Ariz.,  there 
is  an  extensive  area,  northwest  of  the  camp,  that  has  the  same 
formation  as  that  surrounding  the  mines ;  but  thus  far  no  ore- 
deposits  of  value  have  been  found  in  it,  though  it  is  not  lacking 
in  veins. 

Of  Grass  valley,  Cal.,  the  U.  S.  Geological  Survey  folio  says : 
"The  veins  occur  in  almost  any  one  of  the  many  rocks  making 
up  the  bed-rock  series.  Excellent  mines  are  located  in  the 
grano-diorite,  diabase,  slate  and  schists."  Evidently  the  surface- 
eruptives  did  not  govern  in  this  case. 

In  the  case  of  several  eruptions,  only  one  of  which  is  associ- 
ated with  ore-bodies,  the  theory  would  be  that  the  one  associ- 
ated with  the  ore-bodies  was  the  deep-seated  one,  which 
brought  some  of  the  mineralized  magma  within  reach  of  the 
vein-making  agencies,  and  that,  while  the  surface-manifestation 
may  have  been  weak,  and  not  different  essentially  from  other 
eruptions  in  the  same  locality,  the  eruption  in  depth  was  radi- 
cally different. 

As  to  the  series  of  veins  in  a  given  district,  we  would  say 
that  the  barren  ones  were  the  products  of  the  shallow  erup- 
tions, while  the  rich  ones  were  the  product  of  an  eruption  that 
brought  a  rich  magma  surface-ward.  In  the  case  of  a  large 
area  of  eruptive  rocks  containing  a  very  small  mineralized  dis- 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     719 

* 

trict,  it  seems  to  me  hard  to  understand  why  the  mineralization 
is  not  much  more  general,  if  the  surface  eruptives  are  account- 
able for  the  metal-values.  If,  however,  these  values  came  from 
a  relatively  small  buried  mass  of  very  richly  mineralized  erup- 
tive rock,  the  restricted  mineralized  surface-area  is  at  once  ex- 
plained. 

Again,  there  are  occasional  mining  districts  in  which  no 
eruptive  rocks  at  all  appear  on  the  surface,  such  as  the  zinc- 
lead  deposits  of  southwestern  Illinois,  and  the  Otago  gold-fields 
of  the  South  Island  of  New  Zealand.  (The  latter  are  described 
byRickard  in  his  discussion  of  Posepny's  Genesis  of  Ore- Deposits.) 
In  such  cases  the  influence  of  a  richly  mineralized  underlying 
laccolite  is  highly  reasonable. 


720    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

• 

No.  27  A. 

« 

The  Formation  and  Enrichment  of  Ore-Bearing  Veins. 
SUPPLEMENTARY  PAPER. 

BY  GEORGE  J.  BANCROFT,  DENVER,  COLO. 

(Spokane  Meeting,  September,  1909.    Trans.,  xl.,  809.) 

AT  the  New  York  meeting  of  the  Institute,  April,  1907,  I 
presented  a  paper  entitled,  The  Formation  and  Enrichment  of 
Ore-Bearing  Veins,1  in  which  paper  I  advanced  the  following 
propositions  : 

(1)  That  the  majority  of  mineralized  veins  are  the  product  of 
expiring  vulcanism ;  (2)  that  most  of  these  veins  were  primarily 
mineralized  by  comparatively  rich  solutions  in  comparatively 
short  periods  of  time ;  (3)  that  the  solutions  gained  their  metal- 
values  from  a  comparatively  rich  source ;  (4)  that  there  is  a  bary- 
sphere  containing  large  amounts  of  the  useful  metals ;  (5)  that 
eruptions  spring  from  various  depths  and  bring  various  kinds 
of  magmas  towards  the  surface;  and  (6)  that  only  those  eruptions 
which  disturb  the  bary sphere  and  bring  a  magma  rich  in  metals 
sufficiently  near  the  surface  to  be  leached  by  vein-making  solu- 
tions are  productive  of  valuable  ore-deposits,  other  eruptions 
producing  barren  veins.  Ore-deposits  due  to  magmatic  segre- 
gation were  not  included  in  this  general  survey. 

As  a  result  of  considerable  further  study  I  have  modified  my 
views  in  some  respects,' while  in  others  I  feel  more  sure  than 
ever  of  the  ground  taken  at  that  time. 

That  ore-bodies  are  infrequent  occurrences  and  born  of  ex- 
traordinary conditions  I  think  is  now  generally  accepted.  The 
theory  that  persisted  for  a  time — namely,  that  ore-bodies  were 
formed  by  the  ordinary  ground-water,  which  consists  of  ex- 
tremely dilute  solutions,  derived  from  leaching  extremely  lean 
surface-rocks,  and  which  must  occupy  enormously  long  periods 
of  time  in  concentrating  the  values  so  leached,  is,  I  think,  now 
pretty  generally  regarded  as  not  applicable  to  the  great  majority 

1  P.  696,  this  volume. 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING   VEINS.     721 

of  our  mining-districts,  although  it  may  account  for  a  few  isolated 
deposits. 

I  note  that  a  few  recent  writers  still  use  this  theory  as  a  sort 
of  "  point  of  departure  "  for  their  discussions,  but  the  majority 
seem  to  realize  that  the  tendency  of  ordinary  ground-water 
circulation  is  to  diffuse  any  soluble  matter  rather  than  to  con- 
centrate it,  and  that  an  unusual  precipitant  must  be  present  to 
provoke  an  important  concentration  under  this  hypothesis. 

That  the  forces  of  expiring  vulcanism  are  the  agencies  which 
account  most  logically  for  ore-bodies  is  an  opinion  very  gen- 
erally held,  not  only  because  of  the  intimate  association  of  ore- 
bodies  with  eruptive  rocks,  but  also  because  the  study  of  active 
volcanoes  and  of  the  springs  rising  near  them  shows  that  ore- 
making  agencies  to  a  limited  extent,  at  least,  are  at  work  there. 
Thus,  A.  Lacroix 2  found  pyrite,  pyrrhotite,  and  galena,  together 
with  sulphates  of  sodium,  potassium,  calcium,  magnesium,  and 
aluminum,  in  the  sublimates  of  fumaroles  on  Vesuvius ;  J.  "W. 
Mallet3  discovered  silver  in  volcanic  ash  at  Cotopaxi  and  Tun- 
guragua;  0.  Silvestri 4  found  copper  in  the  fumes  of  Etna,  while 
traces  of  practically  all  the  common  metals  have  been  found  in 
eruptive  rocks. 

Similarly,  it  has  been  recognized  that  the. period  of  expiring 
vulcanism  could  not  have  been  of  very  long  duration,  geologi- 
cally speaking,  although  it  has  been  shown  that  in  some  dis- 
tricts the  repeated  recurrence  of  eruptive  action  has  had  the 
effect  of  continuing  the  mineralizing  action  through  long 
periods  of  time. 

My  fifth  and  sixth  propositions  have  not  been  so  well  estab- 
lished. I  think  it  is  generally  admitted  that  certain  eruptive 
rocks  produce  mineralized  areas,  while  others  do  not;  this  sug- 
gests most  forcibly  that  the  eruptives  themselves  differed  very 
decidedly  in  the  matter  of  mineral  content;  and  it  seems  rea- 
sonable to  infer  that  those  eruptives  which  'do  produce  mineral 
richness  have  been  rich  themselves  and  probably  originated  at 
great  depth.  The  advance  of  science  has  still  further  substan- 

2  Bulletin  de  la  Societe  Francaise  de  Mineralogie,  vol.  xxx.,  p.  219  (1907). 

3  Proceedings  of  the  Royal  Society,    vol.   xlii.,    p.   1    (1887)  ;  vol.  xlvii.,  p.  277 
(1889-90). 

4  /  Fenomeni   Vulcanici  presentati  deW  Etna,   etc.  (Catania,  1867),  per  Bulletin 
No.  330,  U.  S.  Geological  Survey,  p.  217  (1908). 


722     FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

tiated  the  theory  that  the  earth  has  a  very  heavy  center,  and  it 
is  reasonable  to  suppose  that  this  increased  specific  gravity  is 
partly  due  to  relatively  large  metal-content.  It  is  not,  how- 
ever, generally  conceded  that  it  is  necessary  for  a  mineralizing 
eruptive  to  be  so  rich  in  metals  and  so  heavy  that  it  would 
rarely  or  never  reach  the  surface,  but  would  form  laccolites, 
according  to  my  old  hypothesis.  Nor  do  I  longer  hold  this 
view.  At  that  time  I  remarked : 

"If  it  could  be  shown  that  the  surface  eruptive  rocks  have  a  tendency  to  throw 
off  metals,  as  they  do  steam  and  sulphur,  during  the  cooling  process  this  would 
remove  many  of  my  objections  to  considering  them  the  source  of  the  metals  in  our 
ore-bodies.  In  the  lack  of  such  proof,  however,  we  must  recognize  that  they  are 
extremely  lean,  and  therefore  a  very  unlikely  source  of  mineral  wealth." 

Now,  I  think  there  are  very  good  reasons  for  believing  that 
this  very  thing  is  true — namely,  that  eruptive  rocks  do  have  a 
tendency  to  throw  off  their  metal-content  during  the  cooling 
process,  or,  rather,  as  soon  as  they  reach  a  horizon  of  lessened 
pressure,  which  condition  is  apt  to  be  coincident  with  cooling. 

The  wonderful  crystallographic  researches  of  J.  E.  Spurr, 
Waldemar  Lindgren,  and  others,  have  shown  that  magmas  are 
totally  different  from  dry  melts,  and  the  cooling  of  a  magma  is 
accompanied  by  a  remarkable  series  of  differentiations.  Mr. 
Spurr  has  shown  how  the  metals  would  be  concentrated  either 
in  a  very  base  or  a  very  acid  magma,  and  finally,  in  the  case  of 
the  acid  magma,  would  be  extruded  together  with  pure  silica 
and  water,  thereby  forming  veins.  I  think,  however,  that  those 
who  have  made  a  great  deal  of  the  powerful  agency  of  mag- 
matic  differentiation  have  overlooked  a'  very  active  contem- 
porary agent— namely,  chlorine.  Bromine,  iodine,  and  fluorine 
may  be  equally  active  agencies  in  volcanic  emanations;  but  as 
these  elements  are  relatively  rare,  I  shall  confine  myself  here 
to  the  very  active  part  which  chlorine  may  play  in  carrying 
away  from  the  hot  eruptive  its  metal-content  and  depositing 
the  -same  in  ore-bodies.  These  considerations  have  been  sug- 
gested to  me  by  studying  the  dry-chlorination  process  for  the 
treatment  of  complex  ores,  as  developed  by  J.  L.  Malm,  at 
Corbin,  Mont.,  and  -at  Denver,  Colo.  This  process  depends 
primarily  upon  the  facts  that,  in  the  dry  state,  chlorine  has  a 
greater  affinity  for  the  metals  than  sulphur  or  oxygen,  and  that 
the  chlorides  of  all  the  metals  are  soluble  together  in  hot  water. 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     723 

Thus,  cupric  chloride,  lead  chloride,  zinc  chloride,  gold  chlor- 
ide, and  iron  chloride  are  soluble  in  hot  water  direct,  and  silver 
chloride  is  soluble  in  hot  cupric  chloride. 

Now,  it  is  noticeable  that  chlorine  is  nearly  always  present 
in  volcanic  emanations.  Thus,  J.  W.  Judd  says  : 5 

"The  most  abundant  of  the  substances  which  are  ejected  from  volcanoes  is 
steam  or  water-gas,  which,  as  we  have  seen,  issues  in  prodigious  quantities  during 
every  eruption.  But  with  the  steam  a  great  number  of  other  volatile  materials 
frequently  make  their  appearance.  The  chief  among  these  are  the  acid  gases 
known  as  hydrochloric  acid,  sulphurous  acid,  sulphuretted  hydrogen,  carbonic 
acid,  and  boracic  acid  ;  and  with  these  acid  gases  there  issue  hydrogen,  nitrogen, 
ammonia,  the  volatile  metals  arsenic,  antimony,  and  mercury,  and  some  other 
substances." 

After  dwelling  upon  the  large  amount  of  C02  present  in 
volcanic  gases,  Chamberlin  and  Salisbury  have  the  following 
to  say  with  reference  to  emanations : 6 

"  Sulphur  gases  are  very  common  accompaniments  of  volcanic  eruptions.  They 
take  the  forms  of  sulphuretted  hydrogen  and  sulphurous  acid  and  perhaps  of  sub- 
limated sulphur,  all  of  which  are  liable  to  pass  by  oxidation  and  hydration  into 
sulphuric  acid.  Chlorine  and  hydrochloric  gases  are  also  common,  particularly 
at  high  temperatures.  Fluorine  and  other  gases  are  occasionally  present." 

T.  Wolf  found  that  near  the  crater  of  Cotopaxi  the  fumes 
were  mostly  of  hydrochloric  acid  with-  some  free  chlorine, 
while  at  lower  levels  hydrogen  sulphide  was  found  with  a 
trace  of  sulphur  dioxide.7 

Sainte-Claire  Deville  found  chlorides  of  iron  and  copper  in  a 
fumarole  of  Vesuvius.8 

R.  Bunsen  found  various  metallic  chlorides  in  the  sublimates 
around  fumaroles  of  Mt.  Hecla  in  Iceland.9 

A  characteristic  of  volcanic  emanations  is,  that  chlorine  is 
found  either  free  or  as  the  chloride  of  the  metals,  or  as  hydro- 
chloric acid,  while  a  characteristic  of  hot  mineral  springs  is 
that  the  water  contains  large  quantities  of  the  chlorides  of 
sodium  and  potassium.  Granting  that  such  hot  mineral  springs 

5  Volcanoes:   What  They  Are  and  What  They  Teach,  p.  40  (1881). 

6  Geology,  2d  ed.,  vol.  i.,  p.  619  (1906). 

7  Neues  Jahrbuchfiir  Mineralogie,  Geologic  und  Palaeontologie,  p.  163  (1878). 

8  Bulletin  de  la  Societe  Geologigue  de  France,  Second   Series,  vol.  xiii.,  p.  606 
(1855-56). 

9  Annales  de  Chimie  et  de  Physique,  Third  Series,  vol.  xxxviii.,  p.  215  (1853). 


724     FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

are  related  to  eruptions,  and  that  the  chlorine  in  both  emana- 
tions and  springs  had  a  common  origin,  it  is  evident  that  the 
part  which  has  escaped  by  the  medium  of  spring-water  has 
undergone  certain  reactions,  which  the  part  which  escaped  as  a 
hot  gas,  from  an  open  vent,  did  not  undergo.  Does  not  this 
suggest  what  may  take  place  in  case  the  chlorides  are  extruded 
through  crevices  or  veins  where  they  may  encounter  gradually 
lessened  temperatures  together  with  water  ? 

Now,  it  is  known  that  the  temperature  of  fluid  magmas  may 
range  up  to  3,000°  F.10 

Let  us  suppose  that,  under  a  temperature  of  1,100°  C.,  we 
had  a  magma  which  contained  chlorine,  water-gas,  sulphur, 
silver,  copper,  lead,  iron,  zinc,  and  gold.  Of  course,  there 
would  also  be  other  elements  present,  but,  as  previously  stated, 
I  shall  not  try  to  cover  the  whole  field.  Let  us  suppose  that 
there  is  sufficient  chlorine  to  form  chlorides  with  all  the  metals 
and  an  excess  besides.  Any  hydrogen  present  would  be  com- 
bined with  the  chlorine,  the  affinity  for  chlorine  being  greater 
than  for  sulphur.  E"ow,  let  us  try  to  imagine  what  would  happen 
as  this  magma  approached  the  surface. 

At  the  temperature  given,  the  chlorine  would  attack  all  the 
metals,  except  gold,  and  the  chlorides  would  all  be  gases,  for  it 
is  well  known  that  the  metallic  chlorides  are  all  volatile  at  rela- 
tively low  temperatures. 

The  chloride  of  gold  under  atmospheric  conditions  decom- 
poses at  about  120°  C.  Of  course,  the  volcanic  gases  are  under 
some  pressure  even  when  escaping  from  the  magma,  and,  as 
pressure  raises  the  temperature  of  decomposition,  it  is  difficult 
to  say  just  how  cool  the  magma  must  become  before  the  gold 
would  accompany  the  other  metals. 

The  fact  that  gold  is  often  found  by  itself  in  a  state  of  great 
purity  may  be  accounted  for  by  its  isolation  from  the  other 
metals  as  regards  chemical  reactions.  Thus,  at  Farcum  Hill, 
Breckenridge,  are  found  deposits  of  most  beautiful  crystalline 
gold  by  itself,  while  less  than  a  mile  away  are  large  deposits  of 
complex  ores.  The  complex  ores  occur  in  the  eruptive  dikes 
or  on  the  contacts,  while  the  gold  is  found  in  carbonaceous 
shale.  It  is  well  known  that  carbon  will  precipitate  gold  from 

10  Geology,  Chamberlin  and  Salisbury,  2d  ed.,  vol.  i.,  p.  615  (1906). 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     725 

a  chloride  solution,  as  is  done  in  wet-chlorination  mills,  but  it 
will  not  precipitate  the  other  chlorides. 

The  chlorine  would  not  attack  the  silicates  of  the  eruptive, 
as  is  shown  by  the  experiments  of  Brun,11  who  heated  a  Lipari 
lava  and  observed  the  following  exhalations  : 

From  0°  to  825°,  volatilization  of  water. 

At  825°,  first  evolution  of  chloride  vapors. 

From  874°  to  1,100°,  temperature  of  explosions. 

At  1,100°,  mean  temperature  of  flowing  lava. 

Although  the  dry-chlorination  process  does  not  use  high  tem- 
peratures, Mr.  Malm  has  experimented  with  chlorine  and  the 
ordinary  rock-minerals  at  high  temperatures  and  has  shown 
that  they  do  not  react. 

The  sulphur  would  occur  as  sulphur  gas  and  partly  as  sul- 
phur chloride.  There  would,  of  course,  be  a  great  deal  of 
water-gas  present.  As  the  magma  rose  to  a  horizon  of  less- 
ened pressure  these  gases  would  expand  and  leave  the  magma, 
bursting  out  through  any  veins  or  vents  or  porous  strata  that 
might  provide,  a  means  of  escape.  The  great  distance  to  which 
the  metals  have  penetrated  porous  strata,  as,  for  instance,  at 
Morenci,  Ariz.,  may  be  accounted  for  in  this  way. 

The  farther  from  the  magma  the  gases  traveled  the  cooler 
they  would  become,  and  as  they  became  cooler  they  would  be- 
come a  liquid.  "We  would  then  have  the  chlorides  of  the 
metals  in  a  hot  aqueous  solution,  together  with  sulphur  chlor- 
ide and  elemental  sulphur,  the  latter  in  an  extremely  fine 
state  of  subdivision  (as  it  is  found  in  many  mineral  springs). 

Precipitation  would  not  take  place  till  some  precipitating- 
agent  was  encountered  in  the  rocks. 

The  cooling  of  the  solution  would  throw  down  the  lead  and 
the  lead  only.  Silver  chloride  is  difficultly  soluble  and  easily 
precipitated.  This  may  account  for  the  exceeding  purity  of 
some  lead-deposits  and  the  frequent  association  of  silver  and 
lead. 

If  CaO  in  abundance  were  encountered  all  the  metals  would 
be  precipitated  together.  This  may  account  for  the  complex 
nature  of  many  deposits  in  porphyry-lime  contacts,  as,  for  in- 
stance, at  Leadville,  Rico,  Breckenridge,  etc. 

11  Archives  des  Sciences  Physiques  et  Naturelles,  Fourth  Series,  vol.  xix.,  pp.  439, 
589  (1905). 


726    FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

It  is  fair  to  assume  that  the  heated  eruptive  would  drive  off 
the  CO2  from  any  limestone  in  immediate  contact  with  it. 
The  chloride  gases  emanating  from  the  same  eruptive  would 
find  an  immediate  and  abundant  precipitant  in  the  form  of 
CaO  thus  formed,  or,  in  case  conditions  became  cool  enough 
for  water  to  convert  the  oxide  to  the  hydroxide,  the  latter 
would  be  equally  efficient  as  a  precipitant.  Thus, 


2  MCla  +  xCaO  =  M20X  +  2 

2  MCl^  +  xCaO  +  zH20  =  2  M  (OH)X  +  xCaC!2. 

In  granitic  or  eruptive  rocks,  the  methods  of  precipitation 
are  not  quite  so  simple.  I  have  immersed  pieces  of  Boulder 
County  granite  in  solutions  of  the  metallic  chlorides,  sulphur 
chloride,  and  a  little  free  acid,  and  at  the  end  of  three  days 
there  was  no  appreciable  result.  Again,  I  have  boiled  pieces 
of  the  same  granite  in  strong  hydrochloric  and  sulphuric  acid, 
and  in  half  an  hour  the  reactions  were  very  considerable.  The 
hydrochloric  acid  was  the  more  active.  The  piece  of  granite 
was  eaten  away  considerably.  Examination  of  the  remaining 
piece  with  a  magnifying-glass  showed  that  the  surface  was  re- 
duced to  a  covering  of  spongy  silica  and  white  mica.  Whether 
the  mica  had  been  whitened  by  leaching  the  iron,  or  whether 
only  those  bits  remained  intact  which  had  no  iron,  I  am  not 
prepared  to  say.  In  addition  to  the  piece  remaining  undis- 
solved'(at  the  end  of  30  min.),  there  was  a  sediment  which,  on 
examination,  appeared  to  be  rounded  and  porous  pieces  of 
silica  and  minute  flakes  of  pure  white  mica.  The  test  with 
sulphuric  acid  rendered  the  piece  darker.  Only  a  very  small 
part  went  into  solution.  An  examination  with  a  glass  has 
shown  the  feldspars  to  be  lacking  and  the  surface  to  be  covered 
with  a  coating  of  pearly  silica  and  black  mica.  In  this  connec- 
tion Clarke  says  :  12 

'  '  Hot  waters,  charged  with  sulphuric  or  hydrochloric  acid,  attack  nearly  all 
eruptive  rocks,  dissolve  nearly  all  bases,  and  leave  behind,  in  many  cases,  mere 
skeletons  of  silica." 

On  this  subject  Judd  says:13 

12  Bulletin  No.  330,  U.  S.  Geological  Survey,  p.  408  (1908). 

13  Volcanoes:   What  They  Are  and  What  They  Teach,  p.  41  (1881). 


FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS.     727 

"In  many  volcanoes  the  constant  passage  through  the  rocks  of  the  various  acid 
gases  has  caused  nearly  the  whole  of  the  iron,  lime,  and  alkaline  materials  of  the 
rocks  to  be  converted  into  soluble  compounds  known  as  sulphates,  chlorides,  car- 
bonates, and  bo  rates;  and,  on  the  removal  of  these  by  the  rain,  there  remains  a 
white,  powdery  substance,  resembling  chalk  in  outward  appearance,  but  composed 
of  almost  pure  silica.  There  are  certain  cases  in  which  travelers  have  visited 
volcanic  islands  where  chemical  action  of  this  kind  has  gone  on  to  such  an  extent, 
that  they  have  been  led  to  describe  the  islands  as  composed  entirely  of  chalk." 

F.  Henrich  shares  the  same  view,  claiming  that  the  chlorides 
of  potassium  and  sodium  found  in  sublimates  of  aqueous  fuma- 
roles  were  formed  by  the  action  of  moisture  and  hydrochloric 
acid  on  the  alkaline  silicates  of  the  heated  lavas.14 

We  know  from  observation  underground  that  granitic  and 
other  rocks  are  attacked  by  mineral  solutions  which  produce 
first  a  softening  of  the  rocks,  and  eventually  remove  all  the 
original  constituents  except  the  silica  and  hydrous  alumina 
silicates. 

It  is,  of  course,  difficult  to  reproduce  in  the  laboratory  with  a 
few  simple  salts  the  complex  reactions  that  take  place  far  under- 
ground ;  and  here  at  least  we  must  take  the  evidence  as  we 
find  it,  even  if  it  is  difficult  to  reproduce  the  reactions. 

We  find  chlorine  or  hydrochloric  acid  or  metallic  chlorides 
issuing  from  volcanoes,  and  we  find  sodium,  calcium,  and  po- 
tassium chlorides  issuing  from  mineral  springs;  so  it  seems 
highly  probable  that  the  sodium  and  potassium  silicates  break 
up,  and  the  chlorine,  after  it  has  become  cooled  below  the  boil- 
ing-point of  water,  reacts  with  the  sodium  or  potassium,  drop- 
ping any  metals  with  which  it  may  have  been  combined. 

The  reactions  leading  to  the  formation  of  calcium  chloride 
have  been  explained  above.  The  reactions  with  the  silicates 
would  most  naturally  begin  with  the  free  hydrochloric  acid, 
thereby  liberating  hydrogen,  which  would  combine  with  the 
sulphur  to  form  H2S,  and  this  in  turn  would  precipitate  the 
metals  according  to  the  following  reactions  : 


MC1X  +  XH2S  =  xHCl  +  MS 


and  would  convert  any  metals  already  precipitated  by  other 
agencies  to  the  sulphides,  as  follows : 

14  Zeitschrift  fur  angewandte  Chemie,  vol.  xix.,  No.  30,  p.  1326  (July  27,  1906)  ;, 
vol.  xx.,  No.  5,  p.  179  (Feb.  1,  1907). 


728     FORMATION    AND    ENRICHMENT    OF    ORE-BEARING    VEINS. 

MOX  +  :rH2S  =a>  MS,  +  xll2O 
M  -f  xH2S  =  MS,  -f  zH2. 

The  first  reaction  would  result  in  more  hydrochloric  acid, 
which  would  be  available  to  repeat  the  cycle. 

Whether  the  metals  are  precipitated  by  CaO  or  by  reactions 
with  the  silicates,  they  would  be  almost  at  once  converted  to 
sulphides,  according  to  the  above  reactions;  and  that  is  the 
condition  in  which  we  find  them.  Gold,  which  is  precipitated 
by  carbon,  would  not  be  subject  to  the  action  of  H2S,  and  hence 
would  likely  occur  as  free  gold  in  carbonaceous  formations, 
which  agrees  with  the  facts  as  we  find  them. 

As  stated  above,  I  have  confined  myself,  for  the  sake  of  sim- 
plicity, to  an  arbitrarily-chosen  condition.  It  is  my  purpose  to 
point  out  the  very  active  part  which  the  halogens  may  play  in 
divesting  an  eruptive  of  its  metal-contents,  and  conveying  the 
same  into  neighboring  veins  or  openings  in  the  rocks,  rather 
than  to  prescribe  the  exact  steps  that  are  followed.  It  is  con- 
ceivable that  under  certain  conditions  the  above-mentioned 
reactions  may  be  very  important,  while  in  others  they  may  be 
negligible.  It  is  conceivable  that  in  some  cases  an  eruptive 
may  be  totally  divested  of  its  useful  metals  and  yet  little  of  it 
be  precipitated  short  of  the  atmosphere.  This  may  account  for 
the  Snake  river  placer  gold,  which  is  extremely  fine,  and  so 
often  found  associated  with  volcanic  ash  as  to  provoke  the 
theory  that  it  had  an  atmospheric  origin.  On  the  other  hand, 
a  metalliferous  eruptive  may  be  only  partly  relieved  of  its 
metal-content,  the  residue  remaining  in  a  more  or  less  segre- 
gated form  in  the  body  of  the  eruptive,  as  at  Ely,  Nev.,  where 
the  sedimentaries  adjoining  the  eruptive  area  contain  veins  and 
deposits  of  copper-ore,  while  the  eruptive  itself  contains  large 
masses  of  low-grade  ore  which  appear  to  be  due  to  magmatic 
segregation. 

I  think  these  considerations,  helping  to  explain  some  of  the 
puzzling  things  about  ore-bodies,  maybe  of  service  in  promoting 
progress  towards  the  goal  of  a  perfect  understanding  of  the 
subject. 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  729 

No.  28. 
The  Distribution  of  the  Elements  in  Igneous  Rocks. 

BY  HENRY  S.  WASHINGTON,  NEW  YORK,  N.  Y. 
(Chattanooga  Meeting,  October,  1908.     Tram.,  xxxix.,  735.) 

I.  INTRODUCTION. 

DURING  the  last  twenty  years  or  so  the  chemical  investigation 
of  rocks  has  made  great  advances,  and  it  is  now  generally  rec- 
ognized that  a  knowledge  of  the  chemical  composition  is  as 
essential  as  that  of  the  texture  or  mineral  composition — if  not 
more  so — for  the  proper  classification  of  rocks  and  study  of 
their  origin  and  relationships.  Rock-analyses  have  vastly 
increased  in  number  and,  what  is  of  greater  importance,  in 
quality.  New  and  improved  methods  permit  of  greater  accu- 
racy than  was  possible  in  the  early  days,  and  the  list  of  chemi- 
cal constituents  frequently  determined  has  risen  from  the  seven 
or  eight  of  the  greater  part  of  the  nineteenth  century,  to  twenty 
or  more.  Indeed,  rock-analyses  with  determinations  of  so 
many  constituents  are  now  commonly  made  by  the  chemists  of 
the  United  States  and  Australia,  while  in  Germany,  Great 
Britain,  France,  and  Italy  the  rarer  constituents  are  determined 
more  frequently  than  formerly. 

As  a  consequence  of  this  modern,  accurate  work,  it  has  been 
discovered  that  some  elements  which  were  formerly  supposed 
to  be  rare  are  of  wide-spread  occurrence  and  are  often  present 
in  considerable  amount.  The  fact  is  further  being  developed 
that  the  elements  tend  to  show  certain  relations  of  occurrence 
or  abundance  in  connection  with  each  other.  This  is  a  fact 
which  is  applicable  to  the  rarer  elements,  and  which  also  finds 
a  broad  geological  and  petrological  expression  in  the  recog- 
nition of  petrographic  provinces.  We  are  beginning  to  obtain 
some  definite,  though  as  yet  rudimentary,  knowledge  of  the 
distribution  of  the  elements  among  igneous  rocks, 

Some  of  the  results  along  these  lines  obtained  by  study  of 
the  vast  accumulation  of  analytical  data  now  available  are  \vell 
knowrn  to  petrologists,  while  others  do  not  seem  to  be  so  gener- 

46 


730  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

ally  understood.  To  the  non-petrologist  they  are,  naturally,, 
mostly  unknown,  and,  as  the  general  principles  involved,  and, 
indeed,  some  of  the  specific  instances,  have  a  more  or  less  im- 
portant bearing  on  the  occurrence  and  characters  of  certain 
deposits  of  metallic  ores  and  other  economically  important 
minerals,  a  discussion  of  the  subject  may  be  of  interest  to  ; 
mining  engineers. 

Indeed,  to  the  observations  and  operations  of  mining  engi- 
neers and  mining  interests  generally,  the  petrologist  is  indebted 
and  must  look  for  some  of  his  data.  This  is  especially  true  of 
those  relating  to  the  precious  metals  and  others  of  commercial 
importance,  the  amounts  of  which  usually  present  in  rocks  are 
so  small  as  almost  or  quite  to  defy  detection  by  ordinary  ana- 
lytical methods,  and  whose  presence  is  often  revealed  only 
through  search  for  and  the  exploitation  of  localities  where  they 
have  undergone  concentration.  It  must  be  premised,  however, 
that  our  knowledge  is  at  present  very  uneven,  allowing  fairly 
safe  and  detailed  generalizations  as  regards  some  of  the  ele- 
ments, very  rudimentary  or  general  ones  as  regards  others,  and 
again  allowing  almost  none  at  all. 

II.  GENERAL  CHEMICAL  COMPOSITION  OF  IGNEOUS  ROCKS. 

The  first  and  most  important  fact  to  be  noted  of  igneous 
rocks  is  that,  with  the  exception  of  some  rare  ore-bodies  due 
to  the  differentiation  of  igneous  magmas,  they  are  composed 
almost  wholly  of  silica  and  silicates.  The  vast  majority  of 
igneous  rocks  are  silicate  rocks,  in  which  silica  forms  the  most 
prominent  and  the  never-failing  constituent.  Most  of  the  min- 
erals which  compose  them  are  combinations  of  silica  with 
various  bases,  and  it  is  a  striking  fact  that  the  number  of  min- 
erals which  go  to  make  up  the  majority  of  igneous  rocks,  and 
which  are  most  abundant  and  most  often  met  with,  is  very 
small. 

The  proportions  in  which  these  minerals  may  be  present 
vary  very  widely.  Some  rocks  are  known  which  are  com- 
posed wholly,  or  practically  so,  of  but  one  mineral.  Combina- 
tions of  two  are  not  infrequent,  while  most  rocks  contain  at 
least  three,  and  usually  many  more,  minerals  and  in  the  most 
widely  diverse  proportions.  It  follows,  therefore,  that  the 
chemical  composition  of  igneous  rocks  may  vary  within  very 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  731 

wide  limits,  as  regards  any  or  all  of  the  chemical  constituents ; 
and  that,  furthermore,  some  rocks  may  he  of  very  simple 
chemical  composition,  while  others  may  be  very  complex,  with 
many  constituents  present,  since  the  minerals  themselves  may 
be  either  very  simple  or  highly  complex  in  chemical  compo- 
sition. 

The  most  important  chemical  constituents  (stated  as  oxides, 
in  accordance  with  the  usual  custom)  are  as  follows :  silica, 
Si02;  alumina,  A1203;  ferric  oxide,  Fe203;  ferrous  oxide,  FeO; 
magnesia,  MgO  ;  lime,  CaO ;  soda,  Na20 ;  potash,  K20 ;  and 
water,  H20.  Some  or  all  of  these  major  constituents,  as  they 
are  termed,  are  invariably  present,  so  far  as  known,  and  col- 
lectively they  constitute  about  98  per  cent,  of  all  known  rocks. 
The  chief  oxides,  from  silica  to  potash  inclusive,  enter  into  the 
composition  of  the  most  important  and  most  commonly  occur- 
ring rock-forming  minerals,  as  well  as  the  glass  of  imperfectly 
crystallized  rocks. 

The  role  of  water  is  somewhat  different.  It  would  seem  to 
be  universally  present  in  the  magma,  and  its  presence  (along 
with  that  of  other  substances)  lowers  the  freezing-point  and 
increases  the  tendency  to  crystallization  of  the  liquid  mass. 
Most  of  this  water  is  lost  if  the  magma  reaches  the  surface  and 
it  appears  in  the  enormous  clouds  which  accompany  volcanic 
eruptions  and  the  steam  of  volcanic  fumaroles ;  and  much  of  it 
also  escapes  if  the  magma  solidifies  beneath  the  surface,  giving 
rise  to  subterranean  water-supplies,  which  are  held  by  many  to 
be  an  important  factor  in  the  formation  of  many  ore-deposits. 
A  small  proportion  of  the  water  originally  present  may  remain 
in  the  solidified  rock  in  a  combined  form,  as  part  of  the  more 
complex  mineral  molecules,  those  of  pyroxenes,  amphiboles, 
and  micas,  for  instance;  and  some  may  also  remain  as  inclu- 
sions of  water  in  the  minerals  of  intrusive  rocks. 

There  are  also  almost  invariably  present  in  igneous  rocks 
small  amounts  of  titanium,  phosphorus,  and  manganese,  though 
these  are  often  neglected  and  thus  overlooked  in  the  less  com- 
plete analyses.  Carbon  dioxide  is  also  met  with,  but'  its  pres- 
ence, as  reported  in  analyses  of  igneous  rocks,  is  almost  inva- 
riably due  to  decomposition,  and  it  cannot  be  usually  regarded 
as  an  essential  or  original  constituent  of  rocks. 

In  addition  to  these  most  important  constituents,  the  refine- 


732  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

merits  and  increasing  completeness  of  modern  rock-analysis 
show  that  many  others  are  frequently  present,  often  in  scarcely 
more  than  traces,  but  again  in  very  appreciable  quantities. 
The  most  important  of  these  minor  elements  are :  zirconium, 
sulphur  (as  sulphides  and  as  sulphur  trioxide),  chlorine,  fluor- 
ine, vanadium,  chromium,  nickel,  barium,  strontium,  and 
lithium.  Exceptionally,  others  may  be  determined :  as  boron, 
cobalt,  copper,  gold,  silver,  molybdenum,  the  metals  of  the 
cerium  and  yttrium  groups,  nitrogen,  and  others.  Indeed,  as 
Dr.  Hillebrand1  says,  "  a  sufficiently  careful  examination  of 
these  rocks  would  show  them  to  contain  all  or  nearly  all  the 
known  elements,  not  necessarily  all  in  a  given  rock,  but  many 
more  than  anyone  has  yet  found."  The  researches  of  Sand- 
berger,  Stelzner,  and  Dieulafait  also  point  to  the  same  con- 
clusion. 

Considering  the  quantitative  distribution  of  the  major  con- 
stituents, silica  is  almost  invariably  present  in  igneous  rocks, 
and  almost  always  in  greatest  amount.  In  general,  the  per- 
centage may  vary  from  nearly  80,  as  in  granites  and  rhyolites, 
to  a  minimum  of  about  24  per  cent.  Indeed,  it  may  even  form 
100  per  cent.,  if  some  dikes  consisting  wholly  of  quartz  are 
really  of  igneous  origin,  as  is  believed  to  be  the  case;  while 
in  some  ores  derived  from  igneous  magmas  the  amount  of 
silica  may  drop  almost  to  zero.  Alumina  is  usually  the  next 
most  abundant  constituent,  the  percentage  varying  from  a  maxi- 
mum of  about  60,  as  in  some  corundum-syenites  of  Siberia 
and  Canada,  to  a  minimum  of  zero,  in  certain  rocks  composed 
wholly  of  olivine.  The  two  iron  oxides  each  show  maxima  of 
about  15  per  cent,  except  in  the  rare  iron-ores  due  to  magmatic 
differentiation,  where  they  constitute  together  almost  all  the 
rock.  Magnesia  attains  maxima  of  from  45  to  50  per  cent,  in 
dunites  of  New  Zealand  and  North  Carolina;  while  lime  reaches 
a  maximum  of  about  20  per  cent,  in  the  anorthosites  of  Canada. 
Iron,  magnesia,  and  lime  may  be  practically  absent  in  highly 
siliceous  rocks,  like  granites  and  rhyolites,  and  in  some  syenites. 
Soda  may  be  present  up  to  17  per  cent,  in  some  rare  rocks  in 
which  nephelite  is  abundant;  while  potash  attains  a  maximum 
of  only  about  12  per  cent,  in  some  unusual  rocks  rich  in  leucite, 

1  Bulletin  No.  305,  U.  S.  Geological  Survey,  p.  20  (1907). 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  V33 

which  are  found  in  Italy  and  in  Wyoming.  Both  the  alkalies 
may  be  wholly  wanting  in  rocks  composed  essentially  of 
pyroxene  or  olivine. 

The  amount  of  water  present  in  wholly  crystalline  rocks 
seldom  exceeds  -2  per  cent.,  if  the  rock  is  unaltered,  though 
weathering  very  materially  increases  this  quantity,  and  high 
figures  for  water  are  usually  to  be  attributed  to  this  cause. 
But  some  perfectly  fresh,  glassy  lavas  may  carry  up  to  12  per 
cent,  of  water,  which  was  unable  to  escape  from  the  magma 
owing  to  the  rapidity  of  solidification. 

Titanium  dioxide  may  rarely  reach  figures  of  about  6  per 
cent.,  as  in  some  basalts  of  the  Western  Mediterranean  which 
I  am  now  investigating,  but  is  usually  present  in  much  less 
quantity,  though  it  is  seldom  or  never  entirely  absent.  In  some 
titaniferous  iron-ores  of  igneous  origin,  as  those  of  the  Adiron- 
dacks  and  Norway,  it  may  even  reach  18  per  cent.  The 
amount  of  phosphoric  pentoxide  rarely  exceeds  3  per  cent.,  and 
that  of  manganous  oxide  is  scarcely  ever  more  than  1  per  cent., 
.  the  higher  figures  sometimes  reported  for  this  latter  constituent 
being  almost  invariably  due  to  errors  of  analysis.  It  is  but 
seldom  that  either  of  these  three  elements  is  entirely  absent. 

The  maximum  amounts  of  the  other  minor  constituents  may 
be  briefly  stated,  as  attention  will  thus  be  called  to  their  rela- 
tively great  rarity,  it  being  understood  that  the  maxima  are 
seldom  attained  and  that  very  frequently  these  elements  are 
wholly  absent. 

Zirconium  is  much  less  common  than  the  chemically  related 
titanium,  and  seldom  exceeds  0.20  per  cent.,  though  in  some 
very  exceptional  cases  it  may  reach  2  per  cent.  Chromium 
seldom  occurs  in  amounts  above  0.5  per  cent.,  though  a  few 
rocks  are  known  in  which  it  is  reported  to  range  between  2  and 
3  per  cent.  Mckel  seldom  exceeds  0.20  per  cent.,  and  the 
allied  cobalt  is  scarcely  ever  present  in  more  than  mere  traces. 
The  maximum  amount  of  copper  found  in  unaltered  igneous 
rocks  may  be  placed  at  about  0.2  per  cent,  of  CuO.  Barium 
almost  always  exceeds  strontium  in  quantity,  but  only  very  ex- 
ceptionally exceeds  0.25  per  cent.,  though  some  rocks  are 
known  in  which  about  1  per  cent,  is  present;  while  the  amount 
of  strontium  is  usually  much  less  than  0.1,  but  may  occasion- 
ally reach  0.3  per  cent,  in  the  rocks  very  high  in  barium. 


734  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

Although  figures  of  0.1  or  0.2  per  cent,  have  been  reported  for 
lithium,  these  are  somewhat  doubtful,  and  it  seldom  occurs  in 
more  than  spectroscopic  traces.  Sulphur  and  chlorine  may 
both  be  present  up  to  2  per  cent,  or  slightly  more,  but  both 
usually  occur  only  in  tenths  of  a  per  cent.,  and  the  latter 
amount  is  the  maximum  for  fluorine.  Of  the  other  minor  con- 
stituents the  amounts  present  are  so  small  as  usually  to  be  in- 
significant except  as  to  their  actual  presence. 

III.  THE  AVERAGE  COMPOSITION. 

The  estimation  of  the  average  composition  of  igneous  rocks 
as  a  whole  is  not  such  a  simple  matter  as  may  be  thought  at 
first,  because  of  several  complicating  factors  which  should  be 
taken  into  account,  and  certain  corrections  in  some  of  our  data 
which  should  be  made,  to  obtain  fairly  satisfactory  results.  We 
are  not  yet  in  a  position  to  make  precise  allowance  for  these, 
into  the  discussion  of  which  we  cannot  enter  here,  so  that  the 
results  so  far  obtained  can  be  regarded  as  but  first  approxima- 
tions, only  roughly  correct  but  of  some  value. 

The  most  recent  and  reliable  calculations  are  three  made 
successively  by  Prof.  F.  W.  Clarke,  of  the  United  States  Geolog- 
ical Survey,  two  of  the  igneous  rocks  of  the  British  Isles  by 
Prof.  A.  Harker,  of  Cambridge,  and  one  made  by  myself  some 
years  ago.2 

Clarke's  latest  estimate  is  based  on  more  than  a  thousand 
analyses  of  igneous  rocks  of  the  United  States  made  by  the 
chemists  of  the  Geological  Survey,  and  mine  is  based  on  about 
1,800  analyses  of  igneous  rocks  from  all  parts  of  the  globe, 
and  made  by  many  analysts  of  various  nationalities.  These  are 
shown  respectively  in  columns  I.  and  II.  of  Table  I.,  only  the 
more  important  constituents  being  considered^  and  the  whole 
being  reduced  to  100  per  cent.  Harker's  estimates  are  omitted, 
but  in  general  they  conform  to  those  here  presented. 

It  is  evident  that  the  two  are  very  closely  alike,  the  only 
noteworthy  divergence  being  in  the  amount  of  silica.  The 

2  F.  W.  Clarke,  Bulletin  of  the  U.  S.  Geological  Survey,  No.  148,  p.  12  (1897)  ; 
No.  168,  p.  14  (1900);  No.  228,  p.  18  (1904)  ;  A.  Harker,  Geological  Magazine, 
vol.  xxxvi.,  p.  18  (1899)  ;  Tert  Ign.  Kocks  of  Skye,  p.  416  (1904) ;  H.  S.  Wash- 
ington, Professional  Paper  No.  14,  U.  S.  Geological  Survey,  p.  108  (1903).  I  am 
at  present  engaged  in  new  calculations  of  the  average  rock,  based  on  more  than 
3,000  analyses,  but  this  is  not  yet  ready  for  publication. 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 


735 


TABLE  I. — Average  Composition  of  Igneous  Hocks. 


I. 

United 

States, 

Clarke, 

1904. 

SiO2       .    .     . 

.     60.48 

A1203     .     .     . 

.     15.17 

Fe203    .     .     . 

.       2.61 

FeO       ... 

.       3.44 

Mgo    .    .**; 

.       4.10 

CaO       .     .     . 

.       4.84 

Xa.2O     .     .     , 

.       3.43 

K2O  .... 

2.96 

H20(110°+) 

.       1.48 

H2O  (110°—) 

.       0.41 

Ti(X      .     .     . 

.       0.72 

PA      -     -     • 

.       0.26 

MnO      .     .     . 

.       0.10 

CO2  .... 

S                 .     . 

BaO 

Cl      .... 

OoOo 

V^A2VV3        * 

SrO  .... 

ZrO2       .     .     . 

KiO 

V9(X. 

F 

LioO  . 

100.00 


II. 

III. 

The 

Complete 

World, 

Average, 

Washington, 

Clarke, 

1903. 

1904. 

57.78 

59.87 

O 

15.67 

15.02 

Si 

3.31 

2.58  + 

Al 

3.84 

3.40  + 

Fe 

3.81 

4.06 

Ca 

5.18 

4.79 

Na 

3.88 

3.39 

Mg 

3.13 

2.93 

K 

1.42 

1.46 

Ti 

0.36 

0.40 

H 

1.03 

0.72 

C 

0.37 

0.26 

P 

0.22 

0.10 

S 

0.52  — 

Ba 



0.11 

Mn 

0.11 

Cl 

0.07 

Sr 

0.05  — 

Cr 

0.04 

Zr 



0.03  — 

Ni 



0.03- 

F 



0.03  — 

V 



0.02  + 

Li 

0.01 

100.00 

100.00 

IV. 

Clarke, 
1904. 

47.09 
28.23 

7.99 

4.46 

3.43 

2.53 

2.46 

2.44 

0.43 

0.17 

0.14  — 

0.11 

0.11 

0.089 

0.084 

0.07  — 

0.034 

0.034  — 

0.026  — 

0.023  — 

0.02  + 

0.02  — 

0.01 


100.00 


higher  figure  in  I.  may  be  ascribed  in  part,  as  pointed  out  by 
Clarke,  to  the  inclusion  of  many  separate  silica-determinations, 
which  were  undertaken  on  rocks  comparatively  high  in  this  con- 
stituent; in  part  to  the  inclusion  in  the  estimate  of  some  analy- 
ses of  siliceous  gneisses  and  schists,  rocks  which  were  not 
regarded  in  my  estimate ;  and  probably  in  part  to  the  fact  that 
in  Clarke's  estimate  only  rocks  from  the  United  States  were 
considered.  But  notwithstanding  the  slight  discrepancies  and 
the  uncertainty  introduced  by  non-allowance  for  the  disturbing 
factors  mentioned  above,  the  results  of  the  two  calculations  are 
so  concordant  that  we  may  feel  a  high  degree  of  confidence  in 
the  belief  that  the  data  given  here  approximate  closely  to  the 
average  composition  of  the  earth's  accessible  igneous  rocks. 

In  column  III.  are  given  the  results  of  a  more  complete  esti- 
mate by  Clarke,  which  includes  the  minor  constituents  fre- 
quently present  in  igneous  rocks,  but  which  are  only  deter- 


736  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

mined  in  the  more  complete  analyses,  as  those  made  by  the 
chemists  of  the  II.  S.  Geological  Survey.  It  will  be  seen  that 
the  data  are  in  agreement  with  the  general  composition  of  the 
most  common  rock-forming  minerals,  their  constituents,  silica, 
alumina,  ferric  and  ferrous  oxides,  magnesia,  lime,  soda,  potash, 
and  .water,  making  up  97.9  per  cent. 

The  estimated  amount  of  carbon  dioxide  is  undoubtedly  too 
high,  and  is  due  to  the  number  of  analyses  of  altered  rocks 
which  were  included  in  the  estimates. 

We  may  examine  the  matter  further  and,  resolving  the  oxides 
into  their  elementary  components,  ascertain  the  average  amounts 
of  the  elements  in  the  igneous  crust  of  the  earth.  This  problem 
has  been  studied  by  Clarke  in  the  papers  already  cited,  and  by 
Yogt3  in  Norway.  The  results  of  Clarke's  latest  calculations 
are  given  in  column  IV.  of  Table  I.,  the  figures  including  those 
for  the  minor  constituents  of  column  III.,  just  noticed.  In  an 
earlier  computation  Clarke  introduced  estimates  of  the  ele- 
ments which  make  up  the  air,  the  water  of  the  oceans,  and  such 
non-igneous  rocks  as  limestone  and  coal.  But  the  introduction 
of  these  into  the  calculation  does  not  materially  alter  the  final 
results  from  those  given  here,  in  which  they  are  omitted,  since 
these  bodies  are  of  relatively  very  slight  quantitative  import- 
ance compared  with  the  whole  mass  of  known  rocks,  however 
large  they  may  loom  to  our  eyes.  Ore-bodies  also  are  quite 
negligible  in  this  connection. 

These  data  show  that  oxygen  composes  almost  one-half,  sili- 
con more  than  one-quarter,  and  aluminum  about  one-twelfth  of 
the  earth's  crust  (the  three  together  amounting  to  83.3  per 
cent.),  while  iron,  calcium,  sodium,  magnesium,  potassium,  and 
titanium  follow  after  in  the  order  named  in  decreasingly  small 
amounts.  Thus,  only  nine  elements  together  constitute  99  per 
cent,  of  the  igneous  crust.  This  is  certainly  a  very  remarkable 
fact,  and  one  doubtless  of  great  significance  for  the  proper  under- 
standing of  the  true  constitution  of  our  globe,  could  we  but  in- 
terpret it  aright,  as  some  day  we  may  hope  to  do. 

The  relatively  high  position  occupied  by  titanium,  ninth  on  the 
list  in  the  order  of  abundance,  is  also  a  striking  feature,  as  this 
element  is  commonly  supposed  to  be  rare.  The  establishment 

3  J.  H.  L.  Vogt,  Zeitschrift  fur  praktische  Geologic,  pp.  225-238,  314-325  (July 
and  September,  1898). 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  787 

of  this  fact  is  largely  due  to  the  accuracy  and  completeness  of 
the  rock-analyses  made  by  the  chemists  of  the  U.  S.  Geological 
Survey,  and  its  great  abundance  was  unsuspected  before  they 
began  their  long  series  of  excellent  analyses,  though  its  wide 
distribution  had  been  noted. 

It  is  also  noteworthy  that,  with  the  exception  of  iron,  alumi- 
num, manganese,  and  nickel,  none  of  the  metals  commonly 
used  as  such  appear  in  the  list,  while  others,  which  are  of  very 
limited  practical  application,  are  present.  While  nearly,  if  not 
quite,  all  of  the  elements  are  presumably  present  in  igneous 
rocks,  the  average  amounts  of  those  not  given  in  the  list  are 
so  extremely  small  that  they  may  be  regarded  as  minor  correc- 
tions to  be  applied  in  the  future  to  certain  of  those  here  given, 
since  nearly  all  of  them  would  be  precipitated  and  weighed  in 
the  course  of  analysis  with  some  of  those  more  abundant. 

In  the  important  paper  cited  above,  Vogt  has  discussed  the 
probable  amounts  of  these  missing  elements,  and  a  brief  state- 
ment of  those  of  his  results  which  pertain  "to  the  more  im- 
portant metallurgical  elements  may  be  given.  The  estimates, 
it  must  be  premised,  are  but  approximations,  and  only  indicate 
the  magnitude  of  the  several  amounts  as  percentages  of  the 
earth's  crust.  But  they  serve  to  show  the  average  extremely 
small  quantities  of  many  metals  and  other  elements  which  are 
usually  regarded  as  quite  common  or  at  least  not  very  rare. 

The  percentage  amounts  of  tin,  zinc,  and  lead  are  expressed 
by  a  digit  in  the  third  or  fourth  decimal-place,  that  of  copper 
in  the  fourth  or  fifth,  that  of  silver  in  the  sixth  or  seventh,  that 
of  gold  in  the  seventh  or  eighth,  the  amount  of  platinum  being 
about  the. same.  Mercury  is  rather  more  abundant  than  silver, 
and  arsenic,  antimony,  molybdenum,  and  tungsten  less  than 
copper  and  greater  than  silver;  while  bismuth,  selenium,  and 
tellurium  are  less  abundant  than  silver  but  more  so  than  gold. 

III.  PETROGRAPHIC   PROVINCES. 

More  than  30  years  ago,  Vogelsang4  pointed  out  that  the 
igneous  rocks  of  certain  districts — called  by  him  geognostische 
Bezirke — showed  certain  textural  or  mineral  characters  in  com- 
mon, which  served  to  distinguish  them  from  the  rocks  of  other 

4  H.  Vogelsang,  Zeitschrifl  der  deufschen  geologischen  Gesellschaft,  vol.  xxiv.,  No.  3, 
p.  525  (May- July,  1872). 


738  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

districts.  The  same  idea  was  expressed  later  by  Judd,5  who 
introduced  the  term  Petrographic  Province,  and  was  afterward 
elaborated  by  Iddings,6  who  likened  the  districts  of  similar 
rocks  to  families  and  referred  to  their  relationships  as  "Consan- 
guinity." Neither  Judd  nor  Iddings  seems  to  have  been  aware 
of  Vogelsang's  prior  publication.  The  first  two  statements 
referred  only  to  geological  occurrence  and  to  textural  and  min- 
eralogical  peculiarities ;  while  Iddings,  writing  at  a  time  when 
the  chemistry  of  rocks  had  begun  to  assume  its  due  prominence 
(largely  owing  to  the  earnest  labors  of  the  chemists  of  the  IT. 
S.  Geological  Survey),  showed  that  the  relationship  is  also  in- 
dicated by  the  chemical  composition  of  the  various  rocks,  and 
is  fundamentally  dependent  on  this,  and  he  consequently  de- 
votes much  space  to  the  chemical  evidence  of  consanguinity. 

The  doctrine  of  consanguinity,  as  it  may  be  termed,  has  now 
received  general  acceptance,  and  it  is  commonly  recognized 
that  the  igneous  areas  of  the  earth's  surface  are  divisible  into  dis- 
tricts the  rocks  of  which  show  certain  features  in  common  which 
serve  to  distinguish  them  from  those  of  other  districts.  It  is 
also  assumed  that  the  possession  of  these  common  features, 
especially  those  dependent  on  the  chemical  composition,  indi- 
cates that  the  rocks  of  a  given  district  have  a  common  genetic 
origin,  that  is,  are  derived  from  a  common  parent  body  of 
magma.  The  processes  by  which  this  differentiation  and  de- 
rivation from  a  common  magma  are  brought  about  are  still  ob- 
scure, and  form  the  subject  of  much  modern  investigation  and 
discussion,  into  which  we  cannot  enter  here.  Such  areas  of  re- 
lated rocks  are  usually  called  petrographic  provinces, though  the 
term  comagmatic  region,  which  indicates  more  clearly  .their  deri- 
vation from  a  common  magma,  has  recently  been  introduced.7 

Though  petrographic  provinces  represent  one  of  the  promi- 
nent phases  of  the  distribution  of  the  elements  in  the  earth's 
crust,  and  though  their  existence  is,  in  general,  undeniable,  yet 
their  characters  are  so  complex  and  made  up  of  so  many  factors 
that  the  characterization  in  most  cases  cannot  be  made  very 

5  J.  W.  Judd,  Quarterly  Journal  of  the  Geological  Society,  vol.  xlii.,  pt.  ],  No.  165, 
p.  54  (Feb.  1,  1886). 

6  J.  P.  Iddings,  Bulletin  of  the  Philosophical  Society  of  Washington,  vol.  xii.,  pp. 
128-144  (1892). 

7  H.  S.  Washington,  Carnegie  Publication  No.  57,  p.  5  (1906). 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    BOCKS.  739 

precise  or  the  limits  be  very  sharply  drawn.  Their  study  is  still 
almost  in  its  infancy,  and  the  accumulation  of  many  more  data, 
especially  from  the  analytical  side,  is  needed  before  definitive 
studies  can  be  undertaken,  and  the  characters  of  any  petro- 
graphic  province  be  precisely  defined. 

The  geological  evidence  of  consanguinity  is  at  times  clear. 
Thus,  as  Iddings8  says: 

"  The  constant  recurrence  of  particular  series  of  rocks,  often  with  a  certain  order 
of  eruption  in  different  localities,  and  the  frequent  occurrence  of  such  series  at 
neighboring  centers  of  volcanic  activity,  would  be  enough  to  justify  the  belief  that 
there  was  a  definite  connection  between  the  members  of  a  group." 

On  the  other  hand,  cases  are  known  where  such  geological 
evidence  is  lacking  or  conflicting,  or  where  the  relations  are  so 
generally  observed  as  to  be  meaningless  in  this  connection. 

Geologically  speaking,  a  petrographic  province  may  belong 
to  any  period  of  geologic  time,  or  may  conceivably  extend  over 
more  than  one  period.  The  region  may  be  small  or  large, 
covering  hundreds  or  hundreds  of  thousands  of  square  miles. 
It  may  be  of  any  shape,  forming  an  elongated  band  or  zone,  a 
highly  irregular  area,  or  one  more  or  less  equidimensional.  It 
may  consist  of  a  single,  large  area  of  connected  intrusive  or 
effusive  rocks,  or  of  adjacent  but  isolated  areas. 

The  chemical  characters  which,  being  common  to  the  rocks 
of  a  province,  indicate  consanguinity  are  manifold.  The  rocks 
may  be  uniformly  high  in  soda  or  in  potash,  or  in  potash  and 
lime,  low  in  magnesia  and  high  in  iron,  generally  deficient  in 
silica,  and  so  on.  Throughout  one  province  the  soda  may  in- 
crease relatively  to  potash  as  silica  decreases,  while  in  another 
the  reverse  holds  good.  Or  again,  there  may  be  some  combi- 
nation of  such  two  kinds  of  characters,  called  respectively  abso- 
lute and  serial.  The  subject  is  complicated  by  the  possibility 
of  local  differentiation,  so  that  in  a  region  of  unquestionably 
related  rocks,  we  may  meet  with  some  the  character  of  which 
does  not  conform  to  the  general  law  of  the  region,  but  the 
presence  of  which  is  to  be  explained  by  the  extreme  differenti- 
ation of  some  portion  of  the  general  magma. 

Conforming  to  the  chemical  features,  and  in  general  largely 
dependent  on  them,  are  the  common  mineral ogical  characters. 

8  Loc.  cit.,  p.  43 


740  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

These  are  very  important,  not  so  much  in  themselves,  as  be- 
cause they  often  enable  one  practically  to  determine  the  general 
relationship  without  the  necessity  of  a  long  series  of  analyses. 
The  mineralogical  similarity  may  be  evident  in  two  ways:  either 
by  the  general  presence  of  certain  minerals  which  are  rare  or  are 
not  usually  found  in  certain  kinds  of  rock,  as  the  rare  zirconium 
minerals,  or  neph elite,  or  leucite,  the  occurrence  of  hypersthene 
in  the  basalts  and  andesites,  or  of  biotite  in  peridotites;  or  by 
certain  peculiarities  of  color,  form,  or  other  characters  shown 
among  the  more  usual  mineral  groups,  and  which  are  dependent 
on  the  introduction  of  certain  chemical  constituents  into  the 
molecule,  as  bright  green,  pleochroic  augites  or  blue  horn- 
blendes, due  to  their  containing  much  soda,  purple  augites  or 
red-brown  hornblendes,  due  to  titanium,  and  so  on.  Here 
again  the  possibilities  of  difference  are  numerous,  but  the 
mineralogical  evidence  of  relationship  is  often  so  marked  as  to 
be  unmistakable  to  the  petrographer. 

A  good  illustration  of  such  petrographic  provinces  and  of 
their  distribution  is  furnished  by  the  United  States,  which  may 
be  briefly  described,  though  our  knowledge  is  still  incomplete. 
Stretching  along  and  rather  close  to  the  Atlantic  coast  is  a  zone 
of  small,  isolated  areas  of  igneous  rocks  which  are  chiefly  charac- 
terized by  a  high  content  in  soda,  resulting  in  the  common 
presence  of  nephelite-syenites  and  other  rocks  containing  nephe- 
lite,  peculiar  hornblendes,  and  other  minerals  characteristic  of 
such  magmas.  This  zone  includes  areas  in  Quebec,  New 
England,  New  Jersey,  Arkansas,  Texas,,  extends  into  eastern 
Mexico  and  the  West  Indies,  and  probably  as  far  south  as 
Brazil  and  Paraguay.  Parallel  with  this,  but  usually  farther 
inland,  is  a  second  zone  of  areas  of  rocks  which  are  low  in 
silica  and  the  alkalies,  but  high  in  lime  and  iron.  This  starts 
in  the  great  anorthosite  area  of  eastern  Canada  and  Labrador, 
appears  in  New  England,  the  Adirondacks,  Delaware,  Mary- 
land, and  extends  to  Georgia  and  possibly  farther  south. 
The  rocks  of  this  region  are  typically  gabbros,  diabases,  and 
pyroxenites,  dunite  and  other  peridotites,  with  some  granites 
high  in  lime,  and  are  often  accompanied  by  very  basic  ores  and 
other  products  of  differentiation  which  are  very  rich  in  iron 
and  titanium.  Farther  inland  and  west  of  the  Appalachian 
range  is  another  belt,  less  well  defined  but  apparently  in 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  741 

general  parallel  to  the  others,  of  widely  isolated  small  occur- 
rences of  peculiar  peridotites  and  other  rocks,  low  in  silica  and 
very  high  in  magnesia  and  iron,  with  little  lime  or  soda  but 
much  potash.  This  last  feature  gives  rise  to  the  common  pres- 
ence of  peculiar  micas,  which  distinguish  these  peridotites 
mineralogically  from  those  of  the  preceding  region.  These 
areas  occur  in  Quebec,  New  York,  Pennsylvania,  Kentucky, 
Arkansas,  and  probably  still  farther  south. 

Passing  over  the  broad  central  part  of  the  continent,  where 
igneous  rocks  are  very  sparingly  present,  we  find  a  province 
east  of  the  Rocky  mountains  which  is  characterized  by  high 
alkalies,  especially  potash,  so  that  the  usually  rare  mineral 
leucite  is  here  quite  common.  This  region  is  best  known  in 
Montana,  Wyoming,  and  Colorado,  and  may  possibly  extend 
into  western  Texas.  In  the  region  of  the  Rocky  mountains, 
and  the  cordilleras  generally  the  occurrences  of  igneous  rocks 
are  so  numerous  and  the  relations  so  complex  that  it  is  some- 
what difficult  to  unravel  the  various  petrographic  provinces. 
As  a  whole,  however,  the  igneous  rocks  of  this  part  of  the  con- 
tinent seem  to  belong  to  one  very  extensive  province,  which  is 
continued  into  Alaska  on  the  north  and  along  the  Andes  to  the 
south.  In  general  chemical  character  the  rocks  show  rather 
low  alkalies,  with  more  soda  than  potash,  rather  high  lime,  and 
but  moderate  amounts  of  iron  and  magnesia,  leading  to  the 
abundance  of  such  ordinary  rocks  as  feldspar-basalts,  andesites, 
dacites,  and  some  rhyolites.  There  is  some  evidence  that  the 
province  as  a  whole  may  be  divisible  into  several  subordinate 
districts,  but  it  is  noteworthy  that  rocks  so  high  in  soda  or 
potash  as  to  contain  nephelite  or  leucite  are  practically  unknown 
west  of  the  Rocky  mountains.  There  are  also  indications'  ol 
what  may  be  a  distinct  region  along  the  coast  ranges  which  is 
characterized  by  high  soda  and  generally  high  silica,  but  this 
demands  further  investigation. 

A  number  of  petrographio  provinces  outside  of  the  United 
States  may  also  be  briefly  indicated.  One  of  the  best  known  is 
that  of  southern  Norway,  which  is  prominent  through  the 
classic  researches  of  Brogger,  the  rocks  of  which  are  charac- 
terized by  high  alkalies,  especially  soda,  and  the  presence  of 
many  minerals  elsewhere  rare.  This  is  possibly  connected  with 
the  region  of  the  Kola  peninsula  in  northern  Finland.  The 


742  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

British  Islands,  with,  the  Faeroes,  Iceland,  and  probably  Spitz- 
bergen,  form  another  well-defined  province,  the  rocks  of  which 
resemble  on  the  whole  those  of  our  Rocky  Mountain  region, 
though  they  differ  in  some  respects.  Leaving  aside  Germany, 
Austria,  and  France,  each  of  which  contains  several  petro- 
graphic  provinces,  the  relations  of  which  appear  to  be  some- 
what complex,  in  the  basin  of  the  Mediterranean  we  find  at 
least  three  well-defined  and  quite  distinct  provinces.  In  the 
eastern  part,  including  the  Grecian  archipelago  and  parts  of 
Asia  Minor,  the  rocks  are  rather  siliceous,  with  fairly  high  lime 
and  rather  low  alkalies,  soda  dominating  potash,  so  that  dacites, 
andesites,  and  feldspar  basalts  are  prominent.  Hypersthene  is 
here  rather  common.  The  Italian  peninsula  shows  a  second, 
very  well-defined  province,  which  embraces  seven  distinct 
.volcanic  centers  along  the  west  coast.  The  rocks  of  this  are 
remarkable  for  their  high  content  in  potash,  which  at  times 
reaches  extraordinary  figures,  and  leads  to  the  abundant  pres- 
ence here  of  the  mineral  leucite,  which  is  elsewhere  decidedly 
rare.  Lime  is  also  rather  high,  while  soda,  iron,  and  magnesia 
are  low.  The  other  provinces  of  continental  Italy  have  not  been 
thoroughly  studied  and  are  less  well  known.  In  the  western 
basin  of  the  Mediterranean,  including  localities  in  Spain,  Sar- 
dinia, some  islands  south  of  Sicily,  and  probably  southern 
France,  there  appears  to  be  a  third  province,  which  differs 
from  the  others  in  that  soda  is  much  higher  and  the  more 
basic  rocks  (basalts)  contain  very  large  amounts  of  titanium, 
and  in  other  ways.  This  last  may  be  connected  with  a  province 
in  eastern  Africa,  running  down  the  Great  Rift  valley  and  in- 
cluding parts  of  Madagascar,  in  which  rocks  rich  in  soda  are 
very  common.  A  somewhat  similar  province  appears  to  exist 
in  New  South  Wales  and  Queensland  in  Australia. 

The  descriptions  just  given,  which  are  but  the  barest  sketches 
of  only  some  of  those  which  are  known,  and  with  no  references 
to  authorities,  will  serve  to  give  an  idea  of  some  of  the  leading 
distinguishing  features  of  petrographic  provinces,  and  how 
multifariously  they  are  scattered  over  the  earth's  surface. 
Their  existence  and  distribution  indicate  clearly  that  the  un- 
derlying magma  basins,  or  the  sources  from  which  the  igneous 
rocks  are  immediately  derived,  are  not  everywhere  uniform 
and  alike,  but  that  there  exists  a  certain  heterogeneity  in  the 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  743 

non-sedimentary  parts  of  the  earth's  crust.  It  should,  how- 
ever, be  noted  that  two  provinces,  though  widely  separated, 
may  be  essentially  alike  in  all  their  features,  as  is  the  case 
with  that  of  the  eastern  Mediterranean  and  that  which  extends 
from  the  Andes  to  Alaska. 

IY.  THE  CORRELATION  OF  THE  ELEMENTS. 

The  existence  of  petrographic  provinces  is  a  broad  phase  of 
the  distribution  of  the  elements  among  igneous  rocks,  the  dis- 
tribution being  essentially  a  spacial  one  and  the  evidence  rest- 
ing almost  entirely  on  the  relative  proportions  of  the  most 
abundant  elements.  But  apart  from  this  spacial  distribution 
there  is  evident,  also,  a  correlated  variation  among  the  ele- 
ments ;  that  is,  a  tendency  for  certain  ones  to  increase  or  de- 
crease, to  be  relatively  abundant  or  not,  according  to  the  pres- 
ence or  absence  of  others.  The  causes  of  this  behavior  are 
obscure  and  apparently  complex.  In  part  they  may  be  prob- 
ably referred  to  certain  fundamental  relations  among  the  ele- 
ments, as  shown  by  the  periodic  classification  and  chemical 
affinity ;  in  part  to  the  effect  of  certain  physico-chemical  laws 
leading  to  the  mutual  segregation  of  elements  affected  simi- 
larly; and  possibly  in  part  to  the  degradation  of  some  of  the 
elements,  as  indicated  by  recent  experiments  of  Ramsay.  But 
any  discussion  of  the  causes  is  outside  the  province  of  this 
paper,  in  which  we  can  only  deal  briefly  with  some  of  the  facts 
of  distribution. 

The  study  of  these  mutual  relations  among  the  elements  in 
igneous  rocks  is  of  recent  date,  and  "has  been  made  possible, 
especially  so  far  as  the  rarer  elements  go,  only  by  the  complete- 
ness and  accuracy  of  modern  chemical  analyses  of  rocks.  Such 
analyses  supplement  the  evidence  afforded  by  study  of  min- 
erals, mineralogical  associations,  and  ore-deposits,  and,  dealing 
as  they  do  with  what  must  be  regarded  as*the  ultimate  source 
of  the  ores,  are  of  the  highest  significance  and  importance.  'In 
the  following  brief  discussion,  therefore,  stress  will  be  laid  on 
the  evidence  afforded  by  rock-analyses,  with  some  reference  to 
chemical  mineralogy,  while  ore-deposits,  as  being  more  techni- 
cal and  better  known  to  the  mining  engineer,  will  be  alluded 
to  only  occasionally. 

Considering  first  only  the  most  abundant  elements,  a  study 


744  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

of  the  igneous  rocks  in  general  shows  that  silica,  alumina,  soda, 
and  potash  tend  to  increase  or  decrease  together,  though  not 
always  at  the  same  rate ;  while,  on  the  other  hand,  the  iron 
oxides,  magnesia,  and  lime  tend  to  vary  together  and  in  general 
inversely  as  the  preceding  constituents.  The  more  siliceous 
rocks  almost  invariably  show  relatively  high  alumina  and  alka- 
lies and  low  iron  oxides,  magnesia,  and  lime,  leading  to  the 
common  presence  in  abundance  of  the  alkali  feldspars  and  the 
comparative  paucity  in  calcic  feldspars  and  the  ferromagnesian 
minerals,  which  tend  to  increase  rapidly  with  diminution  in  the 
silica-content.  Highly  siliceous  rocks  which  contain  more  iron, 
magnesia,  and  lime  than  alumina,  soda,  and  potash  are  of  very 
exceptional  occurrence.  The  rule  mentioned  above  is  so 
generally  true  that  it  may  be  regarded  as  the  normal  one 
for  igneous  rocks  in  general,  and  is  commonly  accepted  as 
such  in  petrology. 

At  the  same  time,  there  is  considerable  evidence  that  certain 
subsidiary  relations  obtain  among  the  constituents  other  than 
silica,  which,  while  by  no  means  universal,  are  at  times  very 
pronounced,  and  occasionally  seem  to  supersede  the  more  gen- 
eral law.  Thus,  soda  not  uncommonly  tends  to  vary  with  the 
iron  oxides,  while  potash  shows  similar  relations  to  magnesia, 
resulting  in  the  presence  of  potassium  minerals  in  highly  mag- 
nesian  rocks  and  the  abundance  of  sodium  minerals  in  those 
high  in  iron.  Again,  while  neither  iron  nor  magnesia  shows 
any  marked  affinity  towards  or  tendency  to  vary  with  alumina, 
this  constituent  and  lime  are  occasionally  found  to  occur 
together  in  great  abundance  and  to  the  general  exclusion  of 
the  others.  These  relations  are  also  evident  in  certain  facts  of 
chemical  mineralogy,  as  the  usual  predominance  of  magnesium 
over  iron  in  the  potassic  biotites  and  phlogopites,  the  abundance 
of  soda  and  absence  of  potash  among  the  highly  ferriferous 
augites  and  hornbtendes,  and  the  numerous  silico-aluminates 
containing  much  calcium,  while  those  with  iron  or  magnesium 
are  comparatively  very  rare. 

But  this  tendency  to  selective  and  correlated  variation  among 
the  chemical  constituents  of  igneous  rocks  is  not  confined  to 
those  which  are  present  in  greatest  amount.  It  is  equally  well, 
and  indeed  in  some  respects  more  strikingly,  shown  among  the 
rarer  elements,  both  as  compared  with  those  which  are  most 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  745 

abundant  and  with  each  other.  Furthermore,  the  distribution 
of  some  of  these  rare  elements  would  seem  to  have  important 
bearings  on  some  of  the  problems  of  economic  geology  and  the 
distribution  of  ore-deposits. 

The  general  facts  of  this  distribution  and  variation  of  the 
rare  elements  have  been  summarized  in  several  recent  publi- 
cations,9 but  many  of  the  details  are  still  un-coordinated  and 
widely  scattered  through  the  vast  mass  of  petrographic  litera- 
ture, and  there  are  certain  aspects  and  recent  developments 
which  are  either  neglected,  or  only  briefly  alluded  to,  in  the 
publications  cited. 

It  is  now  commonly  understood  that  certain  elements  are 
prone  to  occur  most  often  and  in  largest  amounts  in  rocks 
which  are  high  in  silica,  the  so-called  "acid"  rocks;  while 
others  are  met  with  similarly  in  those  low  in  silica — the 
"basic"  rocks.  This  is  essentially  the  only  set  of  relations 
recognized  by  Vogt,  while  De  Launay  in  addition  to  these  two 
groups  proposes  two  others,  the  ll  mineralizing  agents "  and 
the  vein-metals. 

Evidence,  however,  is  accumulating  that  the  relations  of  the 
rare  elements  to  the  igneous  rocks  cannot  be  expressed  so 
simply  as  is  done  by  Yogt  and  De  Launay.  Their  relative 
abundance  is  not  dependent  on  the  silica  alone,  and  hence  ref- 
erable only  to  the  "  acidity  "  or  "  basicity  "  of  the  rock.  The 
relations  are  more  complex,  and  dependent,  not  so  much  on  the 
amount  of  silica,  as  on  the  relative  amounts  of  other  constit- 
uents, notably  soda,  potash,  iron,  magnesia,  or  lime.  They 
conform,  on  the  whole,  to  the  general  relations  of  the  most 
abundant  constituents,  some  of  the  rarer  elements  being  char- 
acteristically at  home  in  the  rock  groups  which  show  high 
alumina  and  alkalies,  and  which  include  those  high  in  silica; 
while  others  again  are  most  abundant  in  the  rocks  high  in  iron, 
magnesia,  or  lime,  and  which  consequently  most  often  show 
low  silica  percentages.  Further  than  this,  on  the  one  hand, 
certain  rare  elements  are  not  equally  at  home  in  the  alkalic 

9  J.  H.  L.  Vogt,  Zeitschrift  fur  praktische  Geologic,  p.  326  (September,  1898)  ; 
J.  F.  Kemp,  Ore  Deposits,  3d  edition,  pp.  34-37  (1900)  ;  H.  S.  Washington, 
Manual  of  the  Chemical  Analysis  of  Rocks,  p.  14  (1904)  ;  L.  De  Launay,  La  Science 
Geologigue,  p.  637  (1905)  ;  W.  F.  Hillebrand,  Bulletin  No.  305,  U.  S.  Geological 
Survey,  p.  21  (1907). 

47 


'  746  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

rocks  in  general,  but  are  most  abundant  either  in  those  high 
in  soda  or  in  those  high  in  potash.  On  the  other  hand,  some 
of  the  elements  segregated  in  the  basic  rocks  seem  to  be 
most  at  home  in  those  which  are  highly  calcic,  others  in  those 
which  are  high  in  iron  or  in  magnesia,  though  here  the  evi- 
dence is  not  so  clear  and  the  distinctions  apparently  not  so 
well  marked  as  in  the  preceding  case. 

We  may  consider  first  those  minor  constituents  of  rocks 
which  are  determined  in  the  most  modern  and  complete 
analyses,  and  next  those  which  exist  in  rocks  in  such  small 
amount  as  almost  to  defy  determination  by  the  usual  analytical 
methods,  but  whose  presence  is  made  known  either  miner- 
alogically  or  by  their  segregation  in  ore-deposits.  The  second 
group  includes  almost  all  of  the  commercially  important 
metals  (except  iron  and  manganese),  while  the  former  includes 
many  elements  wThich  are  assuming  an  increased  practical  im- 
portance as  their  economic  possibilities  and  uses  become  better 
known.  In  a  general  way  the  elements  will  be  taken  up  in  the 
order  of  their  positions  in  the  periodic  classification.  No  ref- 
erences will  be  given,  as  an  attempt  to  render  them  complete 
would  unduly  lengthen  the  paper.  This  course  seems  the  more 
advisable,  in  spite  of  the  apparent  injustice  to  those  whose  in- 
valuable work  and  contributions  must  thus  be  ignored,  since 
the  present  paper  may  be  considered  as  merely  a  preliminary 
one  to  a  more  exhaustive  and  monographic  treatment  which  it 
is  hoped  to  publish  later. 

Lithium  is  very  widely  distributed  among  igneous  rocks,  but 
always  in  very  small  amounts.  While  it  frequently  is  to  be 
detected  by  the  spectroscope,  it  seldom  occurs  in  weigh  able 
quantities,  and  the  difficulty  of  its  exact  separation  from  the 
other  alkali  metals  and  its  comparative  unimportance  cause  it 
to  be  but  seldom  estimated  quantitatively.  Although  such 
minute  traces  are  present  in  both  acid  and  basic  rocks,  yet 
it  is  undoubtedly  more  closely  connected  with  those  which 
are  highly  siliceous  and  alkalic.  The  minerals  in  which  it 
forms  an  essential  component,  as  spodumene,  lepidolite,  am- 
blygonite,  and  some  tourmalines,  are  most  often  met  with  in 
granites  and  pegmatites  derived  from  granitic  magmas.  Un- 
fortunately, the  granites  and  pegmatites  which  carry  lithium 
minerals  most  prominently  do  not  appear  to  have  been  analyzed, 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  747 

but  there  is  reason  for  the  belief  that  they  are  sodic  rather  than 
potassic  in  general  character.  The  very  common  association 
of  lithium  with  soda  rather  than  with  potash  in  many  minerals 
also  points  to  the  same  conclusion. 

Beryllium  is  much  like  lithium  in  its  associations,  beryl  and 
other  rarer  minerals  which  contain  it  occurring  for  the  most 
part  in  granites  or  pegmatites.  Few  analyses  exist  of  such 
beryl-bearing  rocks,  and  beryllia  has  seldom  been  estimated 
separately  from  alumina  in  rock-analysis,  but  such  data  as  are 
available  and  the  common  mineralogical  association  of  beryl- 
lium and  sodium  point  to  the  conclusion  that  the  element  is 
most  at  home  in  sodic  magmas. 

Attention  may  be  called  to  the  fact  that  beryl,  in  spite  of 
its  common  occurrence,  is  not  given  in  the  list  of  descrip- 
tions of  the  rock-forming  minerals,  such  as  those  in  the 
standard  works  of  Zirkel,  Rosenbusch,  and  Iddings,  though 
Levy  and  Lacroix  briefly  described  it  in  their  work10  and  it  is 
placed  on  their  large  colored  table  of  bi-refringences.  In  its 
optical  properties  it  closely  resembles  nephelite  and  apatite,  and 
being  hexagonal  in  crystallization  as  well,  might  readily  be 
mistaken  for  one  of  these  minerals.  I  have  noted  the  fact  that 
analyses  of  nephelite-syenites  and  other  highly  sodic  rocks  fre- 
quently show  a  decided  excess  of  alumina  which  cannot  be 
explained  by  the  apparent  mineralogical  composition  of  the 
rock,  and  the  suggestion  is  made  that  this  is  possibly  due  to 
the  presence  of  beryl,  the  beryllia  of  which  would  appear  as 
alumina  in  the  course  of  analysis,  unless  special  means  were 
taken  to  separate  the  two.  On  the  other  hand,  the  excess  of 
alumina  may  be  real  and  due  to  the  composition  of  the  magma. 

Strontium  has  been  shown  by  the  analyses  of  the  U.  S.  Geo- 
logical Survey  to  be  widely  distributed  in  the  rocks  of  this 
country.  I  have  found  it  almost  invariably  when  looked  for  in 
many  European  rocks,  and  it  is  almost  constantly  present  in 
those  of  Australia.  But  it  seldom  occurs  in  more  than  traces, 
and  the  evidence  in  regard  to  its  distribution  is  as  yet  incon- 
clusive, in  spite  of  the  many  modern  analyses  in  which  it  is 
now  determined,  chiefly  because  of  the  small  amounts  usually 
met  with.  It  would  appear  to  be  most  abundant  in  rocks  some- 
what high  in  lime  and  with  moderate  to  rather  low  silica, 

10  Les  Mineraux  des  Roches  (Paris,  1888). 


748  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

though  it  is  worthy  of  note  that  the  highest  figures  recorded  for 
it  are  in  some  rocks  of  Wyoming  which  are  low  in  lime  and 
extraordinarily  high  in  potassium  and  barium.  Being  but  rarely 
a  constituent  of  silicate  minerals,  decisive  evidence  from  this 
side  is  wanting,  though  it  occurs  with  lime  in  some  heulandite 
and  brewsterite. 

Barium  is  another  element  which  the  analyses  of  the  Wash- 
ington chemists  showed  to  be  widely  distributed,  and  almost 
invariably  in  decidedly  greater  amounts  than  strontium.  It  is 
now  often  determined  by  analyses  of  superior  quality,  and  in  a 
recent  study,  embracing  the  rocks  of  Italy,  the  United  States, 
and  New  South  Wales,  I  have  shown  that  it  is  specially  prone 
to  occur  in  potassic  rocks,  sometimes  when  the  potash  is  accom- 
panied by  considerable  lime,  but  that  it  is  rarely  met  with  in 
notable  amount  in  decidedly  sodic  or  calcic  rocks.  Neither  the 
amount  of  silica  nor  the  relative  proportions  of  iron  and  mag- 
nesia, appears  to  be  a  determining  factor  of  much  importance. 
This  association  of  barium  and  potassium  in  igneous  rocks  is 
in  harmony  with  the  mineralogical  evidence.  Barium  is  a  fre- 
quent minor  constituent  in  potassium  minerals,  as  orthoclase, 
muscovite,  and  biotite,  while  potassium  accompanies  barium  in 
hyalophane  and  harmotome.  On  the  other  hand,  barium  is  not 
reported  in  analyses  of  sodium  minerals,  but  occurs  in  small 
amounts  in  the  calcium  zeolites,  brewsterite  and  phillipsite. 
Barium  also  seems  to  tend  to  associate  with  manganese,  as 
shown  by  its  common  occurrence  in  psilomelane,  and  the  occur- 
rence of  minerals  of  the  two  metals  in  certain  mines. 

Boron  is  seldom  or  never  mentioned  in  rock-analyses,  chiefly 
because  of  the  complexity  and  difficulty  of  its  exact  determina- 
tion, especially  in  very  small  amounts.  But  it  is  not  infre- 
quently present  in  weighable  amounts  in  granites  and  peg- 
matites, chiefly  as  a  constituent  of  tourmaline.  The  few 
analytical  data  that  we  have  of  such  tourmaline-bearing  rocks 
are  not  decisive,  but  boron  does  not  appear  to  have  very  decided 
preferences  for  either  soda  or  potash.  Its  associations  in  min- 
erals are  likewise  not  strongly  marked,  but  among  the  silicates 
calcium  is  the  basic  element  which  most  frequently  accompanies 
it,  and  soda  is  more  commonly  met  with  in  boron-bearing  min- 
erals than  is  potash.  Boron  is  commonly  regarded  as  one  of 
the  pneumatolytic  elements. 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  749 

Cerium,  yttrium,  and  the  other  metals  of  the  so-called  "  rare 
earths,"  as  well  as  thorium  and  uranium,  are  only  rarely  deter- 
mined in  rock-analysis.  Minerals  containing  them  are  com- 
monly associated  with  acid  pegmatites,  which,  judging  from 
occurrences  in  Norway,  Greenland,  and  elsewhere,  are  most 
apt  to  be  sodic,  though  the  few  determinations  available  of  the 
rare  earths  are  in  highly  potassic  igneous  rocks. 

Titanium  is,  as  we  have  seen,  far  from  being  the  rare  element 
which  it  was  formerly  considered,  and  it  is  probably  never 
wholly  absent  from  any  rock.  It  is  distinctly  much  more 
abundant  in  basic  than  in  acid  rocks,  and  its  affinities  in  the 
magma  seem  to  be  decidedly  rather  with  iron  than  with  mag- 
nesium, and  still  less  with  lime.  While  it  is  not  commonly 
associated  with  alkalic  rocks,  yet  when  these  are  low  in  silica 
it  shows  a  tendency  to  be  present  in  considerable  amount 
when  the  rock  is  sodic,  as  indicated  by  recent  rock-analyses; 
and  this  tendency  to  association  of  titanium  with  sodium  appears 
mineralogically,  as  in  the  soda-amphiboles,  some  of  which  are 
highly  titaniferous,  and  in  certain  rare  minerals,  as  astrophyl- 
lite  and  rosenbuschite.  Highly  potassic  and  highly  calcic 
rocks  seldom  show  large  amounts  of  titanium,  though  most  of 
the  mineral  titanates  contain  calcium  as  the  base. 

Zirconium.,  so  closely  allied  to  titanium  chemically,  also  shows 
certain  analogies  in  its  magmatic  relations.  While  unlike  tita- 
nium in  being  rare  in  the  basic  rocks,  those  high  in  iron, 
magnesia,  and  lime,  and  referred  by  Vogt  to  the  acid  rocks, 
presumably  because  of  the  common  occurrence  of  zircons  in 
granites,  it  is  now  commonly  recognized  by  petrographers  that 
zirconium  is  by  far  most  abundant  in  the  rocks  which  are  high 
in  soda.  Indeed,  zirconium  maybe  considered  to  be  a  charac- 
teristic minor  chemical  constituent  of  the  sodic  rocks,  whether 
the  silica  be  so  high  that  quartz  is  present,  or  whether  it  be  so 
low  that  nephelite  is  abundant,  as  in  the  nephelite-syenites  and 
phonolites.  Practically  all  modern,  complete  analyses  bear  out 
this  view,  which  is  confirmed  by  the  common  association  of 
sodium  and  zirconium  mineralogically,  as  in  eudialyte,  cata- 
pleiite,  w^dhlerite,  and  the  zirconium  pyroxenes. 

Phosphorus,  as  a  constituent  of  apatite,  is  universally  diffused 
in  small  amounts  through  igneous  rocks,  and  is  most  abundant 
in  the  basic  ones,  though  its  relations  to  the  constituents 


750  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

other  than  silica  are  not  clear.  Study  of  large  collections  of 
analyses  indicates  that  it  is  usually,  but  not  always,  associated 
with  high  lime,  rather  than  with  high  iron  or  magnesia,  and 
in  some  distinctly  sodic  provinces  the  more  basic  rocks  with 
high  soda  and  abundant  nephelite  show  high  figures  for  phos- 
phorus pentoxide.  Some  of  the  phosphates  are  met  with  in 
granitic  and  syenitic  pegmatites. 

Vanadium  has  been  shown  by  the  researches  of  Hillebrand 
to  be  quite  widely  distributed,  but  always  in  very  small  amount 
and  almost  wnolly  confined  to  the  basic  rocks.  As  it  exists  as 
the  sesquioxide,  V20s>  replacing  alumina  and  ferric  oxide  in 
ferro-magnesian  minerals,  it  is  especially  abundant  in  rocks 
composed  largely  of  pyroxene,  hornblende,  or  biotite,  while  it  is 
present  only  in  traces  or  not  at  all  in  rocks  very  rich  in  olivine, 
where  the  iron  is  present  mostly  as  ferrous  oxide,  as  in  the 
peridotites.  It  is  associated  with  iron  rather  than  with  mag- 
nesium, and  occurs  in  most  abundance  in  some  iron-ores  of 
magmatic  origin,  but  no  definite  relations  to  the  alkalies  can  be 
made  out.  Its  common  occurrence  in  ashes  of  coals  and  its 
abundance  in  certain  carbonaceous  deposits  recently  described 
are  noteworthy,  though  outside  the  present  discussion. 

Sulphur  is,  by  far,  more  abundant  in  the  basic  than  in  the 
siliceous  rocks.  It  may  exist,  in  the  oxidized  condition,  in  the 
minerals  hauynite  and  noseliie,  in  which  case  the  rocks  con- 
taining these  minerals  are  almost  invariably  distinctly  sodic; 
or  it  may  form  sulphides,  as  pyrite,  pyrrhotite,  and  chalcopyrite, 
these  being  most  common  in  rocks  rather  high  in  iron,  magne- 
sia, and  lime. 

Chromium,  like  vanadium,  is  a  constituent  of  the  basic 
rocks,  but,  unlike  this,  is  most  abundant  when  magnesia  and 
not  iron  is  high,  and  when  olivine,  rather  than  pyroxene  or 
hornblende,  is  abundant,  in  spite  of  the  fact  that  it  occurs  as 
the  sesquioxide,  Cr203.  Presumably  this  is  because,  instead  of 
replacing  alumina  and  ferric  oxide  in  the  ferromagnesian  min- 
erals, it  is  most  commonly  met  with  in  the  minerals  chromite 
and  picotite.  It  is  reported  to  reach  very  high  figures  again 
in  certain  effusive  rocks  which  are  so  high  in  lime  and  low  in 
silica  that  the  rare  mineral  melilite  is  present. 

Molybdenum  is  seldom  looked  for  in  rock-analysis,  and  our 
knowledge  of  its  magmatic  relations  is  based  almost  wholly  on 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  751 

an  investigation  by  Hillebrand.  He  found  that  it  is  much  less 
•common  and  is  present  in  smaller  quantity  than  vanadium,  and 
that,  unlike  the  latter,  it  is  present  only  in  the  more  siliceous 
rocks,  though  in  quantities  too  small  to  permit  of  further  dis- 
crimination. As  molybdenite  it  occurs  most  often  in  quartzose 
rocks. 

Fluorine  is  almost  universally  present  in  very  small  amount 
as  a  constituent  of  most  apatites,  and  is  usually  regarded  as  a 
"  mineralizing  agent,"  and,  as  such,  is  frequently  present  in 
pneumatolytic  minerals.  As  stated  by  Vogt,  it  seems  to  be 
more  common  in  the  acid  rocks,  but  there  seems  to  be  a 
marked  tendency  on  its  part  to  favor  especially  rocks  which 
are  high  in  soda.  This  is  seen  in  the  fact  that  fluorite  is  fre- 
quently present  as  an  original  constituent  of  such  highly  sodic 
rocks  as  nephelite-syenite,  phonolite,  and  tinguaite;  the  asso- 
ciation of  fluorine  and  sodium  in  certain  rare  minerals,  as  leu- 
cophanite,  meliphanite,  johnstrupite,  rinkite,  .etc.,  which  are 
almost  always  found  in  sodic  rocks ;  and  by  the  recent  dis- 
covery by  Lacroix  of  sodium  fluoride  in  nephelite-syenites  of 
West  Africa. 

Chlorine  resembles  fluorine  in  being  a  pneumatolytic  con- 
stituent, and  is  present  in  igneous  rocks  chiefly  in  the  minerals 
sodalite  and  noselite,  which  are  almost  wholly  confined  to  sodic 
rocks  and  especially  those  which  are  low  in  silica,  in  this  re- 
sembling the  occurrence  of  S03. 

Manganese,  though  as  widely  distributed  as  titanium  and 
phosphorus,  is  usually  present  in  such  small  amounts  as  not  to 
allow  a  clear  judgment  of  its  magmatic  relations,  especially  as 
the  high  figures  often  reported  for  it  are  apt  to  be  due  to  ana- 
lytical error.  As  a  general  rule,  its  amount  is  greater  in  the 
basic  rocks,  and  certain  considerations  indicate  a  preference 
for  rocks  high  in  iron  rather  than  in  magnesia  or  lime,  but  the 
variations  are  not  very  significant.  We  have  already  noted 
above  the  tendency  to  association  of  barium  and  manganese. 

Nickel  is  pre-eminently  at  home  in  the  basic  rocks,  especi- 
ally in  the  peridotites  and  serpentines,  where  it  replaces  iron  in 
the  olivine,  while  it  likewise  occurs  in  small  amounts  in  horn- 
blende, biotite,  and  in  pyrite  and  pyrrhotite.  Certain  rather 
high  figures  reported  for  it  may  be  ascribed  to  analytical  con- 
fusion with  platinum  derived  from  the  utensils  employed;  but 


752  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

researches  now  in  progress  indicate  that  it  may  be  present  in 
considerable  amount  (up  to  about  0.20  per  cent),  not  only  in 
the  "basic"  but  in  the  more  siliceous  rocks  of  certain  localities 
where  its  presence  has  not  hitherto  been  suspected.  It  is 
reasonable  to  suppose  that  it  is  most  apt  to  be  present  in  rocks 
which  are  relatively  high  in  iron  rather  than  in  magnesia  and 
lime,  and  the  results  of  the  investigation  just  mentioned  are  in 
harmony  with  this  supposition. 

Cobalt  almost  always  accompanies  nickel  in  igneous  rocks, 
but  always  in  extremely  small  and  scarcely  weighable  amounts. 

The  elements  belonging  to  the  next  group  to  be  discussed, 
those  which  are  scarcely  detectable  in  igneous  rocks  by  the 
usual  analytical  methods  on  account  of  the  excessively  minute 
amounts  usually  present,  need  not  detain  us  long,  even  though 
they  are  commercially  among  the  most  important.  Since  the 
analytical  data  are  either  very  scanty,  untrustworthy,  or  want- 
ing altogether,  and  their  presence  is  revealed  to  us  mostly 
through  secondary  processes  of  concentration  in  veins,  placers, 
and  other  ore-deposits,  we  are  not  yet  in  a  position  to  generalize 
with  confidence  as  to  the  magmatic  relations  of  most  of  them. 

Furthermore,  having  but  slight  affinity  for  silica,  and  thus 
(with  few  exceptions)  seldom  forming  silicates  or  entering  as 
minor  constituents  into  the  silicate  minerals  of  other  elements, 
we  are  deprived  to  a  very  great  extent  of  this  kind  of  evidence. 

Copper  is  not  infrequently  reported  in  analyses  of  igneous 
rocks,  but,  as  pointed  out  by  Hillebrand,  its  apparent  presence 
may  often  be  attributed  to  contamination  during  the  course  of 
analysis,  or,  as  may  be  suggested  here,  to  confusion  with 
platinum  likewise  due  to  contamination,  as  was  suggested  in 
the  case  of  nickel.  But  notwithstanding  these  sources  of  error 
copper  seems  to  be  widely  distributed  among  igneous  rocksr 
though  in  very  small  amounts.  There  seems  to  be  little  doubt 
that  it  is  most  abundant  in  the  more  basic  rocks,  especially 
those  which  carry  pyroxene  and  hornblende  rather  than  olivine, 
but  no  evidence  seems  to  exist  as  to  its  relations  to  the  chemical 
constituents  other  than  silica. 

Silver  and  gold  have  both  been  detected  analytically  in 
igneous  rocks,  while  metallic  gold  has  also  been  observed  as  an 
apparently  primary  ingredient  of  some  rhyolites  and  granites. 
Both  of  these  metals  are  "  cosmopolitan  in  their  relations,"  as 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  753 

Kemp  puts  it,  and  they  are  known  to  occur  in  such  highly 
siliceous  rocks  as  granite,  rhyolite,  and  quartz-porphyry,  and, 
on  the  other  hand,  in  diabase  and  gabbro.  There  is,  however, 
good  reason  for  the  belief  that  gold,  and  probably  silver  as 
well,  are  most  apt  to  occur  in  rocks  high  in  silica,  but  their 
relations  to  the  other  elements  are  still  quite  unknown. 

Zinc  and  cadmium  (which  latter  is  found  only  in  connection 
with  the  former)  are  also  very  uncertain.  There  is,  however, 
some  reason  for  thinking  that,  zinc  is  more  apt  to  be  present 
in  acid  rocks,  as  granites,  this  opinion  being  based  on  a  few 
analytical  data  and  the  facts  of  some  of  its  occurrences.  The 
common  occurrence  of  zinc  in  limestones,  due  presumably,  at 
least  in  part,  to  the  precipitating  effect  of  the  sedimentary  rock, 
has  no  apparent  bearing  on  its  relations  to  igneous  magmas. 

Mercury  is  considered  by  G.  F.  Becker  to  be  associated  with 
granites,  but  his  evidence  is  not  very  convincing.  Its  usual 
occurrence  in  sedimentary  rocks  tends  to  obscure  its  true  re- 
lations, and,  to  the  best  of  my  knowledge,  it  has  never  been 
looked  for  or  reported  in  an  analysis  of  an  igneous  rock. 

Tin,  as  the  oxide,  cassiterite,  almost  invariably  occurs  as  the 
result  of  pneumatolytic  processes  in  pegmatites,  granites,  and 
other  rocks  high  in  silica,  and  the  mineral  has  been  found  in 
some  rhyolites.  Judging  from  the  common  association  of 
cassiterite  with  lithium  and  beryllium  minerals,  and  the  pres- 
ence of  small  amounts  of  tin  in  certain  feldspars,  micas,  zircons, 
and  in  the  rare  mineral  stokesite,  it  is  probable  that  tin  is  asso- 
ciated rather  with  distinctly  sodic  than  with  potassic  or  calcic 
magmas,  but  much  more  chemical  study  of  the  rocks  in  which 
it  occurs  is  needed  to  elucidate  its  relations. 

Lead  can  often  be  found  in  rocks  by  using  large  amounts  of 
material,  and  is  occasionally  reported,  as  in  the  analyses  of 
rocks  from  British  Guiana  by  J.  B.  Harrison  and  in  those  of 
rocks  from  New  South  Wales.  No  generalization  in  regard  to 
it  is  possible  as  yet,  but  I  am  inclined  to  think  that,  like  zinc, 
it  favors  the  acid  rather  than  the  basic  rocks,  though  it  has 
been  observed  in  both.  The  remarks  in  regard  to  the  occur- 
rence of  zinc  in  limestones  apply  as  well  to  lead. 

Platinum  and  the  other  metals  of  this  group  are,  as  is  well 
known,  most  commonly  found  in  connection  with  peridotites, 
rocks  low  in  silica  and  high  in  magnesia,  though  it  has  been 


754  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

observed  by  Kemp  in  gabbros,  which  were  presumably  con- 
nected genetically  with  peridotitic  rocks.  Recent  developments 
point  to  a  somewhat  wider  distribution  than  was  formerly 
thought  to  be  the  case,  and  indicate  that  platinum  not  infre- 
quently is  associated  with  copper-ores. 

The  true  relations  of  such  elements  as  arsenic,  antimony,  bis- 
muth, selenium  and  tellurium  to  igneous  magmas  are  quite  un- 
known. It  is  possible  that  arsenic  and  selenium  are  most  at 
home  in  the  basic  rocks,  while  antimony,  bismuth,  and  tellu- 
rium are  more  apt  to  occur  in  siliceous  ones. 

We  may  summarize  the  observations  recorded  above  as 
follows:  Of  the  rarer  elements  whose  distribution  is  better 
known,  lithium,  beryllium,  cerium  and  yttrium,  zirconium, 
uranium,  thorium,  sulphur  (as  trioxide),  fluorine,  chlorine,  and 
possibly  tin  occur  most  abundantly  in  sodic  magmas;  barium 
in  potassic  magmas;  titanium,  vanadium,  manganese,  nickel, 
and  cobalt  in  iron-rich  magmas;  chromium  and  platinum  in 
magnesian  magmas;  and  phosphorus  (?)  and  chromium  (?)  in 
calcic  magmas. 

Of  the  other  elements  it  can  only  be  said  that  boron  and 
molybdenum  are  certainly,  and  zinc,  cadmium,  lead,  antimony, 
bismuth,  and  tellurium  are  possibly,  connected  with  magmas 
high  in  silica;  sulphur  and  copper  almost  certainly,  and 
arsenic  and  selenium  possibly,  with  those  low  in  silica;  while 
the  relations  of  gold,  silver,  and  mercury  are  very  uncertain, 
but  they  are  probably  most  at  home  in  acid  rocks. 

This  statement,  it  will  be  seen,  differs  from  that  of  Vogt,  in 
that,  in  the  best-established  cases,  silica  plays  a  less  determina- 
tive role  than  some  of  the  other  major  constituents.  At  the 
same  time,  the  influence  of  the  general  law  of  the  association 
of  the  most  abundant  oxides  comes  into  play,  and  in  a  general 
way  the  potassic  and  sodic  magmas  are  most  apt  to  be  highly 
siliceous  (though  the  facts  of  distribution  are  shown  in  them 
even  when  silica  is  low) ;  while  tljose  which  are  high  in  iron, 
magnesia,  and  lime  are  most  apt  to  be  low  in  silica. 

Possibly  the  most  striking  feature  of  the  distribution  as  thus 
shown  is  the  great  number  of  elements  which  are  prone  to 
occur  in  highly  sodic  magmas.  As  is  well  known,  such  magmas 
are  those  which  show  most  tendency  to  differentiation  and  the 
formation  of  a  great  variety  of  rocks,  many  of  them  character- 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  755 

ized  by  the  presence  of  rare  or  otherwise  unusual  and  interest- 
ing minerals,  and  there  may  probably  be  some  connection  be- 
tween the  two  features  of  these  magmas. 

It  will  be  noted  that  some  of  these  elements,  as  fluorine, 
chlorine,  sulphur  (as  trioxide),  and  boron,  are  among  those  to 
which  is  usually  attributed  the  role  of  so-called  "  mineralizing 
agents,"  they  being  supposed  to  be  present  as  dissolved  vapors 
in  the  magma  and  to  exert  a  marked  effect  on  the  crystalliza- 
tion of  the  mass,  the  formation  of  pegmatites,  and  so  forth.  It 
may  be  argued  that  such  mineralizing  and  pneumatolytic  ele- 
ments are  universally,  and  presumably  quite  uniformly,  dis- 
tributed among  the  rock-magmas,  and  that  their  presence  in 
the  highly  siliceous  and  sodic  rocks  is  due  to  the  greater  vis- 
cosity of  these  when  molten,  which  would  hinder  the  escape  of 
gaseous  constituents,  while  the  basic  magmas  are  more  fluid 
at  low  temperatures  and  would  hence  allow  such  gases  to  escape 
before  or  during  consolidation.  On  the  other  hand,  it  may  be 
urged  that  the  undeniable  distribution,  among  magmas  of  dis- 
tinctly different  general  chemical  characters,  of  elements  to 
which  no  such  mineralizing  or  pneumatolytic  role  can  be 
reasonably  assigned,  as  barium,  beryllium,  zirconium,  titanium, 
manganese,  nickel,  chromium,  and  platinum,  would  lead  to  the 
inference  that  the  apparent  distribution  of  the  gaseous  and 
"  mineralizing "  elements  in  igneous  rocks  is  real  and  not 
dependent  on  physical  causes.  The  subject  is  highly  complex, 
and  our  knowledge  of  the  fundamental  facts  and  of  the  physico- 
chemical  laws  involved  is  as  yet  inadequate  for  solution  of  the 
problem,  further  discussion  of  which  would  be  outside  the  scope 
of  this  paper. 

V.  PRACTICAL  CONSIDERATIONS. 

When  the  facts  of  the  relations  of  the  occurrence  of  the 
rarer  elements  to  the  chemical  characters  of  igneous  magmas 
are  considered,  it  is  evident  that  their  distribution  over  the 
earth's  surface  must  be  largely  determined  by  that  of  the  petro- 
graphic  provinces.  In  other  words,  in  any  given  petrographic 
province  those  rarer  elements  and  minerals  containing  them 
would  be  most  apt  to  occur  abundantly  which  show  a  correla- 
tive tendency  to  association  with  the  characteristic  major  con- 
stituents of  the  province.  Thus,  zirconium-bearing  minerals 
and  those  of  the  "  rare  earths  "  should  be  most  abundant  in 


756  DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS. 

provinces  whose  magmas  are  highly  sodic  and  where  such  rocks 
as  nephelite-syenite  and  phonolite  are  common;  while  chro- 
mium, nickel,  and  platinum  would  not  be  expected  in  thesey 
but  would  rather  be  likely  to  occur  in  provinces  where  such 
rocks  as  gabbros  and  peridotites  are  the  prevailing  ones. 

This  idea  has  been  recognized  by  Spurr11  in  his  proposed/ 
term  of  "  metallographic  provinces,"  which  is  based  largely  on 
ore-associations,  and  which  he  applies  more  especially  to  those 
metals  of  most  economic  importance,  such  as  gold,  silver,  cop- 
per, lead,  and  zinc.  The  probable  very  close  connection  between 
"  petrographic "  and  "  metallographic"  provinces  is  pointed  out 
by  him,  but  the  two  classes  seem  to  be  regarded  by  him  as  dis- 
tinct, at  least  to  a  certain  extent. 

When  we  deal  with  such  complex  bodies  as  veins  and  other 
ore-deposits,  the  matter  is  complicated  by  such  factors  as  geo- 
logical structure,  the  existence  of  faults,  the  occurrence  of  the 
igneous  rock  as  plutonic  masses,  dikes  or  effusive  flows,  climatic 
conditions,12  and  other  disturbing  features.  These  may  tend 
either  to  favor  or  to  retard  the  processes  of  concentration  which 
result  in  economically-exploitable  metalliferous  deposits.  But 
these,  .though  undoubtedly  of  the  highest  commercial  import- 
ance, are  subsidiary  to  the  more  fundamental  facts  of  the  dis- 
tribution of  the  elements  in  igneous  magmas,  and  it  seems  rea- 
sonable to  suppose  that  a  study  of  these  latter  features  should 
be  susceptible  of  results  of  great  practical  importance. 

It  seems  that,  at  present,  the  knowledge  gained  by  exact 
chemical  analysis  that  the  granites  of  a  certain  region  contain 
minute  traces  of  gold  or  of  copper,  would  be  of  little  use  in  guid- 
ing one  in  the  search  for  the  location  of  a  gold-  or  a  copper-mine. 
The  prospector  must  always  remain  a  valuable,  indeed  an  invalu- 
able, member  of  the  mining  fraternity.  We  cannot  enter  here 
into  the  vast  and  vexed  subject  of  the  genesis  of  ore-deposits, 
but  if  it  were  known  by  future  researches  that,  for  instance, 
gold  or  copper  is  normally  associated  with  magmas  of  a  certain 
general  chemical  character,  a  knowledge  of  this  might  con- 
ceivably be  of  material  assistance  in  a  search ;  not  so  much  by 

11  Trans.,   xxxiii.,    336  (1902)  ;   Professional  Paper  No.   42,    U.    S.   Geological 
Survey,  p.  276  (1905)  ;  and  No.  55,  p.  128  (1906). 

12  H.  V.  Winchell,  Popular  Science  Monthly,  vol.  Ixxii. ,  No.  6,  pp.  534  to  542 
(June,  1908). 


DISTRIBUTION    OF    ELEMENTS    IN    IGNEOUS    ROCKS.  757 

indicating  the  exact  position  of  a  favorable  location,  but,  in  a 
more  general  way,  by  leading  the  prospector  to  confine  his 
attention  to  a  given  region  of  favorable  igneous  rocks,  and  to 
disregard  one  whose  rocks,  on  theoretical  grounds,  would  prob- 
ably result  in  loss  of  time  and  effort.  Such  a  knowledge  could 
be  gained,  not  only  by  the  complex  and  laborious  methods  of 
accurate  and  minutely  complete  chemical  analysis,  but  more 
readily,  at  least  in  many  conceivable  cases,  by  simple  petro- 
graphical  examination  and  field-study  of  the  most  abundant 
and  characteristic  rock-minerals. 

These  considerations,  it  is  true,  are  scarcely  applicable  as  yet 
to  search  for  such  metals  as  gold,  silver,  or  copper,  concerning 
the  magmatic  relations  of  which  our  knowledge  is  of  the  vaguest 
description.  But,  in  view  of  what  has  been  ascertained  by 
petrographical  and  chemical  means  of  the  distribution  of  other 
elements,  it  is  not  unreasonable  to  think  that  we  shall  eventually 
obtain  well-founded  and  definite  knowledge  concerning  the  dis- 
tribution of  these  also.  Indeed,  the  opinion  may  be  expressed 
that  future  petrographers  will  wonder  at  the  fact  that,  for 
instance,  the  presence  of  such  deep-seated  and  extensive  deposits 
of  copper  as  those  at  Buite,  Mont.,  and  in  Shasta  county,  Cal., 
was  so  long  unsuspected,  and  that  their  discovery  came  as  a 
surprise. 

At  the  present  time  a  knowledge  of  the  distribution  of  the 
elements  is  practically  applicable,  not  so  much  to  the  metals  of 
greatest  human  utility,  as  to  certain  elements  the  economic 
possibilities  of  which  are  only  recently  beginning  to  be  appre- 
ciated as  their  chemical  and  physical  properties  and  the  appli- 
cation of  these  to  commercial  and  economic  purposes  are  be- 
coming better  known.  Some  illustrations  may  be  permitted  of 
the  practical  application  of  the  facts  set  forth  in  the  preceding 
pages. 

If,  for  instance,  one  were  in  a  new  country  or  were  engaged 
in  a  search  for  minerals  containing  such  elements  as  zirconium, 
uranium,  the  rare  earths,  or  beryllium,  one  would  welcome  a 
district  of  highly  sodic  igneous  rocks,  where  albitic  granites, 
neph elite-syenites,  and  phonolites  were  abundant;  in  this  the 
chances  of  success  would  be  most  favorable.  If  the  rocks  were 
prevailingly  gabbros,  diabases,  or  feldspar-basalts  one  would 
reasonably  assume  that  such  minerals  could  not  be  expected  to 


758  DISTRIBUTION    OP    ELEMENTS    IN    IGNEOUS    ROCKS. 

occur,  at  least  in  such  amount  as  to  repay  exploitation,  and 
they  would  be  neglected,  or  prospected  for  platinum  or  chro- 
mium, let  us  say.  Similarly,  if  the.  platinum  metals  were  found 
in  the  sands  of  a  river  the  water-shed  of  which  covered  areas 
of  gabbros,  granites,  and  limestones,  one  would  naturally  turn 
to  and  explore  the  first  in  an  attempt  to  trace  the  grains  to  their 
source,  and  would,  with  good  reason,  leave  the  others  alone. 

Instances  of  this  kind  could  be  multiplied,  and,  indeed, 
some  present  applications  of  the  general  principles  are  now 
practiced  not  infrequently,  but  without  any  suspicion  of  the 
true  principles  underlying  them  or  realization  of  their  more 
general  applicability.  Thus,  in  certain  districts  the  occurrence 
of  topaz  or  spodumene  may  be  recognized  as  generally  indi- 
cating the  possible  or  probable  presence  of  cassiterite,  without 
appreciation  of  the  more  general  and  fundamental  fact  that  the 
conjunction  of  tin,  fluorine,  and  lithium  is  due  to  the  distinctly 
sodic  character  of  the  igneous  rocks. 

With  increase  in  our  knowledge  of  the  origin  of  ore-deposits, 
and  a  general  agreement  as  to  their  ultimate  source  in  igneous 
rocks  (whatever  be  the  divergence  of  views  as  to  the  processes 
of  concentration),  the  probability  of  the  future  importance  of 
such  observations  as  have  been  outlined  above,  from  a  practical 
as  well  as  from  a  theoretical  standpoint,  is  fairly  evident.  We 
cannot  as  yet  predict  the  probable  presence  of  gold,  silver,  or 
copper  in  economic  quantities  from  the  petrographical  and 
chemical  study  of  the  country-rock ;  but  the  time  may  come 
(and  our  increasing  knowledge  of  igneous  rocks  justifies  us  in 
a  certain  degree  of  confidence  that  it  will  come)  when  such 
seemingly  erudite  and  impractical  studies  will  be  able  to  guide 
us  in  certain  regions,  as  to  either  the  probable  absence  or  pres- 
ence of  ore-bodies  of  such  metals. 

The  problem  is  admittedly  very  complex,  and  is  one  which 
has  not  yet  been  studied  enough  to  do  much  more  than  enable 
us  to  make  a  few  broad  guesses  at  the  truth.  But  we  are 
beginning  to  discern  some  glimmer  of  light,  and  the  fact 
that  we  cannot  make  out  clearly  our  guiding  stars,  veiled  as 
they  are  by  the  mists  of  imperfect  knowledge,  should  not 
cause  us  to  disdain  such  help  as  glimpses  of  them  may  now 
afford,  or  underrate  their  possible  importance  when  the  mists 
shall  have  been  dispelled. 


MANGANESE    AND    GOLD-ENRICHMENT.  759 


No.  29. 

The  Agency  of  Manganese  in  the  Superficial  Alteration  and 

Secondary  Enrichment  of  Gold-Deposits  in  the 

United  States.* 

BY   WILLIAM   H.    EMMONS,    CHICAGO,    ILL. 

(Canal  Zone  Meeting,  November,  1910.    Trans.,  xlii.,  3.) 
CONTENTS. 

PAGE. 

I.  INTRODUCTION  AND  SUMMARY, 760 

II.  SALTS  CONTAINED  IN  THE  WATERS  OP  GOLD-  AND  SILVER-MINES  IN 

NON-CALCAREOUS  KOCKS, 764 

1,  Sulphates;  2,  Chlorides;  3,  Carbonates  and  Alkaline  Earths; 
4,  Alumina  ;  5,  Nitrates  ;  6,  Phosphates  ;  7,  Silica  ;  8,  Iron  ; 

9,  Manganese;  10,  Copper. 

III.  CHEMICAL  EXPERIMENTS  IN  THE  SOLUTION  AND  DEPOSITION  OF  GOLD,     771 

IV.  DISCUSSION  OF  EXPERIMENT.*, .        .     776 

1,  Nitrates  ;  2,  Manganese  Oxides  ;  3,  Lead  Oxides  ;  4,  Ferric  Com- 
pounds ;  5,  Efficiency  of  Ferric  Iron  and  of  Cupric  Copper  to 
Supply  Nascent  Chlorine,  Compared  with  that  of  Manganitic 
Manganese  ;  6,  The  Amount  of  Chlorine  Necessary  for  the  So- 
lution of  Gold  in  the  Presence  of  Manganese  Compounds  ;  7, 
The  Precipitation  of  Gold. 
V.  THE  TRANSFER  OF  GOLD  IN  COLD  SOLUTIONS,  .  .  .  .  .  785 

1,  Kestatement  of  the  Processes  as  Related  to  Secondary  Enrich- 
ment ;  2,  Association  of  Gold  with  Manganese  Oxides  ;  3,  The 
Oscillating,  Descending,  Undulatory  Water-Table ;  4,  The 
Several  Successive  Zones  in  Depth  ;  5,  Criteria  for  the  Recogni- 
tion of  Secondary  Enrichment ;  6,  Lateral  Migration  of  Man- 
ganese-Salts from  the  Country- Rock  to  the  Ore  ;  7,  Concentra- 
tion in  the  Oxidized  Zone  ;  8,  Vertical  Relation  of  Deep-Seated 
Enrichment  of  Gold  to  Chalcocitization  ;  9,  Vertical  Relations 
of  Silver-Gold  and  Gold-Silver  Ore  in  Deposits  Carrying  Both 
Metals. 

VI.  REVIEW  OF  MINING-DISTRICTS, 805 

Gold-Provinces  of  the  United  States, .806 

1,  Southern  Appalachian  Districts  ;  2,  Black  Hills,  S.  D.  ;  3,  Tread- 
well  Mine,  Alaska;  4,  Berner's  Bay,  Alaska;  5,  Mother  Lode 
District,  Cal. ;  6,  Nevada  City  and  Grass  Valley,  Cal. ;  7,  Ophir 
District,  Cal. ;  8,  Silver  Peak,  Nev.  ;  9,  Philipsburg,  Mont.  ; 

10,  Other  Montana  Districts;  11,  Edgemont,  Nev.  ;  12,  Lead- 
ville,  Colo.  ;  13,  Georgetown,  Colo. ,  Silver-Lead  Deposits  ;  14, 
Auriferous  Deposits  of  the  Georgetown  Quadrangle,  Colo.  ;  15, 
San  Juan,  Colo.  ;  16,  Cripple  Creek,  Colo.  ;  17,  Summit  Dis- 
trict, Colo. ;  18,  Bodie,  Cal.  ;  19,  Exposed  Treasure  Mine,  Cal.  ; 
20,  Tonopah,  Nev.  ;  21,  Goldfield,  Nev.  ;  22,  Manhattan,  Nev.  ; 
23,  Annie  Laurie  Mine,  Utah  ;  24,  Bullfrog  District,  Nev.  ;  25, 
Gold  Circle,  Nev. ;  26,  Delamar  Mine,  Nev. 

*  Published_by  permission  of  the  Director  of  the  U.  S.  Geological  Survey. 


760  MANGANESE    AND    GOLD-ENRICHMENT. 

I.  INTRODUCTION  AND  SUMMARY. 

FERRIC  iron,  cupric  copper,  and  manganitic  manganese  are 
present  in  many  mineral  waters,  and  under  certain  conditions 
any  one  of  them  will  liberate  chlorine  from  sodium  chloride  in 
acid  solutions.  Nascent  chlorine  dissolves  gold.  Each  of  these 
compounds  will  thus  release  chlorine  at  high  temperatures,  and 
at  low  temperatures  in  concentrated  solutions.  In  cold,  dilute 
solutions,  ferric  iron  will  not  give  nascent  chlorine  in  appreci- 
able quantity  in  34  days,  and  cupric  copper  is  probably  even 
less  efficient ;  but  manganitic  compounds  (supplied  by  pyrolu- 
site,  etc.)  liberate  chlorine  very  readily.  In  a  cold  solution  con- 
taining only  1,418  parts  of  chlorine  per  million,  considerable 
gold  is  dissolved  in  14  days  when  manganese  is  present.  It 
should  be  expected,  then,  that  those  auriferous  deposits,  the 
gangues  of  which  contain  manganese,  would  show  the  effects  of 
the  solution  and  migration  of  gold  more  clearly  than  non-man- 
ganiferous  ores. 

Gold  thus  dissolved  is  precipitated  by  ferrous  sulphate.  It  is, 
therefore,  natural  to  suppose  that  gold  in  such  solutions  could 
not  migrate  far  through  rocks  containing  pyrite,  since  it  would 
be  quickly  precipitated  by  the  ferrous  sulphate  produced  through 
the  action  of  air,  oxidizing  waters,  or  the  gold-solution  itself, 
upon  the  pyrite.  But  the  dioxide  and  higher  oxides  of  manga- 
nese react  immediately  upon  ferrous  sulphate,  converting  it  to 
ferric  sulphate,  which  is  not  a  precipitant  of  gold.  Conse- 
quently, manganese  is  not  only  favorable  to  the  solution  of  gold 
in  cold,  dilute  mineral  waters,  but  it  also  inhibits  the  precipitat- 
ing action  of  ferrous  salts,  and  thus  permits  the  gold  to  travel 
further  before  final  deposition. 

These  statements  apply  to  the  action  of  surface-waters  de- 
scending through  the  upper  parts  of  an  auriferous  ore-deposit, 
since  such  waters  are  cold,  dilute,  acid  (i.e.,  oxidizing)  solutions. 
In  deeper  zones,  where  they  attack  other  minerals,  they  lose 
acidity,  until  the  manganese  compounds,  stable  under  oxidiz- 
ing conditions,  are  precipitated  together  with  the  gold.  Thus, 
manganite,  as  well  as  limonite  and  kaolin,  is  frequently  found 
in  secondary  (i.e.,  dissolved  and  reprecipitated)  gold-ores.  More- 
over, in  the  precipitation  of  secondary  copper  and  silver  sul- 
phides, ferrous  sulphate  is  generally  formed ;  and,  consequently, 
the  secondary  silver  or  copper  sulphides  frequently  contain  gold. 


MANGANESE    AND    GOLD-ENRICHMENT.  761 

Those  deposits  in  the  United  States  in  which  a  secondary 
enrichment  in  gold  is  believed  to  have  taken  place  are,  almost 
without  exception,  manganiferous.  Since  secondary  enrich- 
ment is  produced  by  the  downward  migration,  instead  of  the 
superficial  removal  and  accumulation,  of  the  gold,  it  should 
follow  that  both  gold-placers  and  outcrops  rich  in  gold  would 
be  found  more  extensively  in  connection  with  non-manganif- 
erous  deposits ;  and  this  inference  is  believed  to  be  confirmed 
by  field-observations. 

The  problem  is  not  as  simple  as  this  preliminary  statement 
of  it  may  seem  to  indicate.  Some  of  the  numerous  and  com- 
plex data  bearing  upon  it  are  collated  and  discussed  in  the 
pages  that  follow. 

Among  the  papers  which  treat  the  superficial  alteration  and 
secondary  enrichment  of  copper-,  gold-,  and  silver-deposits,  are 
those  of  S.  F.  Emmons,1  Weed,2  Penrose,3  Winchell,4  Van  Hise,5 
Kemp,6  and  Eickard.7  The  processes  upon  which  the  changes 
depend  are  clearly  outlined  in  these,  and  subsequent  work  has, 
in  a  large  measure,  confirmed  the  premises  stated.  The  chem- 
ical laws  and  physical  conditions  controlling  secondary  enrich- 
ment have  been  reviewed  in  several  reports  more  recently 
published  and  examples  illustrating  the  processes  have  been 
multiplied.  The  papers  of  Lindgren,  Eansome,  Spencer,  Bout- 
well,  Irving,  Graton,  McCaskey,  Spurr,  and  Garrey  and  Ball 
are  particularly  valuable.  Such  work  has  shown  that  the  sec- 
ondary enrichment  of  pyritic  copper-deposits  is  an  important 
and  almost  universal  process;  that  many  silver-deposits  are 
enriched  by  superficial  agencies ;  but  that  many  gold-deposits 
do  not  show  deep-seated  secondary  enrichment. 

T.  A.  Eickard8  has  brought  out  clearly  the  processes  by 

1  The  Secondary  Enrichment  of  Ore-Deposits,  Trans.,  xxx.,  177  to  217  (1900). 

2  The  Enrichment  of  Gold  and  Silver  Veins,  Trans.,  xxx.,  424  to  448  (1900). 

3  The  Superficial  Alteration  of  Ore- Deposits,  Journal  of  Geology,  vol.  ii.,  No.  3, 
pp.  288  to  317  (Apr. -May,  1904). 

4  Bulletin  of  the  Geological  Society  of  America,  vol.  xiv.,  pp.  269  to  276  (1902). 

5  Some  Principles  Controlling  the  Deposition  of  Ores,  Trans.,  xxx.,  27  to  177 
(1900). 

6  Secondary  Enrichment  in  Ore-Deposits  of  Copper,  Economic  Geology,  vol.  L, 
No.  1,  pp.  11  to  25  (Oct.-Nov.,  1905). 

7  The  Formation  of  Bonanzas  in  the   Upper  Portions  of  Gold-Veins,  Trans., 
xxxi.,  198  to  220  (1901). 

8  Loc.  cit. 

48 


762  MANGANESE    AND    GOLD-ENRICHMENT. 

which  gold-deposits  may  be  enriched  relatively  near  the  sur- 
face in  the  oxidized  zone  by  the  removal  of  valueless  minerals 
which  are  more  readily  dissolved  than  gold.  On  the  problem 
of  deeper-seated  precipitation  of  gold  below  the  zone  of  oxi- 
dation there  is  less  evidence.  In  some  mines,  however,  the 
transportation  and  deep-seated  precipitation  of  gold  is  clearly 
shown,  as  was  pointed  out  long  ago  by  Weed. 

While  engaged  in  the  investigation  of  certain  auriferous 
deposits  in  the  Philipsburg  quadrangle,  Montana,  for  the  U.  S. 
Geological  Survey,  I  was  confronted  by  evidence  gained  in  two 
important  mines,  which  seemed  to  be  conflicting  on  this  point. 
In  one  of  them,  the  Cable  mine,  there  was  no  evidence  that 
gold  had  been  concentrated  by  cold  solutions  below  the  zone 
of  oxidation,  but  in  the  Granite-Bimetallic  lode  there  was 
enrichment  of  both  gold  and  silver  below  the  zone  of  leached 
oxides.  The  richer  silver-minerals  occur  in  cracks  and  in 
small  fissures  cutting  across  the  banding  of  the  primary 
deposits  and  are  related  very  distinctly  to  the  present  topog- 
raphy of  the  country.  The  evidence  therefore  appeared  to  be 
conclusive  that  these  minerals  were  deposited  by  cold  mineral 
waters  and  that  their  metallic  contents  had  been  dissolved  from 
portions  of  the  lode  higher  up.  The  enriched  silver-ore  carries 
considerably  more  gold  than  the  primary  ore  in  the  bottom  of 
the  mine,  and  more  than  the  upper  portion  of  the  oxidized 
zone,  including  the  outcrop.  No  placers  have  been  formed  from 
this  deposit,  although  it  has  produced  considerable  gold.  On 
the  other  hand,  important  placers  have  been  developed  just 
below  the  outcrop  at  the  Cable  mine.  Clearly  there  has  been 
a  kind  of  selection  in  the  operation  of  the  processes  of  solution 
and  precipitation  of  gold. 

Although  the  ores  of  the  two  deposits  differ  in  other  respects, 
the  most  striking  difference  is  in  the  manganese-content.  The 
abundance  of  manganese  in  the  Granite-Bimetallic  manifests 
itself  in  the  characteristic  coloration  of  the  ores — pink  in  the 
unoxidized,  brown  or  black  in  the  oxidized  zone.  In  the 
Cable,  manganese  is  practically  absent.  The  difference  in 
manganese-content  is  so  striking  as  to  suggest  a  causal  rela- 
tionship with  the  equally-marked  difference  in  the  amount  of 
secondary  enrichment. 

The  use  of  manganese  in  the  chlorination  process  to  give 


MANGANESE    AND    GOLD-ENRICHMENT.  763 

free  chlorine,  which  dissolves  gold,  is  well  known.  Le  Conte 9 
said  as  early  as  1879  that  free  chlorine  is  the  most  important 
natural  solvent  of  gold,  and  Richard  Pearce,  in  his  presiden- 
tial address  before  the  Colorado  Scientific  Society,  in  1885, 
recorded  experiments  in  which  gold  had  been  dissolved  in  hot 
sulphate  solutions  with  common  salt  and  manganese  dioxide.10 
Don  obtained  similar  results  with  more  dilute  solutions.11  It 
appeared  desirable,  therefore,  to  ascertain  whether  these  reac- 
tions are  carried  on  appreciably  in  cold  dilute  solutions  similar 
to  mine-waters ;  and  Nicholas  Sankowsky  and  Clarence  Russell, 
in  a  seminar  on  the  Chemistry  of  Ore-Deposits,  which  I  con- 
ducted at  the  University  of  Chicago,  compiled  all  available 
analyses  of  waters  from  gold-  and  silver-mines  in  non-calcareous, 
rocks.  A.  D.  Brokaw  conducted  a  series  of  experiments  at  my 
request,  using  cold  dilute  solutions  of  compositions  suggested 
by  the  analyses.  He  performed  other  experiments  also,  show- 
ing the  action  of  manganese  dioxide  on  ferrous  salts,  which  are 
applicable  to  the  study  of  the  precipitation  of  gold.  During 
the  progress  of  this  investigation,  "W.  J.  McCaughey,  of  the 
Bureau  of  the  Mint,  Washington,  D.  C.,  published  his  valua- 
ble paper  on  the  solvent  effect  of  ferric  and  cupric  salt  solutions 
upon  gold,12  and  this  in  a  large  measure  supplemented  the  work 
carried  on  in  the  seminars  at  the  University  of  Chicago, 

The  experiments  conducted  by  Brokaw  showed  that  man- 
ganese in  the  presence  of  chlorides  and  sulphates  is  very 
much  more  efficient  in  the  reactions  dissolving  gold  than 
are  the  other  salts  which  are  common  in  mine-waters.  To 
verify  these  results  by  field-evidence,  the  review  of  the  lit- 
erature was  taken  up  in  greater  detail,  and  there  also  the 
results  indicate  a  marked  difference  in  the  behavior  of  the 
cold  dilute  mineral  waters  in  the  presence  and  in  the  absence 
of  manganese.  Lindgren's  classification  of  the  gold-deposits  of 
North  America  has  been  of  great  value  in  reviewing  these 
deposits;  since  in  the  United  States  manganese  is  rarely  a 
garigue-mineral  in  the  primary  gold-deposits  as  old  as  the 
early  Cretaceous  California  gold-veins,  whereas  it  is  frequently 

9  Elements  of  Geology,  p.  285. 

10  Proceedings  of  the  Colorado  Scientific  Society,  vol.  ii.,  p.  3  (1885-87). 

11  Trans.,  xxvii.,  654  (1897)  ;  p.  176,  this  volume. 

18  Journal  of  the  American  Chemical  Society,  vol.  xxxi.,  No.  12,  pp.  1261  to  1270 
(Dec.,  1909). 


764  MANGANESE    AND    GOLD-ENRICHMENT. 

present  in  very  appreciable  quantities  in  those  deposits  which 
were  formed  nearer  the  surface  and  which  are  related  to  intru- 
sives  of  Tertiary  age.  Possibly  this  difference  is  due  to  con- 
ditions of  temperature  and  pressure  which  prevailed  when  the 
deposits  were  formed.13  Since  there  are  no  data  which  show 
the  effect  of  highly-carbonated  waters  on  these  reactions,  I 
have  as  far  as  possible  eliminated  examples  of  gold-deposits  in 
limestone,  and  the  discussion  is  confined  mainly  to  deposits  in 
non-calcareous  rocks.  I  have  not  attempted  to  review  exhaust- 
ively the  evidence  afforded  by  deposits  outside  of  the  United 
States  with  respect  to  the  hypothesis  suggested,  but  some  of 
these  deposits  appear  to  supply  accurate  confirmatory  data. 

In  a  statistical  study  of  outcrops,  to  ascertain  whether  gold 
is  more  extensively  leached  in  manganiferous  lodes  than  in  the 
outcrops  of  those  which  do  not  carry  manganese,  and  whether 
placers  are  more  frequently  developed  in  connection  with  non- 
man  ganiferous  lodes,  the  reports  of  Dr.  R.  W.  Raymond,14 
written  soon  after  the  discoveries  of  many  of  the  deposits,  have 
been  of  great  value. 

I  wish  to  acknowledge  my  indebtedness  to  my  colleagues  of 
the  U.  S.  Geological  Survey,  and  to  many  other  geologists 
whose  accurate  observations  I  have  drawn  upon  to  test  the 
hypothesis.  Their  conclusions  respecting  the  secondary  en- 
richment of  gold  appear  to  support  the  hypothesis,  and,  differ- 
ing as  they  do  with  respect  to  the  migration  of  gold  in  partic- 
ular deposits,  they  become  reconciled  when  inspected  from 
this  view-point,  and  thus  they  are  themselves  supported.  Dr. 
R.  C.  Wells,  of  the  U.  S.  Geological  Survey,  has  read  critically 
certain  portions  of  this  paper,  where  the  principles  of  physical 
chemistry  are  involved. 

II.    SALTS  CONTAINED  IN  THE  WATERS  or  GOLD-  AND  SILVER- 
MINES  IN  NON-CALCAREOUS  ROCKS. 

The  composition  of  mine-waters  depends  upon  the  character 
of  the  ore  and  wall-rock  and  the  position  of  the  deposit  with 
respect  to  bodies  of  salt  water.  There  are  certain  compounds 
which  are  generally  present,  and  some  which  nearly  •  always 
predominate.  Of  the  few  analyses  which  have  been  made  of 

13  W.  Linlgren,  The  Relation  of  Ore-Deposition  to  Physical  Conditions,  Eco- 
nomic Geology,  vol.  ii.,  No.  2,  pp.  105  to  127  (Mar. -Apr.,  1907). 

14  Mines  and  Mining  West  of  the  Rocky  Mountains  (1868-1875). 


MANGANESE    AND    GOLD-ENRICHMENT.  765 

waters  from  gold-mines,  a  large  proportion  are  incomplete; 
and  it  is  not  always  stated  whether  compounds  not  reported 
were  looked  for.  Sankowsky  and  Russell,  utilizing  all  data 
available  to  them,  recalculated  the  analyses  to  the  ionic  form- 
of  statement,  and  where  necessary  to  parts  per  million,  and 
made  a  general  average  of  the  results.  Where  compounds 
were  not  reported  in  the  analyses  it  was  assumed  that  they 
were  not  present.  Arsenic,  antimony,  and  other  elements, 
small  traces  of  which  must  be  present  in  some  waters,  are  not 
reported.  Since  the  averages  were  obtained  by  dividing  the 
sums  by  the  total  number  of  analyses  (29)  and  not  by  the 
number  of  analyses  showing  a  particular  element,  and  since 
some  analyses  are  incomplete,  any  corrections  applied  for  this 
source  of  error  would  tend  to  increase  the  number  of  parts  per 
million  indicated.  On  the  other  hand,  some  of  the  mine-waters 
wrere  taken  from  places  protected  from  the  more  active  vadose 
circulation,  and  are  clearly  more  concentrated  than  the  major 
part  of  the  waters.  The  average  of  analyses,  although  a  rude 
approximation,  is  useful,  since  it  gives  some  quantitative  value 
to  their  factor  in  the  problem,  and  indicates  the  general  nature 
of  the  cold  solutions  in  which  the  metals  are  transported. 

TABLE  I. — Average  of  29  Analyses  of  Waters  taken  from  Gold-, 

Silver-,  and  Gold-Silver  Mines  in  Non-  Calcareous  Rocks. 

(Compiled  by  N.  Sankowsky  and  C.  Russell.) 


Number  of 

Absent  or 

Parts  Per  Million. 

Determinations. 

Not  Determined. 

Cla... 

873.10 

22 

7 

so,  

....        7,292.29 

13 

16 

C03  

77.59 

7  • 

22 

N03a  

0.06 

1 

28 

P04  

0.00 

traces  in  2 

27 

SiO,  

34.94 

12 

17 

K  

17.25 

7 

22 

Na«  

261.20 

9 

20 

Li  

0.10 

1 

28 

Ca  

295.00 

11 

18 

Sr  

0.06 

1 

28 

Mg  

242.44 

9 

20 

Al  

333.65 

6 

23 

Mn  

30.91 

6 

23 

Ni  . 

trace 

traces  in  3 

26 

Co  

trace 

traces  in  3 

26 

Cu  

5.09 

2 

27 

Zn  

2.70 

5 

24 

Fen  

277.66 

22 

7 

Feiii  

603.07 

25 

4 

H  (in  acids), 

97.26 

10 

19 

«  Probably  too  high  (see  discussion). 


766  MANGANESE    AND    GOLD-ENRICHMENT. 

1.  Sulphates. 

Primary  gold-ores  generally  carry  pyrite,  which,  oxidizing 
at  or  near  the  surface,  yields  ferrous  sulphate,  ferric  sulphate, 
and  sulphuric  acid.  The  acid  is  not  formed  directly  from 
galena,  PbS,  or  from  zinc-blende,  ZnS,  but  pyrite,  FeS2,  carries 
more  sulphur  than  is  required  to  supply  S04  radical  to  satisfy 
the  iron,  even  if  ferric  sulphate,  Fe2(S04)3,  is  formed  instead  of 
FeSO4.  As  lately  shown  by  Buehler  and  Gottschalk,15  galena 
and  zinc-blende  dissolve  very  much  more  slowly  in  the  absence 
of  FeS2.  The  reaction  probably  requires  free  acid,  which  the 
iron  sulphide,  owing  to  its  excess  of  sulphur,  supplies.  The 
sulphuric  acid  from  pyrite  is  increased  also  by  the  hydroliza- 
tion  of  ferric  sulphate  and  the  deposition  of  limonite . 

In  Table  I.  the  sulphate  radical  (7,292  parts  per  million)  is 
nearly  ten  times  as  abundant  as  all  other  negative  ions  and 
is  also  in  excess  of  bases,  so  that  on  any  basis  of  adjustment  to 
form  salts  much  H2S04  remains.  The  table  shows  also  an  aver- 
age of  97.26  parts  per  million  of  hydrogen  in  acid.  In  view  of 
the  low  atomic  weight  of  hydrogen,  this  indicates  the  strongly 
acid  character  of  the  solutions. 

2.  Chlorides. 

Chlorine  is  present  in  most  mine-waters.  In  22  out  of  the 
29  analyses  it  is  reported  as  traces  or  as  determined  quantities. 
The  average  of  29  analyses  shows  873  parts  per  million,  but  if 
the  one  abnormally-rich  sodium-chloride  water  of  Silver  Islet, 
Lake  Superior,  is  excluded,  the  remaining  28  analyses  show 
but  111  parts  per  million.  This  figure  is  probably  a  better 
average.  It  would  be  further  reduced  some  2  or  3  parts  by 
excluding  the  waters  of  the  Geyser  mine,  Silver  Cliff,  Colo., 
which  may  have  come  from  a  deep  source.  With  these  two 
exceptions,  it  is  noteworthy  that  the  waters  from  mines  remote 
from  salt  water  contain  less  chlorine  than  those  near  the  sea  or 
in  undrained  areas.  The  distribution  of  chlorine  is  an  impor- 
tant element  in  the  migration  of  gold,  and  therefore  I  shall  con- 
sider the  sources  of  chlorine  in  some  detail. 

The  salt  in  sedimentary  rocks  may  be  dissolved  by  ground- 
water.  From  the  available  analyses  it  appears  that  this  source 
is  of  less  importance  than  would  be  supposed.  The  chlorine- 

15  Economic  Geology,  vol.  v.,  No.  1,  p.  30  (Jan.,  1910). 


MANGANESE    AND    GOLD-ENRICHMENT.  767 

content  of  composite  samples  of  78  shales  and  of  253  sand- 
stones was  only  a  trace,  while  an  analysis  of  a  composite  of  345 
limestones  showed  only  0.02  per  cent.16  A  few  rock-making 
minerals,  such  as  chlor-apatite,  scapolite,  haiiyne,  and  nosean, 
contain  combined  chlorine ;  but  of  these  all  but  apatite  occur 
mainly  in  very  rare  types  of  rocks.  In  some  rocks  chlorine  is 
present  probably  as  NaCl  in  the  solid  particles  contained  in 
fluid  inclusions.  The  work  of  R.  T.  Chamberlin,  A.  Gautier, 
and  others  has  shown  that  many  granular  igneous  rocks,  when 
heated  to  high  temperatures,  give  off  gases  equal  to  several 
times  their  own  volume.  While  further  inquiry  of  this  char- 
acter is  desirable,  it  is  probably  true  that  in  general  but  little 
chlorine  is  present  in  such  gases.  But  gases  from  certain 
volcanic  rocks,  such  as  obsidian,  often  contain  a  high  proportion 
of  chlorine  and  chlorides.  Albert  Brun 17  has  shown  that  some 
of  the  Krakatoa  lavas  contain  gases  which  equal  about  one-half 
the  volume  of  the  rock,  and  that  more  than  half  of  such  gases 
consists  of  chlorine,  hydrochloric  acid,  and  sulphur  mono- 
chloride. 

Apatite,  though  widespread  in  igneous  rocks,  is  a  very  stable 
mineral,  and  consequently  cannot  be  looked  upon  as  an  important 
source  of  chlorine,  although  it  may  contribute  small  amounts 
when  exposed  to  favorable  conditions  of  weathering.  The  aver- 
age chlorine-content  of  igneous  rocks  is,  according  to  F.  W. 
Clarke,  0.07  per  cent. 

Chlorine  is  present  in  nearly  all  natural  waters.  Its  chief 
source  is  from  finely-divided  salt  or  salt  water  from  the  sea  and 
from  other  bodies  of  salt  water.  The  salt  is  carried  by  the  wind 
and  precipitated  with  rain.18  The  amount  of  chlorine  in  natu- 
ral waters  varies  with  remarkable  constancy  with  the  distance 
from  the  shore ;  several  determinations  very  near  the  seashore 
show  from  10  to  30  parts  of  chlorine  per  million;  a  few  miles 
away  it  is  generally  about  6  parts  per  million ;  50  miles  from 
shore  it  is  generally  less  than  1  part  per  million.  A  surface- 

16  F.  W.  Clarke,  Bulletin  No.  330,  U.  S.  Geological  Survey,  p.  27  (1908). 

17  Quelques  Recherches  sur  le  Volcanisme  aux  Volcans  de  Java.     Cinqui£me 
partie.     Le  Krakatau.     Archives  des  Sciences  physiques  et  naturelles,  Geneve,  vol. 
xxviii.,  No.  7  (Juillet,  1909). 

18  D.  D.  Jackson,  The  Normal  Distribution  of  Chlorine  in  the  Natural  Waters 
of  New  York  and  New  England,  Water  Supply  and  Irrigation  Paper  No.  144,  U.  S. 
Geological  Survey  (1905). 


768  MANGANESE    AND    GOLD-ENRICHMENT. 

water  from  a  reservoir  at  Leadville  contained  1.14  parts  of  Cl 
per  million.19  The  isochlores  parallel  the  shore-line  with  great 
regularity,  as  indicated  in  the  map,  Fig.  1,  taken  from  Jackson's 
report.  The  amount  of  chlorine  contributed  from  this  source 
even  near  the  seashore  appears  small  (from  6  to  10  parts  per 
million) ;  but  it  may  be  furthur  concentrated  in  the  solutions 
by  evaporation  or  by  reaction  with  silver,  lead,  etc.,  forming 
chlorides,  which  in  the  superficial  zone  may  subsequently  be 
changed  to  other  compounds.  In  arid  countries,  as  suggested 
by  C.  B.  Keyes,  dust  containing  salt  doubtless  contributes 
chlorine  to  the  mine-waters.  Penrose,20  discussing  the  distri- 
bution of  the  chloride  ores,  pointed  out  long  ago  that  these 
minerals  form  most  abundantly  in  undrained  areas. 

3.   Carbonates  and  Alkaline  Earths. 

The  analyses  in  Table  I.  do  not  include  those  from  mines  in 
limestones.  The  carbonate  reported  gives  an  average  of  77 
parts  per  million.  In  the  acid  waters  under  consideration,  the 
carbonates  of  the  bases  would  necessarily  be  present  as  bicar- 
boiiates,  although  this  fact  is  not  indicated  in  the  analyses. 

Even  in  non-calcareous  rocks  considerable  calcium  (295  parts 
per  million)  and  magnesium  (242  parts)  are  carried  by  the 
waters.  They  are  derived  in  part  from  reactions  between  the 
acid  sulphates  and  the  silicates  of  the  wall-rock. 

4.  Alumina. 

In  some  waters  aluminum  sulphate  is  abundant  (the  average 
of  aluminum,  333  parts  per  million).  It  forms  where  sulphate 
waters  attack  kaolin,  setting  free  Si02  and  taking  alumina  into 
solution.  The  above  average  is  probably  high  on  account  of 
one  concentrated  alum-water  in  a  Comstock  mine.21 

5.  Nitrates. 

Nitrates  are  not  abundant  in  mine-waters.  In  one  analysis 
only22  is  N03  reported  (1.60  parts  per  million),  and  this  in  a 
deep-seated  water  of  questionable  genesis. 

19  S.  F.  Emmons,  Geology  and  Mining  Industry  of  Leadville,  Colorado,  Mono- 
graph No.  XII. ,  U.  S.  Geological  Survey,  p.  552  (1886). 

20  Journal  of  Geology,  vol.  ii.,  No.  3,  p.  314  (April-May,  1894). 

21  Bulletin  of  the  Department  of  Geology,  University  of  California,  vol.  iv.,  No.  10, 
p.  192  (1904-06). 

22  Geyser  Mine,  Silver  Cliff,  Colo.     See  S.  F.  Emmons,  Seventeenth  Annual  Re- 
port, U.  S.  Geological  Survey,  Part  II.,  p.  462  (1895-96). 


MANGANESE    AND    GOLD-ENRICHMENT. 


769 


770  MANGANESE    AND    GOLD-ENRICHMENT. 

6.  Phosphates. 

Traces  only  of  P04  are  reported  from  two  mine-waters ;  others 
contained  none,  if  determinations  were  made. 

7.  Silica. 

Silica  (35  parts  per  million)  appears  high  for  acid  waters. 
The  analyses  include  a  manganiferous  sulphate  water  from  the 
Gomstock,  abnormally  high  in  silica.23 

8.  Iron. 

Iron  is  the  most  abundant  metal  in  the  waters  of  gold-mines. 
Ferric  iron  (603  parts  per  million)  is,  according  to  these  analy- 
ses, more  than  twice  as  abundant  as  ferrous  iron  (277  parts  per 
million).  Probably  too  little  attention  has  been  given  to  the 
state  of  oxidation  of  iron  in  unaltered  mine-waters.  Ferrous 
salts  in  solution,  when  exposed  to  air,  rapidly  become  ferric ; 
yet,  so  far  as  I  know,  no  mine-water  which  has  clearly  not  had 
access  to  air  has  been  examined  with  respect  to  the  state  of 
oxidation  of  the  iron.  Ferrous  iron  is  much  more  abundant 
below  than  above  the  water-table. 

9.  Manganese. 

If  manganiferous  minerals  are  present  in  the  primary  ore, 
they  oxidize  in  the  upper  portion  of  the  deposit  to  manganese 
dioxide  or  other  high  oxides  of  manganese;  and  these,  in  turn, 
oxidize  ferrous  sulphate,  in  the  presence  of  sulphuric  acid,  to 
ferric  sulphate.  Consequently,  the  iron  in  manganiferous  waters 
is  likely  to  be  in  the  oxidized  state. 

10.   Copper. 

One  analysis  shows  147  parts  of  copper  per  million.  Two 
other  analyses  show  traces.  Small  amounts  must  be  present  in 
many  other  waters,  since  gold-ores  often  carry  copper.  Possibly, 
small  traces  of  the  heavy  metals  were  not  looked  for  in  many 
of  the  waters  analyzed. 

23  Bulletin  of  the  Department  of  Geology,  University  of  California,  vol.  iv.,  No.  10, 
p.  192  (1904-06). 


MANGANESE    AND    GOLD-ENRICHMENT.  771 

III.  CHEMICAL  EXPERIMENTS  IN  THE  SOLUTION  AND 
DEPOSITION  OF  GOLD. 

The  superficial  alteration  of  gold-deposits  and  the  migration 
of  gold  in  the  deposits  take  place  at.  low  temperatures.  At  the 
very  surface  the  temperatures  range  between  0°  and  50°  C. 
and  pressures  do  not  exceed  one  atmosphere.  At  the  normal 
gradient  of  increase,  the  temperatures,  even  several  thousand 
feet  below  water-level,  would  not  exceed  100°  C.,  and  in  the 
main  are  considerably  lower.  The  general  character  and,  ap- 
proximately, the  concentration  of  the  solutions  are  known  from 
the  analyses  of  mine-waters.  The  conditions  are  fairly  constant. 
From  the  mass  of  chemical  data  relating  to  the  subject,  the  fol- 
lowing experiments  seem  to  be  particularly  suggestive  in  con- 
nection with  the  present  problem. 

1.  Stokes24  placed  gold  leaf  in  a  solution  containing  25  g.  per 
liter  of  ferric  sulphate,  and,  after  heating  to  200°  C.,  found  that 
not  a  trace  of  gold  had  been  deposited  in  the  cold  part  of  the 
sealed  tube  in  which  the  experiment  was  carried  on.     This  ex- 
periment does  not  confirm  the  statement  frequently  made  that 
ferric  sulphate  will  dissolve  gold. 

2.  Don25  exposed  to  air  finely-divided  gold  and  auriferous 
sulphide  ores  in  solutions  containing  from  1  to  20  g.  of  ferric 
chloride  and  ferric  sulphate  per  liter  of  water ;  and  after  several 
months  no  gold  had  been  dissolved.     Presumably  the  gold  was 
not  mixed  with  the  sulphide  in  all  of  the  experiments. 

3.  "W.  J.  McCaughey,26  upon  boiling  for  several  hours  50  cc. 
of  HC1  (sp.  gr.  1.178)  diluted  to  125  cc.  with  250  mg.  of  gold, 
found  there  was  no  loss  of  gold. 

4.  In  a  bent  tube  Stokes27  heated  gold   leaf  for  16  hr.  at 
200°  C.  in  a  solution  composed  of  85  g.  of  cupric  chloride  and 
133  cc.  of  20  per  cent.  HC1  in  a  liter  of  water.    The  gold  leaf  was 
dissolved  and  redeposited  in  the  upper  portion  of  the  tube.     He 
writes  the  reaction  as  follows : 

Au  +  3  CuCl2  **  AuCl3  +  3  CuCl. 

24  Economic  Geology,  vol.  i.,  No.  7,  p.  650  (July-Aug.,  1906). 

25  Trans.,  xxvii.,  598  (1897)  ;  p.  173,  this  volume. 

26  Journal  of  the  American  Chemical  Society,   vol.  xxxi.,  No.  12,  p.  1263  (Dec., 
1909). 

27  Op.  cit.,  vol.  i.,  p   649. 


772 


MANGANESE    AND    GOLD-ENRICHMENT. 


5.  Stokes28  heated  gold  leaf  to  200°  C.  in  a  closed  tube  con- 
taining a  solution  of  25  g.  of  ferric  sulphate  and  0.01  g.  of  NaCl. 
Gold  was  dissolved  in  40  hours. 

6.  Stokes29  found  that  at  200°  C.  gold  leaf  was  dissolved  in  a 
mixture  of  2  parts  of  20  per  cent,  solution  of  ferric  chloride  and 
1  part  of  20  per  cent,  solution  of  HC1. 

7.  W.  J.  McCaughey30  dissolved  gold  at  from  38°  to  43°  C., 
in  hydrochloric  acid  solutions  of  ferric  sulphate.     The  results 
are  indicated  by  the  curves  in  Fig.  2.     Solution  A  contained 
1  g.  of  iron,  introduced  as  ferric  sulphate,  and  25  cc.  of  HC1  (sp. 


80  100 

TIME,  HOURS 


1-,'U 


140 


160 


180 


FIG.  2. — DIAGRAM  SHOWING  THE  BATE  OF  SOLUTION  OF  GOLD  IN  CONCEN- 
TRATED SOLUTIONS  OF  HYDROCHLORIC  ACID  AND  FERRIC  SULPHATE. 
(Illustrating  Experiment  No.  7,  by  McCaughey. ) 

gr.  1.178)  in  a  solution  diluted  to  125  cc.  containing  250  mg.  of 
gold  rolled  to  0.009  in.  Solution  B  contained  the  same  amount 
of  iron  sulphate  and  50  cc.  of  HC1.  Solution  C  contained  2  g. 
of  Fe  as  ferric  sulphate  and  25  cc.  of  HC1.  Solution  D  had 
twice  the  concentration  of  A.  The  diagram  shows  the  amount 
of  gold  dissolved  after  different  periods  of  treatment. 

8.  McCaughey31  found  that  gold  is  dissolved  at  from  38°  to 
43°  C.  in  a  strong  solution  of  cupric  chloride  and  HC1.     The 

28  Economic  Geology,  vol.  i.,  No.  7,  p.  650  (July- Aug.,  1906). 

29  Idem,  p.  650. 

30  Journal  of  the  American  Chemical  Society,  vol.  xxxi.,  No.  12,  p.  1263  (Dec., 
1909). 

31  Idem,  p.  1264. 


MANGANESE    AND    GOLD-ENRICHMENT. 


773 


amounts  dissolved  are  shown  by  the  curves  in  Fig.  3.  Solution 
A  contained  1  g.  of  Cu  as  cupric  chloride  and  25  cc.  of  HC1 
(sp.  gr.  1,178) ;  solution  _B,  1  g.  of  Cu  as  CuCl2  and  50  cc.  of 
HC1;  solution  (7,  2  g.  of  Cu  as  CuCl2  and  25  cc.  of  HC1;  and 
solution  D,  2  g.  of  Cu  as  CuCl2  and  50  cc.  of  HC1;  the  final  so- 
lution being  in  all  cases  diluted  to  the  volume  of  125  cc.  The 
diagram  shows  that  D,  which  was  twice  as  concentrated  as  A, 
dissolved  about  12  times  as  much  gold. 


•20 


40 


GO  80  100 

TIME,  HOURS 


180 


FIG.  3. — DIAGRAM  SHOWING  THE  SOLUBILITY  OF  GOLD  IN  CONCENTRATED 

SOLUTIONS  OF  HYDROCHLORIC  ACID  AND  CUPRIC  CHLORIDE. 

(Illustrating  Experiment  No.  8,  by  McCaughey.) 

9.  Richard  Pearce32  placed  native  gold  in  a  flask  contain- 
ing hydrated  manganese  dioxide  with  40  g.  of  salt  and  5  or  6 
drops  of  H2S04.    After  heating  for  12  hr.  appreciable  gold  had 
been  dissolved. 

10.  T.  A.  Rickard33  extracted  99.9  per  cent,  of  the  gold 
from  rich  manganiferous  ore  with  a  solution  of  ferric  sulphate, 
common  salt,  and  a  little  H2SO4. 

11.  Don 34  found  that  1  part  of  HC1  in  1,250  parts  of  H20,  in 
the  presence  of  Mn02,  dissolves  appreciable  gold. 

A  number  of  experiments  on  the  solubility  of  gold  in  cold 
dilute  solutions  were  made  at  my  request  by  A.  D.  Brokaw.35 
The  nature  of  these  experiments  is  shown  by  the  following 
statements,  in  which  (a)  and  (b)  represent  duplicate  tests  : 


32  Trans.,  xxii.,  739  (1893). 

33  Trans.,  xxvi.,  978  (1896). 

34  Trans.,  xxvii.,  599  (1897) ;  p.  175,  this  volume. 

85  Journal  of  Geology,  vol.  xviii.,  No.  4,  pp.  321  to  326  (May-June,  1910). 


774  MANGANESE    AND    GOLD-ENRICHMENT. 

12.  Fe2  (S04)3  +  H2S04  +  Au. 

(a)  no  weighable  loss.     (34  days.) 
(6)  no  weighable  loss. 

13.  Fe2  (SO4)3  +  H2S04  +  Mn02  +  Au. 

(a)  no  weighable  loss.     (34  days.) 
(6)  0.00017  g.  loss.c 

c  This  duplicate  was  found  to  contain  a  trace  of  Cl,  which  probably  accounts  for 
the  loss. 

14.  FeCl3  +  HC1  +  Au. 

(a)  no  weighable  loss.     (34  days.) 
(6)  no  weighable  loss. 

15.  FeCl3  +  HC1  +  Mn02  +  Au. 

(a)  0.01640  g.  loss.     Area  of  plate,  383  sq.  mm. 

(34  days.) 
(6)   0.01502  g.  loss.     Area  of  plate,  348  sq.  mm. 

In  each  experiment  the  volume  of  the  solution  was  50  cc. 
The  solution  was  one-tenth  normal  with  respect  to  ferric  salt 
and  to  acid.  In  experiments  13  and  15,  1  g.  of  powdered 
manganese  dioxide  was  also  added.  The  gold,  assaying  999 
fine,  was  rolled  to  a  thickness  of  about  0.002  in.  ;  cut  into 
pieces  of  about  350  sq.  mm.  area,  and  one  piece,  weighing  about 
0.15  g.,  was  used  in  each  duplicate. 

To  approximate  natural  waters  more  closely,  a  solution  was 
made  one-tenth  normal  as  to  ferric  sulphate  and  sulphuric  acid, 
and  one  twenty-fifth  normal  as  to  sodium  chloride.  Then  1  g. 
of  powdered  manganese  dioxide  was  added  to  50  cc.  of  the 
solution,  and  the  experiment  was  repeated.  The  time  was  14 
days. 


16a.  Fe2  (S04)3  +  H2S04  +  STaCl  +  Au. 

~No  weighable  loss. 
166.  Fe2  (S04)3  +  H2S04  +  STaCl  +  Mn02  +  Au. 

Loss  of  gold,  0.00505  gram. 

The  loss  is  comparable  to  that  found  in  experiment  15,  allow- 

ing for  the  shorter  time  and  the  greater  dilution  of  the  chloride. 

To  determine  whether  the  free  acid  or  the  ferric  chloride  is 


MANGANESE    AND    GOLD-ENRICHMENT. 


775 


the  solvent,  experiment  17  was  made,  in  which   50  cc.  of  one- 
tenth  normal  HC1  was  used  with  1  g.  of  powdered  Mn02. 

17.  HC1  +  Mn02  +  Au. 

Loss  of  Au,  0.01369  g.     Time,  14  days. 

In  experiment  18,  sodium  hydroxide  was  added  to  50  cc.  of 
one-tenth  normal  ferric  chloride  solution  until  the  precipitate 


0.04          0.08  0.12  0.16  0.20  0.25 

GRAMS  FE  AS  FERROUS  SALT  IN  125  cc. 

FIG.  4. — DIAGRAM  ILLUSTRATING  THE  EFFECT  OF  FERROUS  SULPHATE  IN 
SUPPRESSING  THE  SOLUBILITY  OF  GOLD  IN  FERRIC  SULPHATE  SOLUTIONS, 
WHERE  GOLD  is  DISSOLVED  AS  CHLORIDE. 

(Illustrating  Experiment  No.  19,  by  McCaughey. ) 

formed  barely  re-dissolved   on  shaking,  after  which   1    g.  of 
powdered  Mn02  was  added. 

18.  FeCl3  +  Mn02  +  Au. 

Loss  of  Au,  0.00062  g.     Time,  14  days. 


776  MANGANESE    AND    GOLD-ENRICHMENT. 

These  results  show,  that  in  the  presence  of  manganese 
dioxide,  free  hydrochloric  acid  is  more  efficient  than  ferric 
solutions.36 

19.  McCaughey's  experiments  show  the  effect  of  very  small 
amounts  of  ferrous  sulphate  on  solutions  of  gold  in  ferric  sul- 
phate.    To  a  solution,  125  cc.,  containing  1  g.  of  iron  as  ferric 
sulphate  and  25  cc.  of   HC1,  ferrous   sulphate  was  added  in 
quantities    containing  from  0.01    to    0.26  g.  of   ferrous  iron. 
The   solutions  were    immersed   in    boiling  water    and    subse- 
quently 250  mg.  of  gold  was  added.     The  dissolved  gold  was 
determined  at  the  end  of  1  hr.  and  3  hr.     At  the  end  of  3  hr. 
the  gold  dissolved  was  greater,  probably  because  some  ferrous 
sulphate  had  changed  to  ferric  sulphate.     Even  0.01  g.  of  the 
ferrous  iron  greatly  decreases  the  solubility  of  gold  in  the  ferric 
sulphate  and  HC1    solution,  and    0.25  g.  of   ferrous  sulphate 
drives  nearly  all  the  gold  out  of  solution.     These  experiments 
are  illustrated  by  Fig.  4,  in  which  the  horizontal  lines  represent 
ferrous  salt  put  in  the    mixture    and   the  vertical   lines   the 
amount  of  gold  (in  milligrams)  dissolved  by  chlorine  in  the 
solution.     The  lower  curve  represents  conditions  at  the  end  of 
1  hr.,  the  upper  curve  at  the  end  of  3  hr.,  when  some  of  the 
ferrous  salt  had  oxidized  by  contact  with  the  air. 

20.  To  determine  the  rate  at  which  ferrous  sulphate,  in  the 
presence  of  sulphuric  acid  and  manganese  dioxide,  would  be 
oxidized  to  the  ferric  salt,  Brokaw  made  the  following  experi- 
ment : 

100  cc.  of  1.6  normal  FeS04  was  acidified  with  sulphuric 
acid  and  shaken  vigorously  with  5  g.  of  powdered  Mn02. 
After  5  min.,  the  solution  was  filtered.  No  ferrous  iron  was 
detected  by  the  ferricyanide  test,  showing  that  the  iron  had 
been  completely  oxidized  to  the  ferric  state. 

IV.  DISCUSSION  OF  EXPERIMENTS. 
1.  Nitrates. 

Dilute  acid  nitrate-chloride  waters  readily  dissolve  gold, 
since  they  are  equivalent  to  weak  aqua  regia.  The  chlorine 

36  Brokaw,  Journal  of  Geology,  vol.  xviii.,  No.  4,  pp.  322  to  323  (May- June, 
1910). 


MANGANESE    AND    GOLD-ENRICHMENT.  777 

set  free  by  the  reaction  oxidizing  HC1  is  more  active  than  a 
solution  of  chlorine  in  water,  and  converts  gold  into  gold 
chloride.  For  present  purposes  we  may  consider  that  the 
reaction  is  as  follows  : 

9  HC1  +  3  HIST03  +  2  Au-6  H20  +  3  NOC1  4-  2  AuCl3. 

Nitrosyl  chloride,  NOC1,  which  is  formed  in  this  reaction, 
does  not  react  directly  with  gold,  but  is  thought  by  some  to 
affect  the  reaction  favorably  as  a  catalytic  agent.  Whether  this 
is  true  or  not,  in  each  of  the  reactions  by  which  gold  is  dis- 
solved in  chloride  solution  its  solvent  power  may  be  ascribed  to 
its  "  nascent  "  state.  In  this  reaction,  as  in  those  which  follow, 
the  presence  of  an  element  with  more  than  one  valence  is  a 
necessary  condition,  and  its  valence  is  reduced  as  gold  passes 
into  solution. 

The  reaction  given  above,  3  HC1  -f  NH03,  may  be  written 
as  follows : 37 

O 


Cl  —  ;H  +  H  —  O  —  j  N  I  =  O  +  2  H  I  Cl  _>  2  H2O  +  C12  +  Cl  —  N  =  O. 

The  chlorine  reacts  with  gold,  forming  soluble  gold  chloride. 
2  Au  +  3  Cl2-»2  AuCl3. 

With  regard  to  the  latter  reaction,  Dr.  R.  C.  Wells,  of  the 
U.  S.  Geological  Survey,  supplied  the  following  note : 

"  The  reaction  (2  Au  -f  3  C12^2  AuCl3)  aims  to  express  the 
initial  and  final  stages,  but  says  nothing  of  the  mechanism  of 
the  reaction  or  the  necessity  for  the  chlorine  being  in  the  i  nas- 
cent' state.  In  accordance  with  present  theories,  a  *  nascent' 
chlorine  atom,  while  taking  a  negative  charge  to  form  chloride, 
allows  the  corresponding  positive  charge  to  ionize  the  gold, 

Au  +  O  =  Au  '. 

This  ionization  occurs  with  greater  difficulty  in  the  case  of 
gold  than  with  almost  any  other  metal.  The  aurous  ion  passes 
with  great  readiness  into  the  auric  ion,  Au""".  Moreover, 
both  ions  form  complexes  with  chlorides.  The  effectiveness  of 

37  Alexander  Smith,  General  Inorganic  Chemistry,  p.  449  (1907). 

49 


778  MANGANESE    AND    GOLD-ENRICHMENT. 

chlorine  in  dissolving  gold  in  accordance  with  this  theory  may 
be  ascribed  partly  to  the  production  of  the  complex  gold 
chloride  ions,  thus  removing  the  gold  ions  from  solution  with 
such  effectiveness  that  more  gold  ionizes,  and  thus  the  process 
continues  until  equilibrium  is  established." 

In  the  29  analyses  of  mine-waters  NO3  is  reported  from  but 
one  (Geyser  mine,  Silver  Cliff,  Colo.,  1.6  parts  per  million), 
and  this  is  a  water  of  questionable  genesis.  Possibly,  nitrates 
are  more  abundant  than  is  indicated  by  the  analyses  ;  and  if  so, 
they  must  increase  the  solvent  power  of  chloride  solutions; 
but  the  data  at  present  available  do  not  indicate  that  they  affect 
the  superficial  reactions  to  any  important  extent. 

2.  Manganese  Oxides. 

That  gold  is  dissolved  in  moderately  dilute  solutions  con- 
taining salt  and  manganese  oxides  is  shown  by  experiments 
11,  15  and  16.  The  reaction  with  manganese  used  to  prepare 
chlorine  commercially  is  illustrated  by  the  following  equation  : 
(The  reaction  is  not  so  simple  as  stated.  It  is  discussed  later.) 


Mnim02  +  2  ¥aCl  4-  3  H2S04  -*  2  H20  +  2  ]STaHS04  + 
MnuS04  +  2  01. 

At  the  beginning  of  the  reaction  the  manganese  has  a  valence 
of  four  ;  at  the  end  a  valence  of  two.  With  acid  the  reaction 
may  be  as  follows  : 

Mn02  +  HC1  -  2  H2O  +  MnCl2  +  C12. 

Besides  the  presence  of  a  chloride,  some  other  conditions 
are  essential  to  the  solution  of  gold.  There  appear  to  be  two. 
One  is  that  some  other  substance  must  also  be  present  which 
is  capable  of  being  reduced  so  as  to  liberate  chlorine  —  as,  for 
example,  a  ferric  salt  which  may  be  reduced  to  the  ferrous,  a 
cupric  to  the  cuprous,  the  higher  manganese  salts  to  the  lower, 
etc.  The  other  is  the  evolution  of  "  nascent  "  chlorine.  This 
is  particularly  illustrated  by  the  action  of  aqua  regia  or  the  pro- 
duction of  chlorine  by  hydrochloric  acid  and  pyrolusite.  In 
short,  any  of  a  number  of  methods  of  producing  free  chlorine 
would  be  effective  in  the  solution  of  gold.  Possibly  both  of  the 
conditions  just  mentioned  may  in  the  last  analysis  be  identical. 


MANGANESE    AND    GOLD-ENRICHMENT.  779 

The  essential  point  is  that  the  atomic  chlorine  in  a  state  of 
molecular  exchange  or  evolution  is  able  to  combine  with  the 
gold.  For  present  purposes  the  gold  may  be  considered  to 
dissolve  as  gold  chloride,  although  chemical  investigations  favor 
the  theory  that  a  complex  ion  containing  gold  is  formed.  The 
only  consideration  which  becomes  important  in  its  geological 
aspect  is  the  presence  of  the  compounds  which  not  only  admit 
of  easy  changes  of  valence,  but  which  act  upon  hydrochloric 
acid  with  the  production  of  free  chlorine. 
In  mine-waters  chlorine  is  supplied  as  Nad. 

166.  Fe2  (S04)3  +  H2S04  +  STaCl  +  Mn02  +  Au 

N/10  N/10        N/25        1  g.  -  0.15  g. 

0.00505  g.  loss  of  gold  by  solution  in  14  days  (cold). 

Under  the  same  conditions  without  manganese  there  was  no 
weighable  loss  (see  experiment  16a). 

As  used  herein  the  normal  solution  contains  1  g.-equiva- 
lent  of  the  solute  in  1  1.  of  solution.  A  solution  normal  with 
respect  to  chlorine  contains  1  g.  of  chlorine  times  35.45,  the 
molecular  weight  of  chlorine,  in  1  1.  of  solution. 

In  this  experiment  the  concentration  of  Cl  (1,418  parts  per 
million)  is  not  so  great  as  has  been  observed  in  a  few  mine- 
waters,  and  not  more  than  three  times  as  great  as  Don  deter- 
mined in  waters  from  a  number  of  Australasian  mines.38  The 
solutions,  however,  contain  more  chlorine  than  the  average  of 
29  analyses  of  mine-waters  (873  parts  of  Cl  per  million),  con- 
siderably more  than  that  of  28  analyses  (111  parts  of  Cl  per 
million),  and  more  than  most  mine-water  analyses  from  Ameri- 
can gold-mines. 

Manganese  is  abundant  in  many  gold-bearing  deposits ;  is 
sparingly  represented  in  some ;  and  from  a  very  large  number 
it  has  not  been  reported.  The  chief  primary  minerals  are  the 
carbonates  (rhodochrosite  and  manganiferous  calcite),  the  sili- 
cate (rhodonite),  amethystine  quartz,  and  the  less  abundant 
sulphite,  alabandite.  Some  rock-making  minerals  carry  small 
amounts  of  manganese.  It  readily  forms  sulphates,  chlorides,, 
etc.,  and  is  dissolved  by  acid  mine- waters.  In  the  29  analyses 
of  Table  I.  it  is  reported  from  6  mines.  In  some  waters  it  i& 

38  Trans.,  xxvii.,  654  (1897)  ;  p.  176,  this  volume. 


780  MANGANESE    AND    GOLD-ENRICHMENT. 

abundant.  The  average  of  the  29  shows  30.9  parts  per  million. 
Even  a  little  manganese  generally  stains  the  gossan  black  or 
chocolate-brown,  and  consequently  it  is  readily  recognized  in 
the  oxidized  ores.  Manganese  changes  its  valence  more  read- 
ily than  other  elements  common  in  gold-ores  and  it  is  in  many 
respects  unique  among  the  elements.  The  following  note  is 
abridged  from  Alexander  Smith,  General  Inorganic  Chemistry, 
p.  737: 

It  stands  on  the  left  side  of  the  eighth  column  of  the  periodic  table  ;  the 
right  side  of  that  column  is  occupied  by  the  halogens.  It  is  never  univalent  as 
the  halogens  are  ;  but  the  heptoxide,  Mn2O7,  and  corresponding  permanganic  acid, 
HMnO4,  are  in  many  ways  closely  related  to  the  heptoxide  of  chlorine  and  per- 
chloric acid,  HC1O3.  Permanganic  acid  is  a  very  active  acid.  Contrary  to  the 
habit  of  feebly  acidic  and  feebly  basic  oxides  such  as  those  of  zinc,  aluminum  and 
tin,  the  basic  oxides  of  manganese  are  not  at  all  acidic  and  the  acidic  oxides, 
with  the  possible  exception  of  Mn2O3,  are  not  also  basic.  There  are  thus  five 
rather  well  defined  sets  of  compounds  showing  five  different  valences  of  the 
element. 

These  include  maiiganosite  (MiiO),  pyrochroite  (MnO.H20), 
itnanganite  (Mn203.H2O),  hausmannite  (Mri304),  pyrolusite 
(Mn02),  psilomelane,  etc. 

3.  Lead  Oxides. 

Lead  oxide,  like  manganese  oxide,  is  said  to  facilitate  the 
solution  of  gold39  when  added  to  solutions  of  ferric  sulphate 
and  sodium  chloride.  Lead  is  both  bivalent  and  quadrivalent 
and  forms  corresponding  oxides  and  hydroxides.  These,  how- 
ever, are  generally  not  abundant  in  the  oxidized  zones  of  lead- 
bearing  ore-deposits,  probably  because  the  lead  carbonate  and 
the  sulphate  are  relatively  insoluble  in  water  and  usually  are 
formed  instead  of  the  oxides.  Lead  is  reported  in  but  one  of 
the  29  analyses  of  water  from  gold-  and  silver-mines,  tabu- 
lated above,  and  in  this  case  the  water  carried  but  1.35  parts 
per  million.  Many  gold-deposits  contain  but  little  lead  and 
some  contain  none.  It  is  believed  to  be  of  very  subordinate 
importance  in  connection  with  the  solution  of  gold. 

4.  Ferric  Compounds. 

As  shown  by  experiments,  gold  is  not  dissolved  by  hydro- 
chloric acid,  by  ferric  sulphate,  or  by  ferric  chloride.  It  is 

39  Victor  Lehner,  Journal  of  the  American  Chemical  Society,  vol.  xxvi.,  No.  5,  p. 
552  (May,  1904). 


MANGANESE    AND    GOLD-ENRICHMENT.  781 

dissolved  at  38°  C.  in  concentrated  solution  containing  both 
ferric  sulphate  and  hydrochloric  acid. 

5.    The  Efficiency  of  Ferric  Iron  and  Cupric  Copper  to  Supply 

Nascent  Chlorine,  Compared  with  that  of  Manganitic 

Manganese. 

As  shown  by  experiment  4,  a  concentrated  solution  of  CuCl2 
with  HC1  dissolves  appreciable  gold  at  200°,  and  Fig.  3  shows 
that  a  solution  containing  1  g.  of  copper  as  cupric  chloride  and 
25  cc.  of  HC1  (sp.  gr.,  1.178)  in  125  cc.  of  solution  at  38°  +  , 
dissolves  0.23  mg.  of  gold  in  163  hr.  Since  cupric  copper  and 
ferric  iron  are  present  in  many  mineral  waters,  the  nature  of 
these  reactions  should  be  considered  in  some  detail  in  order  to 
compare  their  efficiency  with  that  of  manganitic  manganese. 

Solutions  of  ferric  sulphate  with  sulphuric  acid  and  salt  dis- 
solve gold  at  high  temperatures.  Concentrated  solutions  of 
ferric  sulphate  and  hydrochloric  acid  dissolve  gold  at  from  38° 
to  43°  C.  In  the  cold,  the  reaction  may  go  on  in  concentrated 
solutions,  but  in  those  approximating  the  concentration  of  mine- 
waters  (and  one  of  them  considerably  more  concentrated  than 
most  mine-waters)  no  weighable  loss  of  gold  was  obtained. 
With  Mn02  under  the  same  conditions  there  was  a  very  appre- 
ciable loss  in  a  solution  containing  only  1.4  g.  of  01  in  a  liter. 
It  appears,  therefore,  that  the  action  of  ferric  iron  on  gold  in 
cold  dilute  mine-waters  with  H2S04  and  NaCl  is  probably  neg- 
ligible ;  for  the  experiments  with  ferric  iron  in  such  solutions, 
without  manganese,  extended  over  a  period  of  34  days  without 
weighable  loss  of  gold. 

Many  auriferous  deposits  contain  copper;  and  it  is  desirable 
to  compare  the  efficiency  of  cupric  with  ferric  salts  and  with 
manganitic  salts  in  similar  solutions.  Since  the  reactions  which 
give  nascent  chlorine  are  conditioned  upon  the  presence  of 
some  element  that  changes  its  valence  in  the  reactions,  and 
since  the  processes  underground  take  place  in  sulphate  solu- 
tions, it  did  not  appear  necessary,  after  ferric  salt  had  been 
shown  to  be  incompetent, to  conduct  experiments  with  copper; 
for,  as  is  well  known,  cuprous  salts,  though  they  may  be  pres- 
ent, have  never  been  detected  in  acid  sulphate  mine-waters, 
whereas  ferric  and  ferrous  sulphate  are  very  common  in  such 
waters. 


782  MANGANESE    AND    GOLD-ENRICHMENT. 

Fig.  2  shows  that  in  163  hr.  a  solution  carrying  2  g.  of  fer- 
ric iron  as  sulphate  and  50  cc.  of  HC1  (sp.  gr.  1.178)  diluted 
to  125  cc.,  with  250  mg.  of  gold  in  the  solution,  dissolves  6 
mg.  of  gold.  In  the  same  time,  as  shown  by  Fig.  3,  a  solu- 
tion containing  2  g.  of  copper  as  cupric  chloride  and  50  cc.  of 
HC1  diluted  to  125  cc.,  dissolves  but  2.84  mg.  of  gold,  the  same 
amount  of  gold  being  exposed.  These  results  indicate  that,  in 
concentrated  solutions  at  least,  cupric  salt  is  less  efficient  than 
ferric  sail.  Comparing  the  details  of  the  curves,  however,  it 
appears  that  the  reaction  with  ferric  salt  is  probably  near  a 
state  of  equilibrium ;  but  the  experiment  with  cupric  salt  sug- 
gests that,  given  a  longer  time,  considerably  more  gold  may 
be  dissolved.  It  cannot  be  concluded,  therefore,  that  the  sol- 
vent action  of  a  cupric  salt  would  be  less  than  that  of  a  ferric 
salt,  if  a  very  much  longer  time  were  allowed  to  lapse  before 
the  loss  of  gold  in  the  two  experiments  was  ascertained,  al- 
though the  experiments  suggest  that  this  is  probable. 

The  curves  of  Fig.  3  show  that  a  dilution  of  the  concen- 
trated solution  of  cupric  chloride  and  hydrochloric  acid  greatly 
decreases  the  amount  of  gold  dissolved  under  the  same  condi- 
tions. For  example,  the  solution  containing  2  g.  of  copper  as 
cupric  chloride  and  50  cc.  of  HC1  (sp.  gr.  1.178)  dissolved  2.84 
mg.  of  gold  in  163  hr.  Under  the  same  conditions  a  solution 
of  the  same  salts,  but  of  one-half  the  concentration,  dissolved 
only  0.23  mg.  of  gold  in  163  hr.  It  thus  appears  that  a  dilu- 
tion of  the  solution  to  one-half  decreases  its  solvent  action  (2.84 
divided  by  0.23)  to  about  one-twelfth.  If  the  solvent  were 
diluted  to  approximately  the  strength  of  mine- waters,  it  should 
be  expected  that  the  efficiency  of  cupric  salt  in  these  reactions 
would  be  almost  immeasurably  decreased.  Indeed,  the  lower 
curve,  A,  in  Fig.  3,  strongly  suggests  this,  and  indicates  also 
that  the  reaction  with  cupric  salt  at  this  concentration  is  near- 
ing  completion ;  for  about  half  as  much  gold  (0.11  mg.)  was 
dissolved  by  this  solution  in  66  hr.  as  was  dissolved  in  163  hr. 
(0.23  mg.).  It  is  improbable  that  the  character  of  this  curve 
would  greatly  change  if  the  reaction  continued  over  a  period 
twice  as  long,  and,  projecting  the  curve  to  14  days,  in  order 
that  the  solvent  action  of  cupric  salt  may  be  compared  with 
that  of  manganitic  salt,  it  appears  that  in  14  days  0.48  mg.  of 
gold  would  be  dissolved  in  waters  of  this  concentration,  assum- 


MANGANESE    AND    GOLD-ENRICHMENT.  783 

ing  that  the  gold  dissolved  is  in  proportion  to  the  time  exposed, 
thus  giving  the  advantage  to  cupric  salt.  The  experiments 
with  MnO2  were  carried  on  at  about  18°  C.,  and  those  with 
cupric  salt  at  from  38°  to  45°  C. 

The  gold  dissolved  (experiment  166)  in  the  dilute  solution 
with  manganese  was  more  than  10  times  as  much  as  that  dis- 
solved with  the  cupric  salt  (experiment  8).  The  hydrochloric 
acid  (sp.  gr.  1.178)  with  cupric  chloride  contained  34.99  per 
cent,  of  HC1  and  34  per  cent,  of  01.  Disregarding  the  01  in- 
troduced by  cupric  chloride,  the  solution  used  (25  cc.  diluted 
to  125  cc.)  contained  6.8  per  cent,  of  01.  The  solution  with  man- 
ganese dioxide  (one-twenty-fifth  normal)  contained  but  0.14 
per  cent,  of  01.  The  chlorine  (in  acid)  in  the  experiment  with 
copper  was  thus  49  times  as  much  as  the  total  chlorine  in  the 
experiment  with  manganese. 

The  amount  of  solution  used  in  experiment  8,  with  cupric 
salt,  was  2.5  times  as  much  as  the  amount  of  solution  used  in 
experiment  166,  with  manganese,  but  the  area  of  gold  exposed 
was  not  so  great.  In  experiment  8,  the  gold  was  rolled  to  a 
thickness  of  0.009  in.  and  cut  into  1-mm.  squares,  whereas  that 
used  in  experiment  166  was  rolled  to  a  thickness  of  0.002  in., 
exposing  areas  of  about  350  sq.  mm.  In  the  experiment  with 
copper  250  mg.  of  gold  was  introduced,  whereas  only  150  mg. 
was  introduced  in  experiment  166.  Correcting  for  areas  ex- 
posed, a  cupric  solution  50  times  as  concentrated  as  the  man- 
ganitic  solution  with  respect  to  chlorine  will  dissolve  about  one- 
fifth  as  much  gold  where  equal  areas  are  exposed.  In  other 
words,  the  action  with  manganese  appears  to  be  more  than  250 
times  as  efficient  as  with  cupric  salt,  even  if  it  is  assumed  that 
further  dilution  would  not  decrease  the  solvent  action  of  cupric 
salt  in  a  geometrical  ratio,  as  is  indicated  by  the  curves  in 
Fig.  3.  Comparing  the  end-points  of  curves  A  and  Z>,  Fig.  3, 
it  is  seen  that  a  dilution  of  the  solution  to  one-half  decreases 
the  solvent  action  with  cupric  salt  to  about  one-twelfth.  If 
further  dilution  to  one-twenty-fifth  normal  HOI  decreases  the 
solvent  action  with  cupric  salt  in  this  ratio,  then  the  efficiency 
of  the  solution  with  cupric  salt  would  be  about  T  00^  -^-^  as 
great  as  with  Mn02.  It  is  thus  shown  that  the  efficiency  of 
cupric  salt  compared  with  that  of  manganitic  salt  under  these 
conditions  is  somewhere  between  0.004  and  0.000001. 


784  MANGANESE    AND    GOLD-ENRICHMENT. 

6.    The  Amount  of  Chlorine  Necessary  for  the  Solution  of  Gold 
in  the  Presence  of  Manganese  Compounds. 

In  experiment  15  (a),  with  Mn02,  0.01640  g.  of  gold  was  dis- 
solved in  34  days  with  solution  one-tenth  normal  with  respect 
to  chlorine.  A  solution  with  but  40  per  cent,  as  much  Cl  (ex- 
periment 166)  dissolved  31  per  cent,  as  much  gold  in  14  days  as 
was  dissolved  in  the  more  concentrated  solution  in  34  days. 
These  results  show  that  in  15  (a)  conditions  are  probably  ap- 
proaching equilibrium  and  also  that  the  solvent  power  of  chlo- 
rine is  approximately  proportional  to  the  amount  present.  That 
a  weighable  quantity  of  gold  is  dissolved  when  only  a  trace  of 
chlorine  is  present  is  shown  by  experiment  13  (6),  in  which 
chlorine  was  introduced  without  intention. 

7.    The  Precipitation  of  Gold. 

Although  gold  is  readily  precipitated  by  organic  matter,  this 
reaction  is  not  of  great  importance  in  igneous  rocks.  There 
ferrous  sulphate  is  the  chief  precipitating-agent.  Ferrous  sul- 
phate is  formed  by  the  oxidation  of  pyrite,  but  in  the  presence 
of  oxygen  and  H2S04  it  becomes  ferric  sulphate,  which  does 
not  precipitate  gold.  Below  the  water-table,  where  pyrite  is 
more  abundant  and  free  oxygen  less  abundant,  ferrous  sulphate 
may  persist  in  the  mine- waters.  Ferrous  sulphate  is  so  effective 
as  a  precipitant  of  gold  that  it  is  used  for  that  purpose  in  metal- 
lurgical processes.  Experiment  19,  by  W.  J.  McCaughey,  shows 
that  a  minute  amount  of  ferrous  sulphate  greatly  decreases  the 
solubility  of  gold,  although  it  does  not  precipitate  it  completely. 
With  excess  of  ferrous  salt  practically  all  of  the  gold  is  pre- 
cipitated. Don40  has  shown  that  many  of  the  sulphate  mine- 
waters  of  New  Zealand  and  Australia  contain  abundant  ferrous 
iron ;  and  that  such  waters  will  first  precipitate  gold,  but  after 
oxidation  will  dissolve  it. 

Ferrous  sulphate  is  formed  in  the  upper  part  of  a  lode  above 
the  water-table ;  but,  owing  to  the  open  condition  of  that  part  of 
the  lode,  air  is  freely  admitted  and  ferric  sulphate  forms,  at  the 
expense  of  ferrous  sulphate  and  sulphuric  acid.  This  reaction 
takes  place  almost  instantaneously  if  Mn02  is  present  (experi- 
ment 20),  for  ferrous  sulphate  and  manganese  dioxide  are  under 

40  Trans.,  xxvii.,  599  (1897)  ;  p.  175,  this  volume. 


MANGANESE    AND    GOLD-ENRICHMENT.  785 

these  conditions  incompatible.  Manganese  dioxide  then  not 
only  releases  the  solvent  for  gold,  but  eliminates  the  salt  which 
precipitates  it.  It  is  doubtful  whether  appreciable  amounts  of 
gold  are  ever  carried  far  below  the  water-table  in  mines  where 
the  waters  carry  ferrous  sulphate,  but,  in  the  presence  of  MnO2, 
ferrous  sulphate  may  be  eliminated  below  the  water-table. 

When  manganese  dioxide  takes  part  in  the  reactions  by 
which,  under  the  conditions  named,  gold  is  dissolved,  trans- 
ported and  precipitated,  the  manganese  salt  is  itself  "changed. 
At  the  surface  pyrolusite,  Mn02,  forms,  for  there  an  excess  of 
oxygen  prevails ;  and  this  mineral  is  commonly  found  in  the 
gossan  of  manganiferous  lodes.  When  solutions  containing 
H2S04  and  Nad  react  on  Mn02  there  is  a  tendency  to  form 
MnS04,  and  some  manganese  goes  into  solution  as  sulphate, 
but  salts  of  manganese  with  higher  valence  may  also  form.  In 
this  connection  Dr.  R.  C.  Wells  has  offered  the  following  state- 
ment : 

"  In  an  acid  solution  containing  some  free  chlorine,  such  as  has  been  assumed 
to  be  effective  in  dissolving  gold,  there  would  also  be  a  tendency  towards  the 
formation  of  permanganic  acid.  On  the  other  hand,  the  production  of  the  chlorine 
necessarily  results  in  the  reduction  of  the  manganese  compound.  Now  a  mangan- 
ous  salt  is  known  to  react  with  permanganate  to  reproduce  MnO2,  and  this  illus- 
trates the  tendency  of  manganese  to  pass  with  ease  from  one  stage  of  oxidation  to 
another.  The  precipitation  of  manganese  will  occur  more  and  more  as  the  solu- 
tion loses  its  acidity.  It  is  well  established  that  manganous  salts  in  an  acid  envi- 
ronment are  very  stable  ;  but  in  neutral  or  alkaline  solutions  they  oxidize  more 
vigorously,  one  stage  of  their  oxidation  being  the  manganic  salt  which  hydrolyzes 
into  Mn2O3.H2O  (manganite),  with  even  greater  ease  than  ferric  salts  into  limonite. 

"In  these  ways  the  migration  of  an  acidic  solution  would  result  in  the  transpor- 
tation of  both  gold  and  manganese.  But  in  a  region  of  basic,  alkaline  and 
reducing  environment  the  manganese  would  be  re-precipitated,  the  free  acid  neu- 
tralized, the  chlorine  absorbed  by  the  bases  and  removed,  and  owing  to  the  accu- 
mulation of  the  ferrous  or  other  reducing  salts,  the  gold  would  be  re-precipitated. " 

V.  THE  TRANSFER  OF  GOLD  IN  COLD  SOLUTIONS. 

1.  Restatement  of  the  Processes  as  Related  to  Secondary 
Enrichment. 

Every  theory  of  secondary  enrichment  of  the  metals  consists 
essentially  of  three  parts  :  (a)  solution,  (6)  transportation,  (<?) 
precipitation. 

(a)  As  already  stated,  there  is  in  the  upper  part  of  the  ore- 
deposit,  where  oxidation  prevails,  abundance  of  ferric  sulphate 


786  MANGANESE    AND    GOLD  ENRICHMENT. 

and  sulphuric  acid.  A  little  salt,  NaCl,  or  other  chloride,  is 
generally  present.  The  H2S04,  reacting  upon  Nad,  gives 
HC1,  which,- in  the  presence  of  Mn02,  gives  nascent  chlorine, 
which  dissolves  gold.  Some  manganese  goes  into  solution  as 
sulphate,  but  certain  higher  manganates  are  probably  formed 
as  well. 

(6)  This  chemical  system  will  move  downward  under  hydro- 
static head.  If  it  comes  into  a  zone  containing  pyrite  it  will 
react  upon  the  pyrite,  and  in  the  oxidation  of  the  latter  more 
iron  sulphates  and  acid  will  be  formed.  If  manganese  dioxide 
is  present,  or  if  permanganic  acid  had  been  formed,  no  gold 
will  be  precipitated,  and  the  system,  with  gold  still  in  solution, 
will  move  to  greater  depths  before  ferrous  sulphate  can  be- 
come effective. 

(c)  But  as  the  system  moves  downward,  where  no  new 
sources  of  oxygen  are  available,  the  excess  of  acid  is  removed. 
There  are  many  ways  by  which  acidity  is  reduced  along  with 
these  reactions,  but  the  principal  one  is  probably  the  kaoliniza- 
tion  of  sericite  and  feldspar.  In  these  reactions  sodium,  potas- 
sium, calcium,  magnesium,  and  other  sulphates  are  formed 
from  acid  and  silicates;  the  silica  remaining  as  Si02  and 
kaolin  ;  the  alkalies  and  alkalic  earth  sulphates  going  into  solu- 
tion. As  the  acidity  decreases,  iron  and  manganese  compounds 
tend  to  hydrolyze  and  deposit  oxides.  At  this  stage  of  oxida- 
tion FeS04  becomes  increasingly  prominent,  and  not  only  com- 
pletely inhibits  further  solution  of  gold  but  becomes  increas- 
ingly effective  as  a  precipitant.  Thus  manganite  is  probably 
precipitated  with  gold.  The  fractures  in  the  primary  pyritic 
gold-ore  below  the  water-level  thus  become  coated  with  a 
manganiferous  gold-ore,  which  may  be  very  rich.  The  excess 
of  oxygen  which  the  system  has  carried  down  is  used  up  in  the 
manner  indicated,  and  in  this  process  limonite  is  formed,  con- 
sequently the  manganiferous  gold-ore  deposited  in  the  fissures 
and  cracks  contains  iron  and  kaolin  as  well  as  manganese 
oxides. 

2.  Association  of  Gold  with  Manganese  Oxides. 

Oxidized  manganiferous  ore  frequently  carries  silver41  with- 
out gold.  In  the  oxidized  zone  such  ore  should  be  common; 

41  Mining  and  Scientific  Press,  vol.  xciv.,  No.  25,  p.  796  (June  22,  1907). 


MANGANESE    AND    GOLD-ENRICHMENT.  787 

but  in  the  sulphide  zone  different  relations,  according  to  the 
requirement  of  the  theory,  should  generally  be  shown.  In 
this  zone  the  manganese  acts  not  so  much  as  a  solvent  for  gold, 
but  rather  as  an  agent  which  delays  precipitation  by  converting 
the  ferrous  sulphate,  which  precipitates  gold,  to  ferric  sulphate. 
The  gold  has  presumably  been  dissolved  higher  up,  but  it  trav- 
eled downward  in  solution  in  cracks  in  the  primary  sulphide 
ore.  It  would  be  expected  that  the  deeper-seated  manganif- 
erous  ore,  unlike  the  lean  ore  in  the  oxidized  zone,  would  be 
rich  in  gold.  S.  F.  Emmons  informs  me  that  there  is  a  com- 
mon feeling  among  the  miners  in  Colorado  that  manganese  is 
a  very  good  sign  of  rich  ore.  The  same  feeling  exists  in  the 
minds  of  many  prospectors  elsewhere.  F.  L.  Ransome  says  ^ 
that  in  the  Camp  Bird  and  Tomboy  mines  black  oxide  of  man- 
ganese occurs  in  the  deeper  workings  (year  1901),  and  usually 
indicates  good  ore.  In  these  cases,  according  to  Rausome, 
"  The  oxide  appears  to  be  associated  with  post-mineral  fractur- 
ing .  .  .  and  to  have  been  deposited  later  than  the  bulk  of  the 
ore."  In  general,  the  gold-deposits  near  Telluride  and  Ouray 
show  very  little  secondary  enrichment  and  the  primary  ore  is 
rich  enough  to  pay  handsomely,  but  the  small  rich  manganese 
streaks  may  be  rationally  explained  by  the  processes  indicated. 
In  the  deposition  of  chalcocite  ferrous  sulphate  is  formed,  and 
this  would  readily  precipitate  the  gold  if  any  were  held  in  the 
solution.  .  The  relation  of  chalcocitization  and  deep-seated  pre- 
cipitation of  gold  is  discussed  on  p.  798. 

In  the  oxidized  zone  small  bunches  of  very  rich  mangan- 
iferous  gold-ore  are  often  found.  I  have  seen  such  ore  above 
the  sulphide  zone  in  certain  camps  in  Nevada.  Such  bunches 
of  rich  ore  were  probably  formed  when  they  were  surrounded 
by  sulphides,  but  were  overtaken  by  the  oxidized  zone,  which 
moves  progressively  downward,  and  the  gold  in  the  rich  ore 
has  not  yet  been  dissolved.  Such  ores  should  in  general  be 
more  abundant  and  richer  in  the  lower  part  of  the  oxidized 
zone  than  near  the  apex,  where  they  have  been  exposed  for 
longer  periods  to  the  solutions  dissolving  gold.  They  may 
be  compared  with  the  rich  partly-oxidized  chalcocite  which 
appears  near  the  surface  in  certain  copper-mines.  Such  ore 

42  A  Keport  on  the  Economic  Geology  of  the  Silverton  Quadrangle,  Colorado, 
Bulletin  No.  182,  U.  S.  Geological  Survey,  p.  101  (1901). 


788  MANGANESE    AND    GOLD-ENRICHMENT. 

remains  above  the  water-level  because  the  table  has  been  de- 
pressed more  rapidly  than  the  copper  sulphide  has  been  dis- 
solved. The  mutual  relation  of  these  processes  is  discussed  by 
W.  Lindgren  in  his  monograph  on  the  copper-deposits  of  the 
Clifton-Morenci  district,  Arizona.43 

3.  The  Oscillating,  Descending,  Undulatory  Water-Table. 
The  terms  "  water-table  "  and  "  level  of  ground-water  "  are 
generally  used  to  describe  the  upper  limit  of  the  zone  in  which 
the  openings  in  rocks  are  filled  with  water.  This  upper  limit 
of  the  zone  of  saturation  is  not  a  plane,  but  a  warped  surface. 
It  follows  in  general  the  topography  of  the  country,  but  is  less 
accentuated.  It  is  not  so  deep  below  a  valley  as  below  a  hill, 
but  it  rises  with  the  country  towards  the  hill-top  and  in  general 
is  higher  there  than  in  the  valley.  Nor  is  it  stationary.  In 
dry  years  it  is  deeper  than  in  wet  years,  and  in  dry  seasons  it 
is  deeper  than  in  wet  seasons.  The  difference  of  elevation  be- 
tween the  top  of  this  zone  in  a  wet  year  and  in  a  dry  year  is 
normally  greater  under  the  hill-top  than  on  the  slopes  and  in 
the  valleys,  "in  mines  where  the  ground  is  open  the  level  of 
ground-water  probably  changes  with  every  considerable  rain. 
Consequently,  there  is  a  zone  above  ground-water  in  dry  periods 
but  below  it  in  wet  periods,  and  in  hilly  countries  this  may  be 
of  considerable  vertical  extent.  Thus  the  water-table  oscillates, 
though  in  general  moving  downward  with  degradation  of  the 
land-surface.  It  is  in  this  zone  of  oscillation  of  the  water-table 
that  chemical  activity  is  most  varied.  Without  any  change  in 
the  character  of  the  drainage  or  of  the  more-constant  condi- 
tions controlling  the  water-circulation,  the  chemical  composi- 
tion of  the  solutions  affecting  this  zone  may  change  from  season 
to  season.  They  may  at  one  time  be  ferric  sulphate  or  oxidiz- 
ing waters  and  at  another  time  ferrous  sulphate  or  reducing 
waters,  since,  after  a  wet  season,  the  ferrous  sulphate  waters 
from  below  would  tend  to  rise,  after  dilution  with  fresh  water 
added  by  the  rains.  Consequently,  the  minerals  of  this  zone 
may  include,  besides  thet  residual  primary  and  secondary  sul- 
phides, the  oxides,  native  metals,  chlorides,  sulphides,  carbo- 
nates, etc.  Between  the  top  of  this  zone  and  the  surface  or 
the  apex  of  the  deposit  chemical  activity  is  probably  slow,  be- 

4S  Professional  Paper  No.  43,  U.  S.  Geological  Survey,  p.  232  (1905). 


MANGANESE    AND    GOLD-ENRICHMENT.  789 

cause  there  is  a  scarcity  of  sulphides  and  other  easily-altered 
minerals  to  supply  the  salts  upon  which  the  chemical  activity 
of  ground-water  in  a  large  measure  depends.  As  the  country 
is  eroded,  this  zone  also  descends ;  and  if  .a  mineral  or  metal 
persists  long  enough,  the  upper  limit  of  the  zone  of  active 
change  passes  below  it.  The  mineral  is  thus  "  marooned," 
and,  not  being  exposed  to  mineral-laden  waters,  it  may  ulti- 
mately be  exposed  at  the  outcrop  of  the  deposit. 

4.    The  Sever o.l  Successive  Zones  in  Depth. 

As  is  clearly  set  forth  by  S.  F.  Emmons,  W.  H.  Weed,  and 
others,  many  metalliferous  lodes,  when  followed  from  the  sur- 
face down  the  dip,  show  characteristic  changes.  Below  the 
outcrop,  the  upper  part  of  the  oxidized  portion  of  the  lode 
may  be  poor.  Below  this  there  may  be  rich  oxidized  ores ; 
still  farther  down,  rich  sulphide  ores;  and  below  the  rich 
sulphides,  ore  of  relatively  low  grade.  Such  ore  is  commonly 
assumed  to  be  the  primary  ore,  from  which  the  various  kinds 
of  ore  above  have  been  derived.  The  several  types  of  ore  have 
a  rude  zonal  arrangement,  the  so-called  "zones"  being, like  the 
water-table,  highly  undulatory.  They  are  related  broadly  to  the 
present  surface  and  to  the  hydrostatic  level,  but  are  often  much 
more  irregular  than  either;  for  they  depend  in  large  measure  on 
the  local  fracturing  in  the  lode  which  controls  the  circulation  of 
underground  waters.  Any  zone  may  be  thick  at  one  place  and 
thin,  or  even  absent,  at  another.  If  these  zones  are  platted  on 
a  longitudinal  vertical  projection,  it  is  seen  that  the  primary 
sulphide  ore  may  project  upward  far  into  the  zone  of  secondary 
sulphides,  or  into  the  zone  of  enriched  oxides,  or  into  the  zone 
of  leached  oxides,  or  may  even  be  exposed  at  the  surface.  The 
zone  of  secondary  sulphide  enrichment  (which  is  not  every- 
where present)  may  project  upward  far  into  the  zone  of  rich 
oxidized  ore,  or  into  the  zone  of  leached  oxides,  or  may  outcrop 
at  the  surface.  The  zone  of  sulphide  enrichment  nearly  always 
contains  considerable  primary  ore,  and  very  often  the  secondary 
ore  is  merely  the  primary  ore  containing  in  its  fractures  small 
seams  of  rich  'minerals.  The  zone  of  enriched  oxides  is  gen- 
erally found  above  the  water-table  when  the  latter  is  at  the 
lowest.  The  zone  often  extends  to  the  outcrop.  Indeed,  it  is 
at  such  places  that  most  mines  are  discovered,  for  in  districts 


790  MANGANESE    AND    GOLD-ENRICHMENT. 

not  known  to  contain  metalliferous  deposits  a  lean  or  barren 
outcrop  is  generally  not  extensively  explored  by  prospectors. 
In  regions  of  rapid  erosion,  and  especially  of  rugged  topogra- 
phy, the  conditions  for  the  exposure  of  rich  oxides,  or  even 
rich  sulphides  or  primary  ore,  are  more  favorable.  In  places 
along  the  outcrop  of  a  deposit  where  erosion  is  rapid  the  richer 
oxidized  or  sulphide  ores  may  be  exposed,  whereas  in  other 
places,  protected  from  erosion,  and  therefore  exposed  longer 
to  solution,  the  same  outcrop  is  frequently  leached.  It  is  evi- 
dent that  the  amount  of  metal  remaining  in  the  upper  part  of 
the  oxidized  zone  and  at  the  outcrop  depends  upon  the  ratio 
between  the  rate  at  which  the  metal  is  dissolved,  and  the  rate 
at  which  the  valueless  constituents  are  dissolved  and  removed. 
Under  certain  conditions  gold  is  removed  very  slowly,  and  the 
removal  of  valueless  constituents  may  effect  a  concentration  at 
the  very  apex  of  the  lode ;  while  under  other  conditions,  favor- 
able to  the  solution  of  gold,  it  is  removed  more  rapidly  than 
the  valueless  constituents  (such  as  silica  and  iron),  and,  in 
consequence,  the  apex  and  the  upper  portion  of  the  zone  below 
it  are  leached.  In  a  country  not  subject  to  erosion  it  would  be 
supposed  that  the  outcrops  of  manganiferous  lodes  would  be 
everywhere  leached;  but  rapid  erosion  may  remove  the  upper 
part  of  the  lode  before  it  is  completely  leached,  and,  under  fa- 
vorable conditions,  placers  accumulate  from  the  debris  of  the 
apex. 

It  thus  appears  that  all  of  these  zones  except  that  of  the  pri- 
mary ore  are,  broadly  considered,  continually  descending;  so 
that  ore  taken  from  the  outcrop  may  represent  what  was  once 
primary  ore ;  afterwards,  enriched  sulphide  ore ;  still  later, 
oxidized  enriched  sulphide  ore  ;  later  still,  leached  oxidized 
enriched  sulphide  ore;  and  finally  become  the  surface-ore. 
Through  more  rapid  erosion  at  some  particular  part  of  the 
lode,  any  one  of  these  zones  may  be  exposed ;  and  hence  an 
outcrop-ore  of  any  character  is  possible.  Consequently,  longi- 
tudinal assay-plans,  showing  the  changes  of  value  in  depth, 
though  highly  suggestive,  and  especially  so  when  gold  and 
silver  are  shown  separately,  are  supplemented  by  studies  of 
the  paragenesis  and  by  physiographic  studies,  in  order  that 
the  approximate  rate  of  erosion  of  the  lode  at  various  places 
may  be  known.  In  the  absence  of  such  knowledge,  it  is  gener- 


MANGANESE    AND    GOLD-ENRICHMENT.  791 

ally  impossible  to  tell  the  genesis  of  a  particular  sample  of  ore 
from  a  mine,  although  this  may  sometimes  be  done.  When  all 
the  data  are  assembled,  however,  greater  confidence  may  be 
placed  in  the  conclusion,  since  all  the  factors  in  the  problem 
are  intimately  related. 

5.   Criteria  for  the  Recognition  of  Secondary  Enrichment. 

I  shall  not  attempt  to  review  all  the  criteria  for  the  recog- 
nition of  secondary  enrichment.  They  involve  practically  all 
available  data  relating  to  the  geology  and  physiography  of  the 
region,  as  well  as  the  observed  characteristics  of  its  ore-deposits. 
But  each  group  of  deposits  may  be  studied  with  certain  gen- 
eral criteria  in  view.  Among  these  are :  (1)  the  vertical  dis- 
tribution of  the  richer  portions  of  the  lode  with  respect  to  the 
present  surface  and  to  the  level  of  ground-water;  (2)  the  miner- 
alogy of  the  richer  and  poorer  portions  of  the  deposits,  and  the 
character  and  vertical  distribution  of  the  component  minerals ; 
(3)  the  paragenesis,  or  the  structural  relations  shown  by  the 
earlier  ore  and  that  which  has  been  introduced  subsequently. 

In  applying  these  principles,  it  should  be  remembered  that 
circulation  is  generally  controlled  by  post-mineral  fracturing ; 
that  the  changes  depend  upon  climate  and  rapidity  of  erosion, 
and  are  affected  by  regional  changes  of  climate,  etc.  Although 
the  mineralogy  of  the  ore  is  a  useful  aid,  there  are  many  min- 
erals which  are  precipitated  from  cold  solutions  and  also  from 
ascending  hot  solutions,  and  there  are  many  others,  the  genesis 
of  which  is  uncertain.  Of  th'e  minerals  formed  in  the  zone  of 
secondary  sulphide  enrichment,  few,  if  any,  are  known  posi- 
tively to  form  under  such  conditions  only.  There  are  some, 
however,  such  as  chalcocite  and  covellite,  which  nearly  every- 
where are  clearly  of  secondary  origin.  Ruby  silver  is  fre- 
quently, but  not  always,  secondary.  Other  minerals,  such  as 
chalcopyrite,  bornite,  argentine,  etc.,  have  no  definite  indicative 
value  unless  their  occurrence  suggests  that  they  are  later  than 
the  primary  ore.  Where  minerals,  known  to  have  formed 
elsewhere  by  processes  of  secondary  sulphide-enrichment,  are 
clearly  later  than  primary  ore,  there  is  a  strong  presumption 
that  they  were  deposited  by  cold  descending  waters.  If  it  can 
be  shown,  in  addition,  that  they  do  not  extend  to  the  bottom 
of  the  mine,  but  are  related  to  the  present  topography  of  the 


792  MANGANESE    AND    GOLD-ENRICHMENT. 

country,  then  this  presumption  may  be  regarded  with  consider- 
able confidence  as  confirmed. 

Where  paragenetic  evidence  suggests  secondary  enrichment, 
it  should  be  determined  whether  the  later  minerals  are  those 
commonly  formed  by  secondary  processes,  for,  as  shown  by 
Weed  and  others,  certain  minerals,  such  as  enargite  and  rho- 
dochrosite,  may  be  deposited  by  ascending  solutions  in  open- 
ings in  older  ore-bodies. 

With  respect  to  gold,  the  problem  is  difficult,  because  the 
native  metal  is  the  only  stable  gold-mineral  known  to  be  de- 
posited from  cold  dilute  solutions.  Consequently,  the  appli- 
cable criteria  are  limited;  and  the  vertical  distribution  of 
the  richer  ore,  though  suggestive,  is  not  in  itself  conclusive. 
Lindgren  and  Ransome,  in  their  studies  at  Cripple  Creek,  have 
shown  that  the  richer  ore-bodies  may  have  in  general  a  rela- 
tionship to  elevation,  where  there  is  little  or  no  evidence  of 
deep*seated  secondary  enrichment.  The  maximum  deposition 
by  ascending  hot  waters  may  be  greater  at  one  horizon  than 
at  another ;  and  the  rich  ore,  though  showing  broadly  certain 
variations  with  depth,  is  in  no  way  related  to  the  water-table. 
If,  however,  it  can  be  shown  that  rich  seams  of  ore  cross  the 
primary  ore  and  do  not  extend  downward  as  far  as  the  bottom 
of  the  primary  ore,  but  are  related  to  the  present  topography 
of  the  country,  and  if  it  is  known  that  the  associated  minerals 
which  fill  such  openings  are  those  which  may  be  deposited  by 
cold  waters,  the  evidence  of  their  secondary  origin  is  practi- 
cally conclusive.  As  already  shown,  seams  of  gold  with  .limo- 
nite  and  manganese  oxides  occur  in  such  relations.  Similar 
ore  frequently  contains  chalcocite  and  argentite  also.  Such 
occurrences  could  with  great  confidence  be  attributed  to  de- 
scending waters ;  and  since  it  is  known  that  they  are  commonly 
related  to  the  present  surface,  a  fair  presumption  is  that  they 
will  disappear  in  depth. 

In  the  practical  application  of  such  reasoning  to  gold-bearing 
deposits  it  will  sometimes  be  necessary  to  discriminate  between 
the  oxidized  manganiferous  gold-ore  which  has  "resulted  simply 
from  the  oxidation  of  a  primary  manganiferous  ore  like  one 
containing  rhodochrosite,  and  that  which  has  been  deposited  in 
fractures  in  the  sulphides  lower  down.  In  other  words,  it  is 
desirable  to  know  whether  rich  manganiferous  ore  in  the  upper 


MANGANESE    AND    GOLD-ENRICHMENT.  793 

part  of  a  mine  is  residual  from  a  primary  ore-body,  and  there- 
fore will  probably  prove  extensive,  or  represents  the  result  of 
concentration  under  more  deeply  seated  conditions  after  the 
manner  indicated  above.  This  discrimination  may  be  easy  in 
the  sulphide  zone,  where  the  fractures  with  rich  manganif- 
erous  ore  are  clearly  shown;  but  in  the  oxidized  zone  one 
must  rely  upon  the  shape  and  distribution  of  the  rich  bunches. 
If  they  are  related  to  cracks  in  the  mass  of  the  oxidized  ore, 
the  inference  is  warranted,  in  the  absence  of  other  evidence, 
that  they  are  residual  secondary  ore,  and,  being  genetically 
related  to  the  present  topographic  surface,  are  limited. 

The  tellurides  and  selenides  of  gold  are  seldom  or  never  de- 
posited from  cold  solutions;  hence  native  gold  is,  as  already 
stated,  the  only  gold-mineral  which  may  be  so  deposited.  But 
native  gold  is  deposited  by  primary  processes  also,  and  is  by 
far  the  most  abundant  gold-mineral  so  deposited.  Conse- 
quently, in  distinguishing  between  primary  gold  and  gold 
deposited  by  cold  solutions,  one  must  rely  upon  associated 
minerals.  When  secondary  chalcocite  or  certain  secondary 
silver-minerals  are  deposited,  the  attendant  reactions  precipitate 
gold.  Consequently,  the  richer  bunches  of  gold-ore  in  the  oxi- 
dized zone,  residual  from  secondary  ore  formed  under  the 
deeper-seated  conditions,  may  carry  also  considerably  more 
copper  and  silver  than  the  primary  ore.  But  copper,  and 
(unless  cerargyrite  is  formed)  silver  also,  are  more  readily 
leached  than  gold,  even  when  manganese  is  present.  Hence, 
the  evidence  of  this  character  may  have  been  destroyed. 

With  respect  to  other  minerals  associated  with  the  secondary 
gold-ore,  we  are  not  warranted,  in  the  present  state  of  our 
knowledge,  in  drawing  definite  conclusions.  From  the  nature 
of  the  reactions,  I  think  it  may  be  possible  to  show  that  man- 
ganite,  Mn203.H2O,  is,  under  conditions  of  incomplete  oxida- 
tion, more  often  associated  with  the  rich  gold  in  such  relations 
than  pyrolusite,  MnO2, ;  for,  as  already  observed,  the  lower 
oxide  is  more  likely  to  be  precipitated  than  the  higher,  when 
secondary  gold  is  deposited  under  deep-seated  conditions.  But 
under  oxidizing  influences  the  manganese  oxides  change  their 
character  so  readily  that  this  criterion,  if  it  has  any  value,  is 
probably  not  applicable  to  ores  in  the  upper  part  of  the  oxi- 
dized zone,  where  they  have  been  exposed  to  more  highly 

50 


794  MANGANESE    AND    GOLD-ENRICHMENT. 

oxygenated  waters  for  a  longer  time.  I  make  these  sugges- 
tions with  respect  to  the  character  of  the  manganese  oxides 
associated  with  the  rich  ore,  not  because  I  think  the  reactions 
which  precipitate  manganese  are  well  enough  understood  to 
give  a  positive  paragenetic  value  to  the  oxidized  manganese- 
minerals  themselves,  but  in  the  hope  that  others  will  ascertain 
and  report  the  character  of  the  manganese  oxide  associated 
with  gold  in  the  deeper  zone  and  in  the  residual  products  from 
that  zone.  The  streak  of  manganite  is  reddish  brown,  some- 
times nearly  black,  whereas  the  streak  of  pyrolusite  is  black  or 
bluish  black;  but  mixtures  and  pseudomorphs  of  the  minerals 
occur,  and  it  is  sometimes  almost  impossible  to  determine 
which  oxide  is  present. 

In  some  gold-veins  44  the  vein-cavities  near  and  even  a  con- 
siderable distance  below  the  oxidized  zone  are  filled  with  a 
brown  or  black  mud,  which  is  frequently  very  rich.  It  is  not 
safe  to  assume  that  the  gold  in  such  cavities  was  carried  to  its 
present  position  in  solution  and  precipitated  by  ferrous  sul- 
phate. The  fine  pulverulent  ore  which  collects  in  the  cracks 
is  rich  in  gold,  and  may  have  been  carried  downward  in  sus- 
pension. But  such  ore  will  generally  show  a  horizontal  strati- 
fication, which  will  seldom  be  shown  by  the  ore  deposited  from 
solution.  As  suggested  above,  manganite,  rather  than  pyrolu- 
site, is  probably  formed  when  gold  is  precipitated.  Such  mud, 
deposited  from  suspension,  may  contain  either  pyrolusite  or 
manganite  or  both;  but  it  is  rational  to  assume  that  the  mud 
formed  by  precipitation  in  the  deeper  zone  carries  very  little 
pyrolusite,  but  is  mainly  manganite. 

6.  Lateral  Migration  of  Manganese-Salts  from  the  Country  - 

Rock  to  the  Ore. 

Clarke's  analyses 45  show  that  igneous  rocks  carry  an  average 
of  0.1  per  cent,  of  manganese  oxide,  and  many  basic  rocks 
carry  from  0.2  to  0.9  per  cent.  Where  basic  dikes  have  cut 
an  ore-body,  they  doubtless  contribute  manganese  to  the  waters 
circulating  in  the  deposit.  The  ore  of  the  Haile  mine,  in  South 
Carolina,  is  cut  by  basic  rocks ;  and  the  ore-bodies  of  the 
Delamar  mine,  in  Nevada,  are  crossed  by  a  basic  dike.  Both 

41  Cripple   Creek,  Professional  Paper   No.  54,  U.  S.  Geological   Survey,  p.  199 
(1906). 
45  Bulletin  No.  330,  U.  S.  Geological  Survey  (1908). 


MANGANESE    AND    GOLD-ENRICHMENT.  795 

of  these  deposits  show  secondary  enrichment  of  gold ;  and  in 
both  the  better  ore  is  found  along  .the  dikes.  In  general,  how- 
ever, the  manganese  from  the  country-rock  cannot  safely  be 
assumed  to  have  migrated  extensively  into  the  ore-deposit,  for 
many  analyses  of  mine-waters  do  not  show  manganese ;  but 
where  manganiferous  rocks  are  intimately  fractured  and  filled 
with  seams  of  ore  it  would  be  supposed  that  the  reactions 
requiring  manganese  could  take  place. 

The  experiments  of  Dr.  Eugene  C.  Sullivan,  performed  at 
the  request  of  S.  F.  Emmons,  in  the  investigation  of  another 
problem,  have  an  important  bearing  here  and  Mr.  Emmons 
has  kindly  permitted  me  to  publish  them  in  advance  of  his  own 
paper.  In  so  doing,  I  have  abridged  somewhat  the  statements 
of  Dr.  Sullivan. 

A  sample  of  the  lower  white  porphyry  from  the  Thespian  mine,  Leadville,  Colo.r 
was  finely  ground  and  treated  with  carbonic  acid  and  with  sulphuric  acid  ;  the 
rock  contained  0.8  per  cent,  of  iron  and  0.033  per  cent,  of  manganese.  The  ratio 
is  about  24  to  1. 

Carbonic  Add. — 20  g.  of  the  porphyry  was  taken  in  40  cc.  of  water,  and  carbon 
dioxide  was  passed  into  the  mixture  for  some  hours.  In  20  cc.  of  the  solution  0.03 
mg.  of  manganese  were  found  and  no  iron.  The  results  are  probably  correct  for 
manganese  to  0.01  rag.  Less  than  0.01  mg.  of  iron  would  have  been  detected,  if 
present.  To  preclude  the  possibility  that  the  solution  of  manganese  was  facili- 
tated by  its  reduction  with  metallic  iron  introduced  from  the  hammer  in  pounding 
up  the  sample,  another  portion  was  similarly  treated  after  metallic  iron  and  mag- 
netite had  been  removed  by  a  hand-magnet.  In  this  case  0.1  mg.  of  manganese 
and  0.02  mg.  of  iron  were  found  in  20  cc.  of  solution. 

Sulphuric  Acid. — 20  g.  of  the  powdered  porphyry  stood  over  night  in  contact 
with  40  cc.  of  one-tenth  normal  sulphuric  acid  (0.196  g.  of  H2SO4  in  40  cc. ).  This 
has  roughly  the  same  molecular  concentration  as  a  saturated  solution  of  carbon 
dioxide.  The  filtrate,  20  cc.,  contained  1.05  mg.  of  iron,  all  in  the  ferrous  condi- 
tion, and  1  mg.  of  manganese.  The  experiment  was  repeated  under  the  same  con- 
ditions, e  x  cept  that  contact  between  the  rock-powder  and  the  acid  was  of  but  a 
few  minutes'  duration  ;  1.20  mg.  of  iron,  practically  all  ferrous,  and  0.90  mg.  of 
manganese  were  found  in  20  cc.  of  solution.  One-tenth  of  a  milligram  is  about 
the  limit  of  accuracy  in  these  cases. 

Potassium  Sulphate.  —Neither  iron  nor  manganese  could  be  detected  in  the  solu- 
tion after  treatment  of  the  rock-powder  with  potassium  sulphate. 

Manganese  is  therefore  more  readily  extracted  from  the  rock  than  iron  under 
surface-conditions  ;  for,  although  it  is  present  in  the  ratio  of  only  1  :  24  as  com- 
pared with  iron,  yet  carbonic  acid  takes  out  more  than  three  times  as  much  man- 
ganese as  iron,  and  sulphuric  acid  gives  a  ratio  of  about  1  :  I.46 

As  to  the  precipitation  of  the  two  metals  from  a  mixture  of  their  salts  in  solu- 

46  Penrose,  The  Chemical  Relation  of  Iron  and  Manganese  in  Sedimentary 
Rocks,  Journal  of  Geology,  vol.  i.,  pp.  356  to  370  (May-June,  1893).  Vogt,  Bog 
Manganese-Ores,  Zeitsehri/t  filr  praktische  Geologic,  vol.  xiv.,  p.  217  (July,  1906). 


796  MANGANESE    AND    GOLD-ENRICHMENT. 

lion,  the  following  experiment  shows  that  ferrous  compounds  are  more  readily 
oxidized  and  precipitated  than  manganous  compounds.  Ferrous  sulphate  solution 
and  manganous  sulphate  solution  weVe  mixed  in  equi-molecular  quantities  (50  cc. 
containing  2  mg.-molecules  of  each  i.  e.,  0. 112  g.  of  iron  and  0.110  g.  of  man- 
ganese), with  sufficient  powdered  calcite  (Iceland  spar)  to  react  with  one  of  the 
metals  (0.200  g.-molecule  of  calcite).  During  four  weeks  the  mixture,  in  a  roomy 
flask,  was  occasionally  shaken,  the  stopper  at  the  same  time  being  removed  for  a 
moment  to  allow  free  access  of  air.  At  the  end  of  that  time  all  but  1.5  mg.  of  the 
iron  had  been  precipitated,  while  the  manganese  was  in  solution  in  practically  the 
same  quantity  as  originally.  Calcite,  however,  when  in  contact  with  manganous 
salts  alone,  in  the  presence  of  air,  will  precipitate  the  manganese  as  a  higher  oxide 
or  hydroxide,  especially  at  elevated  temperature. 

It  thus  appears  that  some  manganese  is  probably  contributed 
to  the  ore-deposits  from  the  country-rock.  I  believe,  however, 
that  said  additions  are  small,  except  where  space-relations  of 
ore  and  country-rock  are  peculiarly  favorable.  In  the  upper 
parts  of  a  vein  the  circulation  is  in  general  downward,  and  is 
controlled  very  closely  by  fractures,  which  are  more  abundant 
in  the  upper  zone, 'where  the  rocks  are  in  general  more  exten- 
sively shattered.  Gouge-seams  on  the  walls  would  also  limit 
the  circulation,  and  tend  to  keep  the  vein  free  from  waters  of 
the  country-rock.  Where  calcite  or  other  carbonates  are  present 
to  precipitate  the  small  amount  of  manganese  in  the  solutions, 
one  would  suppose  that  the  opportunities  for  slight  additions 
would  be  increased.  Manganese  carbonate  is  less  soluble  than 
calcite,  and  the  latter  could,  under  favorable  conditions,  be  re- 
placed by  manganese  compounds.  One  part  of  calcium  carbo- 
nate is  soluble  in  1,428  parts  of  water  saturated  with  carbon 
dioxide,  while  one  part  of  manganese  carbonate  is  soluble  in 
2,000  parts  of  water  so  saturated.47 

In  my  own  experience  I  have  found  only  trivial  stains  of 
manganese  in  those  lodes  where  it  was  not  present  in  the 
gangue  of  the  primary  ore ;  and,  in  view  of  its  wide  distribu- 
tion in  igneous  rocks,  I  believe  that  the  lateral  migration  of 
manganese  into  the  ore  under  the  conditions  which  generally 
prevail  is  very  subordinate.  Though  the  amount  so  contrib- 
uted may  facilitate  the  solution  of  gold,  it  is  probably  inade- 
quate to  form  sufficient  higher  manganates  or  similar  salts  to 
suppress  effectively  the  action  of  ferrous  sulphate.  Under 
such  conditions  the  gold  could  not  travel  to  the  reducing-zone 
below  the  water-level,  but  would  be  precipitated  practically  at 
the  place  where  it  had  been  dissolved. 

47  Lassaigne,  in  Comey's  Dictionary  of  Solubilities  (1896). 


MANGANESE    AND    GOLD-ENRICHMENT.  797 

7.   Concentration  in  the  Oxidized  Zone. 

The  concentration  of  gold  in  the  oxidized  zone  near  the 
surface,  where  the  waters  remove  the  valueless  elements  more 
rapidly  than  gold,  is  fully  treated  hy  T.  A.  Bickard  in  his 
paper  on  the  Bonanzas  in  Gold-Veins.48  Undoubtedly  this  is 
an  important  process  in  lodes  which  do  not  contain  manganese, 
or  in  manganiferous  lodes  in  areas  where  the  waters  do  not 
contain  appreciable  chlorine.  In  the  oxidized  zone  it  is  some- 
times difficult  to  distinguish  the  ore  which  has  been  enriched 
by  this  process  from  ore  which  has  been  enriched  lower  down 
by  the  solution  and  precipitation  of  gold,  and  which,  as  a  result 
of  erosion,  is  now  nearer  the  surface.  It  cannot  be  denied 
that  tine  gold  migrates  downward  in  suspension;  but  in  all 
probability  this  process  does  not  operate  to  an  important  extent 
in  the  deeper  part  of  the  oxidized  zone.  If  the  enrichment  in 
gold  is  due  simply  to  the  removal  of  other  constituents,  it  is 
important  to  consider  the  volume-  and  mass-relations  before 
and  after  enrichment,  and  to  compare  them  with  the  present 
values.  In  some  cases,  it  can  be  shown  that  the  enriched  ore 
occupies  in  the  lode  about  the  same  space  as  was  occupied 
before  oxidation.  Jjet  it  be  supposed  that  a  pyritic  gold -ore 
has  been  altered  to  a  limonite  gold-ore,  and  that  gold  has 
neither  been  removed  nor  added.  Limonite  (sp.  gr.  from  3.6 
to  4),  if  it  is  pseudomorphic  after  pyrite  (sp.  gr.  from  4.95  to 
5.10)  and  if  not  more  cellular,  weighs  about  75  per  cent,  as 
much  as  the  pyrite.  In  those  specimens  which  I  have  broken, 
cellular  spaces  occupy  in  general  about  10  per  cent,  of  the 
volume  of  the  pseudomorph.  With  no  gold  added,  the  ore 
should  not  be  more  than  twice  as  rich  as  the  primary  ore,  even 
if  a  large  factor  is  introduced  to  allow  for  Si02  removed  and 
for  such  cellular  spaces. 

Rich  bunches  of  ore  are  much  more  common  in  the  oxidized 
zone  than  in  the  primary  sulphides  of  such  lodes.  They  are 
present  in  some  lodes  which  carry  little  or  no  manganese  in  the 
gangue,  and  which  below  the  water-level  show  no  deposition 
of  gold  by  descending  solutions.  Some  of  them  are  doubtless 
residual  pockets  of  rich  ore  which  were  richer  than  the  main 
ore-body  when  deposited  as  sulphides,  but  others  are  very 

*8  Trans.,  xxxi.,  198  to  220  (1901). 


798  MANGANESE    AND  •  GOLD-ENRICHMENT. 

probably  ores  to  which  gold  has  been  added  in  the  process  of 
oxidation  near  the  water-table  by  the  solution  and  precipitation 
of  gold  in  the  presence  of  the  small  amount  of  manganese  con- 
tributed by  the  country- rock.  In  view  of  the  relations  shown 
by  the  chemical  experiments  it  is  probable  that  very  little 
manganese  will  accomplish  the  solution  of  gold,  but,  as  already 
stated,  it  requires  considerably  more  manganese  to  form  ap- 
preciable amounts  of  the  higher  manganese-compounds  which 
delay  the  deposition  of  gold,  suppressing  its  precipitation  by 
ferrous  sulphate.  In  the  absence  of  larger  amounts  of  the 
higher  manganese-compounds,  the  gold  would  probably  be 
precipitated  almost  as  soon  as  the  solutions  encountered  the 
zone  where  any  considerable  amount  of  pyrite  was  exposed  in 
the  partly-oxidized  ore ;  for  Buehler  and  Gottschalk  have  lately 
shown  that  oxygenated  solutions  attack  pyrite  and  dissolve  it 
in  a  comparatively  short  time,  and  McCaughey  has  shown  that 
even  traces  of  the  ferrous  sulphate  thus  formed  precipitate  gold 
almost  immediately.  From  this  it  follows  that  deposits  show- 
ing only  traces  of  manganese,  presumably  supplied  from  the 
country-rock,  are  not  enriched  far  below  the  zone  of  oxidation. 

8.    Vertical  Relation  of  Deep-Seated  Enrichment  of  Gold  to 
Chalcodtization. 

In  several  of  the  great  copper-districts  of  the  West  (see 
group  3,  p.  806)  gold  is  a  by-product  of  considerable  value.  In 
•another  group  of  deposits,  mainly  of  Tertiary  age  (see  group  4, 
p.  807),  and  younger  than  the  copper-deposits,  silver  and  gold 
are  the  principal  metals,  and  copper,  when  present,  is  only 
a  by-product.  But  in  some  of  these  precious-metal  ores  chal- 
cocite  is,  nevertheless,  the  most  abundant  metallic  mineral, 
often  constituting  2  or  3  per  cent,  of  the  vein-matter.  Fre- 
quently it  forms  a  coating  over  pyrite  or  other  minerals. 
Some  of  this  ore,  appearing  in  general  not  far  below  the  water- 
table,  is  fractured,  spongy  quartz,  coated  with  pulverized  chal- 
cocite.  It  frequently  contains  good  values  in  silver,  and  more 
gold  than  the  oxidized  ore  or  the  deep-seated  sulphide  ore. 
Clearly,  the  conditions  which  favor  chalcocitization  are  favor- 
able also  to  the  precipitation  of  silver  and  gold. 

The  exact  chemical  reaction  which  yields  chalcocite  is  not 


MANGANESE    AND    GOLD-ENRICHMENT.  799 

known.  At  100°  C.,  according  to  Dr.  H.  K  Stokes,49  the  re- 
action with  pyrite  is  probably  about  as  follows : 

5  FeS2  +  14  CuS04  +  12  H20  =  7  Cu2S  +  5  FeS04  +  12  H2S04. 

In  the  cold,  the  reaction  may  differ  in  details,  but  without 
doubt  much  ferrous  and  acid  sulphate  is  set  free.  Attendant 
reactions  confirm  this  statement;  for,  if  calcite  is  present,  gyp- 
sum is  formed  by  the  reaction  of  H2S04  on  lime  carbonate ; 
and,  if  the  wall-rocks  are  sericitic,  kaolin  is  formed  by  the  acid 
reacting  upon  potassium-aluminum  silicate,  the  potash  going 
into  solution  as  sulphate.  The  abundant  ferrous  sulphate  must 
quickly  drive  the  gold  from  solution,  and  it  apparently  follows 
that  there  may  be  no  appreciable  enrichment  of  gold  below  the 
zone  where  chalcocitization  is -the  prevailing  process.  In  de- 
posits such  as  those  of  disseminated  chalcocite  in  porphyry, 
where  the  chalcocite' occurs  in  flat-lying  zones  related  to  the 
present  surface,  and  where  the  ore  from  which  chalcocite  was 
derived  carried  gold,  and  suitable  solvents  were  provided, 
there  should  be  a  comparatively  even  distribution  of  gold, 
which  should  increase  and  decrease  with  the  chalcocite  of  the 
secondary  ore.  A  different  ratio  of  values  should  be  found  in 
the  oxidized  low-grade  capping  above  the  chalcocite,  for  the 
solution  of  gold,  even  under  the  most  favorable  conditions, 
appears  to  lag  behind  the  solution  of  copper,  and  this  should 
be  more  marked  in  these  deposits,  since  in  all  available  analyses 
the  porphyries  are  low  in  manganese,  and  rhodochrosite  is  not 
noted  in  the  primary  ore.  I  am  informed  that  a  fairly-constant 
ratio  between  copper  and  gold  is  very  noticeable  in  the  dis- 
seminated deposits  at  Ely  and  at  Bingham.  That  whatever 
gold  is  present  in  the  rock  below  chalcocitized  pyrite  is  not  a 
result  of  deposition  from  cold  solution,  is  reasonably  certain 
under  the  conditions  named. 

9.    Vertical  Relations  of  Silver-Gold  and  Gold-Silver  Ore  in 
Deposits  Carrying  Both  Metals. 

This  paper  will  not  discuss  in  detail  the  processes  of  second- 
ary enrichment  of  silver-deposits — a  subject  already  treated  in 

49  Unpublished  MSS.  quoted  by  Lindgren  in  Professional  Paper  No.  43,  U.   S. 
Geological  Survey,  p.  183  (1905),  and  in  Weed's  translation  of  Beck's  text-book. 


800  MANGANESE    AND    GOLD-ENRICHMENT. 

our  Transactions  by  S.  F.  Emmons,  W.  H.  Weed,  and  C.  R. 
Van  Hise.  There  are,  however,  certain  deposits  mainly  asso- 
ciated with  Tertiary  rocks,  in  which  both  silver-  and  gold- 
values  are  important.  Examples  are  the  Comstock  lode,  Tono- 
pah,  Tuscarora,  etc.  Where  physical  conditions  are  favorable, 
deposits  of  this  type  should  show  in  "general  a  concentration  of 
gold  at  certain  horizons,  and  of  silver  at  other  horizons,  de- 
pending upon  the  composition  of  the  mine-waters  and  other 
factors.  The  determination,  in  such  mines,  of  the  principles 
controlling  the  mutual  relations,  especially  in  the  deeper  zones 
of  the  gold-silver  and  the  silver-gold  ore-bodies,  would  have 
great  practical  value.  So  far  as  I  know,  no  record  of  experi- 
ments with  solutions  containing  both  sulphates  and  chlorides 
and  a  mixture  of  gold  and  silver  is  available.  The  solubilities 
of  silver-salts  lately  determined  by  Kohlrausch  (quoted  by  Alex- 
ander Smith)  are  suggestive.  He  found  that  at  18°  C.  a  sat- 
urated aqueous  solution  of  AgS04  contains  5.5  g.  per  liter;  but 
at  this  temperature  water  holds  in  solution  only  0.0016  g.  of 
silver  chloride  per  liter.  That  silver  is  held  in  solution  by 
mine-waters  carrying  sulphates  and  chlorides  was  shown  by 
J.  A.  Reid.50  Such  waters  in  a  Comstock  mine  carried  about 
188  mg.  of  silver  and  4.15  mg.  of  gold  in  a  ton  of  solution. 

The  effect,  on  a  manganiferous  silver-ore,  of  a  solution  carry- 
ing chlorides  would  be  to  liberate  chlorine,  which  would  react 
with  silver  to  form  "  horn-silver."  This  would  be  fixed  in  the 
manganiferous  ore,  and  such  a  silver-ore  would  be  compara- 
tively stable.  The  oxidized  manganiferous  silver-ore  at  Lead- 
ville,  Colo.,51  and  at  Neihart,  Mont.,  in  which  silver  is  generally 
supposed  to  be  carried  largely  as  chloride,  may  have  originated 
in  this  manner.  On  the  other  hand,  rich  ores  could  hardly  be 
formed  where  the  solutions  carried  abundant  sulphuric  acid 
and  little  or  no  chlorine,  for  the  soluble  silver  sulphate  would 
be  formed,  and  the  manganiferous  ore  leached.  To  determine 
the  genesis  of  such  manganiferous  ore,  it  is  desirable  to  know 
the  silver-content  of  the  primary  rhodochrosite,  for,  as  indi- 
cated above,  two  interpretations  of  the  phenomenon  are  other- 
wise possible. 

50  Bulletin  of  the  Department  of  Geology,  University  of  California,  vol.  iv.,  No.  10, 
p.  193  (1904-06). 

51  S.  F.  Emmons,  Monograph  No.  XII.,  U.  S.  Geological  Survey,  p.  562  (1886). 


MANGANESE    AND    GOLD-ENRICHMENT.  801 

As  pointed  out  by  Penrose,52  silver  chlorides  are  formed 
extensively  in  arid  countries,  at  or  very  near  the  surface.  Fre- 
quently the  workable  ore  gives  out  a  few  feet  down.  At  many 
places  in  Nevada,  the  so-called  "  chloriders  "  stripped  the  sur- 
face over  considerable  areas;  but  where  the  unoxidized  ore 
was  encountered  the  mines  were  abandoned.  At  some  of  these 
places  the  chloride  ore  carried  little,  if  any,  more  gold  than  the 
unoxidized,  unprofitable  silver-gold  ore  below.  The  primary 
ore  of  many  of  these  deposits  carries  relatively  little  pyrite ; 
and  the  inspection  of  a  number  of  them  gives  the  impression 
that  the  siliceous  ores  are  more  favorable  than  the  more  highly 
pyritic  ores  to  the  formation  of  a  surface  chloride  zone.  Man- 
ganese oxides  are  not  necessary  for  the  formation  of  the  chloride 
zone.  In  many  of  them  manganese  is  absent.  If  it  is  present 
in  appreciable  amount,  if  the  physical  conditions  for  a  down- 
ward circulation  in  the  lode  are  favorable,  and  if  the  primary 
ore  carries  gold,  it  would  be  reasonable  to  expect  an  enrich- 
ment of  gold  below  the  zone  of  the  chloride-enrichment  of 
silver.  In  the  presence  of  strong  acid  sulphate  waters,  silver, 
like  gold,  is  dissolved  from  the  outcrop ;  and  in  some  mines, 
where  both  metals  are  present  in  important  quantities,  the 
outcrop  and  the  oxidized  zone  for  a  short  distance  below  are 
leached  of  both  silver  and  gold. 

The  migration  of  both  metals  with  selective  solution  and  pre- 
cipitation is  suggested  by  the  relation  of  silver-gold  and  gold- 
silver  ore-bodies  on  the  Comstock  lode.  The  Comstock  lode, 
which  has  produced  more  than  $200,000,000  silver  and  $150,- 
000,000  gold,  is  a  broad  fault-zone  in  late  Tertiary  rocks.  The 
ore-shoots  occur  here  and  there  in  this  zone,which  is  developed 
more  than  4,000  ft.  below  the  surface.53  Since  the  deposits 
were  formed  there  has  been  extensive  fracturing.  In  the  lode 
there  are  great  bodies  of  "  sugar  "  quartz  which  are  due,  ac- 
cording to  Becker,54  to  this  movement.  Over  considerable 
spaces  one  cannot  obtain  fragments  of  rock  as  large  as  one's  fist 


62  Journal  of  Geology,  vol.  ii.f  No.  3,  p.  314  (Apr. -May,  1894). 

53  Clarence  King,  Geological  Exploration  of  the  40th  Parallel,  vol.  iii.,  Mining  In- 
dustry (1870);  John  A.  Church,  The  Comstock' Lode  (1879);    G.  F.  Becker,  Mono- 
graph No.  777. ,  U.  S.  Geological  Survey  (1882);  J.  A.  Reid,  Bulletin  of  the  Depart- 
ment of  Geology,  University  of  California,  vol.  iv.,  No.  10,  pp.  177  to  199  (1904-06). 

54  Op.  tit,  p.  272. 


802  MANGANESE    AND    GOLD-ENRICHMENT. 

which  do  not  show  fissures.  There  were  clearly  two  periods 
of  movement,  one  before  the  deposition  of  the  primary  ore  and 
one  following  it.  The  latter  movement,  mainly  parallel  to  the 
lode,  gave  conditions  for  an  active  circulation  of  water  after  the 
primary  deposition.  According  to  Dr.  Becker,  "it  is  possible 
that  the  seams  of  rich  ore  in  the  great  bonanza  represent  a  de- 
position posterior  to  the  final  cessation  of  movement,"  and  "  it 
is  also  by  no  means  impossible  that  some  of  the  richer  ores  have 
been  redeposited,  forming  at  the  expense  of  surrounding  bodies 
of  lower  grade." 55  As  already  remarked,  analysis  of  the  vadose 
water  of  the  Comstock  shows  that  it  contains  both  gold  and 
silver.  It  is  noteworthy  that  this  water  contains  much  manga- 
nese, presumably  as  sulphate.  Some  associated  placers  were 
developed,  but  they  are  of  very  subordinate  value  compared 
with  that  of  the  lode.  Oxidation  extended  downward  as  far 
as  500  ft.  According  to  Clarence  King,56  "  a  zone  of  manga- 
nese oxide  occupies  the  entire  length  of  the  lode  from  the  out- 
crop 200  ft.  down."  The  upper  part  of  this  manganiferous 
zone  was  probably  not  of  high  grade  in  general,  especially  in 
the  uppermost  portions.  I  infer  that  the  outcrop  and  the  ore 
immediately  below  were  in  general  not  so  rich  as  the  ore  lower 
down.  The  longitudinal  projections57  show  that  many  of  the 
stopes  carried  from  below  stop  some  distance  below  the  surface. 
Von  Richthofen  (quoted  by  Becker)  says  that  "  the  propor- 
tion of  gold  to  silver  decreased  during  the  early  period  of 
working  the  lode,  but  is  now  (1865)  on  the  increase  again," 
Presumably,  silver  at  the  very  surface  was  leached  more 
rapidly  than  gold.  The  vadose  waters,  as  shown  by  Reid,58 
are  rich  in  ferric  sulphate ;  and  his  analyses,  as  well  as  others, 
show  the  presence  of  chlorides  in  appreciable  amounts.  The 
conditions  appear  to  have  been  favorable  for  the  solution  of 
both  silver  and  gold  in  the  upper  levels,  even  in  the  compara- 
tively short  geological  period  which  has  elapsed  since  the  pri- 
mary ores  were  deposited.  The  bonanza  ore  below  consisted 
largely  of  stephanite,  polybasite,  argenite,  and  other  dark,  rich 

55  Monograph  No.  IIL,  U.  S.  Geological  Survey,  p.  273  (1882). 

56  Geological  Exploration  of  the  4Qth'Parallel,  vol.  iii.,  Mining  Industry,  p.  75  (1870). 

57  Becker,  op.  cit. 

58  Bulletin  of  the  Department  of  Geology,  University  of  California,  vol.  iv.,  No.  10, 
pp.  177  to  199  (1904-06). 


MANGANESE    AND    GOLD-ENRICHMENT.  803 

silver-minerals,  and  in  places,  according  to  Dr.  Becker,  ap- 
peared to  fill  fractures  which  involved  the  primary  ore.  It  is 
well  known  that  this  rich  ore  was  more  abundant  in  the  upper 
than  in  the  lower  levels.  When  I  visited  the  district  in  1907 
I  was  informed  by  the  foreman  at  the  Consolidated  Virginia 
that  large  bodies  of  the  hydrothermally-altered  porphyry  on 
the  Sutro  level  and  below,  which  contained  considerable  pyrite, 
etc.,  carried  also  considerable  gold  and  silver,  although  below 
the  limit  of  profitable  mining.  Very  few  of  the  ore-bodies 
which  had  been  worked  at  those  levels  were  then  accessible. 
The  deposits  in  the  upper  levels  yielded,  according  to  Rich- 
thofen,  from  $70  to  $107  a  ton,  whereas  in  later  years  the 
average  value  of  the  ore  was  not  more  than  $37. 

It  thus  appears  that  the  evidence  of  the  Comstock  lode,  from 
the  surface  down,  is  favorable  to  the  hypothesis  that  extensive 
solution  and  deposition  of  gold  and  silver  has  taken  place, 
while  it  is  insufficient  to  show  to  what  extent  the  great  bonan- 
zas owed  their  values  to  such  processes.  In  ores  formed  so 
near  the  surface,  there  is  always  the  possibility  that  ascending 
hot  waters  deposited  the  maximum  portion  of  their  gold  and 
silver  at  the  horizon  where  they  encountered  cold  oxygenated 
solutions.  Sulphate  may  form,  in  such  mixtures,  and  ferrous 
sulphate  tends  to  drive  both  gold  and  silver  out  of  solution. 
The  proportion  of  gold  to  silver  was  presumably  higher  in  the 
upper  part  and  in  the  lower  part  of  the  lode  than  in  the  middle 
portion.  When  Richthofen  made  his  report,  he  estimated  that 
the  lode  had  produced,  to  the  close  of  1865,  $15,250,000  of 
gold  and  $32,750,000  of  silver  (gold  equals  47  per  cent,  of  the 
silver) ;  whereas  Becker  reports  the  amount  recovered  from  1865 
to  1881  as  $87,121,988  of  gold  and  $105,548,157  of  silver  (gold 
equals  83  per  cent,  of  the  silver).  If  much  of  the  change  is 
due  to  reworking  by  descending  waters,  the  greater  gold-values 
in  the  upper  portions  of  the  bonanzas  indicate  that  gold  was 
dissolved  less  readily  than  silver,  and  silver  precipitated  less 
readily  than  gold,  in  the  sulphate-rich  water  of  this  mine. 

The  relation  of  "  horn-silver  "  to  the  surface  is  different  from 
hat  shown  in  the  "  chloride  mines  "  mentioned  above.  Ac- 
cording to  Clarence  King,59  silver  chloride  is  accidental,  although 

59  Op.  cit.,  p.  82. 


804  MANGANESE    AND    GOLD-ENRICHMENT. 

rare  small  crystals  were  found  at  the  outcrop  in  the  Gold  Hill 
group.  It  occurred,  however,  at  the  900-ft.  level  of  the  Yellow 
Jacket,  where,  judging  from  the  descriptions,  it  was  present  in 
considerable  amount. 

Ferrous  sulphate  precipitates  both  silver  and  gold  in  acid 
solutions.  The  precipitation  of  gold  is,  however,  many  times 
more  rapid  and  more  effective  than  that  of  silver.  Where  sil- 
ver chloride  is  not  precipitated,  one  would  suppose  that  cold 
solutions  would  transfer  the  silver  to  greater  depths  than  gold. 
Since  silver  chlorides  are  not  abundant  (King),  this,  if  no  other, 
is  an  argument  for  the  hypothesis  that  the  lower-grade  gold- 
silver  ores  ($37  a  ton  or  less,  Becker  60),  which  were  worked  in 
the  levels  below  the  great  silver-gold  bonanzas,  were  in  the 
main  primary.  These  ore-bodies  were  not  accessible  to  me 
when  I  visited  the  Comstock  mines,  and  the  speculation  is  not 
based  on  paragenetic  evidence. 

The  relations  of  silver-gold  to  gold-silver  ores  in  the  Exposed 
Treasure  mine,  near  Mojave,  differ  from  those  at  the  Com- 
stock. In  the  surface-zone,  horn-silver  has  been  formed  in 
considerable  amount.  The  proportion  of  gold  to  silver  in  this 
zone  is  1 :  72  (weight).  In  the  lower  friable  siliceous  ores,  the 
proportion  of  gold  to  silver  is  1 :  12  ;  and  in  the  sulphide  ores 
below  the  water-table,  where  the  gold-content  had  increased 
150  per  cent,  above  the  average  in  the  friable  siliceous  ores, 
the  proportion  of  gold  to  silver  was  as  1  to  2.61  The  Exposed 
Treasure  ores  are,  like  those  of  the  Comstock,  manganiferous. 

It  thus  appears  that  there  are  two  types  of  enrichment  in 
deposits  of  manganiferous  gold-  and  silver-ores.  In  one  of 
them  silver  chloride  is  concentrated  in  the  manganiferous  oxi- 
dized ores  of  the  upper  levels,  and  gold  is  concentrated  below. 
In  the  other,  silver  chloride  is  subordinate,  while  both  gold  and 
silver  are  concentrated  below  the  oxidized  zone.  Possibly  the 
difference  could  be  explained  if  the  amount  of  chlorine  were 
determined  in  the  waters  of  deposits  of  both  types.  Silver 
.chloride  is  soluble  in  an  excess  of  alkaline  chlorides.  Those 
deposits  in  which  horn-silver  is  not  present  may  have  been 
leached  by  waters  unusually  rich  in  chlorides. 

60  Monograph  No.  III.,  U.  S.  Geological  Survey,  p.  18  et  seq.  (1882). 

61  Courtenay  DeKalb,  Trans.,  xxxviii.,  319  (1907). 


MANGANESE    AND    GOLD-ENRICHMENT.  805 

VI.  REVIEW  OF  MINING-DISTRICTS. 

The  purpose  of  this  inquiry  is  to  ascertain  whether  the  ore- 
deposits  of  the  United  States  give  evidence  that  gold  is  more 
readily  transferred  in  manganiferous  deposits  than  in  deposits 
which  do  not  contain  manganese,  a  hypothesis  suggested  by 
the  chemistry  of  the  processes  of  solution  and  precipitation. 

1.  If  gold  is  more  readily  dissolved  in  manganiferous  de- 
posits, it  would  be  supposed  that  placers  form  less  readily  from 
pyritic  manganiferous  lodes  than  from   lodes  containing  no 
manganese.     If,  in  areas  where  the  waters  carry  appreciable 
chlorine,  placers  have  formed  as  extensively  from  such  lodes 
as  from  lodes  free  from  manganese,  then  the  hypothesis  fails. 

2.  The  manganiferous  lodes,  in  areas  of  chloride  waters,  as 
in  the  undrained  areas  of  the  Great  Basin,  should  in  general 
show  less  gold  at  the  outcrop  and  in  the  upper  portion  of  the 
oxidized  zone  than  below.     In  silver-gold  deposits,  however, 
silver,  on  account  of  the  insolubility  of  the  chloride,  may  re- 
main, or  be  concentrated,  in  the  oxidized  manganiferous  zone. 
Bunches  of  rich  gold-ore  carrying  oxidized  manganese  in  the 
oxidized  zone  are  not  necessarily  fatal  to  the  theory;  for,  as 
already  stated,  these  are  probably  residual  from  the   zone  of 
secondary  enrichment.     An  extensive  enrichment  in  gold  of 
the   oxidized  manganiferous  ores  at  the    surface,   which  are 
shown  not  to  be   residual  from  the   zone   of  secondary  ores, 
would  indicate  that  the  selective  processes  lack  quantitative 
value,  if  the  waters  carry  chlorine,  and   if  the  primary  ores, 
from  which  the  manganiferous  oxidized  ores  are  derived,  carry 
appreciable  pyrite  to  supply  sulphate. 

3.  If  in  certain  lodes  gold  migrates  below  the  water-table,  it 
should  be  precipitated  quickly  by  ferrous  sulphate.     But  Mn02 
converts  ferrous  sulphate  to  ferric   sulphate,  which  does   not 
precipitate  gold.     Hence,  MnO2  favors  the  solution  of  gold,  and 
converting  the  ferrous  salt  to  ferric  sulphate  removes  the  pre- 
cipitant.    Consequently,  if  auriferous  lodes  show  enrichment 
in  the  deeper  zone  but  related  to  the  present  surface  of  the 
country,  manganiferous  lodes  should,  the  other  favorable  con- 
ditions provided,  show  greater  differences  in  values  with  respect 
to  gold  than  lodes  free  from  manganese. 


806  MANGANESE    AND    GOLD-ENRICHMENT. 

Gold-Provinces  of  the  United  States. 

As  Lindgren 62  pointed  out  in  1902,  the  principal  gold-de- 
posits of  the  United  States  may  be  divided  into  four  groups. 
The  deposits  of  each  group  belong  mainly  to  one  metallogenetic 
epoch,  and  certain  relationships  are  clearly  shown.  This  classi- 
fication, which  has  thrown  much  light  on  the  genesis  of  the 
deposits,  is  useful  as  an  instrument  for  study  and  for  compari- 
son of  the  deposits  with  respect  to  the  problem  of  the  migra- 
tion of  gold  in  them. 

1.  The  Appalachian  gold-deposits,  and  those  of  the  Home- 
stake  type  in  South  Dakota,  are  the  most  important  representa- 
tives   of  the    oldest   group.     These    deposits   generally  yield 
placers,  are  usually  low  grade  below  the  water-level  and  are 
singularly  free   from    bonanzas.      They   are,  in    general,  not 
greatly  leached  near  the  surface,  and  may  have  been  enriched 
by  the  removal  of  other  material  more  rapidly  than  gold.     At 
only  one   of  them,  the  Haile  mine,  in  South.  Carolina,  it  is 
thought  probable  that  gold  has  been  carried  below  the  water- 
level.    The  Homestake  mines  show  little  evidence  of  secondary 
enrichment  by  transfer  of  gold,  as  will  appear  in  the  review  that 
follows.     Judging  from   descriptions,  practically  all  of  these 
deposits  are  free  from  manganese. 

2.  The  California  gold-veins  and  related  deposits  in  Nevada 
(Silver  Peak)   and   in  Alaska  (Treadwell,  etc.)    are   younger 
than  the  Appalachian  deposits,  and  were  probably  formed  in 
the  main  in   early  Cretaceous  times.     These  deposits,   where 
physiographic  conditions  are  favorable,  have  generally  yielded 
rich  placers.     At  many  places,  moreover,  the  ore  is  worked  at 
the  very  surface,  and,  as  will  appear  in  the  subsequent  review, 
there  is  very  little  evidence  of  the  migration   of  gold  to  the 
deeper  zones.     In  the  places  where   detailed  work  has  been 
done,  rhodochrosite  is  never  a  gangue-mineral,  although  man- 
ganese oxide  does  occur  in  traces  in   the   country-rock,  and 
rhodochrosite  is  found  in  a  few  places  in  veinlets  in  the  min- 
ing-districts but  not  associated  with  the  gold-veins. 

3.  The  deposits  of  the  third  group  are  later  than  the  early 
Cretaceous,  and  some  of  them  are  probably  early   Tertiary. 

62  The  Gold  Production  of  North  America,  Trans.,  xxxiii.,  790  to  845  (1902); 
p.  424,  this  volume.  Metallogenetic  Epochs,  Economic  Geology,  vol.  iv.,  No.  5, 
pp.  409  to  420  (Aug.,  1909). 


MANGANESE    AND    GOLD-ENRICHMENT.  807 

They  are  extensively  developed  in  Montana,  Nevada,  Utah,  and 
Colorado.  Mr.  Lindgren  calls  this,  group  the  Central  Belt. 
Many  of  its  deposits  have  yielded  considerable  gold,  and  in 
certain  other  districts  very  closely  related  genetically  (Butte, 
Georgetown  silver-gold  lodes,  Cortez  Nevada,  Tintic,  etc.) 
much  gold  has  been  obtained  as  a  by-product  to  copper-  or 
silver-mining.  Some  of  these  deposits  have  yielded  placers 
and  some  have  not.  At  Philipsburg  and  Neihart,  Mont, 
Georgetown,  Colo.,  and  elsewhere,  the  deposits  show  a  second- 
ary enrichment  of  silver  below  the  water-table.  At  Philips- 
burg,  and  probably  at  some  other  places,  an  enrichment  in 
gold  accompanies  this  concentration  of  silver.  Some  of  the 
lodes  of  group  3  carry  much  manganese,  and  some  carry  none. 
Present  data  are  meager  for  most  of  these  districts.  The  deter- 
mination of  gold  from  the  surface  down  in  a  large  number  of 
deposits  would  serve  as  a  useful  check  to  the  conclusions  based 
upon  the  chemistry  of  the  processes  involved  in  its  solution 
and  precipitation. 

4.  Group  4  includes  the  most  recent  ore-deposits  in  the 
United  States.  All  of  them  are  Tertiary,  and  most  of  them  are 
Miocene  or  Pliocene.  In  general,  they  were  formed  relatively 
near  the  surface,  and  in  some  places  it  is  highly  probable  that 
not  more  than  a  thousand  feet  of  vein-material  has  been  re- 
moved by  erosion  since  the  ores  were  deposited.  The  majority 
of  these  deposits  carry  silver,  arid  in  many  of  them  its  value  is 
greater  than  that  of  the  gold  ;  but  they  have  supplied,  notwith- 
standing, about  25  per  cent,  of  the  gold-production  of  North 
America.  They  are  typically  developed  in  Nevada  (Corn- 
stock,  Tonopah,  Goldfield,  Tuscarora,  Gold  Circle) ;  California 
(Bodie);  Idaho  (De  Lamar);  South  Dakota  (later  than  Home- 
stake  type) ;  Colorado  (Cripple  Creek,  Idaho  Springs,  Rosita 
Hills,  San  Juan,  etc.) ;  Montana  (Little  Rockies,  Kendall,  etc.). 
Many  occurrences  in  Mexico  should  probably  be  placed  here, 
and  likewise  those  of  the  Aleutian  Islands,  described  by  Becker. 
The  deposits  of  this  group  have  not  supplied  much  placer-gold. 
They  have  not  been  exposed  to  erosion  so  long  as  the  older 
deposits.  In  general,  the  gold  is  finely  divided.  It  may  have 
been  scattered  or  it  may  have  been  redissolved  and  deposited 
lower  down.  Many  of  these  deposits  are  in  arid  countries, 
where  conditions  for  working  placers  are  not  favorable ;  but, 


808  MANGANESE    AND    GOLD-ENRICHMENT. 

even  those  in  well-watered  districts  supply  relatively  little 
placer-gold.  Manganese  is  abundant  in  some  of  these  deposits 
(Comstock,  Exposed  Treasure,  Tonopah) ;  it  is  very  sparingly 
present  in  others  (Little  Rockies) ;  in  still  others  (Goldfield)  it 
is  almost  entirely  absent. 

A  few  small  placers  are  associated  with  the  manganiferous 
lodes,  although  at  some  places,  as  at  Tuscarora,  Nev.,  they 
seem  to  have  been  derived  from  veins  near-by  which  are  not 
manganiferous,  as  is  probably  the  case  with  some  deposits  of 
group  3  (Butte,  Philipsburg).  Many  of  the  California  veins 
(group  2)  carry  rich  ore  at  the  very  surface,  but  the  Tertiary 
gold-veins  are-  generally  richer  in  gold  a  few  feet  below  the 
surface  than  at  the  outcrop.  Doubtless,  many  of  them  would 
have  been  overlooked  if  it  had  not  been  for  the  concentration 
of  horn-silver  and  argentiferous  pyromorphite  at  the  surface. 
At  many  of  these  deposits,  however,  good  gold-ore  is  found 
only  a  few  feet  below  the  surface. 

It  thus  appears  that  practically  all  of  the  manganiferous 
gold-deposits  of  the  United  States,  so  far  as  they  have  been  de- 
scribed, may  be  included  in  groups  3  and  4 ;  that  nearly  all 
described  deposits  where  relations  indicate  a  migration  of  gold 
belong  to  the  same  groups ;  that  placers  are  much  less  abun- 
dantly developed  than  in  groups  1  and  2  ;  and  that  outcrops 
less  frequently  supply  gold ;  that  secondary  enrichment  below 
the  water-table,  if  carried  on  at  all,  proceeds  with  extreme  slow- 
ness in  groups  1  and  2,  but  may  be  more  pronounced  in  de- 
posits of  groups  3  and  4.  Not  all  of  these  deposits  carry  man- 
ganese, however,  and  those  which  do  not  carry  it  should  be 
expected  to  show  relationships  more  nearly  approximating 
those  of  groups  1  and  2. 

5.  Some  deposits  formed  at  hot  springs  carry  gold.  As  a 
rule,  traces  only  are  found  in  the  sinters,  and  at  many  places 
even  traces  are  not  detected.  This  is  readily  explained  when 
it  is  noted  that  these  springs  frequently  carry  both  sulphates 
and  iron.  If  the  sulphates  are  due  to  contamination  with  oxy- 
genated surface-waters,  then  such  waters,  before  complete  oxi- 
dation, would  precipitate  gold.  Since  only  a  little  ferrous  sul- 
phate precipitates  practically  all  of  the  gold  in  a  solution,  it 
would  be  supposed  that  the  major  deposition  would  be  some 
distance  below  the  surface,  where  oxygen-bearing  waters  first 


MANGANESE    AND    GOLD-ENRICHMENT.  809 

contaminated  the  hot  solutions,  and  not  at  the  surface.  The 
same  argument  should  apply  to  silver  also,  although  the  action 
of  the  ferrous  salt  on  solutions  carrying  silver  is  not  nearly 
so  rapid  as  on  solutions  carrying  gold.  In  the  hot  solutions, 
manganese,  even  if  it  were  present,  would  probably  not  hold 
the  gold  or  silver  in  solution  by  oxidizing  ferrous  salts,  for 
ascending  hot  waters  deposit  manganous  rather  than  man- 
ganitic  compounds. 

1.  Southern  Appalachian  Districts. — The  gold-deposits  of  the 
southern  Appalachians  are  among  the  oldest  gold-deposits  of 
the  United  States,  and  were  probably  formed,63  in  the  main,  3 
or  4  miles  below  the  surface  at  the  time  of  deposition.  Many 
of  them  are  in  mica-schist  and  other  crystalline  rocks,  and 
some  are  closely  associated  with  granitic  intrusions.  Some  are 
cut  by  diabasic  intrusives,  presumably  later  than  the  ore.  The 
deposits  have  yielded  considerable  placer-  and  lode-gold.  The 
minerals,  according  to  Graton,64  include  quartz,  sericite,  biotite, 
fluorite,  gold,  pyrite,  galena,  blende,  pyrrhotite,  chalcopyrite, 
magnetite,  etc.  Manganese-minerals  are  not  mentioned.  In 
Becker's  tabulation  of  the  minerals  of  the  gold-mines  of  the 
southern  Appalachians,  compiled  from  all  previous  descriptions 
and  including  mines  not  described  by  Graton,  pyrolusite  is 
mentioned  in  only  three  mines  and  rhodochrosite  in  one.65 

Few  of  these  deposits  have  been  extensively  explored  in 
depth,  and  consequently  data  respecting  the  vertical  distribu- 
tion of  the  gold-values  are  meager.  Many  of  them  are  profit- 
able near  the  surface,  partly  by  reason  of  the  rotten  condition 
of  the  rock,  which  renders  it  more  easily  worked,  and  partly 
because  gold  is  accumulated  or  enriched  by  the  removal  of 
valueless  material.  In  general  there  is,  according  to  Graton, 
very  little  evidence  for  or  against  the  theory  of  the  migration 
of  gold;  but  such  migration,  if  it  has  taken  place,  has  been 
extremely  slow,  for  areas  which  have  probably  been  exposed 
since  Tertiary  time  show  a  marked  concentration  at  and  near 
the  surface.  Possibly  some  gold  has  been  transferred  to  lower 

63  Lindgren,  Bulletin  No.  293,  U.  S.  Geological  Survey,  p.  124  (1906). 
6*  Idem,  p.  62. 

65  Sixteenth  Annual  Report,  U.  S.  Geological  Survey,  Part  III.  t  Mineral  Resources 
of  the  U.  S.,  p.  277  (1894-95). 

51 


810  MANGANESE    AND    GOLD-ENRICHMENT. 

levels  at  the  Haile  mine,  South  Carolina,66  where  the  limit  of 
profitable  mining  is  in  general  less  than  200  ft.  below  the  limit 
of  complete  oxidation.  In  this  zone  scales  of  pyrite  and  free 
gold  are  found  in  joint-cracks,  indicating  a  comparatively  re- 
cent age.  The  deposits  are  cut  by  basic  dikes.  Prior  to 
Graton's  work,  many  thought  that  the  primary  deposition  of 
gold  was  genetically  related  to  the  dikes,67  since  the  workable 
ore  appears  to  be  limited  to  the  area  cut  by  them.  If  the 
basic  dikes  (like  most  basic  rocks)  carry  manganese,  then  our 
hypothesis  supports,  and  is  supported  by,  Graton's  opinion  that 
secondary  enrichment  has  probably  taken  place,  and  the  con- 
flicting views  of  Graton  and  Maclaren  respecting  the  genesis 
of  the  ores  are  thus  reconciled. 

Certain  ore-deposits  of  Alabama  recently  described  by  H.  D, 
McCaskey68  comprise  fissure-veins  in  granite  and  lenticular 
bodies  in  schists.  The  principal  minerals  are  quartz,  pyrite,. 
and  gold.  Some  garnet  is  found  in  the  vein-quartz  at  Pine- 
tuckey.  Weathering  extends  to  water-level  (from  40  to  80  ft. 
below  the  surface).  The  ores  are  oxidized  above  this  level 
and  are  generally  free-milling,  but  below  this  level  the  ore  i& 
not  profitably  amalgamated  so  far  as  explored  in  depth.  The 
ores  are  fairly  regular  in  width  and  values,  and  no  evidences 
of  enrichment  below  the  water-level  are  recorded. 

2.  Black  Hills,  S.  D. — The  principal  gold-deposits  of  the 
Black  Hills 69  are  in  pre-Cambrian  schists  which,  like  the  ore- 
bodies,  are  cut  by  Tertiary  intrusives.  Since  the  Cambrian 
conglomerates  contain  placer-gold,70  some  of  the  ores  must 
have  been  deposited  in  pre-Cambrian  times.  The  most  impor- 
tant deposits  are  comprised  in  the  Homestake  belt,  about  £ 
miles  long  and  2,000  ft.  wide.  The  principal  minerals  are 
quartz,  dolomite,  calcite,  pyrite,  arsenopyrite,  and  gold,  with 
which  are  associated  the  minerals  of  the  schist :  quartz,  ortho- 
clase,  hornblende,  biotite,  garnetj  tremolite,  actinolite,  titaniter 
and  graphite.71  The  ores,  though  uniformly  of  low  grade,  are 

66  Graton,  Bulletin  No.  293,  U.  S.  Geological  Survey,  p.  67  (1906). 

67  Maclaren,  Gold,  pp.  57,  592  (1908). 

68  Bulletin  No.  340,  U.  S.  Geological  Survey,  p.  36  (1908). 

69  Irving,  Emmons,  and  Jaggar,  Professional  Paper  No.  26,  U.  S.  Geological  Sur- 
vey (1904). 

70  W.  B.  Devereux,  Trans.,  x.,  469  (1881-82). 

71  J.  D.  Irving,  loc.  cit.,  p.  90. 


MANGANESE    AND    GOLD-ENRICHMENT.  811 

very  profitable.  Some  of  the  ores  at  the  surface  were  below 
the  average  tenor,  while  other  surface-ores  were  two  or  three 
times  as  rich  as  the  average.  The  values  extend  downward  as 
far  as  exploration  has  gone,  and  are  fairly  uniform  to  1,000  ft. 
or  more  below  the  surface.  In  general,  according  to  S.  F. 
Emmons,  secondary  enrichment  by  surface-leaching  has  had 
relatively  small  importance.72 

3.  Treadwell  Mines,  Alaska. — At  the  Treadwell  mines,  Doug- 
las Island,  Alaska,  large  dikes  of  albite-diorite  intrude  green- 
stones and  schist,  and  the  shattered  diorite  has  been  extensively 
replaced  by  mineralizing  solutions,  and  cemented  by  low-grade 
gold-ore.     The  minerals  include  quartz,  albite,  rutile,  chlorite, 
epidote,   calcite,  siderite,  pyrite,  pyrrhotite,   magnetite,   chal- 
copyrite,  and  molybdenite.     Manganese-minerals  are   not  re- 
ported. 

The  mines  have  been  developed  2,000  ft.  down  the  dip. 
According  to  A.  C.  Spencer,73  the  ore  shows  no  progressive 
change  in  appearance  or  values  with  increasing  depth.  In  the 
lowest  level  it  is  quite  as  rich  as  in  the  upper  workings ;  and 
it  is  evident  that  changes  on  the  dip  are  no  greater  than  along 
the  strike.  Nothing  in  the  character  of  the  ore  indicates  any 
important  concentration  of  values  by  oxidizing  waters.  The 
fact  that  extensive  placers  were  not  formed  is  not  opposed  to 
the  view  expressed  by  Spencer  that  the  gold  has  not  been 
transferred ;  the  country  has  been  recently  glaciated,  and  sur- 
face-accumulations have  been  scattered.  The  gold  accumulated 
at  the  apex  since  glacial  time  was,  indeed,  recovered  by  sluicing. 

4.  Berner's  Bay,  Alaska. — According  to  Adolph  Knopf,  the 
lodes  of  the  Berner's  Bay  district  are  fissure-veins  in  diorite. 
There  is  no  evidence  of  secondary  enrichment  of  gold  or  of 
leaching  near  the  surface.    The  deposits  contain  no  manganese. 

5.  The  Mother  Lode  District,  Cal— The  Mother  Lode   dis- 
trict, as  described  by  F.  L.  Ransome,74  is  an  area  of  crystalline 
schists  and  altered  igneous  rocks  with  intruded  granodiorite 
and  related  rocks.     The  deposits  are  fissure-veins,  which  gen- 
erally trend  northwestward,  and,  at  many  places,  parallel  the 
schistosity  of    the    country- rock.     The   ore   does   not  contain 

72  Professional  Paper  No.  26,  U.  S.  Geological  Survey,  p.  79  (1904). 

73  Bulletin  No.  287,  U.  S.  Geological  Survey,  pp.  32  and  115  (1906). 

74  Mother  Lode  District,  Folio  No.  63,  U.  S.  Geological  Survey,  p.  3. 


812  MANGANESE    AND    GOLD-ENRICHMENT. 

manganese-minerals.  Placers  are  abundantly  developed,  and  at 
many  places  rich  ore  is  found  at  the  very  surface.  According 
to  Ransome,  there  is  no  evidence  that  the  mines  grow  suddenly 
richer  at  any  -arbitrary  depth,  nor  is  there  any  recognizable 
regular  change  in  the  value  of  pay-shoots  with  depth,  below 
the  zone  of  superficial  weathering.  Some  of  these  deposits  are 
very  regular  and  uniform  in  values,  and  have  been  developed 
to  very  great  depth. 

6.  Nevada  City  and  Grass  Valley,  Cal. — The  area  of  Nevada 
City  and  Grass  Valley 75  includes  metamorphosed  Carboniferous 
sedimentary  rocks,  compressed  into  isoclines,  and  associated 
igneous  rocks  less  intensely  metamorphosed.  Above  these 
are  slates  with  associated  diabase  and  serpentine.  These  rocks 
are  folded  and  metamorphosed,  but  are  not  so  intensely  com- 
pressed as  the  Carboniferous.  Intruded  into  these  rocks  are 
great  bodies  of  granodiorite,  probably  of  early  Cretaceous 
age.  The  ore-deposits  are  strong  fissure-veins,  formed  after 
the  granodiorite  intrusions.  The  minerals  are  quartz,  chalce- 
dony, magnetite,  sericite,  mariposite,  pyrite,  pyrrhotite,  chalco- 
pyrite,  galena,  blende,  scheelite,  arsenopyrite,  tetrahedrite, 
stephanite,  and  cinnabar.  Some  earthy  manganese-ore  occurs 
in  small  fissures  in  the  granodiorite,  but  not  in  connection  with 
the  quartz  veins. 

Near  the  surface76  the  upper  part  of  a  vein  is  generally 
decomposed,  forming  a  mass  of  limonite  and  quartz.  The 
decomposition  seldom  extends  more  than  200  ft.  on  the  incline 
of  a  vein  dipping  45°,  or  more  than  150  ft.  below  the  surface. 
Fresh  ore  is  sometimes  found  almost  at  the  surface.  The  sur- 
face-ore is  generally  richer  than  the  fresh  ore  below,  owing  to 
the  liberation  of  gold  from  the  sulphides  and  the  removal  of 
substances  other  than  gold.  In  this  process,  silver  is  also 
partly  removed.  In  some  of  the  mines,  the  lodes  have  been 
followed  down  the  dip  for  2,000  or  even  3,000  ft.  The  unoxi- 
dized  ore  shows  no  gradual  diminution  of  tenor  in  the  pay- 
shoots  below  the  zone  of  surface-decomposition.  "  Within  the 
same  shoot  there  may  be  many  and  great  variations  of  the 
tenor,  but  there  is  certainly  no  gradual  decrease  of  it  from  the 

75  Waldemar  Lindgren,  Seventeenth  Annual  Report,  U.  S.  Geological  Survey,  Part 
II.  (1895-96). 

76  Loc.  cil.,  p.  128. 


MANGANESE    AND    GOLD-ENRICHMENT.  813 

surface  down."  77     Important  placer-deposits  were  formed  from 
these  veins. 

7.  The   Ophir  District,   Cal. — The   rocks    of   the   Ophir  dis- 
trict 78  comprise  amphibolite-schists  and  massive  amphibolites, 
with  intrusions  of  granodiorite.    These  rocks  are  cut  by  quartz 
veins  which  fill  co-ordinate  fissures.     The  minerals  are  gold, 
electrum,  some  iron,  copper  and  arsenical  pyrites,  with  galena, 
blende,  tetrahedrite,  and  molybdenite.     The  gangue  is  mainly 
quartz  with  a  little  calcite.     The  proportion  of  gold  to  silver 
varies  by  weight  from  1:1  to  1 : 10,  the  values  of  gold  pre- 
dominating.    Certain  small  ore-shoots,  in  veins  in  the  amphi- 
bolite,  carry  more  than  the  usual  tenor  of  gold ;  and  the  richest 
shoots  are  usually  found  where  veins  cross  the  belts  rich  in  iron. 
According  to  Lindgren,  such  ore-bodies  may  have  been  en- 
riched by  leaching.     The  common  statement,  that  the  gold- 
vein  becomes  barren  as  the  depth  from  the  surface  increases, 
is  not  justified,  in  his  opinion,79  by  the  evidence  afforded  in  the 
mines.     The  extensive  development  of   placers,  the  value  of 
the  ore  near  the  surface,  and  the  occurrence  of  valuable  ore- 
shoots  just  below  the   surface,  are  opposed  to  the  notion  of 
extensive  migration  of  gold  in  these  deposits. 

8.  Silver  Peak,  Nev. — According  to  J.   E.  Spurr,80  the  de- 
posits of  Silver  Peak,  Nev.,  are  lenticular  masses  and  fissure- 
veins  in  Palaeozoic  sedimentary  rocks.     Genetically,  they  are 
related  very  closely  to  granitic  rocks,  which,  as  shown  by  Mr. 
Spurr,  have  alaskitic  or  pegmatitic  phases.    They  are  probably 
post-Jurassic,  and  should  be  grouped  with  the  California  gold- 
veins,  with  which  geologically  they  have  much  in   common. 
Of  the  Drinkwater  and   Crowning  Glory  deposits,  which  are 
the  most  important  examples,  Spurr  says  that  no  decided  en- 
richment of  the   ores  by  oxidation  can  be  established.     The 
ores  in  the  upper  tunnel  seem  to  have  been  locally  richer  than 
any  found  in  the  lower  tunnel;  but  this  difference  has  no  evi- 
dent relation  with  the  surface,  and  is  probably  original.     The 
values  are  finely  disseminated  gold  and  auriferous  sulphides, 

77  Op.  cit.,  p.  163. 

78  Waldemar  Lindgren,  Fourteenth  Annual  Report,  U.  S.    Geological  Survey,  Part 
II.,  p.    252  (18*2-93'. 

79  Idem,  p.  279. 

so-  Professional  Paper  No.  55,  U.  S.  Geological  Survey  (1906 j. 


814  MANGANESE    AND    GOLD-ENRICHMENT. 

scattered  through  vitreous  quartz.  The  character  of  the  ore 
affords  no  ground  for  supposing  any  great  concentration  by 
surface-waters,  since  the  minerals  are  not  easily  reached  by 
percolating  waters.  No  ore-shoots  correspond  to  the  fractures 
which  cross  the  ore — an  indication  that  the  waters  which  cir- 
culated along  such  subsequent  fractures  had  little  effect  in  the 
redistribution  of  values. 

9.  Philipsburg,  Mont. — The  Philipsburg  quadrangle  is  an 
area  of  sedimentary  rocks,  ranging  from  pre-Cambrian  to  late 
Cretaceous,  with  intrusions  of  quartz-monzonites  and  related 
rocks,  probably  belonging  to  the  same  period  of  intrusion  as 
that  of  the  Butte  granites  and  other  batholiths  in  Montana. 
The  most  important  ore-deposits  in  this  quadrangle  are  those 
of  the  Granite-Bimetallic  and  the  Cable  mines. 

The  Granite-Bimetallic  is  a  strong  fissure-vein  in  quartz  - 
monzonite,  which  carries  chiefly  silver,  but  also  an  important 
amount  of  gold.  There  is  conclusive  paragenetic  evidence  of 
the  secondary  enrichment  of  silver  below  the  water-level,  and 
the  rich  silver-ore  carries  also  more  gold  than  the  low-grade 
silver-ore  in  the  bottom  of  the  mine.  The  outcrop  of  this 
deposit  carried  some  silver,  but  very  little  gold ;  and,  after  the 
discovery,  the  location  was  allowed  to  lapse,  by  reason  of  the 
small  assay-returns  from  the  gossan.  Richer  ore  appeared  not 
far  below  the  surface  and  extended  down  to  the  10th  level. 
The  shoot  of  high-grade  ore,  which  extended  for  about  a  m  ile 
along  the  strike  of  the  deposit,  followed,  in  a  broad  way,  the 
present  rugged  surface.  The  gangue  is  rich  in  manganese. 
Some  migration  of  gold  has  undoubtedly  taken  place.  No 
associated  placers  have  been  developed. 

At  the  Cable  mine  the  deposits  are  included  in  a  long,  thin 
block  of  limestone,  in  contact  on  either  side  with  quartz-mon- 
zonite.  The  principal  minerals  are  calcite,  quartz,  pyrrhotite, 
pyrite,  magnetite,  and  chalcopyrite,  with  chlorite,  muscovite, 
and  other  silicates.  At  one  or  two  places  small  traces  of  man- 
ganese dioxide  have  been  noted  in  the  oxidized  ore,  but  it  is 
very  much  less  abundant  than  in  the  deposits  of  the  Granite- 
Bimetallic  type.  This  deposit  yielded  important  placers.  Good 
ore  was  found  at  or  very  near  the  surface ;  and,  according  to 
the  best  obtainable  data,  the  values  increased  somewhat  for  a 
short  distance  below  the  surface.  Some  concentration  has 


MANGANESE    AND    GOLD-ENRICHMENT.  815 

taken  place  by  the  removal  of  calcite  and  other  valueless  ma- 
terial more  rapidly  than  gold ;  but  there  is  no  evidence  of 
secondary  enrichment  in  gold  below  the  water-table.  The 
indications  are,  that  the  gold  has  not  been  extensively  trans- 
ported since  the  deposit  was  formed. 

10.  Other  Montana  Districts. — The  secondary  enrichment  of 
gold-  and  silver-deposits  at  Neihart,  at  Butte,  and  in  other 
Montana  districts,  has  been   described  by  W.   H.   Weed,  in 
various  papers.     These  deposits  generally  contain  appreciable 
manganese.    In  that  respect  they  differ  from  the  Idaho  deposits 
described  by  Lindgren,  which  do  not  carry  rhodochrosite  or 
appreciable  manganese  dioxide.    With  some  notable  exceptions, 
such  as  the  De  Lamar  deposits,  the  Idaho  veins  are  probably 
•older  than  those  of  Montana,  and,  as  Lindgren  has  pointed  out, 
should  be  grouped  with  the  early  Cretaceous  California  gold- 
veins-  rather  than  with  the  late  Cretaceous  or  early  Tertiary 
group,  to  which  most  of  the  Montana  deposits  belong.     The 
Idaho  veins  which  have  been  closely  studied  do  not  give  evi- 
dence of  the  downward  migration  of  gold. 

11.  Edgemont,  Nev. — The  gold-deposits  at  Edgemont,  Elko 
•county,  Nev.,  which  should  be  classed  with  group  3,  are  in  an 
-area  of  quartzite,  with  intrusions  of  granodiorite.     The   de- 
posits are  fissure-veins,  and  their  gold-values  are  comparatively 
uniform.     The  ore  consists  of  pyrite,  galena,  and  arsenopyrite 
in  a  gangue  of  quartz.     Copper  carbonates  and  manganese- 
minerals  are  rare  or  absent.     The  ore  is  stoped  practically  to 
the  surface.     There  has  probably  been  a  slight  amount  of  en- 
richment by  removal  of  certain  substances  in  the  oxidized  zone 
more  rapidly  than  gold;   there  is  no  evidence  that  gold  has 
been  transferred  below  the  water-level  by  descending  surface- 
waters.81 

12.  Leadville,  Colo. — The  deposits  of  Leadville  yield  silver, 
lead,  and  gold.    The  country  is  an  area  of  Palaeozoic  limestones 
and  quartzites,  with  intrusive  sills  and  dikes  of  porphyries.82 
Some  of  these   deposits  carry  in  the  upper  horizons  a  large 
amount  of  manganese;  and  this  ore  is  frequently  rich  in  silver, 
presumably  in  the  form  of  the  native  metal   or  as  chloride. 

81  W.  H.  Emmone,  Bulletin  No.  408,   U.  S.  Geological  Survey  (1910). 

82  S.  F.  Emraons,  Geology  and  Mining  Industry  of  Leadville,  Colorado,  Mono- 
graph No.  XI L,  U.  S.  Geological  Survey  (1886)  ;  and  S.  F.  Emmons  and  J.   D. 
Irving,  BuUetin  No.  320,  U.  S.  Geological  Survey  (1907). 


816  MANGANESE    AND    GOLD-ENRICHMENT. 

Assays  of  this  ore,  showing  the  amount  of  gold  contained  in 
it,  are  not  available  to  me.  According  to  the  requirements  of 
the  theory  under  investigation,  it  would  be  expected  to  be  low 
in  gold  in  this  upper  zone,  where  the  waters  probably  carry 
ferric  salts  and  chloride.  Of  considerable  interest  in  this  con- 
nection are  some  small  fractures  in  the  quartzite  at  a  lower 
horizon,  which,  as  Mr.  Emmons  informs  me,  often  carry  small 
amounts  of  high-grade  manganiferous  gold-ore.  This  ore  he 
regards  as  a  deposit  from  descending  waters.  Possibly  it  is  the 
gold  leached  out  above,  where  ferric  salts  predominate,  and  was 
carried  to  greater  depth  by  the  manganiferous  solutions  which 
delay  the  action  of  ferrous  sulphate  as  a  precipitant  of  gold. 

13.  Georgetown,  Colo.,  Silver-Lead  Deposits. — The  silver-lead 
lodes  of  Georgetown  and  Silver  Plume,  Colo.,  are  of  early 
Tertiary  age.  The  veins  cut  crystalline  schists  and  Tertiary 
igneous  rocks.  According  to  Spurr,  Garrey  and  Ball,83  several 
thousand  feet  of  overlying  rocks  have  been  eroded  since  the 
ores  were  deposited,  and  some  of  the  values  in  the  eroded  por- 
tions of  the  lodes  have  migrated  to  the  portions  still  remaining. 
The  principal  metallic  minerals  are  argentiferous  galena  and 
blende,  with  pyrite  and  chalcopyrite ;  the  ores  usually  carry 
about  $2  gold  per  ton.  The  silver-values  are  mainly  in  poly- 
basite,  freibergite,  argentite,  pyrargyrite,  and  proustite.  The 
gangue  is  quartz,  chalcedony,  barite,  with  carbonates  of  lime, 
iron,  manganese,  and  magnesia. 

The  rich  silver-minerals  were  the  last  to  be  deposited,  and 
form  on  the  walls  of  the  fractures  in  the  older,  baser  ore,  or  cut 
the  older  deposits.  The  zone  of  complete  oxidation  extends 
from  5  to  40  ft.  below  the  surface.  The  oxidized  ore  often 
contains  several  hundred  ounces  of  silver  per  ton.  Below  this 
ore  are  friable  black  sulphides  and  secondary  galena.  This 
secondary  ore,  according  to  Spurr  and  Garrey,  is  rich  in  silver 
and  lead  and  carries  more  gold  than  occurs  at  greater  depth. 
This  ore  cuts  the  primary  sulphide ;  and  the  latter,  which  may 
have  contained  from  20  to  30  oz.  of  silver  per  ton,  is  enriched 
to  more  than  200  oz.  per  ton. 

Quoting  from  Spurr  and  Garrey: 84 

83  Professional  Paper  No.  63,  U.  S.  Geological  Survey,  p.  136  (1908). 

84  J.  E.  Spurr  and  G.  H.  Garrey,  Professional  Paper  No.  63,  U.  S.  Geological 
Survey,  p.  144  (1908). 


MANGANESE    AND    GOLD-ENRICHMENT.  817 

"  Below  the  zone  where  soft  secondary  sulphides  occur  and  irregularly  overlap- 
ping the  lower  portion  of  this  zone  the  rich  ores  contain  polybasite,  argentiferous- 
tetrahedrite,  and  ruby  silver,  better  crystallized  and  more  massive  than  the  pulve- 
rulent sulphides,  but  also  subsequent  in  origin  to  the  massive  galena-blende  ore. 
These  richer  ores  diminish  in  quantity  as  depth  increases,  though  gradually  and 
irregularly,  so  that  the  lower  portion  of  the  veins  contains  relatively  less  silver  and 
lead.  The  best  ore  in  most  veins  has  been  found  in  the  uppermost  500  feet, 
although  good  ore  extends  locally  down  to  700  or  800  feet,  and  in  the  Colorado- 
Central,  and  to  a  minor  extent  in  other  veins,  down  to  a  thousand  feet  or  more." 

14.  Auriferous  Deposits  of  the  Georgetown  Quadrangle,  Colo- 
rado.— The  auriferous  deposits  of  the  Georgetown  quadrangle 
are  mainly  at  Idaho  Springs  and  in  the  Empire  district, 
although  some  are  developed  near  Georgetown  in  the  area  of 
the  silver-lead  deposits.  As  shown  by  Spurr  and  Garrey,  the 
gold-lodes  are  probably  of  later  age  than  the  silver-lead  de- 
posits. They  cut  the  crystalline  schists  and  the  Tertiary  por- 
phyries, but  are  genetically  related  to  alkali-rich  intrusive  rocks 
of  middle  or  late  Tertiary  age.  They  carry  pyrite,  chalcopy- 
rite,  chalcocite,  quartz,  adularia,  and  gold,  with  minor  amounts 
of  barite,  fluorite,  telluride,  etc.  Carbonates  of  iron,  magne- 
sium, lime,  and  manganese  occur,  but  are  relatively  rare.  In 
many  of  the  mines  the  ore  averages  from  1  to  2  oz.  of  gold 
and  from  20  to  40  oz.  of  silver  per  ton.  The  lodes  are  usually 
oxidized  at  the  surface  and  from  15  to  70  ft.  downward.  They 
have  yielded  some  moderately-productive  placers.  In  several 
mines,  the  oxidized  is  much  richer  than  the  average  ore. 
Below  the  zone  of  oxidation,  secondary  chalcopyrite  and  chal- 
cocite prevail  for  several  hundred  feet  from  the  surface,  but 
decrease  at  greater  depth.  There  is  an  important  enrichment 
of  gold  and  silver,  coincident  with  the  occurrence  of  the  cop- 
per-minerals. As  stated  by  Spurr  and  Garrey : 

"In  the  mines  mentioned  a  portion  of  the  copper  which  has  contributed  to  the 
enrichment  of  the  original  sulphides  has  been  derived  from  the  oxidized  zone,  but 
it  seems  unlikely  that  this  has  been  the  case  with  the  gold  and  silver,  which,  like 
the  enriched  superficial  portions  of  the  argentiferous  veins,  must  have  been  derived 
from  the  overlying  portions  of  the  lodes  which  are  now  eroded.  .  .  . 

' '  On  the  whole,  the  strongest  evidence  of  the  reworking  of  the  ores  by  surface 
waters  is  afforded  by  markedly  cupriferous  ores.  .  .  .  Apart  from  this,  how- 
ever, and  from  the  probable  partial  reconstruction  of  galena  near  the  surface  in 
some  mines,  the  evidence  of  rearrangement  of  the  ores  by  descending  waters  is  in 
general  not  nearly  so  great  as  in  the  Georgetown  district,  and  such  reworking  has- 
probably  taken  place  to  a  considerably  less  extent." 


818  MANGANESE    AND    GOLD-ENRICHMENT. 

15.  San  Juan,  Colo. — The  gold-deposits  of  the  San  Juan  re- 
gion,85 including  those  near  Telluride,  Silverton,  and  Ouray, 
are,  as  shown  by  Ransome,  of  varied  character.  '  They  are 
mainly  Tertiary,  and  should  be  classed  with  group  3  or  4 
above  named.  The  lead-silver  deposits  and  the  stocks  near 
Ironton  are  not  here  considered. 

In  this  elevated  area  the  ground  is  frozen  much  of  the  year, 
and  the  rapid  erosion  is  due  largely  to  mechanical  disintegra- 
tion. Secular  decay  or  oxidation  of  the  ores,  according  to 
Ransome,  is  not  as  a  rule  very  extensive,  and  is  at  some  places 
negligible.  Purington  has  pointed '  out,  however,  that  the  out- 
crops of  the  San  Juan  lodes  are,  in  general,  of  lower  grade 
than  the  ore  a  few  feet  below  the  surface,  possibly  by  reason  of 
the  migration  of  gold  in  suspension.  Many  of  the  lodes  are 
tight,  and  do  not  appear  to  offer  favorable  conditions  for  down- 
ward migration  of  waters.  The  country  is  well  drained,  and 
chlorine  is  probably  not  abundant  in  the  mine-waters.  The 
conditions  for  deep-seated  enrichment  are  therefore  not  par- 
ticularly favorable,  although  some  concentration  has  taken 
place  locally  by  the  leaching  and  removal  of  the  less- valuable 
materials  from  the  ore.  The  workable  ore  appears  to  be 
mainly  of  primary  origin. 

At  some  places  the  gangue  includes  manganiferous  minerals. 
There  is  some  evidence  that  gold  was  transported  to  a  limited 
extent.  As  Ransome  points  out,86  in  the  Tomboy  and  Camp 
Bird  mines,  black  oxide  of  manganese  occurs  in  the  deepest 
workings  (in  1901)  and  usually  indicates  good  ore.  These 
little  sheets  of  rich,  dark,  manganiferous  ore,  which  fill  post- 
mineral  fractures,  Ransome  regards  as  later  than  the  general 
mass  of  the  ore.  It  is  reasonable  to  suppose  that  they  repre- 
sent the  deposition  from  solutions  which  dissolved  gold  in  the 
upper  portion  of  the  lode,  where  ferric  salts  prevail,  and  which, 
in  the  presence  of  manganese,  were  able  to  transport  their  load 
to  greater  depths,  but  which,  coming  into  contact  with  pyrite, 

85  F.  L.  Ransome,  A  Keport  on  the  Economic  Geology  of  the  Silverton  Quad- 
rangle,  Bulletin  No.  182,  U.  S.  Geological  Survey  (1901)  ;   and  C.  W.  Purington, 
Preliminary  Report  on  the  Mining  Industries  of  the  Telluride  Quadrangle,  Eigh- 
teenth Annual  Report,  U.  S.  Geological  Survey,  Part  III.,  p.  745  (1896-97)  ;  Puring- 
ton, Woods,  and  Doveton,  The  Camp  Bird  Mine,  Ouray,  Colo.,  Trans.,  xxxiii.,  499 
to  550  (1902). 

86  Op.  cit.,  p.  101. 


MANGANESE    AND    GOLD-ENRICHMENT.  819 

were  ultimately  reduced  and  forced  to  give  up  their  gold  when, 
through  the  oxidation  of  pyrite,  ferrous  sulphate  had  been 
formed. 

16.  Cripple  Creek,  Colo. — The  gold-deposits  of  Cripple 
Creek,  Colo.,  have  yielded  some  $200,000,000  gold  and  less 
than  $1,000,000  silver.  The  lodes  are  fissure-veins  and  replace- 
ment-deposits in  volcanic  breccia,  in  Tertiary  intrusive  rocks, 
and  in  granite.  The  fissures,  according  to  Lindgren  and  Ran- 
some,87  were  formed  at  about  the  same  time  as  the  intrusion  of 
associated  basic  dikes,  and  represent  a  late  phase  of  volcanic 
activity.  The  deposits  are  probably  of  middle  or  late  Tertiary 
age,  and  were  formed  by  hot  ascending  waters,  relatively  near 
the  surface.  Calaverite  is  the  chief  primary  constituent;  native 
gold  is  rarely  present  in  the  unoxidized  ores.  Pyrite  is  widely 
distributed;  tetrahedrite,  stibnite,  and  molybdenite  are  spar- 
ingly present.  The  gangue  is  quartz,  fluorite,  adularia,  carbo- 
nates (including  rhodochrosite),  some  sulphates,  etc.  Some  of 
the  deposits  were  workable  at  the  surface,  but  the  placers  which 
have  formed  are  relatively  unimportant.  Although  rhodochro- 
site is  subordinate  in  amount,  the  highly-fractured  country- 
rock  contains  appreciable  manganese  (0.20  ±  per  cent.).  Ac- 
cording to  Lindgren  and  Ransome,  the  processes  of  oxidation 
were  attended  by  the  formation  of  kaolin,  hydrous  silica,  and 
oxides  of  iron  and  manganese.  Manganese  oxides  are  often 
present  in  the  oxidized  zone,  and,  according  to  Penrose,  form 
nodules  in  the  Pharmacist  and  Summit  mines.  They  result 
from  the  alteration  of  rhodochrosite,  manganiferous  calcite, 
or  other  minerals,  and  are  generally  distributed  in  the  oxidized 
zone  as  stains  filling  cracks  and  fissures.88  Daring  oxidation, 
manganese  is  greatly  concentrated  in  the  seams  of  the  rock. 
In  general,  the  lower  part  of  the  zone  of  oxidation  is  above 
water-level,  and  usually  less  than  200  ft.  below  the  surface.  In 
some  places  silver  has  been  completely  leached  from  the  oxi- 
dized ores.  Horn-silver  is  not  noted. 

Whether  a  slight  enrichment  of  gold  has  taken  place  in  the 
oxidized  zone  it  is  not  easy  to  decide.  Lindgren  and  Ran- 
some are  inclined  to  the  belief  that  the  oxidized  zone  as  a  whole 

87  Professional  Paper  No.  54,  U.  S.  Geological  Survey  (1906). 

88  Idem,  p.  123. 


820  MANGANESE    AND    GOLD-ENRICHMENT. 

is  somewhat  richer  than  the  corresponding  telluride  zone.89  If 
this  is  true,  no  extensive  downward  migration  of  gold  can  have 
taken  place.  The  trivial  enrichment  in  the  oxidized  zone  may 
have  resulted  from  the  removal  of  some  constituents  of  the  pri- 
mary ore. 

If  gold  was  dissolved  in  the  Cripple  Creek  deposits,  it  was 
precipitated  again  at  practically  the  same  horizon ;  for,  in  these 
deposits,  the  zone  in  which  solution  takes  place  is  as  rich  or 
richer  than  that  in  which  precipitation  usually  takes  place.  The 
ground  is  open,  providing  paths  for  downward-circulating 
waters,  but  it  should  be  remembered  that,  while  the  ore-bear- 
ing complex  is  very  pervious  to  water,  it  is  surrounded  by 
impervious  rocks.  After  the  volcanic  rocks  had  been  drained 
in  mining,  the  flow  of  water  was  comparatively  small.  Lind- 
gren  and  Ransome  have  compared  the  volcanic  complex  to  a 
"  sponge  in  a  cup."  As  shown  by  them,  the  conditions  for  a 
circulation  of  atmospheric  water  were  most  unfavorable — a  fact 
which  had  an  important  bearing  on  their  conclusion  that  the 
ores  had  been  formed  by-magmatic  waters.  In  the  absence  of, 
a  circulation,  the  gold  could  not  be  transported.  A  check  to 
this  reasoning  with  respect  to  a  downward  circulation  is  the 
fact  that  in  the  porous,  brecciated  mass,  filled  with  stagnant 
water,  the  oxidation  extended  downward  to  a  depth  generally 
less  than  200  ft,  and  even  in  this  zone  residual  sulphides  are 
often  present.  If  the  solutions  did  not  carry  oxygen  down- 
ward, it  would  be  supposed  that  they  could  not  carry  gold ; 
and  if  the  latter  had  been  dissolved  at  the  higher  levels,  in 
the  absence  of  a  circulation  it  could  not  descend.  There  is 
some  evidence  which  may  be  interpreted  as  an  indication  that 
the  gold  migrated  laterally,  or  possibly  that  it  has  been  pre- 
cipitated essentially  in  place  from  cold  solution.  'Richard 
Pearce  ^  has  recorded  analyses  of  oxidized  and  unoxidized  ore. 
The  material  for  the  analyses  was  taken  from  a  section  drawn 
clear  across  the  two  diiferent  portions  of  the  specimen.  The 
analyses  show  that  the  oxidized  ore  carries  14.58  oz.  of  gold  per 
ton,  or  2.34  oz.  more  gold  than  the  unoxidized  ore,  and  that  all 
the  silver  has  been  leached  out.  In  ore  so  rich  such  a  con- 

89  Professional.  Paper  No.  54,  U.  S.  Geological  Survey,  p.  203  (1906). 

90  Further  Notes  on  Cripple  Creek  District,  Proceedings  of  the  Colorado  Scientific 
Society,  vol.  iv.,  pp.  11  to  16  (1894-96). 


MANGANESE    AND    GOLD-ENRICHMENT.  821 

centration  may  result  merely  from  leaching-out  of  the  sub- 
stances other  than  gold ;  but,  on  the  other  hand,  the  analyses 
of  the  altered  rock  indicate  that  little  leaching  of  the  silicate 
minerals  has  taken  place,  and  that  the  oxidized  portion  was 
originally  richer  than  the  unoxidized,  or  else  that  some  gold 
had  been  added.  Since  0.27  per  cent,  of  Mn02  is  present  in 
the  oxidized  ore,  while  none  is  reported  in  the  unoxidized  ore, 
it  appears  that  Mn02  was  added  in  the  process  of  secondary 
alteration,  and  it  is  possible  that  the  same  solutions  added  gold 
and  iron. 

If  the  gold  was  dissolved  in  the  Cripple  Creek  "  sponge,"  it 
was  precipitated  in  the  stagnant  solutions  where  they  were  in 
contact  with  pyrite.  In  the  absence  of  a  downward  circulation 
of  water,  such  lateral  migration  would  not  be  unlikely. 

The  results  of  oxidation  processes  are  described  as  follows  :91 

"  Thorough  oxidizing  decomposition  will  destroy  the  original  structure  of  this 
vein.  In  sheeted  lodes  with  many  small  parallel  fissures  and  joints  the  latter  may 
become  effaced  and  the  lode  appears  as  a  homogeneous  brown,  soft  mass.  In  other 
cases  a  central  seam  may  be  retained  and  usually  appears  as  a  streak  of  soft,  more  or 
less  impure  kaolin  ;  in  other  cases  it  may  be  filled  by  white  compact  alunite,  more 
rarely  by  jasperoid  or  opaline  silica.  Crusts  of  comb  quartz,  if  originally  present, 
lie  included  in  the  clayey  seams,  but  neither  the  original  fluorite  nor  the  carbonates 
are  ordinarily  preserved.  Very  rich  oxidized  ore  sometimes  fills  the  central  cavi- 
ties of  the  lode  like  a  thick  brown  mud  of  limonite,  kaolin,  and  quartz  sand,  and 
easily  flows  out  when  the  vein  is  opened. ' ' 

It  should  not  be  inferred,  however,  where  channels  are  large 
and  open  that  the  rich,  gold-bearing  brown  mud  is  necessarily 
a  deposit  from  solution.  It  may  have  been  carried  down  in 
suspension ;  for  similar  rich  mud,  with  2  oz.  of  gold  per  ton, 
was  found  on  the  floor  of  the  12th  level  of  the  Gold  Coin  mine 
after  it  had  been  filled  with  water  and  allowed  to  stand. 

It  thus  appears  that  the  conditions  at  Cripple  Creek,  which 
at  first  appear  fatal  to  the  hypothesis,  may  be  rationally  ex- 
plained, when  it  is  recalled  that  downward  migration  of  gold 
depends  not  only  upon  solution  and  precipitation,  but  requires 
a  circulation,  and  that  conditions  for  a  circulation  here  were 
peculiarly  unfavorable.  They  show  also  that  conditions  for  a 
relatively  rapid  circulation  are  prerequisite,  if  the  dissolved 
gold  is  to  be  carried  below  the  zone  of  mixed  oxides  and  sul- 
phides. 

91  Professional  Paper  No.  54,  U.  S.  Geological  Survey,  p.  199  (1906). 


822  MANGANESE    AND    GOLD-ENKICHMENT. 

17.  Summit  District,  Colo. — This  district  is  located  south- 
west of  Alamosa  near  the  Rio  Grande-Conejos  county-line. 
According  to  R.  C.  Hills,92  the  metal-bearing  horizon  is  near 
the  middle  of  the  Tertiary  eruptive  series  of  south  and  south- 
west Colorado.  The  associated  rocks  are  andesites,  trachytes, 
rhyolites,  etc. ;  but,  unlike  the  eruptives  of  most  Tertiary  dis- 
tricts in  this  province,  these  rocks  appear  to  have  been  closely 
compressed,  yielding  a  series  which,  as  shown  in  Mr.  Hills'& 
sketches,  are  probably  isoclinals.  Some  features  of  the  ore- 
deposits  are  puzzling;  but,  whatever  their  genesis,  they  illus- 
trate very  clearly  the  theory  of  secondary  enrichment — a  fact 
which  was  fully  recognized  by  Mr.  Hills  as  long  ago  as  1883. 

The  ore-bodies,  so  far  as  exposed,  are  rudely  tabular  and 
approximately  vertical.  The  ore  is  chiefly  quartz  and  pyrite, 
but  contains  some  enargite,  galena,  sphalerite,  and  other  min- 
erals. Placers  appear  to  be  of  subordinate  importance.  The 
mineralized  matter  may  be  separated  into  three  divisions  :  (1) 
the  impoverished  zone  near  the  apex;  (2)  the  zone  of  rich  and 
partly-oxidized  ore;  and  (3)  the  low-grade  sulphides.  The 
zone  of  impoverishment,  with  two  exceptions,  includes  the  out- 
crops of  all  the  lodes  and  extends  downward  to  50  ft.  or  more. 
The  zone  of  incompletely-oxidized  ore  extends  to  a  depth  vary- 
ing from  a  few  feet  to  300  ft.  In  this  zone  the  quartz  is 
colored  dark  brown  by  oxides,  and  the  more-highly  auriferous 
material  is  characterized  by  an  abundance  of  brown  oxide. 
The  gold  in  this  ore  carries  only  about  0.025  silver.  All  the 
bonanzas  were,  according  to  Mr.  Hills,  confined  to  this  zone. 
In  some  places  gold  appears  in  a  disseminated  form  in  innum- 
erable small  grains,  so  aggregated  as  to  resemble  a  continuous 
sheet  of  metal.  Locally,  the  grains  unite  and  form  flat  nug- 
gets, one  or  more  ounces  in  weight.  The  occurrence  of  this 
richer  material  is  confined,  according  to  Mr.  Hills,  to  the  im- 
mediate vicinity  of  a  central  channel  which  has  been  filled  with 
earthy  matter,  fragments  of  rock  and  iron  oxides.  Some  of 
the  rich  seams  of  gold  powder  have  been  introduced  into  frac- 
tures which  cut  barite.  Below  the  rich  and  partly-oxidized 
ore,  the  primary  sulphides  appear  to  have  been  unworkable 
under  conditions  then  existing.  There  is,  however,  in  three 
mines 93  a  concentration  of  silver  at  greater  depth  than  that  of 

92  Proceedings  of  the  Colorado  Scientific  Society,  vol.  i.,  p.  20  (1883-84). 

93  Op.  cit.t  p.  35. 


MANGANESE    AND    GOLD-ENRICHMENT.  823 

the  gold-bonanzas.  Mr.  Hills  ascribes  the  two  rich  outcrop- 
ping ore-bodies,  which  are  exceptional  in  this  district,  to  in- 
tense kaolinization  on  either  side  of  the  ore-bodies,  causing 
the  country-rock  to  be  much  more  readily  eroded  than  the 
extremely  hard  quartz  outcrop.  This  consequently  remained 
considerably  above  the  general  surface,  forming  a  precipitous 
ridge,  which  was,  as  he  explains,  protected  from  solution, 
which  went  on  more  vigorously  below,  in  the  places  where 
snow  and  water  accumulated. 

Although  Mr.  Hills  mentions  brown  oxides  at  several  places, 
he  does  not  say  that  they  are  manganiferous. 

Dr.  Raymond94  says  that  the  oxides  include  those  of  pur- 
plish hue. 

18.  Bodie,  Cal. — The  deposits  of  Bodie,  Cal.,  are  east  of  the 
Sierras,  near  the  State-line.     They  are   not  of  the  California 
type,  but  are  associated  with  andesite  and  belong  to  the  late 
Tertiary  group   so   extensively  developed  in  Nevada.     R.  P. 
McLauglilin  95  has  described  the  most  important  mines.     The 
lodes  are  fissure-veins  in   andesite.     Nearly  all  strike   north- 
ward and  are  approximately  parallel.     The  ore  carries  about 
equal  amounts  of  gold  and  silver.     The  deposits  are  developed 
extensively  to  a  depth  of  500  ft.  below  the  surface.     One  shaft 
is  1,000  ft.,  another  1,200  ft.  deep.     Outcrops  of  encouraging 
value    are    rare.     Almost   without   exception   the  veins   have 
failed  to  carry  pay-ore  beyond  500  ft.  below  the  surface ;  but 
above  this  depth  occur  large,  rich  ore-bodies,  which,  according 
to  McLaughlin,  carry  ore  worth  as  high  as  $400  a  ton.    Fault- 
ing and  displacement  are  probably  of  later  date  than  the  period 
of    vein-formation.     Some   of   the   oxidized  ore   carries  man- 
ganese dioxide.     It  is  "  loose  and  clayey  in  texture  and  carries 
some  silver  to  the  exclusion  of  gold."  96 

19.  Exposed    Treasure    Mine,    Cal. — The  Exposed  Treasure 
mine,97  which  is  near  Mojave,  has  produced  considerable  gold 
and  silver.     It  is  in  an  area  of  granitic  rocks  cut  by  quartz- 
porphyry  and   capped  by  rhyolite.     The   lodes  are  probably 
Tertiary  (group  4).     The  Exposed  Treasure  vein   dips  about 
45°  E.  and  is  a  sheeted  brecciated  zone.     Considerable  fissur- 
ing  has  taken  place  since  the  ore  was  deposited. 

94  Mines  and  Mining  West  of  the  Rocky  Mountains,  vol.  x.,  p.  329  (1875). 

95  Mining  and  Scientific  Press,  vol.  xciv.,  No.  25,  p.  796  (June  22,  1907). 

96  Idem,  p.  796. 

97  Courtenay  De  Kalb,  Trans.,  xxxviii.,  310  to  320  (1907). 


824  MANGANESE    AND    GOLD-ENRICHMENT. 

"  .  .  .  While  the  lodes  are  continuous,  and  often  of  great  width,  sometimes 
being  40  ft.  and  more  from  wall  to  wall,  the  pay-streaks,  from  4  to  15  ft.  in  width, 
lie  in  well-defined  chutes  and  overlapping  sheets  or  lenses.  It  is  noteworthy  that 
only  those  chutes  or  lenses  which  now  reach  the  surface  contained  important 
quantities  of  calcite  and  manganese  dioxide." 

The  oxidized  ores  contain  much  Mn02,  the  concentrates  car- 
rying 12  per  cent.  In  the  altered  oxidized  ore  are  kernels  of 
ore  containing  pyrite,  chalcopyrite,  galena,  and  sphalerite,  and 
these  are  richer  in  the  precious  metals  than  the  altered  friable 
ore.  As  observed  by  De  Kalb  : 

"  .  .  .  The  altered  ore  bore  manifest  signs  of  extensive  leaching,  and  where 
it  had  become  almost  completely  decolorized  by  the  removal  of  iron,  the  precious 
metal  contents  had  nearly  disappeared,  and  such  ore  never  contained  copper  except 
in  the  form  of  chrysocolla. 

"  The  absence  of  sulphides  in  all  the  [oxidized]  ores,  except  in  the  cherty  skele- 
tons, and  in  the  undecomposed  kernels  of  hard  ore,  was  very  complete.     The  mill- 
concentrates  (150  into  1)  had  an  average  composition  of  SiO2,  30  ;  FeO,  37    .    ,    . 
and  MnO2,  12  per  cent.     These  concentrates  never  contained  more  than  1.5  per 
cent,  of  sulphur. 

' '  In  the  lower  friable  siliceous  ores,  the  ratio  of  gold  to  silver  was  as  1  to  1 2, 
while  in  the  upper  mangano-calcite  ores  the  ratio  was  1  to  72.  Assays  of  gold-scale, 
and  of  coarse  gold  panned  out,  from  all  parts  of  the  mine,  showed  'a  remarkably 
uniform  alloy  of  1  part  of  gold  to  0.461  part  of  silver.  The  silver  in  the  upper 
portion  of  the  mine  was  present  almost  wholly  in  the  form  of  silver  chloride. 

"On  the  assumption,  from  the  evidence,  that  the  abundance  of  chlorides  would 
prevent  the  leaching-out  of  the  silver  and  its  reconcentration  below  water-level, 
and  that  the  ferric  and  cupric  sulphates  would  have  abstracted  large  quantities  of 
the  gold,  which  would  be  re-deposited  lower  down  together  with  the  copper  in  the 
form  of  secondary  enrichments,  it  was  natural  to  predict  an  ore  below  permanent 
water  rich  in  these  metals,  and  relatively  lean  in  silver.  It  would  be  difficult  to 
•conceive  a  nicer  justification  of  theory  than  that  which  was  afforded  when  develop- 
ment at  length  extended  below  water-level.  The  ore  consisted  of  a  hard  bluish- 
gray  mass  of  original  chert-cemented  breccia,  re-cemented  by  quartz,  with  partial 
replacement  of  the  granite  and  quartz-porphyry  by  silica,  heavily  impregnated  with 
sulphides,  among  which  were  considerable  quantities  of  chalcopyrite,  bornite,  and 
some  covellite.  The  gold-content  of  the  ore  had  increased  150  per  cent,  above  the 
a,verage  in  the  friable  siliceous  ores  on  the  upper  levels,  and  the  ratio  of  the  gold  to 
silver  was  as  1  to  2." 

20.  Tonopah,  Nev. — The  deposits  at  Tonopah,  Nev.,  are 
silver-gold  replacement-veins  in  andesite.  They  are  of  mid- 
dle or  late  Tertiary  age,  but  possibly  somewhat  older  than  the 
Comstock  lode.  Placers  are  not  developed.  The  primary  ore, 
according  to  J.  E.  Spurr,98  is  composed  of  quartz,  adularia,  seri- 
cite,  carbonates  of  lime,  magnesia,  iron,  and  manganese,  with 
argentite,  stephanite,  polybasite,  chalcopyrite,  pyrite,  galena, 

98  Professional  Paper  No.  42,  U.  S.  Geological  Survey,  p.  90  (1905). 


MANGANESE    AND    GOLD-ENRICHMENT.  825 

blende,  silver  selenide,  and  gold  in  an  undetermined  form. 
The  zone  of  oxidation  extends  to  greater  depth  in  the  more 
highly  fractured  places ;  and  for  this  reason  the  brittle  and 
more  broken  lodes  are  more  deeply  oxidized  than  the  wall-rock. 
The  Mizpah  vein  is  for  the  most  part  oxidized  to  a  depth  of 
700  ft.  Standing  ground-water  is  lacking.  The  oxidized  ore 
contains  limonite  and  manganese  dioxide,  with  plentiful  horn- 
silver  and  some  bromides  and  iodides  of  silver.  The  so-called 
oxidized  ore  from  the  outcrop  down  is,  according  to  Spurr,  a 
mixture  of  original  sulphides  (and  selenides),  together  with 
secondary  sulphides,  chlorides,  and  oxides.  At  a  depth  of  500 
ft.  (in  the  Montana  Tonopah  mine)  good  crystals  of  argentite, 
polybasite,  and  chalcopyrite  have  been  formed  freely  in  cracks 
and  druses  of  the  sulphide  ore.  These  minerals  are  later  than 
the  massive  ore;  but  it  cannot  be  shown  that  they  were  not 
deposited  upon  it  by  ascending  waters.  The  case  of  dark  ruby- 
silver  (pyrargyrite)  is  different,  however,  for  this  is  formed  in 
cracks  in  the  oxidized  ore,  and  some  argentite  fringes  minute 
particles  of  horn-silver  as  if  secondary  to  it.  "  The  evidence 
therefore  favors  the  view  that  these  secondary  sulphides  in  the 
oxidized  zone  originated  from  descending  surface  waters,  and 
probably  part,  but  not  all,  of  the  sulphides  in  druses  in  the 
sulphide  ore  have  a  similar  origin." 

The  waters  which  descend  through  the  oxidized  zone  carry 
sulphates  and  chlorides,  and  "wad"  is  plentiful;  but  judging 
from  the  fairly-constant  proportion  of  gold  to  silver  (about  1  to 
100  by  weight)  there  has  been  little  selective  migration  of  gold 
and  silver  during  oxidation,  although  the  vein  has  been  en- 
riched to  some  degree  by  downward  penetration  of  minerals 
leached  from  the  outcrop  as  it  was  eroded.  The  rich  ore- 
shoots,  though  partly  oxidized,  seem  to  be  in  the  main  original 
without  thorough  rearrangement.  According  to  Mr.  Spurr, 
this  may  be  ascribed  in  part  to  the  relatively  scanty  supply  of 
water  in  this  arid  region. 

21.  Goldfidd,  Nev.— The  ledges  of  Goldfield  are  in  middle 
or  late  Tertiary  rocks,  and,  according  to  F.  L.  Rarisome,  were 
probably  deposited  within  1,000  ft.  of  the  surface  at  the  time 
of  deposition.  Ransome  states  convincingly  the  hypothesis 
that  these  deposits  were  formed  by  hot  ascending  solutions 
which  mingled  with  descending  sulphate-water  contaminated 

52 


826  MANGANESE    AND    GOLD-ENRICHMENT. 

by  the  oxygen  of  the  air.  Although  the  deposits  are  probably 
the  most  remarkable  bonanzas  of  native  gold-ores  carrying  little 
silver  which  have  yet  been  discovered,  it  does  not  appear  that 
they 'have  been  enriched  to  any  considerable  extent  since  they 
were  deposited,  for,  as  remarked  by  Ransome,  it  is  difficult  to 
harmonize  the  extent  and  intensity  of  alunitization  which  ac- 
companies the  gold  with  the  hypothesis  of  the  oxidation  and 
enrichment  of  lean  deposits  during  erosion.  The  mine-waters 
are  rich  in  sulphates;  and,  judging  from  the  geographical 
position  of  the  deposits,  they  probably  carry  chlorides.  Man- 
ganese dioxide  is  practically  unknown  in  these  ores,  which  in 
this  respect  differ  from  the  ores  at  Tonopah  and  from  a  great 
many  Tertiary  deposits  of  the  Great  Basin  province.  No  work- 
able placer-deposits  have  been  discovered ;  yet  notwithstanding 
the  fact  that  there  may  have  been  several  hundred  feet  of  vein- 
matter  removed  from  these  deposits  since  they  were  formed, 
there  is  little  reason  to  suppose  that  much  gold  has  migrated 
into  the  existing  bonanzas  from  above.  The  gold  is  very  finely 
divided,  and  could  easily  have  been  scattered,  if  it  had  been 
eroded  with  the  ledges.  As  shown  by  the  analyses  of  deposits 
elsewhere  that  were  formed  close  to  the  surface  by  ascending 
hot  waters,  they  seldom  carry  much  gold.  The  maximum 
deposition  is  lower  down ;  for,  as  soon  as  the  ascending  hot 
waters  are  contaminated  by  ferrous  sulphate  from  the  surface, 
gold  must  be  precipitated. 

The  evidence  offered  at  Goldfield  is  not  out  of  harmony 
with  the  conclusion  that,  in  the  absence  of  manganese,  gold  is 
not  readily  transported  in  mine-waters. 

22.  Manhattan,  Nev. — The  gold-deposits  at  Manhattan,  al- 
though inclosed  in  schists,  are  in  an  area  of  Tertiary  volcanic 
activity,  and  should  be  classed  with  the  deposits  formed  in  Ter- 
tiary times.  Although  the  schists  contain  stringers  of  gold  of 
uncertain  genesis,  the  principal  deposits  are  steeply-dipping 
lodes  of  quartz  and  calcite,  stained  with  iron  and  manganese 
oxides.  Some  placers  are  developed.  Rich  ore  was  found 
very  near  the  surface,  but  it  was  richer  a  few  feet  below  the 
outcrop  than  at  the  surface.  Some  fracturing  has  taken  place 
since  the  deposits  were  formed.  In  many  instances  the  gold 
of  the  pockets  of  rich  ore  is  intimately  associated  with  iron  and 


MANGANESE    AND    GOLD-ENRICHMENT.  827 

manganese  oxides."  In  view  of  the  fact  that  the  unaltered 
sulphides  had  not  been  encountered  when  the  mines  were 
visited,  the  character  of  the  primary  ore  is  unknown  to  me. 

23.  Annie  Laurie  Mine,    Utah. — The  Annie  Laurie  mine,100 
175  miles  south  of  Salt  Lake,  is  in  an  area  of  dacite,  rhyolite 
and  rhyolite-tuff,  and  probably  belongs  to  the  later  Tertiary 
group.    The  vein  is  poorly  exposed  at  the  surface,  being  largely 
covered  by  morainal  material.     Mr.  Lindgren  says : 

"  The  quartz  forms  an  almost  continuous  sheet  along  the  vein,  rarely  less  than 
3  feet  in  thickness  and  often  expanding  to  a  width  of  20  feet  or  more.  As  a  rule 
the  walls  are  poorly  defined  and  slickensides  indicating  motion  are  rare.  In 
places  it  contains,  parallel  to  the  walls,  streaks  of  iron  oxides  and  black,  sooty, 
manganese  ores.  .  . 

"The  mine-workings  have  not  penetrated  below  the  zone  of  oxidation,  and 
neither  the  quartz  nor  the  country-rock  seem  to  contain  any  unoxidized  sulphides." 

In  the  absence  of  extensive  post-mineral  fracturing,  one  would 
suppose  that  the  conditions  for  migration  of  gold  were  not  par- 
ticularly favorable.  Since  the  workings  had  not  penetrated 
sulphide  ore  at  the  date  of  Lindgren's  report,  direct  evidence 
was  lacking. 

24.  The  Bullfrog  District,  Nev.—In  the  Bullfrog  district 101  the 
principal  deposits  are  fissure-veins  in  rhyolite.     The  minerals 
include  pyrite,  quartz,  and  manganiferous  calcite.      Enough 
manganese  is  present  in  the  calcite  to  stain  much  of  the  oxi- 
dized ore  chocolate-brown  or  black.    No  placers  are  developed. 
The  outcrops  were  comparatively  poor,  but  within  a  few  feet 
of  the  surface  good  ore  was  encountered,  and  some  of  the  de- 
posits were  worked  by  open-cut.     Some  of  the  ore-deposits 
decrease  in  value  below  the  400-ft.  level,  where  ore  carrying 
less  than  $5  per  ton  is  encountered.     Since  the  ore  above  this 
level  carried  many  times  this  value,  it  appears  that  there  has 
been  a  secondary  concentration  by  surface-waters,  and  that  the 
rich  ore  is  related  to  the  present  topographic  surface. 

25.  Gold  Circle,  Nev.—The  deposits  of  Midas,  (Sold  Circle102 

99  G.  H.  Garrey  and  W.  H.  Emmons,  Bulletin  No.  303,  U.  S.  Geological  Survey, 
pp.  84  to  93  (1907). 

100  Waldemar  Lindgren,  Bulletin  No.  285,  U.  S.  Geological  Survey,  pp.  87  to  90 
(1906). 

101  Ransome,  Emmons,  and  Garrey,  Bulletin  No.  407,    U.  S.  Geological  Survey 
(1910). 

102  w.  jj   Emmons,  Bulletin  No.  408,  U.  S.  Geological  Survey  (1910). 


828  MANGANESE    AND    GOLD-ENRICHMENT. 

district,  are  in  an  area  of  late  Tertiary  rhyolites.  The  lodes 
are  replacement-veins  and  sheeted  zones  and  carry  consider- 
ably more  gold  than  silver  (value).  In  the  oxidized  zone 
some  of  the  ore  is  rich,  but  the  sulphides  are  comparatively 
regular  in  value  and  give  no  evidence  of  extensive  secondary 
enrichment.  Some  oxidized  ore-shoots  appear  to  have  been 
increased  in  value  by  the  removal  of  substances  more  soluble 
than  gold.  The  minerals  are  chiefly  quartz  and  pyrite.  In 
the  oxidized  zone  are  seams  of  very  rich  gold-ore,  composed 
of  manganese,  limonite,  kaolin,  and  soft  hydrous  silica. 

26.  Delamar  Mine,  Nev. — The  Delamar  mine,  in  southeast- 
ern Nevada,  is  in  quartzite  cut  by  porphyry  dikes  of  acid 
composition.  It  is  presumably  a  Tertiary  deposit,  and  is  pro- 
visionally classed  with  group  4.  The  ore-body  described  by 
S.  F.  Emmons 103  is  related  to  a  strong  zone  of  fracturing  which 
strikes  with  the  quartzite,  but  dips  about  75°,  or  nearly  at 
right  angles  to  the  dip  of  the  quartzite.  The  ore  is  in  shoots, 
or  zones  of  crushed  quartzite.  The  chief  ore-body,  which  is, 
roughly  speaking,  a  long  and  comparatively  thin,  nearly  up- 
right cylinder,  is  divided  into  four  parts  by  a  dike  of  quartz- 
porphyry  and  a  more  basic  dike,  which  cross  nearly  at  right 
angles  in  the  ore-body.  The  ore  follows  the  line  of  intersec- 
tion of  the  two  dikes  rather  closely.  The  ore  at  the  bottom  of 
the  mine  consists  of  quartz  and  pyrite,  which  fill  fractures  in 
the  altered  quartzite.  Where  the  dikes  cross  in  the  ore-body 
the  light-colored  dike  appears  to  be  continuous,  but  notwith- 
standing this  the  line  of  the  dark  dike  across  the  light  one  is 
generally  marked  by  a  slight  stain  of  manganese  dioxide, 
which,  as  stated  by  Mr.  Emmons,  is  characteristic  of  the 
"  black  "  dike,  and  perhaps  gives  it  that  name. 

Oxidation  extends  as  far  down  as  the  tenth  level.  The  ore 
that  has  been  found  below  that  level  is  too  poor  in  grade  to  pay 
for  mining.  The  gold-ore  carries  silver  and  some  copper. 
The  tenor  in  gold  increased  from  the  surface  downward  to 
about  the  7th  level,  although  the  values  were  not  evenly  dis- 
tributed. Some  lots  of  ore  ran  as  high  as  30  oz.  per  ton,  and 
the  richer  parts  of  the  mine  averaged  from  $30  to  $70  per  ton. 
At  the  10th  level  they  had  decreased  to  $4  or  $5  per  ton. 

103  Trans.,  xxxi.,  658  to  675  (1901). 


COGNATE    PAPERS.  829 


COGNATE  PAPERS  NOT  REPUBLISHED  IN  THIS 

VOLUME. 

Many  papers  which  were  considered  for  printing  in  this  vol- 
ume were  not  chosen  because,  though  possessing  merit,  their 
material  did  not  seem  to  constitute  essential  additions  to  the 
science  of  ore-deposits.  A  brief  statement  with  regard  to  each 
is  here  given. 

The  Detection  and  Estimation  of  Small  Quantities  of  Gold  and 
Silver.  By  Luther  Wagoner,  San  Francisco,  Cal.  (Mexican 
Meeting,  November,  1901.  Trans.,  xxxi.,  798-810.) — This 
paper  contains  some  determinations  of  small  amounts  of  gold 
and  silver  in  rocks  and  in  sea-water  by  Luther  Wagoner,  which 
in  part  confirm  and  in  part  differ  from  those  already  given  by 
Don.  It  is  for  chemists  to  determine,  in  the  case  of  such  dif- 
ferences, which  of  the  two  is  the  more  trustworthy,  primarily 
by  a  discussion  of  methods,  but  more  satisfactorily  by  a  new 
series  of  determinations.  In  such  work,  the  practical  impossi- 
bility of  procuring  reagents  that  are  absolutely  free  from  silver 
or  gold  is  a  serious  handicap. 

The  Geology  and  Copper-Deposits  of  Bisbee,  Arizona.  By  F. 
L.  Ransome,  Washington,  D.  C.  (Albany  Meeting,  February, 
1903.  Trans.,  xxxiv.,  618-642.) — This  paper  is  an  abstract  of 
the  geological  relations  of  the  district,  which  were  so  accurately 
determined  by  the  author  that  his  work  has  served  as  the  basis 
of  mining  since  it  was  published.  Genetically,  however,  the 
deposits  are  not  typical.  Indeed,  though  some  contact-meta- 
morphic  minerals  are  found  associated  with  the  ore,  the  author 
is  not  willing  to  assign  a  contact-metamorphic  origin  to  it,  but 
contents  himself  with  saying  that  it  is  genetically  connected 
with  the  intrusion  of  the  porphyry  around  the  periphery  near 
which  it  is  mainly  found.  The  action  of  sulphide  secondary 
enrichment  in  the  district  is  very  clear  and  typical. 

Some  Practical  Suggestions  Concerning  the  Genesis  of  Ore-De- 
posits. By  Max  Boehmer,  Denver,  Colo.  (New  York  Meet- 
ing, October,  1903.  Trans.,  xxxiv.,  449-453.) — The  author  of 


830  COGNATE    PAPERS. 

this  paper  is  a  practical  mining  engineer  who  does  not  profess 
to  be  a  geologist.  The  value  of  his  paper  as  a  contribution  to 
theoretical  views  on  ore-genesis  is  impaired  by  the  fact  that 
some  of  his  premises  are  such  as  would  not  be  admitted  by 
geologists  of  the  present  day. 

Yellow  Ocher  Deposits  of  Cartersville  District,  Bartow  County, 
Ga.  By  Thomas  Leonard  Watson,  Granville,  Ohio.  (New 
York  Meeting,  October,  1903.  Trans.,  xxxiv.,  643-666.)— 
This  paper  is  mainly  descriptive  of  the  yellow  ocher  deposits 
of  the  Cartersville  district  of  Georgia.  At  its  close  it  contains 
the  brief  statement  that  the  ore  is  a  metamorphic  replacement 
of  quartzite  by  material  probably  derived  from  pyrite  existing 
somewhere  in  the  neighborhood. 

The  Garnet-Formations  of  Chillagoe  Copper-Field,  North  Queens- 
land, Australia.  By  George  Smith,  Sydney,  N.  S.  W.  (New 
York  Meeting,  October,  1903.  Trans.,  xxxiv.,  467-478.) — 
This  paper  is  an  interesting  and  apparently  accurate  descrip- 
tion of  copper-  and  lead-deposits  in  Australia,  which,  from  their 
association,  are  evidently  of  contact-metamorphic  origin.  The 
author,  while  suggesting  the  possibility  of  this  origin,  does  not 
commit  himself  to  a  belief  in  it,  because  certain  facts  are  to  him 
unaccountable  on  that  theory. 

Observations  on  Mother-Lode  Gold-Deposits,  California.  By 
W.  A.  Prichard,  Kalgoorlie,  Western  Australia.  (New  York 
Meeting,  October,  1903.  Trans.,  xxxiv.,  454-466.) — This 
paper  is  interesting  as  being  the  views  of  an  able  Australian 
mining  engineer  on  California  gold-deposits  along  the  Mother 
Lode.  It  makes,  however,  no  addition  to  our  knowledge  either 
practical  or  theoretical. 

Geology  of  the  Treadwell  Ore-Deposits,  Douglas  Island,  Alaska. 
By  A.  C.  Spencer,  Washington,  D.  C.  (Lake  Superior  Meeting, 
October,  1904.  J!r<ms.,xxxv.,  473-510.) — This  paper  is  an  elabo- 
rate and  detailed  study  of  the  famous  Treadwell  deposit,  made 
in  the  light  of  eight  years'  exploitation,  since  the  previous 
examination  by  D'r.  George  F.  Becker.  Except  for  some  minor 
petrological  changes,  resulting  from  later  developments,  Dr. 
Spencer's  conclusions  as  to  the  genesis  agree  essentially  with 
those  adopted  by  Dr.  Becker. 


COGNATE    PAPERS.  831 

Features  of  the  Occurrence  of  Ore  at  Red  Mountain,  Ouray 
County,  Colo.  By  T.  E.  Schwarz,  Denver,  Colo.  (Washington 
Meeting,  May,  1905.  Trans.,  xxxvi.,  31-39.) — This  paper  is  a 
criticism  of  Ransome's  description  of  the  Yankee  Girl  and 
adjoining  mines  in  the  San  Juan  district,  and  a  contribution  of 
interesting  additional  facts,  by  T.  E.  Schwarz,  who  was  long 
superintendent  of  the  mines.  This  mine  presents  one  of  the 
most  interesting  instances  of  the  action  of  secondary  enrich- 
ment by  downward-circulating  waters. 

Genesis  of  the  Ore-Deposits  at  Bingham,  Utah.  By  J.  M. 
Boutwell,  Washington,  D.  C.  (Washington  Meeting,  May, 
1905.  Trans.,  xxxvi.,  541-580.) — In  spite  of  its  title,  this  paper 
has  been  judged  to  be  more  descriptive  than  theoretical,  inas- 
much as  the  discussions  apply  only  to  this  special  group  of  de- 
posits, which,  like  those  of  Bisbee,  are  not  distinctly  typical  of 
any  one  particular  form  of  genesis,  and  do  not,  therefore,  con- 
stitute a  definite  contribution  to  generally  applicable  theories. 
The  paper  contains,  however,  a  careful  and  detailed  enumera- 
tion and  discussion  of  the  facts  which  bear  upon  the  origin  of 
the  three  classes  into  which  the  author  divides  the  Bingham 
deposits. 

The  Origin  of  Vein- Filled  Openings  in  Southeastern  Alaska. 
By  A.  C.  Spencer,  Washington,  D.  C.  (Washington  Meeting, 
May,  1905.  Trans.,  xxxvi.,  581-586.) — This  paper  is  a  discus- 
sion of  the  physical  strains  which  may  have  produced  the  vein- 
openings  of  the  regions  cited,  and  is  intended  by  the  author  to 
indicate  certain  conditions  under  which  the  deformation  of 
rocks  by  their  own  weight  might  lead  to  the  production  of 
fractures  in  which  vein-deposits  could  be  formed. 

Lead-  and  Zinc-Deposits  of  the  Virginia- Tennessee  Region.  By 
Thomas  Leonard  Watson,  Blacksburg,  Va.  (British  Columbia 
Meeting,  July,  1905.  Trans.,  xxxvi.,  681-737.) — This  paper 
is  a  detailed  and  scientific  description  of  all  the  features  and 
characteristics  of  these  important,  but  little  known,  deposits, 
together  with  a  chemical  and  genetic  discussion.  Only  a  single 
deposit  mentioned  is  connected  genetically  with  igneous  in- 
trusions; the  others,  in  the  opinion  of  the  author,  are  concen- 
trations, along  zones  of  fracture  (largely  structural  anticlines), 


832  COGNATE    PAPERS. 

of  material  originally  disseminated  in  the  sedimentary  rocks. 
The  deposits  in  limestone  have  been  formed  by  replacement 
through  the  agency  of  circulating,  but  not  necessarily  deep- 
seated,  waters. 

The  Secondary  Enrichment  of  Copper -Iron  Sulphides.  By 
Thomas  T.  Read,  New  York,  N.  Y.  (Bethlehem  Meeting, 
February,  1906.  Trans.,  xxxvii.,  297-303.) — This  paper  pre- 
sents the  results  of  experiments  made  by  the  author  to  illus- 
trate the  reactions  that  go  on  in  the  process  of  secondary  en- 
richment. Certain  errors  in  the  experiments  are  shown  in 
the  discussion  by  the  chemist,  E.  C.  Sullivan,1  which  throw 
some  doubt  on  the  accuracy  of  the  results,  but  the  investiga- 
tion is  along  an  important  line,  and  is  instructive,  even  if  all 
the  conclusions  may  not  be  accepted. 

The  Mojave  Mining-District  of  California.  By  Charles  E.  W. 
Bateson,  New  York,  N.  Y.  (Bethlehem  Meeting,  February, 
1906.  Trans.,  xxxvii.,  160-177.) — This  paper  is  descriptive  of 
one  of  the  little-known  mining-districts  of  the  western  mining- 
region  of  southern  California,  with  a  discussion  of  its  general 
geological  relations. 

The  Geology  and  Petrography  of  the  Goldfield  Mining-District, 
Nevada.  By  John  B.  Hastings,  Denver,  .Colo.,  and  Charles  P. 
Berkey,  New  York,  1ST.  Y.  (Bethlehem  Meeting,  February, 
1906.  Trans.,  xxxvii.,  140-159.)— This  paper  is  the  result  of 
a  reconnaissance  of  this  important  district  made  in  May  and 
June,  1905.  It  does  not  contain  any  genetic  conclusions  with 
regard  to  the  ores.  Such  may  be  found,  however,  in  subse- 
quent publications  of  the  U.  S.  Geological  Survey  concerning 
this  district. 

The  Tin-Deposits  of  the  Kinta  Valley,  Federated  Malay  States. 
By  William  R.  Rumbold,  Oruro,  Bolivia,  So.  America.  (Lon- 
don Meeting,  July,  1906.  Trans.,  xxxvii.,  879-889.) 

The  South  African  Tin-Deposits.  By  William  R.  Rumbold, 
Oruro,  Bolivia,  So.  America.  (New  York  Meeting,  April,  1907. 
Trans.,  xxxix.,  783-789.) — These  two  papers,  by  the  same 

1  Trans.,  xxxvii.,  893  to  895  (1906). 


COGNATE    PAPERS.  833 

author,  are  descriptive  of  tin-deposits  in  the  Kinta  valley  of  the 
Malay  States,  and  of  South  Africa,  respectively.  These  descrip- 
tions are  interesting  because  of  the  rarity  of  such  deposits ;  but 
the  papers  contain  nothing  of  genetic  importance,  though  the 
author  is  inclined  to  consider  it  possible  that  some  of  the  Kinta 
valley  deposits  were  formed  in  limestone.  Elsewhere2  the 
author  has  written  an  important  paper  on  the  Bolivian  tin- 
deposits,  in  which  he  disproves  the  hitherto  generally-accepted 
idea  that  these  new  economically-important  deposits  differ 
genetically  from  tin-deposits  in  other  parts  of  the  world. 

Geology  and  Mining  of  the  Tin-Deposits  of  Cape  Prince  of  Wales, 
Alaska.  By  Albert  Hill  Fay,  New  York,  N.  Y.  (Toronto 
Meeting,  July,  1907.  Trans.,  xxxviii.,'  664-682.) — This  paper 
is  a  description  of  the  tin-deposits  of  the  Seward  Peninsula  of 
Alaska.  While  the  tin,  as  elsewhere,  is  genetically  associated 
with  granite,  some  of  it  is  found  in  limestone. 

The  Extraordinary  Faulting  at  the  Berlin  Mine,  Nevada.  By 
Ellsworth  Daggett,  Salt  Lake  City,  Utah.  (New  York  Meet- 
ing, April,  1907.  Trans.,  xxxviii.,  297-309.) — This  paper  is  a 
complete  reconstruction,  by  descriptive  geometry,  of  a  most 
remarkably  faulted  fissure-vein. 

The  White  Knob  Copper-Deposits,  Mackay,  Idaho.  By  J.  F. 
Kemp,  New  York,  N.  Y.,  and  C.  G.  Gunther,  Clifton,  Ariz. 
(New  York  Meeting,  April,  1907.  Trans.,  xxxviii.,  269-296.) 
— This  paper  is  the  description  of  a  singular  occurrence  of 
contact-metam orphic  copper-ore,  which  is  found,  not  in  the 
limestone  which  has  been  intruded  by  granite,  but  in  quartz- 
porphyry  between  this  limestone  and  the  granite,  the  limestone 
itself  being  singularly  free  from  contact-metamorphic  products. 

The  Vein-System  of  the  Standard  Mine,  Bodie,  Cal.—Bj  E. 
Gilman  Brown,  London,  England.  (New  York  Meeting,  April, 
1907.  Trans.,  xxxviii.,  343-357.) — This  paper  is  a  description 
of  a  series  of  very  productive  and  complicatedly-faulted  gold- 
bearing  veins  in  eruptive  rocks. 

The  Ore-Deposits  of  the  Joplin  Region,  Missouri.     By  F.  L. 

2  Economic  Geology,  vol.  iv.,  p.  329  (1909). 


834  COGNATE    PAPERS. 

Clerc,  Denver,  Colo.  (New  York  Meeting,  April,  1907.  Trans., 
xxxviii.,  320-343.) — This  paper  is  an  interesting  account  of 
this  much-described  region  by  one  who  has  long  been  practi- 
cally familiar  with  it,  and  whose  views  as  to  the  genesis  of  the 
ores  differ  in  some  respect  from  those  that  have  been  published 
by  other  geologists. 

Geology  of  the  Exposed  Treasure  Lode,  Mojave,  California. 
By  Courtenay  De  Kalb,  Los  Angeles,  Cal.  (New  York  Meet- 
ing, April,  1907.  Trans.,  xxxviii.,  310-319.) — This  paper  is  a 
description  and  discussion  of  the  geological  relations  of  this, 
the  most  important  deposit  of  the  Mojave  district,  from  the 
genetic  point  of  view. 

The  Occurrence  of  Nickel  in  Virginia*.  By  Thomas  Leonard 
Watson,  Blacksburg,  Va.  (Toronto  Meeting,  July,  1907. 
Trans.,  xxxviii.,  683-697.)  This  paper  is  a  description  of  an 
occurrence  of  nickel  with  pyrrhotite  in  gabbro,  which  is  intru- 
sive in  crystalline  schists.  The  author  does  not  regard  the 
sulphides  as  magmatic  segregations,  but  as  a  later  introduction, 
taking  place  after  the  whole  eruptive  body  had  been  meta- 
morphosed. 

Geology  of  the  Virginia  Barite-Deposits.  By  Thomas  Leonard 
Watson,  Blacksburg,  Ya.  (Toronto  Meeting,  July,  1907. 
Trans.,  xxxviii.,  710-733.) — This  paper  is  a  description  of  the 
manner  of  occurrence  of  the  many  and  varied  barite-deposits 
of  Yirginia.  The  author  regards  this  mineral  as  for  the  most 
part  the  result  of  concentration  by  circulating  waters  of  mate- 
rial once  disseminated  through  the  limestone. 

The  Promontorio  Silver-Mine,  Durango,  Mexico.  By  Francis 
Church  Lincoln,  New  York,  N.  Y.  (Toronto  Meeting,  July, 
1907.  Trans.,  xxxviii.,  734-746.)  This  deposit  is  a  vein  in 
rhyolite-porphyry  carrying  primarily  sulphides  of  lead  and  zinc 
with  less  iron  and  copper.  The  silver  occurs  mainly  in  the 
native  state,  as  the  result  of  secondary  enrichment. 

Ore-Deposits  of  the  Eastern  Gold-Belt  of  North  Carolina.  By 
W.  0.  Crosby,  Boston,  Mass.  (Toronto  Meeting,  July,  1907. 
Trans.,  xxxviii.,  849-856.)  This  paper,  descriptive  of  certain 
gold-mines,  contains  in  the  introduction  a  classification  of  the 


COGNATE    PAPERS.  835 

gold-veins  of  this  region,  based  on  geological  relations  and 
genesis,  which  may  prove  of  practical  use  to  mining  engineers 
in  that  district,  if  its  generalizations  be  confirmed.  The  gold- 
deposits  in  the  central  and  southern  parts  of  the  State  will  be 
found  treated  by  L.  C.  Graton.3 

The  Evergreen  Copper-Deposits,  Colorado. — By  Etienne  A.  Rit- 
ter,  Colorado  Springs,  Colo.  (Toronto  Meeting,  July,  1907. 
Trans.,  xxxviii.,  751-765.) — This  paper  describes  the  occurrence 
of  original  bornite  in  a  fresh-looking  eruptive  rock  of  remark- 
able composition,  which  cuts  the  crystalline  schists.  Accord- 
ing to  the  author,  the  copper-mineral  in  this  dike  is  a  pneuma- 
tolytic  or  sublimation-product,  and  has  not  been  subjected  to 
secondary  enrichment;  whereas,  the  copper-minerals  in  the 
adjoining  schists,  which  include  also  chalcopyrite,  have  been 
secondarily  enriched  to  chalcocite  and  covellite. 

Genesis  of  the  Lake  Valley,  New  Mexico,  Silver-Deposits.  By 
Charles  R.  Keyes,  Socorro,  IS".  M.  (New  York  Meeting,  Febru- 
ary, 1908.  Trans.,  xxxix.,  139-169.) — This  paper  is  a  descrip- 
tion of  the  geological  relations  of  these  long  ago  abandoned  de- 
posits with  the  views  of  the  author  as  to  their  genesis — views 
which  may  not  be  generally  accepted,  but  which,  owing  to  the 
condition  of  the  district,  are  difficult  to  controvert. 

Borax-Deposits  of  the  United  States.  By  Charles  R.  Keyes, 
Des  Moines,  Iowa.  (Spokane  Meeting,  September,  1909. 
Trans.,  xl.,  674-710.)  This  paper  is  a  description  by  the  same 
author  of  the  various  borax-deposits  in  the  western  part  of  the 
United  States,  including  Death  valley,  Furnace  canyon,  and 
the  Mojave  desert,  with  some  considerations  on  the  chemis- 
try of  borax-deposits  in  general. 

8  Bulletin  No.  293,  U.  S.  Geological  Survey  (1906). 


ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS.  837 


A  Selected  List  of  the  More  Important  Contributions  to 
the  Investigation  of  the  Origin  of  Metalliferous  Ore- 
Deposits. 

BY  J.    D.    IRVING,    H.    D.    SMITH,   AND   H.    G.    FERGUSON. 

CONTENTS. 


PAGE. 

INTRODUCTION, 839 

LIST  OF  ABBREVIATIONS  USED, 841 

LIST  OF  REFERENCES  (Alphabetically  Arranged), 847 

GENERAL  TREATISES  ON   MINERAL  DEPOSITS, 908 

ASCENSION  THEORIES, 908 

CAVITIES  IN  KOCKS, -  .  909 

General,      909 

Pore-Spaces, 909 

Amygdaloidal  Cavities, •  .    .  909 

Fissures, .  • 909 

Joints, 909 

Gash- Veins  and  Pitches, 910 

Dolomitization-Cavities, 910 

Saddle-Keefs, 910 

Solution-Cavities, • 910 

Cavities  Due  to  Fissility,  Cleavage,  and  Metamorphism, 910 

Depth  to  which  Cavities  may  Extend  and  Exist.     See  under  Depth. 

CONTACT-METAMORPHIC  DEPOSITS, • 910 

Character  and  Genesis  of, 910 

Chemical  and  Physical  Changes  which  Occur  during  Contact-Meta- 

morphism, • 910 

Contact-Deposits  of  Copper, 910 

Gold  and  Silver, ."..*....,.. 911 

Cobalt, 911 

Silver  and  Lead,     ....*.................  911 

Iron,    i    ............;...  911 

Tin,    %   .   .   .   .   .   .  \    ......    .    .    .   .    . 911 

Zinc, ..."...........  911 

Miscellaneous, 911 

CLASSIFICATION  OF  ORE-DEPOSITS  (Chronologically  Arranged),     .   .   .   .  911 

DEFINITION  OF  TERM  "ORE," - 912 

DEPTH,  INFLUENCE  OF,  ON  ORE-DEPOSITION, .  912 

General, -*.".......  912 

Depth  to  which  Cavities  Extend, .'.*.'. 912 

Changes  in  Primary  Mineralogy  with  Depth, 912 

DESCENSION  THEORIES, 912 


838  ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS. 

DETRITAL  DEPOSITS, 912 

General, 912 

Distribution  of  Gold  in  Placers,  Origin  of  Nuggets,  etc., 913 

Gold-Placers,     • *  • 913 

Stream- Placers, 913 

Fossil-Placers, 913 

Australasia, 913 

Black  Hills, 913 

California, 913 

South  Africa, 914 

Beach- Placers, 914 

^Eolian  Placers, 914 

Tin-Placers, 914 

Platinum-Placers, 914 

General, 914 

Individual  Localities, 914 

Iron-Placers, ,    .  914 

DISSEMINATED  METALS  ORIGINAL,  IN  EOCKS, 914 

General, 914 

In  Eruptive  Rocks, 914 

In  Sedimentary  Eocks, 915 

In  Metamorphic  Eocks, 915 

ELECTRICAL  ACTION  IN  ORE-DEPOSITION, 915 

EMANATIONS  FROM  IGNEOUS  MAGMAS, 915 

General, 915 

Magmatic  vs.  Meteoric  Waters, 916 

Pegmatitic  Ore-Deposits, 916 

Pneumatolysis, 916 

Hydrothermal  Emanations, 916 

EXPERIMENTAL  DATA  APPLIED  TO  ORE-DEPOSITION, 917 

FAULTS  AND  FAULTING, • 917 

FISSURE- VEINS, 917 

General, 917 

Fissures.     (See  especially  also  under  "Cavities  in -Eocks"),     ....  917 

Systems  of, 917 

Origin  of, 918 

Displacements  and  Irregularities  of.     Also  Eelative  Ages,     .    .    .  918 

Classification  of  Fissure- Veins, 918 

Structure  and  Arrangement  of  Mineral  Contents  of  Fissures,     .    .  918 

The  Filling  of  Mineral  Veins, 918 

GEOGRAPHIC  DISTRIBUTION  OF  METALLIFEROUS  DEPOSITS, 919 

GEOLOGIC  AGE  OF  ORE-DEPOSITS, 919 

LATERAL  SECRETION, 919 

MAGMATIC  DIFFERENTIATION, 919 

General  Discussion, 919 

Applied  Chiefly  to  Eocks, 919 

Applied  to  Ore-Deposits, 919 

Of  Oxide  Deposits,  . 919 

Of  Sulphides, •'...'..' 920 

Comparison  with  Solidification  of  Slags, 920 


ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS.  839 

METASOMATISM.     See  Replacement. 

MINERALOGY  OF  METALLIFEROUS  ORES, 920 

ORE-SHOOTS, 921 

General, 921 

Shoots  as  Described  in  Individual  Localities, 921 

ORIGIN  OF  METALLIFEROUS  DEPOSITS, 921 

Historical  Resume's  of  Literature  of  Ore-Deposits, 921 

Summaries  of  Theories  of  Origin  of  Particular  Metals, 921 

Origin  of  Deposits  in  Particular  Districts, 922 

General  Papers  Dealing  with  the  Origin  of  Ore-Deposits  as  a  Whole,  .  922 

OXIDATION.     See  under  Superficial  Alteration. 

ORE-SOLUTIONS, 923 

Nature  and  Origin  of  the  Agent  of  Deposition, 923 

Processes  of  Deposition  from  Solutions, 923 

Temperatures  and  Pressures  of  Solutions  and  Their  Effect  on  the  Re- 
sulting Ore-Deposits, 924 

PRECIPITATION  FROM  SOLUTION.     See  under  Ore-Solutions. 

PHYSICAL  CONDITIONS  OF  ORE-DEPOSITION.     See  under  Ore-Solutions. 

PRESSURE   AND   TEMPERATURE   IN   ORE-DEPOSITION.     See  under  Ore- 
Solutions  ;  also  Contact-Metamorphic  Deposits. 

REGIONAL  METAMORPHISM.    Deposits  Produced  by  It  and  General  Effects 

on  Previously-formed  Deposits, 924 

REPLACEMENT, 924 

General  Discussions, 924 

Criteria  of, 925 

Replacement  Advocated  and  Discussed  for  Individual  Ore-Deposits,    .  925 

SEDIMENTARY  PROCESSES  AS  ORE-BUILDERS, 925 

Ores  Supposed  to  be  a  Direct  Result  of  Sedimentary  Processes,     .    .    .  925 
Ores  Supposed  to  be  Derived  by  Later  Concentration  of  Sedimentary 

Particles  in  Rocks, 925 

SUBLIMATION, 926 

SUPERFICIAL  ALTERATION, 926 

Ground- Water  and  Its  Movement, 926 

Oxidation,      926 

Secondary  Sulphide  Enrichment,      927 

UNDERGROUND  WATERS, 927 

Bibliography, 927 

Mine-Waters, 927 

General  Discussions.    ...        927 

WALL-ROCK  :  EFFECT  OF,  IN  ORE-DEPOSITION, 928 

INTRODUCTION. 

The  purpose  of  this  bibliography  is  to  present  a  list  of  the 

more  important  contributions  to  the  problems  involved  in  the 
origin  of  ore-deposits.  The  literature  of  this  subject  has  be- 
come so  voluminous  that  it  is  a  matter  of  great  difficulty  for 
any  one  to  glance  over  all  that  is  published,  or  even  to  keep 
informed  of  the  appearance  of  new  and  important  papers. 


840  ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS. 

This  difficulty  is  felt  keenly  by  those  whose  work  is  exclu- 
sively concerned  with  the  study  of  ore-deposits,  but  to  a  very 
much  greater  degree  by  mining  engineers,  who  are  chiefly 
occupied  with  business  affairs,  and  who  can  spare  the  time 
only  to  read  those  books  which  seem  immediately  pertinent  to 
the  work  with  which  they  are  at  the  moment  occupied. 

Much  that  is  of  great  practical  value  has  appeared  of  recent 
years  on  this  subject;  many  special  problems  have  been  dis- 
cussed in  the  literature  which  vitally  affect  not  only  the  thought 
of  the  geologist  and  investigator,  but  the  estimates  of  value  and 
plans  for  mining  development  which  are  the  work  of  the 
engineer. 

The  idea  which  is  kept  in  view  in  compiling  this  bibliogra- 
phy is  that  of  grouping  together  all  references  which  refer  to 
any  particular  problem  in  ore-deposition.  Much  of  the  litera- 
ture of  ore-deposits,  and  especially  the  geological  reports  of  Fed- 
eral and  State  surveys,  is  necessarily  geographically  arranged. 
While  attempts  to  find  information  concerning  any  geographic 
locality,  therefore,  offer  no  difficulty,  it  is  often  extremely  difficult 
to  find  discussions  of  any  particular  problem  in  ore-deposition. 
The  writers  have  for  this  reason  attempted  in  this  paper  to 
compile  an  index  according  to  the  problem  upon  which  infor- 
mation is  sought.  Thus  the  secondary  enrichment  of  copper- 
ores,  the  segregation  of  the  sulphides  from  molten  magmas, 
the  relation  of  eruptive  rocks  to  deposits  of  the  metallifer- 
ous ores,  etc.,  are  given  as  headings. 

The  paper  is  arranged  in  two  portions.  In  the  first,  is  a  list 
of  the  more  important  papers  bearing  either  directly  or  in- 
directly on  the  genesis  of  ore-deposits.  The  second  part  is  a 
classification  and  rearrangement  of  the  list  under  separate 
headings  representing  the  departments  and  elements  of  the 
subject.  In  this  way  it  is  possible  to  follow  each  special 
problem  through  the  literature. 

In  presenting  this  list  the  writers  wish  particularly  to  em- 
phasize that  it  makes  no  claim  to  completeness.  A.  few  only 
of  many  possible  titles  are  selected.  The  original  list  of  papers 
is,  therefore,  far  from  exhaustive.  All  works  on  non-metallic 
deposits  have  been  excluded,  as  well  as  all  works  on  general 
geology,  except  those  which  contain  especially  appropriate  dis- 
cussions of  ore-deposits.  Descriptive  reports  on  mining-dis- 


ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS.  841 

tricts  which  offer  no  conclusions  on  genesis,  and  which  attempt 
no  solution  of  problems  connected  with  their  description,  have 
also  been,  for  the  most  part,  excluded,  as  their  inclusion 
would  have  swelled  this  paper  beyond  all  due  proportion. 
Many  references  are  given  to  books  not  primarily  concerned 
with  ore-deposits,  as  these  aid  in  the  comprehension  of  the 
problems  involved.  Except  where  omission  of  titles  has  been 
inadvertent,  the  writers  assume  full  responsibility  for  the 
exclusion  of  papers  which  have  seemed  to  them  of  minor 
importance. 

It  is  hoped,  therefore,  that  this  brief  theoretical  index  will 
be  of  service.  The  writers  are  conscious  that  it  lacks  much 
both  in  amplitude  and  in  the  selection  of  references,  but  it  will 
in  any  event  serve  to  indicate  the  lines  on  which  a  valuable 
bibliography  may  be  compiled. 

ABBREVIATIONS. 

In  order  to  economize  space  the  following  abbreviations  have 
been  used  in  this  bibliography : 

Of  General  Import. 

Hist. — Chiefly  of  historic  interest. 

Rec. — Strongly  recommended  as  of  value  in  the  understanding  of  ore-genesis. 

E.  — Elementary. 

D. — Of  no  especial  importance. 

Des. — Mainly  descriptive,  and  only  incidentally  concerned  with  questions  of  ore- 
genesis. 

Geol. — Dealing  with  geological  problems  which,  though  not  directly  concerned 
with  ore-deposits,  have  important  applications  to  the  subject. 

Rev. — Review  or  reviewed. 

Abbreviations  for  Periodical  Publications. 

Abb.  K.  Bayer.  Akad.  d.  Wissc. — Abbildung  der  Kdniglwhe  Bayer  ische  Akademie  der 
Wissenschaften ;  Munich,  Germany. 

Act.  Soc.  Espanola  d.  Hist.  Nat. — Ada  de  la  Sociedad  Espanola  de  Historia  Natural. 

Am.  Geol. — American  Geologist ;  Minneapolis,  Minn.  (Merged  with  Econ.GeoL, 
1906.) 

Am.  Jour.  Sci. — American  Journal  of  Science  ;  New  Haven,  Conn. 

Ann.  d.  Mines. — Annales  des  Mines  ;  Paris,  France. 

Ann.  d.  Min.  de  Belg. — Annales  des  Mines  de.  Belgiqm  ;  Brussels,  Belgium. 

Ann.  N.  Y.  Acad.  Sci. — Annals  of  the  New  York  Academy  of  Sciences  ;  New  York,  N.  Y. 

Ann.  Rept.  Cal.  State  Min. — Annual  Report  of  the  California  State  Mineralogist ;  Sac- 
ramento, Cal. 

Ann.  Rept.  Smith.  Inst. — Annual  Report  of  the  Smithsonian  Institute  ;  Washington, 
D.  C. 

53 


842  ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS. 

Ann.   Eept.  U.  S.  G.   S. — Annual  Report  of  the   United  States  Geological  Survey ; 

Washington,  D.  C. 

Ann.  Soc.  Geol.  d.  Belg. — Annales  de  la  Societe  Geologique  de  Belgique;    Liege,  Bel- 
gium. 

Archivf.  prak.  Geol. — Archiv  fur  praktische  Geologie;  Vienna,  Austria. 
Ark.  Geol.  Sur. — Geological  Survey  of  Arkansas  ;  Little  Bock,  Ark. 
Aust,  Min.  Stand. — Australian  Mining  Standard  ;  Sydney,  N.  S.  W.,  Australia. 
Australas.  Inst.  Min.  Eng. — Australasian  Institute  of  Mining  Engineers  ;  Melbourne, 

Victoria,  Australia. 

Sal.  Zeit. — Balneologische  Zeitung  ;  Berlin,  Germany. 
Ber.  d.  K.   K.  Ak.  d.  W. — Berichte  der  Kaiserlich  Koniglichen  Akademie  der  Wis- 

senschaft.  ;  Vienna,  Austria. 

Berg-  u.  Hiltt.  Rund. — Berg-und  Huttenmdnnische  Rundschau  ;  Kattowitz,  Germany. 
Berg-  u.  Hiltt.  Zeit. — Berg-  und  Hiittemdnnische  Zeitung  ;  Freiberg,  Germany. 
Bol.    Inst.    Geol.    Mex. — Boletin  del  Institute    Geologico  de  Mexico;    Mexico   City, 

Mexico. 
Bol.  Soc.  Geol.  de  Mex. — Boletin  de  la  Sociedad  Geologica  de  Mexico  ;  Mexico  City, 

Mexico. 
Bull.  A.  I.  M.  E. — Bulletin  of  the  American  Institute  of  Mining  Engineers ;    New 

York,  N.  Y. 
Bull.  Can.  Dept.  Mines. — Bulletin  of  the  Department  of  Mines,  Mines  Branch,  Canada; 

Ottawa,  Canada. 
Bull.    Com.    Geol.    Fin. — Bulletin   de  la   Commission   Geologique  de    la   Finlande  ; 

Helsingfors. 
Bull.  Dept.  Geol.  Univ.  Gal.  — Bulletin  of  the  Department  of  Geology  of  the  University 

of  California;  Berkeley,  Cal. 
Bull.  Dept.  Mines,  Tasm. — Bulletin  of  the  Department  of  Mines,  Tasmania;  Hobart, 

Tasmania. 
Bull.  Geol.  Nat.  Hist.  Sur.  Minn. — Bulletin  of  the   Geological  and  Natural  History 

Survey  of  Minnesota ;  St.  Paul,  Minn. 

Bull.  Geol.  Soc.  Am. — Bulletin  of  the  Geological  Society  of  America  ;  Rochester,  N.Y. 
Bull.  Geol.  Sur.   W.  Aust. — Bulletin  of  the  Geological  Survey  of   Western  Australia; 

Perth,  Western  Australia. 

Bull.  N.  Y.  State  Mus. — Bulletin  of  the  New  York  State  Museum  ;  Albany,  N.  Y. 
Bull.  N.  Z.  Geol.  Sur. — Bulletin  of  New  Zealand  Geological  Survey;   Wellington, 

N.  Z. 
Bull.  No.  Car.  Geol.  Sur. — Bulletin  of  the  North  Carolina  Geological  Survey  ;  Ealeigh, 

N.  C. 

Bull.  Soc.  Beige  de  Geol. — Bulletin  de  la  Societe  Beige  de  Geologie  ;  Brussels,  Belgium. 
Bull.  Soc.    Geol.   de  France. — Bulletin  de  la  Societe  Geologique  de  France;  Paris, 

France. 
Bull.  Soc.  de  VInd.  Min.— Bulletin  de  la  Societe  de  V Industrie  Minerale  ;  St.  Etienne, 

France. 

Bull  U.  S.  G.  S.— Bulletin  of  the  United  States  Geological  Survey  ;  Washington,D.  C. 
Bull.   Wis.  Geol.  Nat.  Hist.  Sur. — Bulletin  of  the  Wisconsin  Geological  and  Natural 

History  Survey  ;   Madison,  Wis. 

Cal.  St.  Min.  Bu. — California  State  Mining  Bureau ;  San  Francisco,  Cal. 
Can.  Dept.  Mines. — Canadian  Department  of  Mines;  Ottawa,  Canada. 
Can.  Geol.  Sur.,  Sum.  Rept. — Summary  Report  of  the  Canadian  Geological  Survey  ; 

Ottawa,  Canada. 
Can.  Min.  Jour. — Canadian  Mining  Journal;  Toronto,  Canada. 


ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS.  843 

Can.  Min.  Rev. — Canadian  Mining  Review ;  Toronto,  Canada. 

Cent.  f.  Min.  Geol.  u.  Pal. — Centralblatt  fur  Mineralogie,  Geologie  and  Paleontologie  ; 

Stuttgart,  Germany. 

Chem.  News. — Chemical  News ;  London,  England. 

Compt.  rend.  Acad.  Sci. — Comptes  rendus  de  1J  Academic  des  Sciences  ;  Paris,  France. 
Compt.  rend.  Cong.  Geol.  Int. — Comptes  rendus  du  Congres  Geologique  Internationale. 

Published  every  three  years  at  the  place  where  the  session  is  held. 
Compt.  rend.  Soc.  de  V Ind.  Min. — Comptes  rendus  de  la  Societe  de  V Industrie  Mine- 
rale;  St.  Etienne,  France. 
Denkschr.  Akad.  Wien. 
Deut.  Naturforsch.  u.  Aert. — Deutsche  Naturforscher  und  Aertze  Gesellschaft ;  Leipzig, 

Germany. 

E.  and  M.  Jour. — Engineering  and  Mining  Journal ;  New  York,  N.  Y. 
Econ.  Geol. — Economic  Geology;  Urbana,  111. 
Ess.  Gluck. — Essener  Gluckauf;  Essen,  Germany. 

Field  Col.  Mas.  Pub. — Field  Columbian  Museum  Publications;  Chicago,  I1L 
Geog.  Jahresheft. — Geognostiche  Jahreshefte;  Cassel,  Germany. 
Geog.  May. — Geographical  Magazine  ;  London,  England. 
Geol.  Centralb. — Geologisches  Centralblatt;  Leipzig,  Germany. 
Geol.  For.   i  Stock.   Fdrhand. — Geologiska  Foreningens  i  Stockholm  F  or  handling  ar  ; 

Stockholm,  Sweden. 

Geol.  Mag. — Geological  Magazine  ;  London,  England. 
Geol.  Sur.  Ark. — Arkansas  Geological  Survey ;  Little  Bock,  Ark. 
Geol.  Sur.  Can. — Geological  Survey  of  Canada  ;  Ottawa,  Canada. 
Geol.  Sur.  Eng.  and  Wales. — Memoirs  of  Geological  Survey  of  England  and  Wales; 

London,  England- 

Geol.  Sur.  Ga. — Geological  Survey  of  Georgia;  Atlanta,  Ga. 
Geol.  Sur.  Gt.  Brit. — Geological  Survey  of  Great  Britain;  London,  England. 
Geol.  Sur.  Ky. — Bulletin  of  Kentucky  Geological  Survey  ;  Lexington,  Ky. 
Geol.  Sur.  N.  S.  W. — Memoirs  of  Geological  Survey  of  New  South  Wales  ;  Sydney, 

Australia. 
Geol.   Sur.    Queensl. — Publications  of  Geological  Survey   of  Queensland;    Brisbane, 

Australia. 
Geol.   Sur.  So.   Aust. — Report  of  Geological  Survey  of  South  Australia;   Adelaide, 

Australia. 
Geol.  Sur.   W.  Aust.— Bulletin  of  the  Western  Australia  Geological  Survey;   Perth, 

Western  Australia. 

Gluckauf. — Gluckauf,  Essen,  Germany. 
Jahrb.  d.  K.  K.  Geol.  Reichsanst. — Jahrbuch  der  Kaiserlich  Koniglichen  Geologische 

Reichsanstalt ;  Vienna,  Austria. 
Jahrb.  d.  Kgl.  Pr.   Geol.  Landesanst. — Jahrbuch  der  Koniglich  Preussichen   Geolog- 

ischen  Landesanstalt  und  Bergakademie  ;  Berlin,  Germany. 
Jahrb.  d.  Naturhist.  Landes.  in   Kdrnten. — Jahrbuch  der  Naturhistorisches   Landes- 

museums  in  Kdrnten;  Klagenfurt,  Austria-Hungary. 
Jahrb.  f.  Berg-  und  Hiitt.   im  Konig.  Sachs. — Jahrbuch  fur  Berg-  und  Hiittenwesen 

im  Konigreich  Sachsen  ;  Freiberg,  Germany. 

Jour.    Am.  Chem.  Soc. — Journal  of  the  American  Chemical  Society;  Easton,  Pa. 
Jour,  and  Proc.  Roy.  Soc.  N.  S.  W. — Journal  and  Proceedings  of  the  Royal  Society  of 

New  South  Wales;  Sydney,  Australia. 

Jour.  Can.  Min.  Inst. — Journal  of  the  Canadian  Mining  Institute;  Montreal,  Canada. 
Jour.  Coll.  Sci.  Imp.    Univ.  Jap. — Journal  of  the  College  of  Science  of  the  Imperial 

University  of  Japan  ;  Tokyo,  Japan. 


844  ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS. 

Jour.  Geol. — Journal  of  Geology  ;  University  of  Chicago,  Chicago,  111. 

Jour.  Iron  and  Steel  Inst. — Journal  of  the  Iron  and  Steel  Institute  ;  London,  England. 

Jour.  Roy.  Inst.  Cornw. — Journal  of  the  Royal  Institution  of  Cornwall;  Truro,  England. 

Jour.  Soc.  Arts. — Journal  of  the  Society  of  Arts;  London,  England. 

K.  K.  Ackerb.  Minist. — Statistich  Jahrbuch  der  Kaiserlich  Kb'niglicher  Ackerbaumin- 
isterium;  Vienna,  Austria. 

K.  K.  Ak.  d.  W.  in  Wien.— Kaiserlich  Kb'nigliche  Akademie  der  Wissenschaft  in 
Wien  ;  Vienna  Austria. 

Mem.  Geol.  Sur.  Eng.  and  Wales. — Memoirs  of  the  Geological  Survey  of  England  and 
Wales;  London,  England. 

Mem.  Geol.  Smt  Ind. — Memoirs  of  the  Geological  Survey  of  India  ;  Calcutta,  India. 

Mem.  Geol,  Suf.  Viet. — Memoirs  of  the  Geological  Survey  of  Victoria;  Melbourne, 
Australia. 

Mem.  Mmes  Dept.  Transvaal. — Memoirs  of  the  Mines  Dept.  Geological  Survey,  Trans- 
vaal, So.  Africa;  Pretoria,  So.  Africa. 

Mem  Mus.  Comp.  Zool.  Har.  Coll. — Memoirs  of  the  Museum  of  Comparative  Zoology 
of  Harvard  College ;  Cambridge,  Mass. 

Mem.  Soc.  Cien.  Ant.  Alz. — Memorias  y  Revista  de  la  Sociedad  Cientiftca  "Antonio 
Alzate"  ;  Mexico  City,  Mexico. 

Mem.  Soc.  Ing  Civ. — Memoires  de  la  Societe  des  Ingenieurs  Civils  de  France;  Paris, 
France. 

Min.  and  Sci.  Press. —  The  Mining  and  Scientific  Press  ;  San  Francisco,  Cal. 

Min.  Ind. — The  Mineral  Industry.  Published  by  the  Engineering  and  Mining  Jour- 
nal, New  York,  N.  Y. 

Min.  Jour. — The  Mining  Journal ;  London,  England. 

Min.  Mag.  (J). — The  Mining  Magazine.  W.  J.  Johnston,  publisher ;  New  York, 
N.  Y. 

Min.  Mag.  (R). — The  Mining  Magazine.    T.  A.  Kickard,  editor  ;  London,  England. 

Min.  Met.  Soc.  — Mining  and  Metallurgical  Society  of  America  ;  New  York,  N.  Y. 

Min.  Res. — Mineral  Resources  of  the  United  States,  U.  S.  Geological  Survey;  Wash- 
ington, D.  C. 

Mineralog.  Mag. — Mineralogical  Magazine ;  London  and  Truro,  England. 

Mines  Dept.  Tasm. — Mines  Department  Tasmania;  Hobart,  Tasmania. 

Mines  Dept.  Trans. — Mines  Department  Transvaal;  Pretoria,  South  Africa. 

Mitt.  d.  Naturwiss.  Vereinsf.  Neuvorkommen  u.  Rilgen. — Mittheilungen  der  Naturwis- 
senshaftliches  Vereinsf iir  Neuvorkommen  und  Rilgen. 

Mitt.  d.  Philomat.  Gesel.  in  Els.  Lothr. — Mittheilungen  der  Philomatischen  Gesellschaft 
im  Elsass- Lb'thringen. 

Mon.  U.  S.  G.  S. — Monograph  of  the  United  States  Geological  Survey  ;  Washington, 
D.  C. 

Monatsb.  d.  D.  Geol,  Gesel. — Monatsberichte  der  Deutschen  Geologischen  Gesellschaft; 
Berlin,  Germany. 

N.  Z.  Inst.  Min.  Eng. — New  Zealand  Institute  of  Mining  Engineers;  Auckland.  New 
Zealand. 

N.  Z.  Mines  Rec. — New  Zealand  Mines  Record;  Wellington,  N.  Z. 

Nat. — Nature;  London,  England. 

Naturf. — Der  Naturforscher  ;  Berlin  and  Tubingen,  Germany. 

Neues  Jahrb.  f.  Min. — Neues  Jahrbuch  fur  Mineralogie,  Geognosie,  Geologic  und  Petre- 
factenkunde;  Heidelberg,  Germany. 

Norsk  Teknisk  Tids. — Norsk  Teknisk  Tidsskrift ;  Christiania,  Norway. 

Ost.  Zeit.  f.  Berg-  u.  Hutt.  —  Osterreichische  Zeitschrift  fur  Berg-  und  Huttenwesen  ; 
Vienna,  Austria. 


ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS. 

Phil.  Mag. — Philosophical  Magazine;  London,  England. 

Poyg.  Ann. — Poggendorff's  Annalen  der  Physik  und  Chemie;  Berlin,  Germany. 

Proc.  Am.  Acad.  Arts  and  Sci.  — Proceedings  of  the  American  Academy  of  Arts  and 
Sciences  ;  Boston,  Mass. 

Proc.  Am.  Assoc.  Adv.  Sci. — Proceedings  of  the  American  Association  for  the  Advance- 
ment of  Science;  Washington,  D.  C. 

Proc.  Am.  Phil.  Soc. — Proceedings  of  the  American  Philosophical  Society;  Philadel- 
phia, Pa. 

Proc.  and  Trans.  Nov.  Scot.  Inst.  Sci. — Proceedings  and  Transactions  of  the  Nova 
Scotia  Institute  of  Science  ;  Halifax,  N.  S. 

Proc.  Colo.  Sci.  Soc. — Proceedings  of  the  Colorado  Scientific  Society  ;  Denver,  Colo. 

Proc.  Gen.  Min.  Assoc.  Que. — Proceedings  of  the  General  Mining  Association  of  the 
Province  of  Quebec ;  Ottawa,  Canada. 

Proc.  Lake  Sup.  Min.  Inst. — Proceedings  of  the  Lake  Superior  Mining  Institute;  Ish- 
peming,  Mich. 

Proc.  Roy.  Soc. — Proceedings  of  the  Royal  Society  of  London;  London,  England. 

Proc.  Roy.  Soc.  Viet. — Proceedings  of  the  Royal  Society  of  Victoria;  Melbourne,  Aus- 
tralia. 

Proc.  Wash.  Acad.  Sci. — Proceedings  of  the  Washington  Academy  of  Sciences  ;  Wash- 
ington, D.  C. 

Prof.  Paper  U.  S.  O.  S. — Professional  Paper  of  the  United  States  Geological  Survey  ; 
Washington,  D.  C. 

Quar.  Jour.  Geol.  Soc. — The  Quarterly  Journal  of  the  Geological  Society  of  London ; 
London,  England. 

Rept.  Brit.  Assoc.  Adv.  Sci. — Report  of  the  British  Association  for  the  Advancement  of 
Science;  London,  England. 

Rept.  Col.  St.  Bu.  Min. — Report  of  the  Colorado  State  Bureau  of  Mines  ;  Denver,  Colo. 

Rept.  Mich.  Acad.  Sci. — Report  of  the  Michigan  Academy  of  Science;  Ann  Arbor,  Mich. 

Rept.  Mich.  State  Geol. — Report  of  the  State  Geologist  of  Michigan;  Lansing,  Mich. 

Rept.  Ont.  Bu.  Mines. — Report  of  the  Ontario  Bureau  of  Mines  ;  Toronto,  Canada. 

Rev.  Gin.  d.  Sci. — Revue  generale  des  Sciences,  pures  et  appliques  ;  Paris,  France. 

Rev.  Univ.  d.' Mines. — Revue  Universelle  des  Mines  et  de  Metallurgie  ;  Liege,  Belgium. 

Rosenb.  Fests. — Rosenbusch  Festschrift. 

Roy.  Soc.  Tasm. — Royal  Society  of  Tasmania;  Hobart,  Tasmania. 

Sch.  Min.  Quar. — School  of  Mines  Quarterly — Columbia  School  of  Mines  ;  New  York. 

Schles.  Ges.f.Vater.  Kult. — Schlessische  GeseUschaftfiir  Vaterlandische  Kultur;  Breslau, 
Germany. 

Sci.  Mon. — Scientific  Monthly,  published  by  the  Colorado  State  School  of  Mines  ; 
Golden,  Colo. 

Sci.  Prog. — Science  Progress;  London,  England. 

Science. — Science.  Weekly  Journal,  published  by  the  American  Association  for 
the  Advancement  of  Science  ;  New  York,  N.  Y. 

Sitz.  d.  Wiirz.  phys.  tried.  Gesel. — Sitzungsberichte  des  Wiirzburger  physikalisch  medi- 
zinischen  Gesellschoft ;  Wiirzburg,  Germany. 

So.  Af.  Assoc.  Eng. — Transactions  of  the  South  African  Association  of  Engineers; 
Johannesburg,  So.  Africa. 

Stahl  u.  Eisen. — Stahl  und  Eisen  ;  Diisseldorf,  Germany. 

Tech.  Quar. — Technology  Quarterly.  Published  by  the  Massachusetts  Institute  of 
Technology  ;  Boston,  Mass. 

Trans.  A.  I.  M.  E. — Transactions  of  the  American  Institute  of  Mining  Engineers ; 
New  York,  N.  Y. 


846  ORIGIN    OF    METALLIFEROUS    ORE-DEPOSITS. 

Trans.  Aust.   Inst.   Min.   Eng. — Transactions  of  the  Australian  Institute  of  Mining 

Engineers;  Melbourne,  Australia. 
Trans.  Fed.  Inst.  Min.  Eng. —  Transactions  of  the  Federated  Institution  of  Mining 

Engineers;  London,  England. 
Trans.   Geol.  Soc.  So.  Af.  —  Transactions  of  the  Geological  Society  of  South  Africa; 

Johannesburg,  South  Africa. 
Trans.  Inst.  Min.  and  Met. — Transactions  of  the  Institute  of  Mining  and  Metallurgy  ; 

London,  England. 

Trans.  Int.  Min.  and  Met.  Cong. — Transactions  of  the  International  Mining  and  Met- 
allurgical Congress. 
Trans.  Min.  and  Geol.  Inst.  Ind.  —  Transactions  of  the  Mining  and  Geological  Institute 

of  India;  Calcutta,  India. 
Trans.   N.    Y.   Acad.  Sci. — Transactions  of  the  New  York  Academy  of  Sciences;  New 

York,  N.  Y. 
Trans.  N.  Z.  Inst.  Min.  Eng. — Transactions  of  the  New  Zealand  Institute  of  Mining 

Engineers;  Auckland,  New  Zealand. 
Trans.  No.  Eng.  Inst.  Min.  and  Mech.  Eng. — Transactions  of  the  North  of  England 

Institute  of  Mining  and  Mechanical  Engineers  ;  Newcastle-upon-Tyne,  England. 
Trans.  Roy.  Geol.  Soc.  Cornw. — Transactions  of  the  Royal  Geological  Society  of  Cornwall ; 

Plymouth,  England. 

Trans.  So.  Af.  Assoc.  Eng. — Transactions  of  the  South  African  Association  of  Engi- 
neers; Johannesburg.  South  Africa. 

Trans.  Wis.  Acad.  Sci. — Transactions  of  the  Wisconsin  Academy  of  Sciences;  Madi- 
son, Wis. 
Tscher.  Min.  u.  Pet.  Mitt. — Tschermak's  Mineralogische  und  Petrographische  Mittheil- 

ungen;  Vienna,  Austria. 

U.  S.  G.  S.  —  United  States  Geological  Survey  ;  Washington,  D.  C. 
Univ.  Geol.  Sur.  Kans. —  University  Geological  Survey  of  Kansas ;  Topeka,  Kan. 
Verhand.  d.  Naturhist.  V.  d.  Pr.  Rheinlande.  —  Verhandlungen  des  Nalurhistorischen 

Vereins  der  Preussischen  Rheinlande  und  Westphalens  ;  Bonn,  Germany. 
Verhand.   d.  Wurzburger   Phys.  Med.    Ges. — Verhandlungen   der  Wurzburger  Physi- 

kalisch-Medizinischen  Gesellschaft ;  Wiirzburg,  Germany. 
Verhand.   Geol.  Reichsanst.  —  Verhandlungen  der  Kaiserlich-Koniglichen  Geologischen 

Reichsanstalt ;  Vienna,  Austria. 
Wat.  Sup.   and  Irr.  Paper.  —  Water  Supply  and  Irrigation  Paper,  U.  S.  Geological 

Survey ;  Washington,  D.  C. 
Wis.    Geol.   Nat.   Hist.   Sur. —  Wisconsin   Geological  and   Natural   History   Survey; 

Madison,  Wis. 

Zeit.  f.  Angew.  Chem. — Zeitschrift  fur  Angewandte  Chemie  ;  Leipzig,  Germany. 
Zeit.  f.  Berg-  Hutt.  u.  Salinenw. — Zeitschrift  fur  Berg-  Hiitten  und  Salinenwesen  in 

dem  Preussichen  Staate  ;  Berlin,  Germany. 
Zeit.  d.  D.  Geol.  Gesel. — Zeitschrift  der  Deutschen  Geologischen  Gesellschaft ;   Berlin, 

Germany. 

Zeit.  f.  Kryst. — Zeitschrift  fur  Krystallographie  und  Miner  alogie;  Munich,  Germany. 
Zeit.f.prak.  Geol. — Zeitschrift  fur  praktische  Geologic;  Berlin,  Germany. 


ALPHABETICAL    LIST    OF    AUTHORS.  847 


ALPHABETICAL  LIST  OF  AUTHORS. 

Numbers  serve  to  distinguish  separate  papers  by  the  same  author.     They  are 
used  in  the  next  chapter  in  referring  to  individual  papers. 

ABBOTT,  C.  E. 

The  Iron-Ore  Deposits  of  the  Ely  Trough,  Vermilion  Kange,  Minn. — Proc. 

Lake  Sup.  Min.  Inst.,  vol.  12,  pp.  116-142  (1907). 
ADAM,  J.  W.  H. 

Versuch  einer  neuen  Behandlungsart  der  Erzlagerstattenlehre.— Zeit.  f.  prak. 

Geol.,  vol.  18,  pp.  5-10  (1910). 
ADAMS,  F.  D. 

1.  On  the  Igneous  Origin   of  Certain  Ores. — Proc.   Gen.  Min.  Assoc.  Que. 
(Jan.  12.  1894). 

2.  An  Experimental  Investigation  into  the  Action  of  Differential  Pressure  on 
Certain  Minerals  and  Rocks,  employing  the  Process  Suggested  by  Professor 
Kick.—  Jour.  GeoL,  vol.  18,  pp.  489-525  (1910). 

3.  An  Experimental  Contribution  to  the  Question  of  the  Depth  of  the  Zone  of 
Flow  in  the  Earth's  Crust.—  Jour.  GeoL,  vol.  20,  pp.  97-118  (1912). 

ADAMS,  G.  I. 

1.  Zinc-  and  Lead-Deposits  of  Northern  Arkansas. — Trans.  A.  I.  M.  E ,  vol. 
34,  pp.  163-174  (1903). 

2.  Zinc  and  Lead  Deposits  of  Northern  Arkansas.— Prof.  P^iper  24,  U.  S.  G.  S. 
(1904).     118  pp. 

ADIASSEURCH,  A.  I. 

A  Journey  to  Central  Asia.  —Trans.  Inst.  Min.  and  Met.,  vol.  17,  pp.  498-527 

(1907-08). 
AGUILERA,  J.  G. 

The  Geological  Distribution  of  the  Mineral  Deposits   of   Mexico. — Trans. 

A.  I.  M.  R,  vol.  32,  pp.  497-  520  (1901). 
ALLEN,  E.  T. 

The  Mineral  Sulphides  of  Iron.— Am.  Jour.  Sci.,  4th  ser.,   vol.  32,  pp.  169- 

236(1911). 
ALLEN,  R.  C. 

The  Occurrence  and  Origin  of  the  Brown  Iron  Ores  of  Spring  Valley,  Wis- 
consin .—llth  Rept.  Mich.  Acad.  Sci.,  pp.  95-103  (1909). 
ANDRE,  G.  C. 

A  Practical  Treatise  on  Coal  Mining  (London,  1879). 
ANDREWS,  A.  C. 

Molybdenum.—  Mineral  Resources  Series,  No.  11,  GeoL'Sur.  N.  S.  W.  (1906). 

17pp. 
ARQALL,  G.  O. 

Recent  Developments  on  Iron  Hill,  Leadville,  Colo. — E.  and  M.  Jour.,  vol.  89, 

No.  5,  p.  261  (1910). 
ARGALL,  PHILIP. 

1.  Nickel  ;  Occurrence,  Geological  Distribution  and  Genesis  of  Its  Ore  De- 
posits.—Proc.  Colo.  Sci.  Soc.,  vol.  4,  pp.  395-421  (1893). 

2.  Rock  Oxidation  at  Cripple  Creek.—  Min.  and  Sci.  Press,  vol.  96,  pp.  883- 
886  (1908). 

3.  Zinc  Resources  of  Canada.     Report  of  the  Commission  to  investigate  the 
Zinc  Resources  of  British  Columbia,  pp.  147-252  (Ottawa,  1906). 

ARNOLD,  RALPH. 

Gold  Placers  of  the  Coast  of  Washington.—  Bull,  260,  U.  S.  G.  S.,  pp.  154- 

157  (1905). 
ASHLEY,  G.  H. 

Geology  of  the  Paleozoic  Area  of  Arkansas  South  of  the  Novaculite  Region. — 
Proc.  Am.  Phil.  Soc.,  vol.  36,  pp.  217-318  (1897). 


848  ALPHABETICAL    LIST   OF    AUTHORS. 

ASTON,  J. 

1.  The  Solidification  of  Alloys  and  Magmas. — Jour.  Geol.,  vol.  17,  pp.  569- 
585  (1909). 

2.  The  Genesis  of  the  Gold  Deposits  of  Barkerville  (British  Columbia). — 
Quar.  Jour. Geol.  Soc.,  vol.  60,  pp.  389-393  (1904). 

3.  Some  Further  Considerations  of  the  Genesis  of  the  Gold  Deposits  of  Bark- 
erville, B.  C.,  and  the  Vicinity.— Geol.  Mag.,  vol.  3,  pp.  514-516  (1906). 

AUSTIN,  W.  L. 

The  Nickel  Deposits  near  Riddles,  Oregon. — Proc.  Colo.  Sci.  Soc.,  vol.  5,  pp. 
173-196  (1894-96). 

BABANEK. 

Die  Erzfiihrung  der  Pribramer  Sandsteine  und  Schiefer,  in  Ihrem  Verhalt- 
nisse  zu  Dislokationen. — 6st.  ZeH.  f.  Berg-  u.  Hull,  vol.    19,  pp.  340-342, 
347-348. 
BABB,  P.  A. 

Dulces  Nombres  Quicksilver  Deposit,  Mexico. — E.  and  M.  Jour.,  vol.  88,  No. 

14,  pp.  684-686  (1909), 
BAGG,  JR.,  R.  M. 

Some  Copper  Deposits  of  the  Sangre  de  Christo  Range,  Colorado. — Econ.  Geol., 

vol.  3,  pp.  739-749  (1908). 
BAIN,  H.  F. 

1.  Zinc  and  Lead  Deposits  of  Northwestern  Illinois.—  Bull.  246,  U.  S.  G.  S. 
(1905).    56pp. 

2.  Zinc  and  Lead  Deposits  of  the  Upper  Mississippi  Valley. — Bull.  294,  U. 
S.  G.S.  (1906).     155pp. 

3.  Sedi  genetic  and  Igneo-geneticOres.—  Econ.  Geol.,  vol.  1,  pp.  331-339(1906). 

4.  Some  Relations  of  Paleogeography  to  Ore  Deposition  in  the   Mississippi 
Valley.— Econ.  Geol,  vol.  2,  pp.  128-144  (1907). 

5.  Types  of  Ore  Deposits  (Introductory  Chapter).     376  pp.  (San  Francisco, 
1911). 

BAIN,  H.  F.,,  and  ULRICH,  E  O. 

The  Copper  Deposits  of  Missouri.—  Butt.  267,  U.   S.    G.  S.    (1905).     52  pp. 
BAIN,  H.  F. ,  and  VAN  HISE,  C.  R. 

Preliminary  Report  on  the  Lead  and  Zinc  Deposits  of  the  Ozark  Region. — 

22d  Ann.  Eept.,  U.  S.  G.  S.,  part  2,  pp.  23-227  (1901). 
BALL,  S.  H. 

1.  Geological  Reconnaissance  in   Southwestern    Nevada  and   Eastern  Cali- 
fornia.— Bull.  308,  U.  S.  G.  S.  (1907).     218  pp. 

2.  Titaniferous  Iron   Ore  of  Iron  Mt.,  Wyoming.—^//.   315,  U.  S.    G.  S., 
p.  206  (1907). 

BALL,  S.  H.,  and  SHALER,  M.  K. 

Mining-Conditions  in  the  Belgian  Congo,  Trans.  A.  I.  M.  E.,  vol.  41,  pp. 

189-219  (1910). 
BANCROFT,  G.  J. 

1.  Kalgoorlie,  West  Australia,  and  Its  Surroundings. — Trans.  A.  I.  M.  E., 
vol.  28,  pp.  88-100  (1898). 

2.  Secondary  Enrichment  at  Cripple  Creek. — E.  and  M.  Jour.,  vol.  75,  pp. 
111-112  (Jan..  17,  1903). 

3.  The  Yaqui  River  Country  of  Sonora,  Mexico. — E.  and  M.  Jour.,  vol.  76, 
pp.  160-162  (1903). 

4.  The  Formation  and  Enrichment  of  Ore-Bearing  Veins. — Trans.  A.  I.  M. 
E.,  vol.  38,  pp.  245-268  (1907)  ;  vol.  40,  pp.  809-817  (1909). 

5.  Cripple  Creek.     Secondary  Enrichment. — E.  and  M.   Jour.,  vol.  74,  pp. 
752-753  (1902). 

BARLOW,  A.  E. 

1.  Report  on  the  Nickel  and  Copper  Deposits  of  Sudbury,  Ontario. — Geol. 
Sur.  Can.,  vol.  14,  part  H  (1904). 

2.  On  the  Origin  and  Relations  of  the  Nickel  and  Copper  Deposits  of  Sud- 
bury, Ontario,  Canada,  with  bibliography. — Econ.    Geol,  vol.  1,  pp.  454- 
466,  545-553  (1906). 


ALPHABETICAL.  LIST    OF    AUTHORS.  849 

BARRELL,  JOSEPH. 

1.  The  Physical  Effects  of   Contact  Metamorphism. — Am.  Jour.  Sci.,  ser.  4, 
vol.  13,  p.  279  (1902). 

2.  Geology  of  the  Marys ville  Mining  District,  Montana  :  a  study  of  igneous 
intrusion  and  contact  metamorphism. — Prof.  Paper  57,  U.  S.  G.  S.  (1907). 
178  pp. 

BARROW,  GEORGE. 

The  High-Level  Platforms  of  Bodmin  Moor  aVid  Their  Relation  to  the  De- 
posits of  Stream  Tin  and  Wolfram. — Quar.  Jour.  Oeol.  Soc.,  vol.  64,  pp. 
384-400  (1908). 

BARUS,  CARL. 

1.  The  Electrical  Activity  of  Ore-Bodies.— 1  Vans.  A.  I.  M.  E.,  vol.  13,  pp. 
417-477  (1884-85). 

2.  On  the  Thermal   Effect  of  the  Action  of  Aqueous  Vapor  on  Feldspathic 
Rocks.—  Sch.  Min.  Quar.,  vol.  6,  pp.  1-23  (1884). 

BASTIN,  E.  S. 

Chemical  Composition  as  a  Criterion  in  Identifying   Metamorphosed   Sedi- 
ments.— Jour.  GeoL,  vol.  17,  pp.  445-472  (1909). 
BATESON,  C.  E.  W. 

The  Mojave  Mining  District  of  California. — Trans.  A.  I.  M.  E.,  vol.  37,  pp. 

160-177  (1906). 
DE  BATZ,  RENE. 

The  Auriferous  Deposits  of  Siberia.— Trans.  A.  I.  M.  E.,  vol.  28,  pp.  452- 

467  (1898). 
BAUMG  ARTEL,  B. 

Beitrag  zur  Kenntniss  der  Kieslagerstatten  zwischen  Klingenthal  und  Gras- 
litz  im  Westlichen  Erzgebirge. — Zeit.  f.  prak.  Geol.,  vol.   13,  pp.  353-358 
(1905). 
BAYLEY,  W.  S. 

1.  The  Menominee  Iron-Bearing  District  of  Michigan. — Mon.  46,  U.  S.  G.  S. 
(1904).     513pp. 

2.  Magnetite  Ores  of  the  Hibernia  Mine.—  Folio  157,  U.  S.  G.  S.  (1908). 
DE  BEAUMONT,  ELIE. 

1.  Bulletin  de  la  Societe  Geologique  de  France,  2d  series,  vol.  4,  p.  1249.    Trans- 
lated by  B.  von  Cotta,  in  his  4.  "Gangstndien,"  under  title,  "  Ueber  die 
vulkanischen  und   Metallischen   Emanationen   oder  Ausstromungen,"    pp. 
329-436  (Freiberg,  1850). 

2.  Dolomitization.—  Bull.  Soc.  GeoL  de  France,  vol.  8,  pp.  174-177  (1836). 
DE  LA  BECHE,  HENRY  T. 

Report  on  the  Geology  of  Cornwall,  Devon,  and  West  Somerset  (London,  1839). 
BECK,  RICHARD. 

1.  Die  Zinnerzlagerstiitten  von  Bangka  und  Billiton. — Zeit.  f.  prak.  GeoL, 
vol.  6,  pp.  121-127  (1898). 

2.  Ueber  die  Erzlager  der  Umgebung  von  Schwarzenberg  im  Erzgebirge. — 
Jahrb.  f.  Berg-  u.  Hutt.  in  Konig.  Sachs.,  A  51,  87  (1902)  ;  A  55-97  (1904). 

3.  Die  Nickelerzlagerstiitten  von  Sohland  a.  d.  Spr.  und  ihre  Gesteine. — Zeit. 
d.  D.  Geol.  GeseL,  p.  296  (1903). 

4.  Uber  die  Beziehungen  zwischen  Erzgiingen  und  Pegmatiten. — Zeit.  f.  prak. 
Geol,  vol.  14,  pp.  71-73  (1906). 

5.  Einige   Bemerkungen    iiber    afrikanische  Erzlagerstatten. — Zeit.  f.  prak. 
GeoL,  vol.  14,  pp.  205-209  (1906). 

6.  On  the  Relation  between  Ore  Veins  and  Pegmatites. — Geol.  Mag.,  Decade 
V,  vol.  3,  No.  1  (1906).    35pp. 

7.  Ore  Veins  and  Pegmatites.— Trans.  Geol.  Soc.  So.  Af.,  vol  8,  p.  147  (1905). 

8.  The  Nature  of  Ore  Deposits.— Trans,  by  Weed,  W.  H.  (New  York,  1909). 
685  pp.     1st  ed.,  2d  imp. 

9.  Lehre  von  den  Erzlagerstatten.     (Berlin,  1909).     2  vols  ,  1082  pp. 

10.  Erlauterungen  zu.  Sect.  Berggiesshiibel  der  Geologische  Specialkarte  von 
Sachsen,  pp.  25-60  (Leipzig,  1889). 

BECKER,  G.  F. 

1.  Geology  of  the  Comstock  Lode  and  the  Washoe  District. — Mon.  3,  U.  S. 
G.  S.  (1882).  422pp. 


850  ALPHABETICAL  LIST  OP  AUTHORS. 

BECKER,  G.  F.  —Continued. 

2.  Summary  of  Geology  of  Comstock  Lode  and  Washoe  District. — 2d  Ann. 
Kept.,  U.  S.  O.  S.,  pp.  291-330  (1881). 

3.  The  Relations  of  the  Mineral  Belts  of  the  Pacific  Slope  to  the  Great  Up- 
heavals.— Am.  Jour,  Sci.,  Ser.  3,  vol.  28,  p.  209  (1884). 

4.  Geology  of  the  Quicksilver  Deposits  of  the  Pacific  Slope. — Mon.  13,  U.  S. 
G.  S.  (1888).     486  pp. 

5.  Summary  of  Geology  of  Quicksilver  Deposits  of  the  Pacific  Slope. — 8th 
Ann.  RepL,  U.  S.  G.  S.,  part  II,  pp.  961-985  (1887). 

6.  The  Structure  of  a  Portion  of  the  Sierra  Nevada  of  California. — Bull.  Geol. 
Soc.  Am.,  vol.  2,  p.  49  (1891). 

7.  Finite  Homogeneous  Strain,  Flow,  and  Rupture  of  Rocks. — Bull.  Geol. 
Soc.  Am.,  vol.  4,  p.  13  (1893). 

8.  The  Finite   Elastic  Stress-Strain  Function.—  Am.  Jour.  Sci.,  vol.  46,  3d 
series,  pp.  337-356  (1893). 

9.  The  Torsional  Theory  of  Joints.— Trans.  A.  1.  M.  E.,vol.  24,  p.  130  (1894). 

10.  Schistosity  and  Slaty  Cleavage.—  Jour.  Geol.,  vol.  4,  p.  429  (1896). 

11.  Quicksilver  Ore  Deposits.—  M in.  Res.  for  1892,  U.  S.  G.  S.,  pp.  139-168 
(1893). 

12.  Gold  Fields  of  the  Southern  Appalachians.—  IQth  Ann.  Eept.,  U.S.  G. 
S.,  part  3,  pp.  251-331  (1895). 

13.  The  Genesis  of  Ore-Deposits.     Discussion  of  paper  by  F.  Posepny. — 
Trans.  A.  I.  M.  E.,  vol.  23,  pp.  602-604  (1893). 

14.  Reconnaissance  of  the  Gold  Fields  of  Southern  Alaska. — 18^  Ann.  RepL, 
U.  S.  G.  S.,  part3,  pp.  1-86  (1897.) 

15.  Some  Queries  on  Rock  Differentiation. — Am.  Jour.  Sci.,  4th  ser.,  vol.  3, 
pp.  21-40  (1897). 

16.  Fractional  Crystallization  of  Rocks. — Am.  Jour.  Sci.,  4th  ser.,  vol.  4,  pp. 
257-261  (1897)'. 

17.  The  Witwatersrand  Banket—  ISth  Ann.  RepL,  U.  S.  G.  S.,  part  5,  pp. 
153-184(1897). 

18.  Auriferous  Conglomerates  of  the  Transvaal. — Am.  Jour.  Sci.,  4th  ser.,  vol. 
5,  pp.  193-208  (Mar.,  1898). 

19.  Experiments  on  Schistosity  and  Slaty  Cleavage.—  Bull.  241,  U.  S.  G.  S. 
(1904).     34  pp. 

20.  Some  Features  of  the  Rand  Banket— Ebon.  Geol.,  vol.  4,  pp.  373-384 
(1909). 

BECKER,  G.  F. ,  and  DAY,  A.  L. 

The  Lineir  Force  of  Growing  Crystals. — Proc.  Wash.  Acad.  Sci.,  vol.  7,  pp. 
283-288  (1905). 

BELL,  J.  M. 

Iron  Ranges  of  Michipicoten  West. — RepL  Ont.  Bu.  Mines,  vol.   14,   part  I, 
pp.  278-355  (1905). 

BELL,  E. 

The  Cobalt  Mining  District.—  Jour.  Can.  Min.  Inst.,  vol.  28,  No.  10,  pp.  246- 

248  (1907). 
BENOIT,  FELIX. 

Gites  de  nickel  de  Nouvelle-Caledonie.  —  Bull.  Soc.  de  VInd.  Min.,  vol.  6,  pp. 
753-804  (1892). 

BERG,  G. 

1.  Die  Magneteisenerzlager  von  Schmiedeberg  im  Riesengebirge. — Jahrb.  d. 
Kgl.  Pr.  Geol.  LandesansL,  pp.  200-267  (1892). 

2.  Beitriige    zur  Kenntniss  der  kontaktmetamorphen  Lagerstatte  von  Balia- 
maden  (Turkey).—  Zeit.  f.  prak.  Geol.,  pp.  365-367  (1901). 

BERGEAT,  ALFRED. 

1.  La  Granodiorita  de  Concepcion  del  Oro  en  el  Estado  de  Zacatecas. — Bol. 
27,  Inst.  Geol.  de  Mex.  (1910). 

2.  Beitriige  zur  Kenntniss  der  Erzlagerstatten  von  Campiglia  Marittima  inbe- 
sondere  des  Zinnstein  Vorkommens  Dortselbst. — NeuesJahrh.f.  Min.,  vol.  1, 
pp.  135-156  (1901). 

3.  Die  Adischen  Inseln. — Abb.  K.  Bayer.  Akad.   d.  Wissc.  II.,  cl.    XX.,  pp. 
192-194  (1899).     With  bibliography. 

4.  Von  den  aolischen  Inseln.—  Zeit.  f.  prak.  Geol.  p.  43  (1899).     With  biblio- 
graphy. 


ALPHABETICAL    LIST    OF    AUTHORS.  851 

BERGEAT,  ALFRED,  and  STELZNER. 

Die  Erzlagerstatten  (Leipzig,  1904-1906).     3  vols.,  1330  pp. 
VON  BEUST,  J.  C. 

Kritische  Beleutung  der  Wernerschen  Gangtheorie  (Freiberg,  1840). 
BEYSCHLAG,  KRUSCH  and  VOGT.     See  Vogt. 
BIDDLE,  H.  C. 

The  Deposition  of  Copper  by  Solutions  of  Ferrous  Salts. — Jour.  Geol.,  vol.  9, 

pp.  430-436  (1901). 
BISCHOF,  G. 

1.  Lehrbuch  der  Chemischen  und  Physikalischen  Geologie.     Edition   2,  4 
vols.,  including  Suppl't  (Bonn,  1863-1871). 

2.  Elements  of   Chemical  and   Physical  Geology.     English  Translation  of. 
Translated  bv  B.  H.  Paul  and  J.  Drummond,  3  vols.     (Cavendish  Society, 
London,  1854-59). 

BLAKE,  W.  P. 

1.  The  Ore  Deposits  of  the  Eureka  District,  Eastern  Nevada. — Trans.  A.  I. 
M.  E.,  vol.  6,  pp.  554-563  (1877-78). 

2.  The  Geology  and  Veins  of  Tombstone,  Arizona  — Trans.  A.  I.  M.  E.,  vol. 
10,  rp.  334-345  (1881-82). 

3.  Tin  Ore  Veins  in  the  Black  Hills  of  Dakota.— Trans.  A.  L  M.  E.,  vol. 
13,  pp.  691-698  (1884-85). 

4.  Iron-Ore  Deposits  of  Southern  Utah.— Trans.  A.   I.   M.   E.,  vol.   14,  pp. 
809-812  (1885-86). 

5.  The  Rainbow  Lode,  Butte  City,  Montana.— Trans.   A.   L  M.   E.}  vol.  16, 
pp.  65-80.  (1887-88). 

6.  The  Copper- Deposits  of  Copper  Basin,  Arizona,  and  their  Origin. — Trans. 
A.  L  M.  E.,  vol.  17,  pp.  479-485  (1888-89). 

7.  The  Mineral  Deposits  of  Southwest  Wisconsin. — Trans.  A.  L  M.  E.,  vol. 
22,  pp.  558-568  (1893). 

8.  The  Zinc-Ore-Deposits  of  Southwestern  New  Mexico.— Trans.  A.  I.  M.  E., 
vol.  24,  pp.  187-195  (1894). 

9.  Notes  on  the  Structure  of  the  Franklinite  and  Zinc-Ore  Beds  of  Sussex 
County,  New  Jersey.— Trans.  A.  L  M.  E.,  vol.  24,  pp.  521-524  (1894). 

10.  Cinnabar  in  Texas.— Trans.  A.  I.  M.  E.,  vol.  25,  pp.  68-76  (1895). 

11.  Gold  in  Granite  and  Plutonic  Rocks. — Trans.  A.  I.   M.  E.,  vol.   26,  pp. 
290-298  (1896). 

12.  The  Caliche  of   Southern  Arizona:    An  Example  of  Deposition  by  the 
Vadose  Circulation.— Trans.  A.  I.  M.  E.,  vol.  31,  pp.  220-226  (1901). 

13.  Copper-Ore  and  Garnet  in  Association. — Trans.  A.  I.  M.  E.,  vol.  34,  pp. 
886-890  (1903). 

BLATCHFORD,  T. 

The  Geology  of  the  Coolgardie  Goldfield.— Bull.   3,  Geol.  Sur.  West.   Aust. 

(1899).     98  pp. 
BLOW,  A.  A. 

The  Geology  and  Ore-Deposits  of  Iron  Hill,  Leadville,  Colorado. — Trans.  A. 
L  M.  E.,  vol.  18,  pp.  145-181  (1889-90). 

BODIFEE. 

tiber  die  Genesis  der  Eisen-  und  Manganerzvorkommen  bei  Oberrosbach  iin 
Taunus.—  Zeit.  f.  prak.  GeoL,  vol.  15,  pp.  309-316  (1907). 

BODLANDER,  G. 

Versuche  iiber  Suspensionen. — Neues  Jahrb.  f.  Min.,  pp.  147-168  (1893). 

BOEHMER,  MAX. 

1.  Some  Practical  Suggestions  Concerning  the   Genesis  of  Ore-Deposits. — 
Trans.  A.  L  M.  E.,  vol.  34,  pp.  449-453  (1903). 

2.  Secondary  Enrichment  and  Impoverishment. — Econ.  Geol.,  vol.  3,  pp.  337- 
340  (1908). 

3.  The  Genesis  of  the  Leadville  Ore-Deposits.— Trans.  A.  L  M.  E.,  vol.  41, 
pp.  162-165  (1910). 

BOKER,  B.  H.  C. 

Mineralausfiillung  der  Inerwerfungsspalten  in  Bergrevier  Werden  und  eini- 
gen  Angrenzenden  Gebreiten.— Berg-  u.  Hiitt.  Zeit.,  pp.  1065-1083  (1906). 


852  ALPHABETICAL    LIST    OF    AUTHORS. 

BORDEAUX,  A. 

Les  Anciens  Chenaux  AurifSres  de  California  —  Ann.  d.  Mines,  vol.  2,  10th 

Ser.,  pp.  217-258  (1902). 
Boss,  C.  M. 

Some  Dike  Features  of  the  Gogebic  Iron-Kange.— Tram.  A.  I.  M.  E. ,  vol. 

27,  pp.  556-563  (1897). 
BOURDAKOFF  and  HENDRIKOFF. 

Description  de  1'  exploitation  de  Platine.     (Ekaterinburg,  1896). 
BOUTWELL,  J.  M. 

1.  Vanadium  and  Uranium  Deposits  in  Southeastern  Utah. — Bull.  260    U.S. 
G.  S.,  pp.  200-210  (1905). 

2.  The  Park  City  Mining  District,  Utah.—  Bull.  213,  U.  S.  G.  S.,  pp.  31-40  ; 
225,  pp.  141-160;  260,  pp.  150-153  (1903-05). 

3.  Iron  Ores  of   the  Uinta  Mountains.—  Bull.  225,  U.  S.  G.  S..  pp.  221-228 
(1904). 

4.  Genesis  of  the  Ore-Deposits  at  Bingham,  Utah.— Trans.  A.  I.  M.  E..  vol. 
36,  pp.  541-580  (1905). 

5.  Economic  Geology  of  the  Bingham  Mining  District,  Utah. — Prof.  Paver  38, 
U.S.  £.51(1905).     413pp. 

6.  Geology  and  Ore  Deposits  of  the  Park  City  District,  Utah. — Prof.  Paper 
77,  U.  X.  G.  S.  (1912).     231pp. 

BOWMAN,  AMOS. 

Mining  Developments  on  the  Northwestern  Pacific  Coast,  and  Their  Wider 

Bearing.— Trans.  A.  I.  M.  E.,  vol.  15,  pp.  707-717  (1886-87). 
BOWRON,  W.  M. 

1.  The  Geology  and  Mineral  Resources  of  Sequachee  Valley,  Tennessee. — 
Trans.  A.  I.  M.  E.,  vol.  14,  pp.  172-181  (1885-86). 

2.  The  Origin  of  Clinton  Ked  Fossil-Ore  in  Lookout  Mountain,  Alabama. — 
Trans.  A.  I.  M.  E.,  vol.  36,  pp.  587-604  (1905). 

BRANNER,  J.  C. 

1.  The  Zinc  and  Lead  Kegion  of  North  Arkansas. — Ark.   Geol.  Sur..  vol.  5 
(1892).     395  pp. 

2.  The  Manganese  Deposits  of  Bahia  and  Minas,  Brazil.— Trans.  A.  I.  M.  E.. 
vol.  29,  pp.  756-770  (1899). 

3.  The  Zinc-  and  Lead-Deposits  of  North  Arkansas.— Trans.  A.  I.  M.  E..  vol. 
31,  pp.  572-603  (1901). 

BRANNER,  J.  C.,  and  NEWSOM,  J.  F. 

1.  Syllabus  of  Economic  Geology. — Stanford  University.  2d  ed .(1900).  368pp. 
BRAUNS,  R. 

1.  Chemische  Mineralogie  (1896). 
BREWER,  W.  M. 

1.  The  Gold-Regions  of  Georgia  and  Alabama. — Trans.  A.  I.  M.  E..  vol.  25, 
pp.  569-587  (1895). 

2.  The  Copper  Deposits  of  Vancouver  Island.— Trans.  A.  1.  M.  E.,  vol.  29, 
pp.  483-488  (1899). 

3.  The  Copper  Deposits  of  Vancouver  Island. — E.  and  M.  Jour.,  vol.  69, 
pp,  465,  526  ;  vol.  70,  p.  34  (1900). 

4.  Some  Observations  Relative  to  the  Occurrence  of  Deposits  of  Copper  Ore 
on  Vancouver  Island  and  Other  Portions  of  the  Pacific  Coast. — Jour.  Can. 
Min.  Inst.,  vol.  9,  pp.  39-48  (1906). 

BROADHEAB,  G.  C. 

The  Southeastern  Missouri  Lead  District.  —  Trans.   A.  I.  M.  E.,  vol.  5,  pp. 

100-107  (1876-77). 
BROCK,  R.  W. 

1.  Original  Native  Gold  in  Igneous  Rocks. — E.  and  M.  Jour.,  vol.  77,  p.  511 
(1904). 

2.  Platinum  in   British  Columbia.—  E.  and.  M.  Jour.,  vol.  77,  pp.  280-281 
(1904). 

BROGGER,  W.  C. 

Die  Mineralien  der  Syenitpegmatitgange  der  Siidnorwegischen  Augit  und 
Nephelinsyenit.—  Zeit.  f.  Kryst.,  vol.  16,  p.  64  (1890). 


ALPHABETICAL    LIST    OF    AUTHORS.  853 

BROOKS,  ALFKED  H. 

1.  A  New  Occurrence  of  Cassiterite  in  Alaska. — Science,  New  Ser.,  vol.  13,  p. 
593  (1901). 

2.  An  Occurrence  of  Stream  Tin  in  the  York  Region,  Alaska. — Min.  Res. 
U.  S.  for  1900,  U.  S.  G.  S.,  pp.  267-271  (1901). 

3.  Placer  Gold  Mining  in  Alaska  in  1902.—  Bull.  213,  U.  S.  G.  S.,  pp.  41- 
48  (1903). 

4.  Stream  Tin  in  Alaska  in  1902.—  Bull.  213,  U.  S.  G.  S..  pp.  92-93  (1903). 

5.  Placer  Mining  in  Alaska  in  1903.—  Bull.  225,  U.  S.  G.  S.,  pp.  43-59  (1904). 

6.  The  Geography  of  Alaska,  with  an  Outline  of  the  Geomorphology. — Rept. 
8th  Int.  Geol.  Cong.,  pp.  204-230  (1905). 

7.  Placer  Mining  in  Alaska  in  1904.—  Bull.  259,    U.  S.   G.  S.,  pp.  18-31 
(1905). 

8.  The  Geology  and  Geography  of  Alaska.     A  summary  of  existing  knowl- 
edge.— Prof.  Paper  45,  U.  S.  G.  S.  (1906).     327  pp. 

9.  The  Kougarok    Region   (Alaska).—  Bull.  314,    U.  S.  G.  S.,  pp.  164-181 
(1907). 

10.  The  Circle  Precinct  (Alaska).—^//.  314,  U.  S.  G.  S.,  pp.  187-204  (1907). 
BROOKS,  A.  H.,  RICHARDSON,  G.  B.,  and  COLLIER,  A.  J. 

A  Reconnaissance  of  the  Cape  Nome  and  Adjacent  Gold  Fields  of  Seward. 

Peninsula,  Alaska.—  U.  S.  G.  S.  (1901).     184  pp. 
BROUGH,  B.  H. 

The  Nature  and  Yield  of  Metalliferous  Deposits. — Jour.  Soc.  Arts,  vol.  48 

(1901).     56pp. 
BROWN,  A.  J. 

The  Formation  of   Fissures  and   the  Origin  of  their  Metallic  Contents. — 

Trans.  A.  /.  M.  E.,  vol.  2,  pp.  215-219  (1873-74). 
BROWN,  E.  P. 

The  Development  of  an  Ore  Shoot  in  Nova  Scotia. — Can.  Min.  Jour.,  vol.  1, 
pp.  457-458  (1907). 

BROWN,  K.  G. 

1.  The  Ore-Deposits  of  Butte  City.—  Trans.  A.  /.  M.  E.,  vol.  24,  pp.  543-558 
(1*94). 

2.  The  Vein-System  of  the  Standard  Mine,  Bodie,  California. — Trans.  A.  I. 
M.  E.,  vol.  38,  pp.  343-357(1907). 

BROWNE,  D.  H. 

1.  The  Distribution  of  Phosphorus  in  the  Ludington  Mine,  Iron  Mountain, 
Michigan  :  A  Study  in  Isochemic  Lines. — Trans.  A.  I.  M.  E.,  vol.  17,  pp. 
616-632  (1888-89). 

2.  Segregation  in  Ores  and  Mattes. — Sch.  Min.  Quar.,  vol.   16,  pp.  297-311 
(1895). 

3.  Notes  on  the  Origin  of  the  Sudbury  Ores. — Econ.  Geol.,  vol.  1,  pp.  467- 
475  (1906). 

BROWNE,  E.  Ross. 

The  Ancient  River  Beds  of  the  Forest  Hill  Divide.— 10th  Ann.  Rept.,  Gal.  St. 

Min.,  pp.  435-465  (1890). 
BRUHNS,  W. 

Uber  Erzlagerstatten.  — Mitt.  d.  philomat.  Gesel.  in  Els.  Lothr. 
BRUN,  A. 

Re"cherches  Sur  L'Exhalaison  Volcanique  (Geneva  and  Paris,  1911). 
BRUNLECHNER,  A. 

Die  Entstehung  und  Bildungsfolge  der  Bleiberger  Erze  und  ihre  Begleiter. — 
Jahrb.  d.  Naturhist.  Landes.  in  Karnten,  vol.  25  (1899).     36  pp. 

BUCKING. 

Das  Grundgebirge  des  Spessarts. — Jahrb.  d.  Kgl.  Geol.  Landesanst.  (1889). 

BUCKLEY,  E.  R. 

1.  Geology  of  the  Disseminated  Lead  Deposits  of  St.  Francois  and  Washing- 
ton Counties,  Missouri. — Missouri  Bu.  of   Geol.   and  Mines,  vol.   9  (1909). 
259  pp. 

2.  Building  and  Ornamental  Stones  (with  many  admirable  colored  plates) . — 


ilding  am 
I.  4,   Wis. 


Bull.  4,  Wis.  Geol.  Nat.  Hist.  Sur.  (1898).     544 -pp. 


854  ALPHABETICAL    LIST    OF    AUTHORS. 

BUCKLEY,  E.  R.,  and  BUEHLER,  H.  A. 

Geology  of  the  Granby  Area. — Missouri  Bu.  of  Oeol.  and  Mines,  vol.  4,  2d 

ser.  (1906).     120pp. 
BUEHLER,  H.  A.,  and  GOTTSCHALK,  V.  A. 

Oxidation  of  Sulphides.—  Econ.  Oeol.,  vol.  5.  pp.  28-35  (1910). 
BURAT,  AMADEE. 

Geologic  Appliquee  ;  Gites  Me'talliferes  (Paris,  1870).     5th  ed.,  505  pp. 
BURGH ARD,  E.  F. 

The   Clinton  Iron-Ore  Deposits  in  Alabama. — Trans.  A.  I.  M.  E.,  vol.  40, 

pp.  75-133  (1909). 
BURCHARD,  E.  F.,  BUTTS,  C.,  and  ECKEL,  E.  C. 

Iron  Ores  of  the  Birmingham  District,   Alabama. — Bull.  400,    U.  S.   Q.  S. 

(1910).     204  pp. 
BUSH,  E.  E. 

The  Sudbury  Nickel  Kegion.—  E.  and  M.  Jour.,  vol.  57,  pp.  245-246  (1894). 

BUTTGENBACH,   H. 

1.  Quelques  Faits  a  propos  de  la  Formation  des  Pe*pites  d'Or. — Ann.  Soc. 
Oeol.  de  Belg.,  vol.  33,  part  II,  pp.  M51-M70  (1905-06). 

2.  Les  Gisements  de  cuivre  de  Katanga. — Ann.  Soc.  Geol.  de  Belg.,  vol.  31, 
(1904). 

CAMERON,  W.  E. 

The  Heberton  Tin  Field.— Queensland  Dept.  of  Mines,  No.  192  (1904). 

CAMPBELL,  A.  C. 

Ore-Deposits.— .E.  and  M.  Jour.,  vol.  30,  pp.  39-40  (July  17,  1880). 
CAMPBELL,  JOSEPH. 

The  Gold-Fields  of  the  Hauraki  Peninsula,  New  Zealand  — Trans.  Inst.  Min. 

Eng.,  vol.  12,  pp.  462-487  (1897). 
CANAVAL,  E. 

1.  Natur  und  Entstehung  der  Erzlagerstatten  am  Schneeberg  in  Tirol. — Zeit. 
f.  prak.  Geol.,  vol.  16,  pp.  479-483  (1908). 

2.  tJber  das  Vorkommen  von  Manganerzen  bei  Wandelitzen  nachst  Volker- 
markt  in  Karnten. — Jahrb.  d.  Naturhist.  Landes.  in  Karnten.,  vol.  28,  pp. 
357-368  (1909). 

CARLYLE,  E.  J. 

The  Pioneer  Iron  Mine,  Ely,  Minn. — Jour.  Can.  Min.  Inst.,  vol.  7,  pp.  335- 

367  (1904). 
CARPENTER,  F.  E. 

Ore- Deposits  of  the  Black  Hills  of  Dakota. — Trans.  A.  I.  M.  E.,  vol.  17,  pp. 

570-598  (1888-89). 
CARTHAUS,  EMIL. 

Die  Sandberger'sche  Erzgangtheorie. — Zeit.  f.  prak.  Oeol.,  vol.  4,  pp.  107-112 
(1896). 

CASE,  W.  H. 

The  Bertha  Zinc-Mines  at  Bertha,  Virginia.— Trans.  A.  I.  M.  E.,  vol.  22,  pp. 

511-536  (1893). 
CATHARINET,  JULES. 

Copper  Mountain,  British  Columbia. — E.  and  M.  Jour.,  vol.  79,  pp.  125-127 

(1905). 
CATLETT,  CHARLES. 

Iron-Ores  of  the  Potsdam  Formation  in  the  Valley  of  Virginia. — Trans.  A.  I. 

M.  E.,  vol.  29,  pp.  308-317  (1899). 
CAYEUX,  L. 

Le  Quartz  Secondaire  des  Mine'rais  de  Fer  Oolithiques  du  Silurien  de  France 
et  son  Eeplacement  en  Profondeur  par  du  Fer  Carbonate*. — Compt.  Rend. 
Acad.  Sci.,  vol.  149,  pp.  1095-1097  (1909). 
CHALMERS,  E. 

The  Sources  and  Distribution  of  the  Gold- Bearing  Alluvions  of  Quebec. — 
Ottawa  Nat.,  vol.  15,  pp.  33-36  (1901). 


ALPHABETICAL    LIST    OF    AUTHORS.  855 

CHALON,  P.  F. 

1.  Note  sur  la  Genese  des  Gisements  Metalliferes  et  des  Roches  Eruptives. — 
Trans.  Int.  Min.  and  Met.  Cong.  (1905).     30  pp. 

2.  La  Genese  des  Gisements  Metalliferes  et  des  Roches  Eruptives.     (Paris, 
1906).     236  pp. 

CHAMBERLIN,  R.  T. 

1.  The  Gases  in  Rocks.— Jour.  GeoL,  vol.  17,  pp.  534-568  (1909). 

2.  The  Gases  in  Rocks. — Publication  106,  Carnegie  Institution  of  Washington 
(1908). 

CHAMBERLIN,  T.  C. 

1.  The  Requisites  and  Qualifying  Conditions  of  Artesian  Wells. — 5th  Ann. 
Rept.,  U.  S.  O.  S.,  p.  125  (1885). 

2.  The  Fault  Problem.— Econ.  GeoL,  vol.  2,  pp.  585-601,  704-724  (1907). 

3.  Geology  of  Wisconsin,  vol.  4  (3882). 
CHANCE,  H.  M. 

1.  Report  on  the  Mining  Methods  and  Appliances  Used  in  the  Anthracite 
Coal  Fields.— 2d  GeoL  Sur.  Penna.,  Rept.  A.  C.,  pp.  6-14  (1883). 

2.  The  Rich   Patch  Iron  Tract,  Virginia.— Trans.  A.  I.  M.  E.,  vol.  29,  pp. 
210-223  (1899). 

3.  The  Discovery  of  New  Gold-Districts.— Trans.  A.  I.  M.  E.,  vol.  29,  pp. 
224-230  (1899). 

4.  The  Iron-Mines  of  Hartville,  Wyoming.— Trans.  A.  I.  M.  E.,  vol.  30,  pp. 
987-1003  (1900). 

5.  Gold-Ores  of  the  Black  Hills,  South  Dakota.— Trans.  A.  I.  M.  E.,\ol. 
30,  pp.  278-285  (1900). 

6.  The  Pyritic  Origin  of  Iron-Ore  Deposits. — E.  and  M.  Jour.,  vol.  86,  pp. 
408-410  (1908). 

7.  The  Origin   of  Bombshell   Ore.— Can.  Min.  Jour.,  vol.   29,  pp.  402-403 
(1908). 

8.  Rock  Pressure  and  Metamorphism. — Min.  and  Sci.  Press,  vol.  97,  pp.  299- 
302  (1908). 

9.  A  New  Theory  of  the  Genesis  of  Brown  Hematite-Ores  ;  and  a  New  Source 
of  Sulphur  Supply.— Trans.  A.  I.  M.  E.,  vol.  39,  pp.  522-539  (1908). 

CHAFER,  M. 

Note  sur  un  Gite  cuivreux  d'  origin  volcanique  du  Caucase  meridional. — Bull. 

Soe.  GeoL  de  France,  vol.  21,  pp.  101-109  (1893). 
CHARPENTIER,  H. 

Geologic  et  Mine"ralogie  Appliques  (Paris,  1900). 
CHAUTARD,  J.,  AND  LEMOINE,  P. 

La  laterisation  et  ses  relations  avec  la  genese  de  quelques  mine"rais  d' alumin- 
ium et  de  fer  et  de  certains  gites  auriferes. — Compt.  Rend.  Mens.  Ind.  Min., 
pp.  119-125  (Apr.,  1908  ;  Abstract  in  GeoL  CentralbL,  vol.  11,  No.  11,  p.  488 
(1908). 
CHIBAS,  E.  J. 

The  Manganese  Deposits  of  the  Department  of  Panama,  Colombia. — Trans.  A. 

I.  M.  E.,  vol.  27,  pp.  63-76  (1897). 
CHISM,  R.  E. 

1.  The  Vallecillo  Mines,  Mexico.— Trans.  A.  I.  M.  E.,  vol.  13,  pp.  351-369 
(1884-85). 

2.  Sierra  Mojada,  Mexico.— Trans.  A.  I.  M.  E.,  vol.  15,  pp.  542-588  (1886- 
87). 

CHRISTY,  S.  B. 

On  the  Genesis  of  Cinnabar  Deposits. — Am.  Jour.  Sci.,  3d  ser. ,  vol.  17,  pp. 

453-463  (1879). 
CHURCH,  J.  A. 

1.  Faulting  in  Veins.— E.  and  M.  Jour.,  vol.  53,  pp.  469-470,  613-614,  637- 
638  (1892). 

2.  The  Cause  of  Faulting.— Trans.  A.  I.  M.  E.,  vol.  21,  pp.  782-792  (1892- 
93). 

3.  The  Tombstone,  Arizona,  Mining  District.— Trans.  A.  I.  M.  E.,  vol.  33, 
pp.  3-37  (1902). 

4.  The  Comstock  Lode  :  its  formation  and  history  (New  York,  1879). 


856  ALPHABETICAL    LIST    OF    AUTHORS. 

CIRKEL,  FRITZ. 

Report  on  the  Chrome  Iron-Ore  Deposits  in  the  Eastern  Townships  of  the 
Province  of  Quebec  (with  Bibliography). — Bull.   29,   Mines  Branch,    Can. 
Dept.  Mines  (1909).     141  pp. 
CLAPP,  C.  H.,  and  BALL,  W.  G. 

The  Lead-Silver  Deposits  of  Newburyport,  Mass.,  and  their  Accompanying 

Contact- Zones.  —Econ.  GeoL,  vol.  4,  pp.  239-250  (1909). 
CLARK,  ELLIS. 

The  Silver-Mines  of  Lake  Vallev,  New  Mexico.— Trans.  A.  I.  M.  E.,  vol.  24, 

pp.  138-167  (1894). 
CLARKE   F  "W 

1.  Some  Nickel  Ores  from  Oregon.— Butt.  60,  U.  S.  G.  S.,  pp.  21-26  (1890). 

2.  The  Data  of  Geochemistry.— B nil.  330,  U.  S.  G.  S.  (1908).     716  pp. 
CLAYPOLE,  E.  W. 

The  Tin  Islands  of  the  Northwest.—  Am.  GeoL,  vol.  9,  pp.  228-236  (1892). 
CLEMENTS,  J.  M. 

The  Vermilion  Iron-Bearing  District  of  Minnesota. — Mon.  45,  U.  S.    G.    S. 

(1903).     463  pp. 
CLEMENTS,  J.  M.,  and  SMYTH,  H.  L. 

1.  The  Crystal  Falls  Iron-bearing  District  of  Michigan. — 19th  Ann.  Rept.,    U. 
S.  G.  S.,  part  3,  pp.  1-151  (1898). 

2.  The  Crystal  Falls  Iron-bearing  District  of  Michigan.—  Mon.  33,  U.  S.  G.  S. 
(1899).     512  pp. 

CLERC,  F.  L. 

The  Ore-Deposits  of  the  Joplin  Region,  Missouri. — Trans.   A.  I.  M.   E.,  vol. 

38,  pp.  320-343  (1907). 
COHEN,  E. 

Uber  die  Entstehung  des  Seifengoldes. — Mitt.   d.   Naturwiss.   Vereins  f.   Neu- 

vorkommen  u.  Riigen,  vol.  19  (1887). 
COLE,  G.  A.  J. 

Aids  in  Practical  Geology  (London,  1906).     431  pp. 

COLEMAN,  A.    P. 

1.  The  Vermilion  River  Placers  (Ontario). — Rept.  Ont.  Bu.  Min.,  vol.  10,  pp. 
151-159  (1901). 

2.  The  Sudbury  Nickel  Field.—  Rept.  Ont.  Bu.  Mines,  vol.  14,  part  3  (1905). 

3.  The  Helen  Iron  Mine,   Michipicoten.  —  Econ.  GeoL,  vol.   1,   pp.  521-529 
(1906). 

4.  The  Sudbury  Laccolithic  Sheet.— Jour.  Geol.,  vol.  15,  p.  759-782  (1907). 

5.  The  Alexo  Nickel  Deposit.  —Econ.  GeoL,  vol.  5,  pp.  373-376  (1910). 

COLLIER,  A.  J. 

1.  Reconnaissance  of  the  Northwestern  Portion  of  Seward  Peninsula,  Alaska. — 
Prof.  Paper  2,   U.  S.  G.  S.  (1902).     70  pp. 

2.  The  Tin  Deposits  of  the  York  Region,    Alaska.— Bull.   229,   U.  S.   G.  S. 
(1904).     61  pp. 

3.  Gold-Bearing  River  Sands  of  Northeastern  Washington. — Bull.  315,  U.  S. 
G.  S.,  pp.  56-70  (1907). 

COLLIER,  A.  J.,  HESS,  F.  L.,  SMITH,  P.  S.,  and  BROOKS,  A.  H. 

The  Gold  Placers  of  parts  of  Seward  Peninsula,  Alaska.— Bull.  328,  U.  S.G. 
&  (1988).     343pp. 

COLLINS,  G.  E. 

The  Relative  Distribution  of  Gold  and  Silver  Values  in  the  Ores  of  Gilpin 
County,  Colorado.— Trans.  Inst.  Min.  and  Met,,  vol.  12,  pp.  480-499  (1902- 
1903). 
COLLINS,  J.  H.- 

On  the  Origin  and  Development  of  Ore  Deposits  in  the  West  of  England. — 
Jour.  Roy.  Inst.  Cornw.  (1895). 

COLTON,  H.  E. 

Notes  on  the  Topography  and  Geology  of  Western  North  Carolina. — Trans. 
A.  I.  M.  E.,  vol.  16,  pp.  839-851  (1887-88). 


ALPHABETICAL    LIST    OF    AUTHORS.  857 

COMBES,  C.  F. 

Trait6  de  1' exploitation  des  mines,  vol.  1  (Paris,  1844). 
COMSTOCK,  T.  B. 

1.  Notes  on  the  Geology  and  Mineralogy  of  San  Juan  County,  Colorado. — 
Trans.  A.  I.  M.  E.,  vol.  11,  pp.  165-191  (1882-83). 

2.  The  Geology  and  Vein-Structure  of  Southwestern  Colorado. — Trans.  A.  I: 
M.  E.,  vol.  15,  pp.  218-265  (1886-87). 

3.  The  Geology  and  Vein-Phenomena  of  Arizona. — Trans.  A.  I.  M.  E '.,  vol. 
30,  pp.  1038-1101  (1900). 

CORNU,  F. 

1.  Uber  die  Paragenese  der  Minerale,  namentlich  die  der  Zeolithe. — 6st.  Zeit. 
f.  Berg-  u.  Hiitt.,  vol.  56,  pp.  89-93  (1908). 

2.  Die  Bedeutung  gelartiger  Korper  in  der  Oxydationszone  der  Erzlagerstat- 
ten.—Zeit.  f.  pra/c.  GeoL,  vol.  17,  pp.  81-87  (1909). 

CORNU,  F.,  and  LAZEREVIC,  M. 

Zur  Paragenesis  der  Knpfererze  von  Bor  in  Serbien. — Zeit.  f.  prole.  GeoL.  vol. 

16,  pp.  153-155  (1908). 
VON  COTTA,  BERNHABD. 

1.  Gangstudien,  herausgegeben  von  B.  von  .Cotta  l-III.  darin   Kollektaneen 
der  Literatur  von  H.  Miiller  (1850-1861 ). 

2.  A  Treatise  on  Ore-Deposits.     Trans,  of  Die  Lehre  von  den  Erzlagerstiitten 
(Freiberg,  1859-1861),  into  English  by  F.  Prime  (New  York,  1870).   575  pp. 

COURTIS,  W.  M. 

Gold-Quartz.— Trans.  A.  L  M.  E.,  vol.  18,  pp.  639-644  (1889-90). 

DE  LA  COUX,    H. 

L'or  ;  (Gites  auriferes  ;  extraction  de  Tor ;  traitement  du  minerai  ;  emplois  et 

anylyse  de  1'or)  (Paris,  1896).     328  pp. 
CRAGOE,  SPENCER. 

Notes  on  the  Mines  of  the  Frontino  and  Bolivia  Company,  Colombia. — Trans. 

A.  L  M.  E.,  vol.  28,  pp.  591-000  (1898). 
CREDNER,  H. 

1.  Beschreibungen  von  Mineralvorkommen  in  Nord  Amerika. — Berg-  u.  Hiitt. 
Zeit.,  p.  209  (1866). 

2.  Elements  der  Geologie,  10th  ed.  (Leipzig,  1906). 

3.  Die  Genesis  des  Siichsischen  Granulitgebirges. — Cent.  f.  Min.  GeoL  u.  Pal.. 
pp.  513-525  (1907). 

CROSBY,  W.  O. 

1.  Absence  of  Joint  Structure  at  Great  Depths. — GeoL  Mag.,  p.   416  (Sept., 
1881). 

2.  Classification  and  Origin  of  Joint  Structure. — Proc.  Bost.  Soc.  Nat.  Hist.. 
vol.  22,  p.  72  (1882). 

3.  On  the  Joint  Structure  of  Rocks.— Tech.  Quar.,  vol.  1,  pp.  245-250  (1887). 

4.  The  Origin  of  Parallel  and  Intersecting  Joints. — Tech.    Quar.,  vol.  6,  p. 
230  (1893)  ;  Am.  GeoL,  vol.  12,  p.  368  (Dec.,  1893). 

5.  A  Classification  of  Economic  Geological  Deposits. — Am.  GeoL,  vol.  13,  pp. 
249-268  (1894)  ;  Tech.  Quar.,  vol.  7,  pp.  27-48  (Apr.,  1894). 

6.  Geological  History  of  the  Hematite  Iron  Ores  of  the  Antwerp  and  Fowler 
Belt  in  New  York.—  Am.  GeoL,  vol.  29,  pp.  233-242  (1902). 

7.  The  Limestone-Granite  Contact- Deposits  of  Washington  Camp,  Arizona. — 
Trans.  A.  L  M.  E.,  vol.  36,  pp.  626-646  (1905). 

CROSBY,  W.  O.,  and  FULLER,  M.  L. 

Origin  of  Pegmatites.  —Am.  GeoL,  vol.  19,  pp.  147-180  (1897). 
CROSS,  WHITMAN. 

Geology  of  Silver  Cliff  and  the  Kosita  Hills,  Colorado.—  17th  Ann.  Rept.,  U. 

S.  G.  S.,  part  2,  pp.  263-403  (1896). 
CROSS,  WHITMAN,  and  PENROSE,  E.  A.  F.,  JR. 

Geology  and  Mining  Industries  of  the  Cripple  Creek  District,  Colorado. — 16^ 

Ann.  Rept.,  U.  S.  G.  S.,  part  2,  pp.  1-209  (1895). 
CROSS,  WHITMAN,  and  SPENCER,  A.  C. 

Geology  of  the  Bico  Mountains,  Colorado. — 2lst  Ann.  Rept,  U.  S.  G.  S.,  part 
2,  pp.  7-165  (1900). 

54 


858  ALPHABETICAL    LIST    OF    AUTHORS. 

CUMENGE,  M.  E. 

Kiinstliche  Darstellung  von  Gold  fiihrendem  Conglonierat. — Reunions  de  St. 
Etienne,  pp.  57-59  (1896)  ;  Rev.  in  Zeit.  f.  prak.  GeoL,  vol.  5,  p.  26  (1897). 
CUMENGE,  E.,  and  ROBELLAZ,  F. 

L'or  dans  la  Nature  (Paris,  1898).     112  pp. 
CURLE,  J.  H. 

Gold  Mines  of  the  World  (London,  1905).     324  pp. 
CURTIS,  J.  S. 

1.  Abstractof  Report  on  Mining  Geology  of  Eureka  District,  Nevada. — 4th 
Ann.  Rept.,  U.  S.  O.  S.,  pp.  221-251  (1884). 

2.  The  Silver- Lead  Deposits  of  Eureka,  Nevada.—  Mon.  7,  U.  S.  G.  S.  (1884). 
200  pp. 

GUSHING,  H.  P. 

The  Direction  of  Movement  and  Nomenclature  of  Faults. — Econ.  GeoL,  vol. 
2,  pp.  433-435  (1907). 

CZYSZKOWSKI,   S. 

The  Deposition  of  Gold  in  South  Africa.—  Am.   GeoL,  vol.  17,  pp.  306-323 
(1896). 

D'ACHIARDI,  A. 

I  Metalli,  Loro  Minerali  e  Miniere  (Milan,  1883). 
DAGGETT,  ELLSWORTH. 

The  Extraordinary  Faulting  at  the  Berlin  Mine,  Nevada. — Trans.  A.  I.  M.  E., 

vol.  38,  pp.  297-309  (1907). 
DAHLBLOM,  TH. 

IJber  Magnetische  Erzlagerstatten  und  deren  Untersuchung  durch  Magne- 
tische  Messungen.    Translated  into  German  by  T.  Uhlich  (Freiberg,  1899) . 
DAHSE. 

Report  of  the  Effuenta  Gold  Mines,  1879  (cited  by  Bergeat-Stelzner  1,  p.  1268). 
DAINTREE,  R. 

Note  on  Certain  Modes  of  Occurrence  of  Gold  in  Australia. — Quar.  Jour.  GeoL 

Soc,,  vol  34,  pp.  431-438  (1878). 
DALMER,  K. 

1.  Die  Erzlager  von  Swarzenberg  im  Erzgebirge. — Zeit.  f.  prak.   GeoL,  vol. 
5,  pp.  265-272  (1897). 

2.  Die  westerzgebirgische  Granitmassivzone. — Zeit.  f.  prak.  GeoL,  vol.  8,  pp. 
297-312  (19UO). 

3.  Der  Altenberg-Graupener  Zinnerzlagerstattendistrict. — Zeit.f.  prak.  GeoL, 
vol.  2,  p.  313  (1894). 

DALY,  HERBERT  J. 

The  Mount  Lyell  Copper  Deposits,  Tasmania. — Trans.  Inst.  Min.  and  Met.,  vol. 

9,  pp.  80-106  (1900-01). 
DALY,  R.  A. 

1.  Mechanics  of  Igneous  Intrusion. — Am.  Jour.  Sci.,  4th  ser.,  vol.  15,  pp. 
269-298;  vol.  16,  pp.  107-126;  vol.  26,  pp.  17-50  (1903-08). 

2.  Differentiation  of  a  Secondarv  Magma  through  Gravitative  Adjustment. — 
Eosenb.  Fests.,  pp.  203-233  (1906). 

DANA,  J.  D. 

Manual  of  Geology,  4th  ed.   (New  York  and  London,  1895).      1087  pp. 

DANNENBERG,  ROBERT. 

Uber  Verwerfungen  (Freiberg,  1884). 
DARAPSKY,  L. 

Tage  oder  Tiefenwasser  ?     (Leipzig,  1903. )     32pp. 
DAUBREE,  ADOLPHE. 

1.  Me"moire  sur    la  relation  des  sources  thermales  de  Plombieres  avec  les 
filons  me'talliferes.—  Ann.  d.  Mines,  5th  ser.,  vol.  13,  pp.   227-256  (Paris, 
1858). 

2.  Etudes  Synthetiques  de  Geologie  Experimental^  (1879).    828  pp. 

3.  Me'moir  sur  la  gisement,  la  constitution  et  1'origine  des  amas  de  minerai 
d'etain.— ^466.  K.  Bayer  Akad.  d.  Wissc.,  vol.  20,  p.  193  (1899). 


ALPHABETICAL    LIST    OF    AUTHORS.  859 

DAUBREE,  G.  A. 

1.  Les  Eaux  Souterraines  aux  Epoques  Anciennes  (Paris,  1887). 

2.  Les  Eaux  Souterrainnes  a  1'Epoque  Actuelle.     2  vols.  (Paris,  1887). 

3.  Recherches  Experimentales  sur  le  role  possible  des  gas  a  hautes  tempera- 
tures doues  de  tres  fortes  pressions  et  animes  d'un  mouvement  fort  rapide 
dans  divers  phenomenesge'ologiques. — Bull.  Soc.  Geol.  de  France,  3d  ser.,  vol. 
19,  p.  313  et  seq.  (1891)  ;   Abstract,  Zeit.  f.   prak.   Geol.,  vol.  1,  pp.  284- 
295  (1893). 

DAVID,  T.  W.  E. 

Geology  of  the  Vegetable  Creek  Tin-Mining  Fields  of  New  England  District, 
New  South  Wales.— Geol.  Sur.  N.  S.   W.,  pp.  4-169  (1887). 

DAVIES,  D.  C. 

A  Treatise  on  Metalliferous  Minerals  and  Mining.     5th  ed.  (London,  1892). 
•  548pp. 
DAY,  D.  T. 

Notes  on  the  Occurrence  of  Platinum  in  North  America. — Trans.  A.  I.  M.  E.t 

vol.  30,  pp.  702-708  (1900). 
DAY,  D.  T.,  and  RICHARDS,  E.  H. 

Useful  Minerals  in  the  Black  Sands  of  the  Pacific  Slope.     (Bibliography.) — 

Min.  Res.  of  U.  S.  for  1905,  pp.  1175-1258. 
DE  BEAUMONT — See  under  B. 
DE  BATZ,  RENE — See  under  B. 
VON  DECHEN,H. 

Die  Nutzbaren  Mineralien  und  Gebirgsarten  irn  Deutschen  Reiche  (Berlin, 

1873). 
DEKALB,  C. 

Diffusion  as  a  Factor  in  Ore  Deposition. — Min.  and  Sci.  Press,  vol.  96,  pp. 
226-227(1908). 

DELAUNAY,   L. 

1.  Formation  des  Gites  Me'talliferes,  2d  ed.  (Paris,  1893).     190  pp. 

2.  L' Argent ;  geologic,  metal  lurgie,  r61e  e'conomique  (Paris,  1896).     382  pp. 

3.  Les  Mines  d'Or  du  Transvaal  (Paris,  1896).     550  pp. 

4.  Contributions  a  1'etude  des  gites  m£talliferes  (Paris,  1897). 

5.  Sur  le  r61e  des  phe'nomenes  d'  alteration  superficielle,  et  de  remise  en  mouve- 
ment dans  la  constitution  des  gites  metalliferes — Ann.  d.  Mines,  9th  ser., 
vol.  12,  pp.  147-227  (August,  1897). 

6.  Contributions  a  1' Etude  des  Giles  Metalliferes. — Ann.  d.  Mines,  9th  ser., 
vol.  12,  pp.  119-227  (1897). 

7.  Recherche,  Captage,  et  Am^nagement  des  Sources  Thermes  Mine"rales,  p. 
80  etseq.  (Paris,  1899). 

8.  Les  Variations  des  Filons  Metalliferes  en  Profondeur. — Rev.  Gen.  d.  Sci., 
vol.  11,  pp.  575-588  (Apr.,  1900). 

9.  Les  Richesses  minerales  de  PAfrique  (Paris,  1903). 

10.  L'Origine  et  les  Caracteres  des  Gisements  de  Fer   Scandinaves. — Ann. 
d.  Miriest,  10th  ser.,  vol.  4,  pp.  49-106  ;  109-211  (1903). 

11.  La  Science  Geologique  (Paris,  1905).     747  pp. 

12.  Application  de  la  Methode  Techtonique  a  la  Mdtallogenie  de  la  Region 
Italie'nne.— Rev.  Gen.  d.Sci.,  vol.  16,  pp.  812-821  (1905). 

13.  La  Metalloge'nie  de  1' Italic. —Published  by  the  10th  International  Geo- 
logical Congress,  Mexico  (1906). 

14.  L'Or  dans  le  Monde  (Paris,  1907).     265  pp. 

15.  The  World's  Gold.      Its  Geology,  Extraction,  and  Political  Economy 
(New  York,  1908). 

16.  Sur  la  formation  des    gisements   d'or. — Compt.   rend.   Acad.    Sci.,   vol. 
149,  pp.  298-300  (Paris,  1909). 

17.  La  me'talloge'nie  de  1'Asie   Russe. — Ann.   d.   Mines,  10th  ser.,  vol.  15, 
pp.  220-295,  303-427  (1909). 

18.  La  Geologic  et  les  Richesses  Minerales  de  1'Asie  (Paris,  1911). 
DELKESKAMP,  R. 

1.  Die  hessichen  und  nassauischen  Manganerzlagerstatten  und  ihre  Ensteh- 
hung  durch  Zersetzung  des  dolomitisirten  Stringocephalenkalkes  resp. 
Zechsteindolomits.—  Zeit.  f.  prak.  Geol,  vol.  9,  pp.  356-365  (1901). 


860  ALPHABETICAL    LIST    OF    AUTHORS. 

DELKESKAMP,  E.— Continued. 

2.  Die  weite  Verbreitung  des  Baryums  in  Gesteinen  und  Mineralquellen  und 
die  sich  heraus  ergebenden  Beweismittel  fiir  die  Anwendbarkeit  der  Lat- 
eralsecretions-    und    Thermal theorie    auf  die   Genesis  der   Schwerspath- 
gange.— Zeit.  f.  prak.  GeoL,  vol.  10,  pp.  117-126  (1902). 

3.  Die  Genesis  der  Thermalquellen  von  Ems,  Wiesbaden  und  Kreuznach  und 
ihre    Beziehungen  zu  den    Erz-und  Mineralgangen  des    Taunus  und  der 
Pfalz.—  Deut.  Naturforsch.  u.  Aert.   (Sept.,  1903). 

4.  Die  Bedeutung  der  Geologic  fiir  die  Balneologie.  —Zeit.  f.  prak.  GeoL,  vol. 
12,  pp.  202-209  (1904). 

5.  Die   Bedeutung  der  Konzentrationsprozesse  fiir  die  Lagerstattenlehre  und 
die  Lithogenesis.—  Zeit.  f.  prak.  GeoL,  vol.  12,  pp.  289-316  (1904). 

6.  Juvenile  and  Vadose  Springs.— Bal  Zeit.,  vol.  16,  No.  5  (1905). 

7.  Vadose  und  juvenile  Kohlensaure. — Zeit.   f.  prak.  GeoL.  vol.  14,  pp.  33- 
47  (1906). 

8.  Fortschritte  auf  dem  Gebiete  der  Erforschung  der  Mineralquellen. — Zeit. 
f.  prak.  GeoL,  vol.  16,  pp.  401-443  (1908). 

DEMARET,  L. 

1.  Les  Giseraents  des  Minerals  de  Cuivre. — Rev.   Univ.  d.  Mines,  vol.  50,  pp. 
234-275  (1900). 

2.  Les  Principaux  Gisements  de  Mine'rais  de  Fer  du  Monde  (Paris,  1903). 61  pp. 

3.  Les  Principaux  Gisements  des  Minerals  de  Mercure  du  Monde. — Ann.  d. 
Min.  de  Belg.,  vol.  9,  pp.  36-112  (1904). 

4.  Les  Principaux  Gisements  des  Mine'rais  de  Manganese  du  Monde. — Ann. 
d.  Min.  de  Belg.,  vol.  10  (1905).     95  pp. 

5.  La  Genese  des  Gisements. — Ann.  d.  Min.  de  Belg. ,  vol.  11,  pp.  541-624 
(1906). 

DENCKMANN,  A. 

Uber  das  Nebengestein  der  Kamsbecker  Erzlagerstatten. — Jahrb.   d.  Kgl.  Pr. 

GeoL  Landesanst.,  vol.  29,  pt.  2,  pp.  243-253  (1908). 
DENNY,  G.  A. 

The  Origin  of  the  Gold  of  the  Eand  Gold  Fields.— Econ.   GeoL ,  vol.  4,  pp. 

470-485  (1909). 
DERBY,  O.  A. 

1.  Notes  on  Brazilian  Gold-Ores.— Trans.  A.  I.  M.  E.,  vol.   33,  pp.  282-287 
(1902). 

2.  On  the  Original  Type  of  the  Manganese  Ore  Deposits  of  the  Queley  Dis- 
trict, Minas  Geraes,  Brazil.—  Am.  Jour.  Sci.,  pp.  213-216  (1908). 

DEVEREUX,  W.  B. 

The  Occurrence  of  Gold  in  the  Potsdam  Formation,  Black  Hills,  Dakota. — 

Trans.  A.  L  M.  E.,vol.  10,  pp.  465-475  (1881-82). 
DEWEY,  F.  P. 

Some  Canadian  Iron  Ores.— Trans.  A.  I.  M.  E.,vo\.  12,  pp.  192-204  (1883-84) 
DICKSON,  C.  W. 

1.  The  Ore-Deposits  of  Sudbury,  Ontario.— Trans.  A.  L   M.  E.,  vol.  34,  pp. 
3-67  (1903). 

2.  Distribution  of  the  Platinum  Metals  in  Other  Sources  than  Placers. — Jour. 
Can.  Min.  Inst.,  vol.  8,  pp.  192-214  (1905). 

3.  Genetic  Relations  of  Nickel-Copper  Ores. — Jour.   Can.   Min.  Inst.,  vol.  9, 
pp.  236-260  (1906). 

DlEULEFAIT. 

1.  Existence  de  la  baryte  et  de  la  strontiane  dans  toutes  les  roches  constitu- 
tives  des  terrains  primordiaux. — Compt.  Rend.  Acad.  Sci.,  vol.  87,  pp.  934- 
936  (1878). 

2.  Diffusion  du  Cuivre  dans  les  roches  primordiales  et  les  dep6ts  Sedimentaires 
qui  en  precedent. — Compt.  Rend.  Acad.  Sci.,  pp.  453-455  (1879). 

3.  Existence  du  Zinc  a  Fe'tat  de  diffusion  complete  dans  les  terrains  dolomi- 
tiques.— Compt.  Rend.  Acad.  Sci.,  vol.  96,  pp.  70-72  (1883). 

4.  Le  manganese  dans  les  terrains  dolomitiques. — Compt.  Rend.  Acad.  Sci., 
vol.  96.  pp.  125-126  (1883). 

5.  Le  manganese  dans  les  eaux  des  mers  actuelles  et  dans  certains  de  leur 
depdts.-  Compt.  Rend.  Acad.  Sci.,  vol.  96,  pp.  718-721  (1883). 


ALPHABETICAL    LIST    OF    AUTHORS.  861 

DIEULEFAIT— Continued. 

6.  Sur  la  presence  constante  du  cuivre  et  du  zinc  dans  les  depots  du  fond  des 
mers.— Compt.  Rend.  Acad.  ScL,  vol.  101,  p.  1297  (1885). 

DlLLER,  J.    S. 

1.  The  Bohemia  Mining  Kegion  of  Western  Oregon. — 20th  Ann.  Rept.,  U.  S. 
G.  S.,  part3,  pp.  1-64  (1899). 

2.  Iron  Ores  of  the  Kedding  Quadrangle,  California. — Bull.  213,  U.  S.  Q.  S.. 
pp.  219-220  (1903). 

3.  Age  of  the  Pre- Volcanic  Auriferous  Gravels  in  California. — Proc.   Wash. 
Acad.  Sci.,  vol.  8,  pp.  405-406  (1907). 

4.  Port  Orford  Folio,  Oregon.—  Folio  89,  U.  S.  G.  S.  (1903). 
D'INVILLIERS,  E.  V. 

The  Cornwall  Iron-Ore  Mines,  Lebanon  County,  Pennsylvania. — Trans.  A.  1. 
M.  E.,  vol.  14,  pp.  873-904  (1885-86). 

DOELTER,  C. 

1.  Minerogeneses  und  Stabilitatsfelder  der  Mineralien. — Tscher.  Min.   u.  Pet. 
Mitt.,  vol.  25,  pp.  79-112  (1906). 

2.  Einige  Versuche  iiber  die  Loslichkeit  der  Mineralien. — Tscher.  Min.  u.  Pet. 
Mitt.,  vol.  11,  pp.  319-330  (1890). 

DON,  J.  R. 

The  Genesis  of  Certain  Auriferous  Lodes. — Trans.  A.  I.  M.  E.,  vol.  27,  pp. 
564-668  (1897). 

DORFFEL,  D. 

The  Balmoral  Cobalt  Lodes.— Trans.  Geol.  Soc.So.  Af.,  vol.  80,  part  v.  (1904). 
DOUGLAS,  JAMES. 

The  Copper  Queen  Mine,  Arizona. — Trans.  A.  I.  M.  E.,  vol.  29,  pp.  511- 

546  (1899). 
DOYLE,  P. 

On  Some  Tin-Deposits  of  the  Malayan  Peninsula. — Quar.  Jour.  Geol.  Soe.t 

vol.  35,  pp.  229-232  (1879). 
DRAKE,  FRANK. 

The  Manganese-Ore  Industry  of  the  Caucasus. — Trans.  A.  I.  M.  E.,  vol.  28, 

pp.  191-208  (1898). 
DRAPER,  W.  M. 

Gold  Deposits  of  Colombia  and  Ecuador.  — E.  and  M.  Jour. ,  vol.  58,  p.  532 

(1894). 
DRESSER,  J.  A. 

Copper  Deposits  of  the  Eastern  Townships  of  Quebec — Eton.  Geol..   vol.  1. 

pp.  445-453  (1906). 
DUNN,  E.  J. 

The  Mount  Morgan  Gold  Mine,  Queensland. — Proc.  Roy.  Soc.  Viet.,  vol.  17 
(new  ser.),  part  II,  pp.  341-355  (1905). 

DUNNINGTON,   F.   P. 

On  the  Formation  of  the  Deposits  of  Oxides  of  Manganese. — Am.  Jour.  Sci., 
3d  ser.,  vol.  36,  pp.  175-178. 

DUNSTAN,  B. 

Some  Croyden  Gold  Mines.— Geol.  Sur.  Queensl. ,  No.  202  (1905).     36  pp. 

DUROCHER. 

Production  artificielle,  par  voie  s6che,  des  principally  minerals  contenus  dans 
les  gites  metalliferes.— Compt.  Rend.  Acad.  ScL,  vol.  32,  p.  623  (1851);  vol. 
42,  p.  850  (1856). 

DUSSERT,  M. 

Etude  sur  les  gisements  metalliferes  de  1'  Alge*rie.—  Ann.  d.  Mines,  vol.  17,  pp. 

24-84,  91-203  (1910). 
DUTTON,  C.  E. 

The  Charleston   Earthquake. —9^   Ann.    Rept,  U.   S.    G.    S.,  pp.    203-528 

(1887-88). 

ECKEL,  E.  C.,  BURCHARD,  E.  F.,  and  BUTTS,  C. 

Iron  Ores,  Fuels,  and  Fluxes  of  the  Birmingham  District,  Alabama. — Bull. 
400,  U.  S.  G.  S.  (1910).  204  pp. 


862  ALPHABETICAL    LIST    OF    AUTHORS. 

EGLESTON,  THOMAS. 

The  Formation  of  Gold  Nuggets  and  Placer  Deposits. — Trans.  A.  I.  M.  E., 

vol.  9,  pp.  633-646  (1880-81). 
ELEVENTH  INTERNAT.  GEOL.  CONG.,  STOCKHOLM,  1910. 

The  Iron-Ore  Kesources  of  the  World  (with  Atlas).   (1910).    2  vol.     1100  pp. 
EMMENS,  S.  H. 

The  Chemistry  of  Gossan.— #.  and  M.  Jour.,  vol.  54,  pp.  582-583  (1892). 
EMMONS,  S.  F. 

1.  Abstract  of  Eeport  on  Geology  and  Mining  Industry  of  Leadville,  Colo. — 
2d  Ann.  Kept.,  U.  S.  G.  S.,  pp.  201-290  (1881). 

2.  Geology  and  Mining  Industry  of  Leadville,  Colorado. — Mon.  12,  U.  S.  G. 
S.  (1886).'     770  pp. 

3.  The  Genesis  of  Certain  Ore-Deposits. — Trans.  A.  I.  M.  E.,  vol.  15,  pp. 
125-147  (1886-87). 

4.  Origin  of  Fissure  Veins.—  Proc.  Colo.  Sci.  Soc.,  vol.  2,  part  3,  p.  189  (1887). 

5.  Notes  on  the  Geology  of  Butte,  Mont. — Trans.  A.  I.  M.  E.,  vol.  16,  pp. 
49-62  (1887-88). 

6.  Structural  Relations  of  Ore-Deposits. — Trans.  A.  I.  M.  E.,  vol.  16,  pp. 
804-839  (1887-88). 

7.  Faulting  in  Veins.—  E.  and  M.  Jour.,  vol.  53,  p.  548  (1892). 

8.  Fluorspar-Deposits  of  Southern  Illinois. — Trans.  A.  I.  M.  E.,  vol.  21,  p. 
31  (1892-93). 

9.  Geological  Distribution  of  the  Useful  Metals  in  the  United  States. — Trans. 
A.  I.  M.  K,  vol.  22,  pp.  53-95  (1893). 

10.  The  Genesis  of  Ore-Deposits.     Discussion  of   Paper  by  F.  Posepny. — 
Trans.  A.  I.  M.  E.,  vol.  23,  pp.  597-602  (1893). 

11.  Some  Mines  of  Rosita  and  Silver  Cliff,  Colorado. — Trans.  A.  I.  M.  E., 
vol.  26,  pp.  773-823  (1896). 

12.  The  Mines  of  Custer  County,  Colo.— 17 th  Ann.  RepL,  U.  S.  G.  S.,  part 
2,  pp.  405-472  (1896). 

13.  The  Secondary  Enrichment  of  Ore- Deposits.— Trans.  A.  I.  M.  E ,  vol.  30, 
pp.  177-217  (1900). 

14.  The  Delamar  and  the  Horn-Silver  Mines  :  Two  Types  of  Ore- Deposits  in 
the  Deserts  of  Nevada  and  Utah.— Trans.  A.  I.  M.  E.,  vol.  31,  pp.  658-683 
(1901). 

15.  Theories  of  Ore  Deposition  Historically  Considered. — Bull.  Geol.  Soc.  Am., 
vol.  15,  pp.  1-28  (1904)  ;  E.  and  M.  Jour.,  vol.  77,  pp.  117-119,  157-159, 
199-200,  237-238  (1904). 

16.  Copper  in  the  Red  Beds.—  Butt.  260,  U.  S.  G.  S.  (1905). 

17.  Useful  Definitions.—  Min.  and  Sci.  Press,  vel.  93,  pp.  355-356  (1906). 

18.  Los  Pilares  Mine,  Nacozari,  Mexico. — Econ.  Geol.,  vol.  1,  pp.  629-643 
(1906). 

19.  The  Cananea  Mining  District  of  Sonora,  Mexico. — Econ.  Geol.,  vol.  5,  pp. 
312-356  (1910). 

20.  Butte  Special  Folio,  Montana.—  Folio  38,  U.  S.  G.  S.   (1897).  8  pp. 
EMMONS,  S.  F.,  and  IRVING,  J.  D. 

The  Downtown  District  of   Leadville,   Colorado.—  Butt.   320,    U.   S.    G.   S. 
(1907).     75  pp. 

EMMONS,  W.  H. 

1.  The  Cashin  Mine,  Colo.— Bull.  285,  U.  S.  G.  S.,  pp.  125-128  (1906). 

2.  Gold  Deposits  of  the  Little  Rocky  Mountains,  Montana.—  Bull.  340,   U.  S. 
G.  S.,  pp.  96-116  (1908). 

3.  A  Genetic  Classification  of  Minerals.—  Econ.  Geol.,  vol. 3, pp. 611-627  (1908). 

4.  Some  Regionally  Metamorphosed  Ore  Deposits  and  the  So-called  Segre- 
gated Veins.— Econ.  Geol.,  vol.  4,  pp.  755-781  (1909). 

5.  Outcrop  of  Ore  Bodies.—  Min.  and  Sci.  Press,  vol.  99,  pp.  751-754  ;  782-787 
(1909). 

6.  A  Reconnaissance  of  Some  Mining  Camps  in  Elko,  Lander,  and   Eureka 
Counties,  Nevada.— BttM.  408,  U.  S.  G.  S.  (1910).     130  pp. 

7.  The  Agency  of  Manganese  in  the  Superficial  Alteration  of  Gold-Deposits. 
—Trans.  A.' I.  M.  E.,  vol.  42,  pp.  3-73  (1911). 

8.  Secondary  Enrichment  in  Granite- Bimetallic  Mine,  Phillipsburg,  Montana, 
—Science,  New  Series,  vol.  27,  p.  92).  (1908). 


ALPHABETICAL    LIST    OF    AUTHORS.  863 

ERHARD. 

Uber  Elektrische  Strome  auf  Erzgiingen. — Jahrb.  f.  Berg-  u.  Hutt  in  Konig. 

Sachs.,  pp.  160-174  (1885). 
ERMTSCH,  KARL. 

Die  gangformigen  Erzlagerstatten  der  Umgegend  von  Massa  Marittima  in 
Toskana  auf  Grund  der  Lottischen  Untersuchungen. — Zeit.  f.  prak.  Geol., 
vol.  13,  pp.  206-241  (1905). 
EUSTIS,  W.  E.  C. 

The  Nickel  Ores  of  Orford,  Quebec,  Canada. — Trans.  A.  I.  M.  E.,  vol.  6,  pp. 

209-214  (1877-78). 
EVANS,  J.  W. 

The  Direction  of  Movement  and  Nomenclature  of  Faults. — Econ.  Geol,  vol. 
2,  pp,  803-806  (1907). 

FAIRBANKS,  H.  W. 

1.  The  Tin  Deposits  at  Temescal,  Southern  California.—  Am  Jour.  Sci.,  4th 
ser.,  vol.  4,  pp.  39-42  ;  Min.  and  Sei.  Press,  vol.  75,  p.  362  (1897). 

2.  The  Relation  between  Ore  Deposits  and  Their  Inclosing  Walls.—  E.  and  M. 
Jour.,  vol.  55,  p.  200  (Mar.  4,  1893). 

FAIRCHILD,  H.  L. 

The  Direction  of  Movement  and  Nomenclature  of  Faults.    Discussion  of  Han- 
some  8.—  Econ.  Geol.,  vol.  2,  p.  184  (1907). 
FARIBAULT,  E.  R. 

1.  No va  Scotia  Gold-Fields.— Can.  Geol.  Sur.  Sum.  Rept,  1901,  pp.  214-221(1902) 

2.  Nova  Scotia  Gold-Fields.— Can.  Geol.  Sur.  Sum.  Rept.,  1902,  pp  399-427 
(1903). 

3.  Gold-Fields  of  Nova  Scotia.— Can.  Geol.  Sur.  Sum.  Rept.,  1903,  pp.  174- 
186  (1904). 

4.  Gold-Fields  of  Nova  Scotia.— Can.  Geol.  Sur.  Sum.  Rept.,  1904,  pp.  319- 
332(1905). 

5.  Gold-Fields  of  Nova  Scotia.— Can.  Geol.  Sur.  Sum.  Rept.,  1905,  pp.  122- 
124  (1906). 

6.  Gold-Fields  of  Nova  Scotia.— Can.  Geol.  Sur.  Sum.  Rept.,  1906,  pp.  147- 
152  (1906). 

7.  The  Gold  Measures  of  Nova  Scotia,  and  Deep  Mining.     Published  by  the 
Mining  Society  of  Nova  Scotia.— Jour.  Can.  Min.  Inst.,vol.  2,  pp.  119-129 
(1899). 

8.  Nova  Scotia,  Deep  Gold  Mining. — Publication  of  the  Commissioner  of  Public 
Works  and  Mines  (1903.) 

FARISH,  J.  B. 

1.  On  the  Ore-Deposits  of  Newman  Hill.— Proc.  Colo.  Sci.  Soc.,  vol.  4,  pp. 
151-164  (1892). 

2.  Interesting  Vein-Phenomena  in  Boulder  County,  Colorado.  —  Trans.  A.  L 
M.  E.,  vol.  19,  pp.  547-553  (1890-91). 

FARRELL,  J.  H. 

Practical  Field  Geology  (New  York,  1912). 
FARRELL,  jT.  K. 

The  Copper  and  Tin  Deposits  of  Katanga. — E.  and  M.  Jour.,  vol.  85,  p.  747- 

753  (1908). 
FARRINGTON,  O.  C. 

Observations  on  the  Geology  and  Geography  of  Western  Mexico,  including 
an  account  of  the  Cerro  Mercado. — Pub.  Field  Col.  Museum,  No.  89,  Geol. 
Ser.  II,  No.  5,  pp.  197-228  ;  E.  and  M.  Jour.,  vol.  78,  pp.  345-346  (1904). 
FAWNS,  SYDNEY. 

1.  Notes  on  the  Mount  Bischoff  Tin  Mine. — Trans.  Tnst.  Min.  and  Met.,  vol. 
14,  pp.  221-249  (1904-05). 

2.  Some  Notes  on  the  Mount  Lyell  Mine,  Tasmania. — Trans.  Inst.  Min.  and 
Met.,  vol.  4,  pp.  279-289  (1895-96). 

3.  Tin  Deposits  of  the  World.— Published  by  Min.  Jour.  (London,  1907).  304  pp 
FAY,  ALBERT  H. 

Geology  and  Mining  of  the  Tin-Deposits  of  Cape  Prince  of  Wales,  Alaska. 
—Trans.  A.  L  M.  E.,  vol.  38,  pp.  664-682  (1907). 


864  ALPHABETICAL    LIST    OF    AUTHORS. 

FERMOR,  L.  L. 

1.  Manganese  in  India. — Trans.  Min.  and  Geol  Inst.  Ind.,  vol.  1.  pp.  69-131 
(1907). 

2.  The  Manganese  Ore- Deposits  of   India. — Mem.  Geol.  Sur.  Ind.,  vol.  37 
(1909).     1294pp. 

FERNEKES,  GUSTAVE. 

Precipitation  of  Copper  from  Chloride  Solutions  by  Means  of  Ferrous  Chlo- 
ride.— Econ.  Geol,  vol.  2,  pp.  580-584  (1907). 
FINCH,  J.  W. 

The  Circulation  of  Underground  Aqueous  Solutions  and  the  Deposition  of 

Lode  Ores.—  Proc.  Colo.  Sci.  Soc.,  vol.  7,  pp.  193-252  (1904). 
FINK,  W. 

Das  Eisenglimmer  am  Gleissingerfels.  Ein  Beitrag  zur  Geologic  und  Berg- 
baugeschichte  des  Fichtelgebirges. — Geog.  Jahresheft.,  vol.  19,  pp.  153-167 
(1906). 

FlNLAY,  J.  R. 

1.  Notes  on  the  Gold-Mines  of  Zaruma,  Ecuador. — Trans.  A.  L  M.  E.,  vol.  30, 
pp.  248-260  (1900). 

2.  The  Mining  Industry  of  the  Coeur  d'  A16nes,  Idaho.— Trans.  A.  I.  M.  E., 
vol.  33,  pp.  235-271  (1902). 

FlNLAYSON,  A.   M. 

1.  Problems  of  Ore  Deposition  in  the  Lead  and  Zinc  Veins  of  Great  Britain. 
Min.  Jour.,  vol.  88,  p.  169  (1910). 

2.  The  Pyritic  Deposits  of  Huelva,  Spain.—  Econ.  Geol.,  vol,  5,  pp.  357-372  ; 
403-437  (1910). 

3.  The  Metallogeny  of  the  British  Isles. — Quar.  Jour.  Geol.  Soc.,  vol.  56,  pp. 
281-298  (1910). 

4.  Secondary  Enrichment  in  the  Copper  Deposits  of  Huelva,  Spain. — Trans. 
Inst.  Min.  and  Met.,  vol.  20,  pp.  61-72,  and  16  pages  of  admirable  discussion 
by  members  of  the  Institute  (1910-1911). 

VON   FlRCKS,  W. 

Die  Zinnerzlagerstatten  des  Mount  Bischoff  in  Tasmanien. — Zeit.  d.  D.  Geol. 

GeseL,  vol.  51,  part  3,  pp.  431-464  (1899). 
FLECK,  HERMAN,  and  HALDANE,  W.  G. 

A  Study  of  the  Uranium  and  Vanadium  Belts  of  Southern  Colorado. — Rept. 

Colo.  St.  Bu.  Min.,  pp.  47-115  (1905-1906). 

FLORES,  T. 

Las  Criaderos  Argentiferos  de  "  Providencia  "  y  "  San  Juan  de  la  Chica," 
San  Felipe.—  Bol.  Soc.  Geol.  Mex.,  vol.  1,  pp.  169-173  (1905). 

FOOTE,  H.  W. 

Criteria  of  Downward  Sulphide  Enrichment. — Econ.  Geol.,  vol.  5.  pp.  485-488 
(1910). 

FORCHHAMMER. 

Uber  den  Einfluss  des  Kochsalzes  auf  die  Bildung  der  Mineralien. — Pogg. 
Ann.,  vol.  91,  pp.  568-585  (1854),  but  especially  vol.  95,  pp.  60-96  (1855). 

FORSTNKR,  WM. 

1.  The  Quicksilver  Resources   of    California. — Bull.  27,   Cal.  St.  Min.  Bu. 
(1908).     273pp. 

2.  The  Genesis  of  the  Copper  Ores  in  Shasta  County,  west  of  the  Sacramento 
River.— Mm.  and  Sci.  Press,  vol.  97,  pp.  261-262  (1908). 

FOSTER,  C.  IE  NEVE. 

Ore  and  Stone  Mining,  5th  ed   (London,  1905). 
VON  FOULLON,  H.  B. 

Uber  Einige  Nickelerzvorkommen. — Jahrb.  d.  K.  K.   Geol.   Reichsanst.,  vol. 

43,  pp.  276-302  (1872), 
FRANCOIS. 

Sur  1'Origine  des  fers  limoneux  et  des  Sables  auriferes  de  1'Ariege  et  de  la 

Haute-Garonne.— Ann.  d.  Mines,  3d  ser.,  vol.  18,  pp.  417-432  (1840). 
FRASER,  COLIN,  and  ADAMS,  J.  H. 

Geology  of  the  Coromandel  Subdivision,  Hauraki,  Auckland. — Bull.  4,  N. 
Z.  Geol.  Sur.  (1907).  154  pp. 


ALPHABETICAL    LIST    OF    AUTHORS.  865 

FRAZEB,  PERSIFOR  (JR.  )• 

1.  A  Study  of  the  Specular  and  Magnetic  Iron  Ores  of  the  New  Red  Sandstone 
in  York  County,  Pa.— Trans.  A.  I.  M.  E.,  vol.  5,  pp.  132-143  (1876-77). 

2.  Missing  Ores  of  Iron.— Trans.  A.  I.  M.  E.,  vol.  6,  pp.  531-542  (1877-78). 
FRAZER,  PERSIFOR. 

1.  Some  Copper  Deposits  of  Carroll  County,  Maryland. — Trans.  A.  I.  M.  E., 
vol.  9,  pp.  33-40  (1880-81). 

2.  The  Whopper  Lode,  Gunnison  County,  Colorado.— Trans.  A.  I.  M.  E.,  vol. 
9,  pp.  249-258  (1880-81). 

3.  The  Iron  Ores  of  the  Middle  James  River.— Trans.  A.  I.  M.  E.,  vol.  11, 
pp.  201-216  (1882-83). 

4.  The  "Centennial"  and  "Lotta"  Gold  Properties,  Coahuila,  Mexico.— 
Trans.  A.  I.  M.  E.,  vol.  14,  pp.  196-205  (1885-86). 

5.  Geogenesis  and  Some  of  Its  Bearings  on  Economic  Geology. — Trans.  A.  I. 
M.  E.,  vol.  35,  pp.  298-308  (1904). 

FRECHEVILLE,  K.  J. 

Great   Main   Lode  of  Dolcoath. —  Trans.  Roy.   Geol.  Soc.   Cornw.,  vol.  10,  pp. 

146-156  (1887). 
FREELAND,  F.  T. 

1.  The  Sulphide  Deposit  of  South  Iron  Hill,  Leadville,  Colorado.— Trans. 
A.  I.  M.  E.,  vol.  14,  pp.  181-189  (1885-86). 

2.  Fault-Rules.— Trans.  A.  I.  M,  E.,  vol.  21,  pp.  491-502  (1892-93). 
FRITSCH. 

tlber  die  Mitwirkung  Elektrischer  Strome  bei  der  Bildung  einiger  Miner- 
alien  (Gottingen,  1862). 

FUCHS,  W. 

Beitriige  zur  Lehre  von  den  Erzlagerstiltten  (1846). 
FUCHS,  E.,  and  DELAUNAY,  L. 

Trait^  des  Gites  Mine'raur  et  Metalliferes  (Paris,  1893.)  2  vols.,  823-1004  pp. 

FUKTTCHI,   U. 

Mineral   Parageneses  in  the   Contact   Metamorphic  Ore  Deposits  found  in 

Japan. — Beitr.  zur  Mineral  von  Japan,  No.  3  (Tokyo,  1907). 
FULLER,  MYRON  L. 

1.  Bibliographic   Review  and  Index   of   Papers  Relating  to   Underground 
Waters.—  Wat.  Sup.  and  Trr.  Paper  120,  U.  S.  G.  S.  (1905).     Covers  years 
1879-1904. 

2.  Total  Amount  of  Free  Water  in  the  Earth's  Crust.  —  Wat.  Sup.  and  Irr.  Paper 
160,  U.  S.  G.  S.,  pp.  59-72  (1906). 

FULTON,  JOHN. 

Mode  of  Deposition  of  the  Iron-Ores  of  the  Menominee  Range,  Michigan. — 
Tram.  A.  L  M.  K,  vol.  16,  pp.  525-536  (1887-88). 

FURLONGE,  W.  H. 

Notes  on  the  Geology  of  the  DeKaap  Gold-Fields  in  the  Transvaal.  —  Trans. 
A.  I.  M.  E.,  vol.  18,  pp.  334-348  (1889-90). 

GABERT.  C. 

Die  Gneise  des  Ergzebirges  und  ihre  Kontaktwirkungen. — Zeit.   d.  D.    Geol. 

Gesel.,  vol.  59,  pp.  308-376  (1907). 
GAETZSCHMANN,  M.  F. 

Die  Auf-  und  Untersuchung  von  Lagerstatten  nutzbarer  mineralien,  2d  ed. 

(1866). 
GAGE,  J.  R. 

On  the  Occurrence  of  Lead  Ores  in  Missouri. — Trans.  A.  I.  M.  E.,  vol.  3,  pp. 

116-125  (1874-75). 
GALE,  H.  S. 

1.  Gold  Placer  Deposits  near  Lay,  Routt  County,  Colorado.—  Bull.  340,  U.  S. 
G.  S.,  pp.  84-95  (1908). 

2.  Geology  of  the  Copper  Deposits  near  Montpelier,  Idaho. — Bull.  430,  U.  S. 
G.  S.,  pp.  112-121  (1910). 

3.  Carnotite  in  Western  Colorado.  —Bull.  340,  U.  S.  G.  fl.,  pp.  256-262  (1908). 

4.  Carnotite  in  Rio  Blanco  County,  Colorado.—  Bull.  315,  U.   S.    G.   S.,  pp. 
110-117  (1907). 


866  ALPHABETICAL    LIST    OF    AUTHORS. 

GARNIER,  J. 

Mines  de  nickel,  cuivre  et  platinedu  District  deSudbury,  Canada. — Mem.  Soc. 

Ing.  Civ.  (Paris,  March,  1891). 
GARRISON,  F.  L. 

1.  Chemical  Characteristics  of  Limonite  Iron  Ores.     The  Genesis  of  Limonite 
Ores  in  the  Appalachians. — E.  andM.  Jour.,  vol.78,  pp.  258, 470-471  (1904). 

2.  Ores  Formed  by  Magmatic  Segregation. — Min.  and  Sci.  Press,  vol.  98,  pp. 
451-456  (1909). 

GASCUEL,  M.  L. 

Gisements  Stanniferes  au  Laos  Francais. — Ann.  d.  Mines,  10th  ser.,  vol.  8,  pp. 
321-331  (1905). 

GAUTIER,  ARMAND. 

1.  Ge'ne'se  des  eaux  thermales  et  ses  rapports  avec  le  volcanisme. — Ann.  d. 


2.  Action  de  1'hydrogene  sulfure  sur  quelques  oxydes  me'talliques  et  Metal- 


Mines,  10th  ser.,  vol.  9,  pp.  316-370  (1906). 

ilfi 

loides.    Applications  aux  ph^nomenes  volcaniques  et  aux  eaux  thermales. — 
Compt.  Rend.  Acad.  Sci.,  vol.  142,  pp.  7-12  (1906). 

3.  Action  de  la  vapeurd'eau  surles  sulfures  au  rouge.    Production  de  Me"taux 
Natifs.     Applications  aux  Phenomenes  Volcaniques. — Compt.  Rend.  Acad. 
Sci.,  vol.  142,  pp.  1465-1470  (1906). 

4.  The  Genesis  of  Thermal  Waters,  and   their  Connection  with  Volcanism 
(Trans.,  by  F.  L.  Eansome).—  Econ.  GeoL,  vol.  1,  pp.  688-697  (1906). 

5.  L' Intervention  et  le  K61e  de  1'Ean  dans  les  Phenomenes  volcaniques. — 
Ann.  d.  Mines,  vol.  16,  10th  ser.,  pp.  213-230  (1909). 

GAUTIER,  F. 

Etudes  sur  la  formation  des  gisements  aurifSres. — Compt.  Rend.  Acad.  Sci.,  pp. 

•99-109  (1901). 
GEBHARDT,  R. 

Beitriige  zur  Kenntniss  der  Beziehungen  zwischen   Erzgjingen    und  faulen 

Euscheln  des  nordwestlichen  Oberharzes  (Rostock,  1899).     38  pp. 
GELKIE,  ARCHIBALD. 

Text-Book  of  Geology,  4th  ed.,  2  vol.  (London,  1882). 
GEIKIE,  J.  S. 

The  Occurrence  of  Gold  in  Upper  Sarawak,  Borneo. — Trans.  Inst.  Min.  and 

Met.,  vol.  15,  pp.  63-79  (1905-06). 
GEORGE,  R.  D. 

The  Main  Tungsten  Area  of  Boulder  County,  Colorado.     (Bibliography). — 
Colo.  Geol.  Sur.,  vol.  9,  pp.  7-103  (1909). 

GHOSE,  A. 

The  Mode  of  Occurrence  of  Manganite  in  the  Manganese  Ore  Deposits  of  the 
Sandus  State,  Bellary,  Madras,  India. — Trans.  Brit.  Inst.  Min.  Eng.,  vol.35, 
partS,  pp.  685-691. 
GILBERT,  G.  K. 

t.  On  the  Origin  of  Jointed  Structure. — Am.  Jour.  Sci.,  3d  ser.,  vol.  24,  p.  50 

(July,  1882). 

2.  Post-Glacial  Joints.— Am.  Jour.  Sci.,  3d  ser.,  vol.  23,  pp.  25-27  (1882). 
GILLETTE,  H.  P. 

Osmosis  as  a  Factor  in  Ore-Formation — Tram.  A.  I.  M.  E.,  vol.  34,  pp.  710- 
TH  (1903). 

GILPIN,  EDWARD,  JR. 

1.  The  Iron-Ores  of  Pictou  County,  Nova  Scotia. — Trans.  A.  L  M.  E.,  vol. 
14,  pp.  54-63  (1885-86). 

2.  The  Nova  Scotia  Gold  Mines.— Trans.  A.  I.  M.  E.,  vol.    14,   pp.  674-689 
(1885-86). 

3.  The  Geological  Relations  of  the  Principal  Nova  Scotia  Minerals. — Trans. 
A.  I.  M.  E.,  vol.  18,  pp.  198-205  (1889-90). 

GLASSER,  M.  E. 

Les  Richesses  Minerales  de  la  Nouvelle  Caledonie.     (Paris,  1904.)     560.  pp. 
Also  Ann.  d.  Mines,  vol.  5,  10th  ser.,  pp.  503-701  (1904). 


ALPHABETICAL    LIST    OF    AUTHORS.  867 

GLENN,  WILLIAM. 

1.  The  Form  of  Fissure-Walls,  as  Affected  by  Sub-Fissuring  and  by  the  Flow 
of  Kocks.— Trans.  A.  I.  M.  E.,  vol.  25,  pp.  499-513  (1895). 

2.  The  Chrome  Ores  of  Turkey.—  19<A  Ann.  Rept.,   U.  S.  G.  S.,  pt.  6,   pp. 
261-264  (1897-98). 

3.  Chromic  Iron.     Occurrence,  Character,  Uses,  etc.,  of. — 17th  Ann.  Rept.,  U. 
S.  G.  S.,  pt.  3,  pp.  261-273  (1895-1896). 

GOLDSCHMIDT,V.    M. 

Die  Kontaktmetamorphose  im  Kristianiagebiet  (Kristiania,  1911).     483  pp. 
GOODCHILD,  J.  G. 

GeoL  Mag.  (May,  1883). 
GORDON,  H.  A. 

Hysteromorphous  Auriferous  Deposits  of  the  Tertiary  and  Cretaceous  Periods 
in  New  Zealand.— Trans.  A.  L  M.  E.,  vol.  25,  pp.  292-301  (1895). 

DE  LA  GOUPILLIERE,  HATON. 

Cours  d' exploitation  des  mines  (Paris,  1883). 
GRABILL,  L.  R. 

On  the  Peculiar  Features  of  the  Bassick  Mine. — Trans.  A.  I.  M.  E ,  vol.  11, 

pp.  110-120  (1882-83). 
GRANGER,  H.  G. 

Gold  in  the  Guyanas.— Trans.  A.  L  M.  E.,  vol.  25,  pp.  516-52-3  (1898). 
GRANGER,  H.  G.,  and  TREVILLE,  E.  B. 

Mining  Districts  in  Colombia.— Trans.  A.  L  M.  E.,  vol.  28,  pp.  33-87  (1898). 
GRANT,  U.  S. 

1.  Preliminary  Report  on  the  Lead  and  Zinc  Deposits  of  Southwestern  Wis- 
consin.— Bull  9,  Wis.  GeoL  Nat.  Hist.  Sur.  (1903).     103  pp. 

2.  Investigations  of  the  Lake  Superior  Iron  Ore  Deposits. — Min.  Mag.  (J.), 
vol.  10,  pp.  175-183  (1904). 

3.  Structural  Relations  of    the  Wisconsin  Zinc  and   Lead  Deposits. — Econ. 
GeoL,  vol.  1,  pp.  233-242  (1905). 

4.  Report  on  Lead  and  Zinc  Deposits  of  Wisconsin. — Bull.  14,  Wis.   GeoL 
Nat.  Hist.  Sur.  (1906).     100  pp. 

GRANT,  U.  S. ,  and  BURCHARD,  E.  F. 

Lead  and  Zinc  Deposits  of  Lancaster  and  Mineral  Point  Quadrangle. — Folio 

145,  U.  S.  G.  S.  (1907). 
GRATON,  L.  C. 

1.  Reconnaissance  of  some  Gold  and  Tin  Deposits  of  the   Southern  Appala- 
chians.— Bull.  293,  U.  S.  G.  S.  (1906).     134  pp. 

2.  The  Occurrence  of  Copper  in  Shasta  County,  California.—  Bull.  430,  U.  S. 
G.  S.,  pp.  71-111  (1910). 

GRESLEY,  W.  S: 

Faulting  in  Veins.—  E.  and  M.  Jour.,  vol.  53,  p.  517  (1892). 
GREENWELL,  G.  C. 

A  Practical  Treatise  on  Mine  Engineering,  3d  ed.  (London,  1889). 
GREGORY,  J.  W. 

1.  Variation  of  Ores  in  Depth.—  Aust.  Mm.  Stand,  vol  20,  pp.  962-963  (1901). 

2.  Factors  that  Control  the  Depth  of   Ore- Deposits. — Trans.  Austral  Inst. 
Min.  Eng.,  vol.  8,  p.  2  (1904). 

3.  The  Mount  Lyell  Mining  Field,  Tasmania.  —  Trans.  Austral.  Inst.  Min. Eng., 
vol.  10,  pp.  26-196  (1905). 

4.  The   Ancient  Auriferous  Conglomerates   of  Southern   Rhodesia. — Trans. 
Inst.  Min.  and  Met.,  vol.  15,  pp.  5<i3-586  (l<)05-0t>). 

5.  The  Mt.  Lyell  Mining  Field.—  Aust.  Min.  Stand,  vol.  34,  p.  34,  (1905). 

6.  The   Mount  Lyell  Mining  Field,  Tasmania,  with   some  account  of    the 
Geology  of  Other  Pyritic  Ore  Bodies.—  Min.  Jour.  (1906). 

7.  Ore  Deposits  and  Their  Distribution  in  Depth. — Min.  Jour.,  vol.  79,  pp. 
583-584,  617  (1906)  ;  N.  Z  Mines Rec.,  vol.  9,  pp.  489-492,  529-531  ;  vol.  10, 


pp.  38-40  (1906). 
J.  Th      ~     -     -     - 


8.  The   Geological  Plans  of  Some  Australian  Mining   Fields. — Sci.   Prog., 
No.  1  (1906).     20  pp. 

9.  The  Ballarat  East  Gold  Field.— Mem.  4,  GeoL  Sur.  Viet.   (1907).     52pp. 


868  ALPHABETICAL    LIST    OF    AUTHORS. 

GREGORY,*J.  W. — Continued. 

10.  The  Origin  of  the  Gold  in  the  Rand  Banket.  —  Trans.  Inst.  Min.  and  Met., 
vol.  17,  pp  2-85  (1907-08). 

11.  Geology  of  the  Inner  Earth;  Igneous  Ore.— Ann.  Rept.  Smith.  Inst.,  pp. 
311-330  (1908). 

12.  The  Origin  of  the  Gold  of  the  Band  Goldfield.—  Econ.  Geol.,  vol.  4,  pp. 
118-129  (1909). 

13.  The  Downward  Enrichment  of  Sulphide  Deposits.     Disc,  of  paper  by  F. 
L.  Eansome.— Econ.  Geol.,  vol.  5,  pp.  678-681  (1910). 

GRIFFITHS,  A.  P. 

The  Oharawai  Quicksilver  Deposits. — Trans.  N.   Z.   Inst.  Min.  Ena.,  vol.  2. 

p.  48  (1910). 
GRIMM,  J. 

Die  Lagerstatten  der  Nutzbaren  Mineralien  (Prague,  1869). 
VON  GRODDECK,  ALBRECHT. 

1.  Die  Lehre  von  den  Lagerstatten  der  Erze  (Leipzig,  1879). 

2.  Bemerkungen  zur  Classification  der  Erzlagerstatten. — Berg-u.  Hiitt.  Zeit., 
pp.  217-220,  229-232  (1885). 

3.  Traite  des  Gites  Metalliferes,  Traduit  par  H.  Kuss  (1884). 
GUDZENT,  DR. 

Die  Bestimmung  der  Radioaktivi tilt  von  Mineral-  und  Thermalquellen. — Zeit 
f.prak.  Geol.,  vol.  18,  pp.  147-149  (1910). 

GUNTHER,  C.   G. 

1.  The  Gold  Deposits  of  Plomo,  San  Luis  Park,  Colorado. — Econ.  Geol.,  vol.  1, 
pp.  143-154  (1906). 

2.  The  Examination  of  Prospects  (New  York,  1912).     222  pp. 
GUNTHER,  S. 

Handbuch  der  Geophysik  (Stuttgart,  1897). 
GURICH,  G. 

1.  Uber  die  Eintheilung   der  Erzlagerstatten. — Schles.    Gen.    f.    Vater.   Kul. 
(Breslau,  1899)  ;  Zeit.  f.  prak.  Geol,  vol.  7,  pp.  173-176  (1899). 

2.  KupfererzlagerstJitte  von  Wernersdorf  bei  Radowenz  in  Bohmen. — Zeit.  f. 
prak.  Geol,  vol.  1,  pp.  370-371  (1893). 

GURLT,  ADOLF. 

On  a  Remarkable  Deposit  of  Wolfram-Ore  in  the  United  States. — Trans.  A.  L 
M.  E.,  vol.  22,  pp.  236-242  (1893). 

HABER,  E. 

Der  Blei-und  Zinkerzbergbau  bei  Ramsbeck  im  Bergrevier  Brilon,  unter  be- 
sonderer  Beriieksichtigung  der  Ge^gnostischen  und  Mineralogischen  Ver- 
haltnisse  der  Erzlagerstatten. — Zeit.  f.  Berg-  Hiitt.  u.  Salinenw.,  vol.  42,  pp. 
74-112  (1894). 

HAGUE,  ARNOLD. 

1.  Geology  of  the  Eureka  District, Nevad a.  —Mon.  20,  U.S.  G.  S.  (1892). 419  pp. 

2.  The  Origin  of  the  Thermal  Waters  in  the  Yellowstone  National  Park.— 
Science,  New  Series,  vol.  33,  pp.  553-568  (1911). 

HALAVATS  and  SJOGREN. 

Das  Eisenerzgebiet  von  Dognacska  und  Moravicza  im   Banate. — Ost.  Zeit.  f. 

Berg-u.  Hiitt.,  vol.  39,  pp.  91-96,  102-106  (1891). 
HALEY,  D.  F. 

The  Auriferous  Antimony  Ore  of  West  Gore,  Nova  Scotia. — E.  and  M.  Jour., 

vol.  88,  No.  15,  pp.  723-724  (1909). 
HALL,  A.  L.,  and  HUMPHREYS.  W.  A. 

1.  Geological  Notes  on  the  Bush  veldt  Tin-Fields.  —  Trans.  Geol.  Soc.  So.  Af., 
vol.  8.  p.  47(1905). 

2.  The  Occurrence  of  Chromite  Deposits  along  the  Southern  and   Eastern 
Margins  of  the  Buschveldt  Plutonic  Complex.  —  Trans.    Geol   Soc.   So.  Af.. 
vol.  11,  pp.  69-77  (1908). 

HALL,  C.  E. 

Geological  Notes  on  the  Manganese  Ore-Deposit  of  Crimora,  Virginia. — 
Trans.  A.  I.  M.  E.,  vol.  20,  pp.  46-49  (1891). 


ALPHABETICAL    LIST    OF    AUTHORS.  869 

HALLA,  OTTO. 

The  Beaches  of  Nome.—  Min.  and  ScL  Press,  vol.  94,  p.  688  (1907). 
HALSE,  EDWARD. 

1.  The  Occurrence  of  Tin-Ore  at  Sain  Alto,  Zacatecas,  with  reference  to  simi- 
lar deposits  in  San  Luis  Potosi,  and  Durango,  Mexico. — Trans.  A.  I.  M.  E., 
vol.  29,  pp.  502-511  (1899). 

2.  The  Occurrence  of  Pebbles,  Concretions,  and  Conglomerate  in  Metallifer- 
ous Veins.— Trans.  A.  I.  M.  E.,  vol.  36,  pp.  154-177  (1905). 

HAMMOND,  J.  H. 

1.   The  Auriferous  Gravels  of  California.-  9th  Ann.  Rept.,  Cal.  State  Min., 


pp.  105-138  (1890). 
5.  G(f  " 


2.  Gold  Mining  in  the  Transvaal,  South  Africa.— Trans.  A.  I.  M.  E.,  vol.  31, 

p.  817  (1901). 
HANCOCK,  E.  T. 

Notes  accompanying  Lectures  on  Geology  Applied  to  Mining  (Houghton, 

Mich.,  1908).     210  pp. 

HANKS,  H.  G. 

Cassiterite  :  Notes  of  Tin  Ores  from  Temescal,  Cal.—  Mh  Ann.  RepL,  Cal.  State 

Mm.,  pp.  115-123  (1884). 
HARBORT,  E. 

Probleme  der  Erzlagerstattengeologie. — Zeit.  f.  prak.  Geol.,  vol.  15,  pp.  372- 

387,  437-441  ;  vol.  16,  pp.  34-44,  71-83  (1907-08). 
HARE. 

Die  Serpentin  Masse  von  Reichenstein  und  die  darin  Vorkommenden  Min- 

eralien  ;  Inaug.  Diss.  (Breslau,  1879). 
HARKER,  A. 

1.  Igneous  Rock-Magmas  as  Solutions. — Sri.  Prog.    (N.  S. ),  vol.  2,  No.  6, 
pp.  239-254  (1907). 

2.  Natural  History  of  the  Igneous  Rocks  (Macmillan  Co.,  New  York,  1909). 
384  pp. 

HARKNESS,  R. 

On  the  Jointings  in  the  Carboniferous  and  Devonian  Rocks  in  the  District 
around  Cork  ;  and  on  the  Dolomites  of  the  same  District. — Qaar.  Jour.  Geol. 
Soc.,  vol.  15,  pp.  86-104  (1859). 
HARRISON,  J.  B.,  FOWLER,  F.,  and  ANDERSON,  C.  W. 

The  Geology  of  the  Goldfields  of  British  Guiana,  and  an  Appendix  giving 
the  Laws  and  Regulations  concerning  the  Mining  Industry  (Dulau,  -Lon- 
don, 1908).     320pp. 
HASTINGS,  J.  B. 

1.  Are  the  Quartz- Veins  of  Silver  Peak,  Nevada,  the  Result  of  Magmatic 
Segregation?—  Trans.  A.  I.  M.  E.,  vol.  36,  pp.  647-654  (1905). 

2.  Sub-Classification  of  Zenogenous  Ore-Deposits.  —  E.  and  M.  Jour.,  vol.  59, 
p.  268  (March  23,  1895). 

3.  Primary  Gold  in  a  Colorado  Granite.  —  Trans.  A.  I.  M.  E.,  vol.  39,  pp. 
97-103  (1908). 

4.  Association  of  Magnetite  with  Sulphides  in  Mineral  Deposits. — Min.  and 
Sri.  Press,  vol.  97,  pp.  333-334  (1908). 

5.  Origin  of  Pegmatite.— Trans.  A.  I.  M.  E.,  vol.  39,  pp.  104-128  (1908). 

6.  Volcanic  Waters.— Trans.  A.  I.  M.  E.,  vol.  39,  pp.  129-138  (1908). 
HATCH,  F.  H. 

1.  Geology  of  the  Witwatersrand  and  other  Districts  in  the  Southern  Trans- 
vaal.— Quar.  Jour.  Geol.  Soc.,  vol.  54,  pp.  73-100  (1898). 

2.  Notes  on  the  Witwatersrand  Gold  Deposits  and   their  Associated  Rocks. — 
Trans.  So.  Af.  Assoc.  Eng.  (1903).     8  pp.       Also  Geol.   Mag.,  vol.  10,  pp. 
543-547  (1903). 

HATCH,  F.  H.,  and  CHALMERS,  J.  A. 

The  Gold  Mines  of  the  Rand  (London,  1895).     306  pp. 
HATCH,  F.  H. ,  and  CORSTORPHINE,  G.  S. 

1.  The  Petrography  of  the  Witwatersrand  Conglomerates,  with  Special  Ref- 
erence to  the  Origin  of  the  Gold. — Trans.  Geol.  Soc.  So.  A/.,  vol.  7,  pt.  3, 
p.  140  (1904). 

2.  The  Geology  of  South  Africa  (London,  1905).     348  pp. 


870  ALPHABETICAL    LIST    OF    AUTHORS. 

HAWORTH,  ERASMUS,  CRANE,  W.  R.,  and  KOGERS,  A.  F. 

Special  Report  on  Lead  and  Zinc. —  Univ.  Geol.  Sur.  Kansas,  vol.  8  (1904). 
543  pp. 

HAYES,  C.  W. 

1.  Geological    Relations    of    the    Iron-Ores    in    the    Cartersville    District, 
Georgia.— Trans.  A.  I.  M.  E.,  vol.  30,  pp.  403-419  (1900). 

2.  Handbook  for  Field  Geologists  (New  York,  1909).     159  pp. 

3.  The  Iron-Ore  Supply  of   the  United  States.  —Bull.  28,  A.  I.  M.  E.,  pp. 
373-379  (Apr.,  1909). 

4.  Iron  Ores  of  the  U.  S.—Bull.  394,  U.  S.  G.  S.,  pp.  70-113  (1909). 
HEADDEN,  W.  P. 

The  Doughty  Group  of  Radium  Bearing  Springs  on  the  North  Fork  of  Gun- 

nison  River,  Colo.—  Proc,  Colo.  Sci.  Soc.,  vol.  8,  pp.  1-30  (1905). 
HEANAGE,  E.  F.,  and  HOLFORD,  W.  G. 

Notes  on  the  Occurrence  of  Gold  in  Primary  Formations. — Trans.  So.  Af. 
.   Assoc.  Eng.,  Johannesburg  (1905). 

HEDBTJRG,  ERIC. 

The  Missouri  and  Arkansas  Zinc-Mines  at  the  Close  of  1900. — Trans.  A.  I. 
M.  E.,  vol.  31,  pp.  379-404  (1901). 

HEIM,  A. 

Untersuchungen  iiber  den  Mechanismus  der  Gebirgsbildung  (Basel,  1878). 

HELMH  ACKER. 

1.  Beitrage  zur  Kenntniss  der  Sekundaren  Goldlagerstatten — Berg-  u.  Hiitt. 
Zeit.,  vol.  50  (1891). 

2.  Uber  das  Vorkommen  des  Goldes  in  Dioriten  und  Serpentinen. — Ost.   Zeit. 
f.Berg-u.  Hutt.,  vol.  28,  pp.  97-99,  110-113,  127-128,  142-144,  155-156 
(1880). 

HENDERSON,  C.  H. 

The  Copper  Deposits  of  the  South  Mountain.— Trans.  A.  I.  M.   E.,  vol.  12, 

pp.  85-90  (1883-84). 
HENRICH,  CARL. 

1.  Notes  on  the  Geology  and  on  some  of  the  Mines  of  Aspen  Mountain, 
Pitkin  County,   Colorado.— Trans.   A.  I.    M.    E.,  vol.    17,  pp.    156-206 
(1888-89). 

2.  Zinc-Blende  Mines  and  Mining  near  Webb  City,  Missouri. — Trans.  A.  I. 
M.  E.,  vol.  21,  pp.  3-25  (1892-93). 

3.  The  Ducktown  Ore- Deposits.— Trans.  A.   I.   M.   E.,  vol.  25,  pp.  173-245 
(1895). 

HENRICH,  F. 

Uber  die  Einwirkung  von  kohlensaurehaltigem  Wasser  auf  Gesteine  und 
iiber  den  Ursprung  und  den  Mechanismus  der  kohlensaurefiihrenden 
Thermen.— Zeit.f.  prak.  Geol.,  vol.  18,  pp.  85-94  (1910). 

HENRICKSON,  G. 

Die  Eisenerzlagerstatten  von  Sydvaranger  und  die  Sonderung  oder  Differen- 
tiation von  Eruptivmassen  durch  Druck. — Ost.  Zeit.  f.  Berg-  u.  Hiitt.,  vol. 
54,  p.  168  (1906). 

HENWOOD,  W.  J. 

1.  On  the  Metalliferous  Deposits  of  Cornwall  and  Devon. — Trans.  Roy.  Geol. 
Soc.  Comw.,  vol.  5  (1843);  vol.  8. 

2.  Observations  on  Metalliferous  Deposits. — Trans.   Roy.    Geol.  Soe.  Cornw., 
vol.  7  (1871). 

3.  On  the  Detrital  Tin-Ore  of  Cornwall.—  Jour.  Roy.  Inst.   Cornw.,   vol.  15 
(1873);  Ann.  d.  Mines,  7th  ser.,  vol.  6,  pp.  114-130  (1874). 

HERMANN,  O. 

Steinbruch's  Industrie  und  Steinbruch's  Geologic  (Berlin,  1899). 

HERSHEY,  O.  H. 

1.  Age  and  Origin  of  Certain  Gold   "Pocket"   Deposits  in  Northern  Cali- 
fornia.— Am.  'Geol.,  vol.  24,  pp.  38-43  (1899). 

2.  Age  and  Origin  of  Certain  Gold  Deposits  on  the  Isthmus  of  Panama. — 
Am.  Geol,  vol.  24,  pp.  73-77  (1899). 

3.  Primary  Chalcocite  in  California.  —Min.  and  Sci.  Press,  vol.  96,  pp.  429- 
430  (1908). 


ALPHABETICAL    LIST    OF    AUTHORS.  871 

HESS,  F.  L. 

The  Arkansas  Antimony  Deposits.—  Bull.  340,  U.  S.  G.  S.,  pp.  241-252  (1908). 
HESS,  F.  L. ,  and  GRATON,  L.  C. 

The  Occurrence  and  Distribution  of  Tin.     (With  bibliography. ) — Bull.  260, 

U.  S.  G.  S.,  pp.  161-187  (1905). 
HEUSLER,  C. 

tJber   die    Beziehungen  von  Erzgangen    zu  Eruptivgesteinen.  —  Verhand.  d. 

NaturhisL  V.  d.  Pr.  Eheinlande,  vol.  58,  pp.  53-65  (1901). 
HEWETT,  D.  F. 
.     New  Occurrence  of  Vanadium  in  Peru. — Trans.  A.  L  M.  E.,  vol.  40,  pp.  274- 

299  (1909). 
HILL,  K.  T. 

1.  The  Occurrence  of  Hematite  and  Marti te  Iron  Ores  in  Mexico. — Am.  Jour. 
Sc>Vvol.*45,  3dser.,  pp.  111-119  (1893). 

2.  The  Upland  Placers  of  La  Cienega,  Sonora,  Mexico. — E.  and  M.  Jour.. 
vol.  73,  pp.  132-134  (1902). 

HlLLE,  F. 

1.  The  Atik-Okan  Nickeliferous  Pyrrhotite  Deposits  and  their  Origin. — Jour. 
Can.  Min.  Inst.,  vol.  9,  pp.  285-301  (1905). 

2.  Correction  in  the  Classification  of  our  Gold  Formations. — Jour.  Can.  Min. 
Inst.,  vol.  8,  pp.  183-191  (1905). 

3.  Some  Iron  Ore  Deposits  in  the  Districts  of  Thunder  Bay  and  Kainy  Eiver, 
Ontario.—  Can.  Dept.  of  Mines  (1908). 

HlLLEBRAND,  W.   F. 

1.  Some  Principles  and  Methods  of  Kock  Analysis.—  Bull.  176,   U.  S.  G.  S.. 
pp.  1-114  (1900). 

2.  The  Analysis  of  Silicate  and  Carbonate  Rocks.— Bull.  422,   U.  S.  G.  S. 
(1910).     239  pp. 

3.  The  Vanadium  Sulphide  Patronite. — Jour.  Am.  Chem.  Soc.,  vol.  29  (1907)  ; 
Am.  Jour.  Sci. ,  4th  ser.,  vol.  24,  pp.  141-151  (1907). 

HILLEBRAND,  W.  F.,  and  RANSOME,  F.  L. 

Carnotite  in  Western  Colorado. — Am.  Jour.  Sci.,  4th  ser.,  vol.    10,  pp.  120- 

144  (1900)  ;  Bull.  262,  U.  S.  G.  S.,  pp.  9-31  (1905). 
HILLEBRAND,  W.  F.,  and  SCHALLER,  -W.  T. 

The  Mercury  Minerals  from  Terlingua,  Texas.  —  Bull.  405,  U.  S.  G.  S.  (1909). 
174  pp. 

HlNTZE. 

Handbuch  der  Mineralogie  (Leipzig,  1889-1891).     2  vols. 
HIXON,  H.  W. 

1.  Magmatic  Waters. — Jour.  Can.  Min.  Inst.,  vol.  10,  pp.  300-320  (1907). 

2.  A  Theory  of  Volcanic  Action  and  Ore  Deposits,  their  Nature  and  Cause. — 
Trans.  Inst.  Min.  and  Met.,  vol.  18,  pp.  202-219,  230-272  (1908-09). 

HOBBS,  W.  H. 

1.  Old  Tungsten  Mine  at  Trumbull,  Conn.—  22d  Ann.  Rept.,  U.   S.   G.  S., 
part  2,  pp.  7-22  (1901). 

2.  Iron  Ores  of  the  Salisbury  District  of  Connecticut,  New  York,  and  Massa- 
chusetts.— Econ.  Geol.,  vol.  2,  pp.  153-181  (1907). 

HOCHSTETTER  and  TELLER. 

Uber  einen  Neuen  Geologischen  Aufschl.  im  Gebiete  der  Karlsbader  Ther- 

men.—  Devkschr.  Akad.   Wien  (1878). 
HODGES,  A.  D.,  JR. 

Notes  on  the  Topography  and  Geology  of  the  Cerro  de  Pasco,  Peru. — Trans. 
A.  I.  M.  E.,  vol.  16,  pp.  729-753  (1887-88). 

H5FER,  H. 

1.  Uber  Verwerfungen.  —  Ost.  Zeit.  f.  Berg-  u.  Hiiit.,  vol.  34,  p.  350  (1886). 

2.  Die  Ausrichtung  der  Verwerfungen. — Ost.  Zeit.  f.  Berg-  u.  HutL,  vol.  29, 
pp.  167-171  (1881). 

3.  Benennung  und  Systematik  der  Lagerstatten  nutzbarer  Minerale. — Zeit.f. 
prak.  Geol.,  vol.  5,  pp.  113-116  (1897). 

4.  Zur  Bestimmung  des  Alters  der  Gange. — Oft*  Zeit.  f.  Berg- u.  Hiitt.,  vol. 
47  (1899).     15  pp. 


872  ALPHABETICAL    LIST    OP    AUTHORS. 

HOFER,  H.— Continued. 

5.  Erdol-Studien.— K.    K.   Ak.  d.  W.  in    Wien,  Math.   Phys.    Class.,  vol.  3, 
No.  1  (July,  1902). 

HOLLTSTER,   O.  J. 

Gold  and  Silver  Mining  in  Utah.  — Trans.   A.   I.   M.   E.,  vol.   16,   pp.  3-18 

(1887-88). 

HOOVER,  H.  C. 

The  Superficial  Alteration  of  Western  Australian  Ore-Deposits.  — Trans.  A. 

I.  M.  E.,  vol.  2«,  pp.  758-765  (1898). 

HOPKINS,  T.  C. 

Cambro-Silurian  Limonite  Ores  of  Pennsylvania. — Bull.  Geol.  Soc.  Am.3  vol. 

II,  pp.  475-502  (1900). 

HORE,  K.  E. 

1.  Origin  of  Cobalt-Silver  Ores  of  Northern  Ontario. — Jour.  Can.  Min.  InsL, 
vol.  11,  pp.  275-286  (1908). 

2.  Origin  of  the  Cobalt-Silver  Ores  of  Northern  Ontario. — Econ.  Geol.,  vol.3, 
pp.  599-610  (1908). 

HORNER. 

Vorkommen  von  Platin  und  Diamanten  auf  Borneo. — Pogg.  Ann.,  vol.  55, 
pp.  526-529  (1842). 

HORNUNG,  F. 

1.  Formen,  Alter  und  Ursprung  des  Kupferschiefererzes. — Zeit.  d.  D.  Geol. 
Gesel.,  vol.  56,  pt.  2,  pp.  207-217  (1904). 

2.  Ursprung  und  Alter  des  Schwerspates  und  der  Erze  im  Harze. — Zeit  d.  D. 
Geol.  Gesel.,  vol.  57,  pts.  2  and  3,  pp.  291-360  (1905). 

3.  Ursprung  und  Alter  des  Schwerpates  und  der  Erze  im  H.a,rze.—Zeit.  d.  D. 
Geol.  Gesel. ,  vol.  57,  No.  2,  pp.  291-320. 

HORWOOD,  C.  B. 

The  Red  Granite  of  Balmoral  and  Its  Relation  to  the  Cobalt  Lodes. — Trans. 
Geol.  Soc.  So.  Af.,  vol.  7,  part  2,  pp.  110-114  (1904). 

HOSKINS,  L.  M. 

Flow  and  Fracture  of  Rocks  as  Related  to  Structure. — IQth  Ann.  Rept.,  U.  S., 

G.  S.,  part  1,  pp.  845-874  (1896). 
HOWE,  J.  L. 

Bibliography  of  the  Metals  of  the  Platinum  Group.  1748-1896  (Washington, 

1898).     318  pp. 
HUNT,  T.  S. 

1.  Chemical  and  Geological  Essays  (1874). 

2.  The  Origin  of  Metalliferous  Deposits.— Trans.  A.   L   M.  E.,   vol.   1,  pp. 
413-426  U871-73). 

3.  The  Ore  Knob  Copper  Mine  and  some  Related  Deposits. — Trans.  A.  I. 
M.  E.,  vol.  2,  pp.  123-131  (1873-74). 

4.  The  Cornwall  Iron  Mine  and  some  Related  Deposits  in  Pennsylvania. — 
Trans.  A.  L  M.  E.,  vol.  4,  pp.  319-325  (1875-76). 

5.  Coal  and  Iron  in  Alabama.— Trans.  A.  L  M.  E.,  vol.   11,   pp.  236-248 
(1882-83). 

6.  The  Iron-Ores  of  the  United  States.— Trans.   A.  L  M.   E.,  vol.  19,  pp. 
3-17  (1890-91). 

HUNT. 

British  Mining  (1884). 
HUSSAK,  E. 

1.  Uber  das  Vorkommen  von  Palladium  und  Platin  in  Brasilien. — Zeit.  /. 
prak.  Geol.,  vol.  14,  pp.  284-293  (1906). 

2.  The  Occurrence  of  Palladium  in  Brazil.  (Abstract).—  Min.  Jour.,  pp.  130- 
131  (1908). 

3.  Der  goldfiihrende,  kiesige  Quarzlagergang  von  Passagem  in  Minas  Geraes, 
Brazilien.—  Zeit.  f.  prak.  Geol.,  vol.  6,  pp.  345-357. 

HUTCHINS,  J.  P. 

1.  The  Essential  Data  of  Placer  Investigations. — E.   and  M.   Jour.,  vol.  84, 
pp.  339-342,  385-387  (1907). 

2.  The  Nomenclature  of  Modern  Placer  Mining. — E.  and  M.  Jour.,  vol.  84, 
pp.  293-296  (1907). 


ALPHABETICAL    LIST    OF    AUTHORS.  873 

IDDINGS,  J.  P. 

Igneous  Rocks.    (Discussions  of  Magmatic  Differentiation  and  Physical  Chem- 

istry:)    (1909.)     464pp. 
INGALLS,  W.  E. 

1.  The  Tin  Deposits  of  Durango,  Mexico.  —  l^ans.  A.  I.  M.  E.,  vol.  25,  pp. 
146-163  (1895). 

2.  The  Silver-Lead  Mines  of  Eureka,  Nevada.—!?,  and  M.  Jour.,  vol.84,  pp. 
1051-1058  (1907). 

VON  INKEY,  B. 

De  la  Relation  entre  I'e'tat  propylitique  des  roches  andesitiques  et  leur  filons 

mine'raux.—  Ccmipt.  Rend.  10th  Cong.  Geol.  Int.,  vol.  1,  p.  501  (1907). 
IRVING,  J.  D. 

1.  A  Contribution  to  the  Geology  and  Ore  Deposits  of  the  Northern  Black 
Hills,  South  Dakota.—  Ann.  N.  Y.  Acad.  Sci.,  vol.  12,  part  2,  pp.  187-340 
(1899). 

2.  Some  Recently  Exploited  Deposits  of  Wolframite  in  the  Black  Hills  of 
South  Dakota.—  Trans.  A.  I.  M.  E.,  vol.  31,  pp.  683-695  (1901). 

3.  Ore  Deposits  of  the  Northern  Black  Hills.  —  Min.  and  Sci.  Press,  vol.  87, 
pp.  166-167,  187-188,  205,  221-222  (1903). 

4.  Ore  Deposits  of  the  Northern  Black  Hills.—  Bull.  225,  U.  S.  G.  S.,  pp. 
123-140  (1904). 

5.  Ore  Deposits  of  the  Ouray  District,   Colorado.—  Bull.  260,  U.  S.  G.  S., 
pp.  50-77  (1905). 

6.  Ore  Deposits  in  the  Vicinity  of  Lake'.City,  Colorado.—  Bull.  260,  U.S.  G.  S., 
pp.  78-84  (1905). 

7.  The  Localization  of  Values  in  Ore-Bodies  and  the  Occurrence  of  "  Shoots'' 
in  Metalliferous  Deposits.—  Econ.  Geol.,  vol.  3,  pp.  143-154  (1908). 

8.  Special    Problems  and   Their  Study  in  Economic  Geology.  —  (Editorial) 
Econ.  Geol.,  vol.  5,  pp.  670-677  ;  Discussion  of,  pp.  772-790  (1910). 

9.  The  Formation  of  Ore-Bodies  by  Replacement  and  the  Criteria  by  means 
of  which  they  may  be  Recognized.  —  Quart.  Bull.  Can.  Min.  Inst.,  No.  17, 
pp.  3-79  (Dec.,  1911). 

10.  Some  Features  of  Replacement  Ore-Bodies  and  the  Criteria  by  which  they 
may  be  Recognized.  —Econ.  Geol.,  vol.  6,  pp.  527-561  ;  619-669  (1911). 

11.  The  Sub-structure  of  Geological  Reports.—  Econ.  Geol.,  vol.  8,  No.  1  (1913). 
IRVING,  J.  D.  ,  and  BANCROFT,  H. 

Geology  and  Ore  Deposits  near  Lake  City,  Colorado.  —  Bull.  478,  U.  S.  G. 

S.  (1911).     128  pp. 
IRVING,  J.  D.,  EMMONS,  S.  F.,  and  JAGGAR,  T.  A.,  JR. 

Economic  Resources  of  the  Northern  Black  Hills  —Prof.  Paper  26,  U.  S.  G.  S. 
(1904).     222  pp. 

IRVING,  R.  D. 

1.  The  Copper-  Bearing  Rocks  of   Lake  Superior.  —  Mon.  5,  U.   S.    G.   S., 
(1883).     464  pp. 

2.  Copper-Bearing  Rocks  of  Lake  Superior.  —  3d  Ann.  Rept.,  U.  S.  G.  S.,  pp. 
89-188  (1883). 

3.  On  the  Origin  of  "the  Ferruginous  Schists  and  Iron  Ores  of  'the  Lake  Su- 
perior Region.—  Am.  Jour.  Sci.,  3d  ser.,  vol.  32,  pp.  255-272  (1886). 

IRVING,  R.  D.,  and  VAN  HISE,  C.  R. 

1.  The  Penokee  Iron-Bearing  Series  of  Michigan  and  Wisconsin.  —  IQth  Ann. 


Rept.,  U.  S.  G.  S.,  part  1,  pp.  341-507  (1890). 
The  Penokee  Iron-Bearing  Series  of 
Mon.  19,  U.  S.  G.  S.  (1892).     534  pp. 


.,      .  .,  ,       . 

2.  The  Penokee  Iron-Bearing  Series  of  Northern  Wisconsin  and  Michigan.  — 


JACKSON,  C.  F.  V. 

Geological  Features  and  Auriferous  Deposits  of  Mount  Morgan.  —  Bull.  18, 

Geol.  Sur.  West.  Aust.  (1905).     22  pp. 
JAGGAR,  T.  A.,  JR. 

How  Should  Faults  be  Named  and  Classified  1—Econ.  Geol.,  vol.  2,  pp.  58-62 

(1907). 
JAQUET,  J.  B. 

1.  Iron  Ore  Deposits  of  New  South  Wales.—  Mem.  2,  Geol.  Sur.,  N.  S.  W. 

55 


874  ALPHABETICAL    LIST    OF    AUTHORS. 

JAQUET,  J.  B. — Continued. 

2.  Platinum  Deposits  of  Millga  Coerls  near  Booken  Hill. — Aust.  Min.  Stand. , 
vol.  9,  p.  50  (1893)  ;  vol.  12,  pp.  720-721  (lt>96). 

3.  The  Occurrence  of  Platinum  in  New  South  Wales.— Geol.  Sur.  N.  S.  W., 
Records  of,  p.  33  (1896). 

4.  Geology  of  the  Broken  Hill  Lode  and  Barrier  Eanges  Mineral  Field,  New 
South  Wales.—  Mem.  Geol.  Sur.  N.  S.   W.,  No.  5  (1»94). 

JAQUET  and  WILLM. 

Les  eaux  mine'rales  de  la  France  (Paris,  1894). 
JENNEY,  W.  P. 

1.  The  Lead  and  Zinc-Deposits  of  the  Mississippi  Valley. — Trans.  A.  I.  M. 
E.,  vol.  22,  pp.  17l-22o  (Ih93). 

2.  The  Chemistry  of  Ore-Deposition. — Trans.  A.  I.  M.  E.,  vol.  33,  pp.  445- 
498  (1902). 

3.  The  Mineral  Crest,  or  the  Hydrostatic  Level  Attained  by  the  Ore-Deposit- 
ing Solutions,  in  Certain  Mining  Districts  of  the  Great  Salt  Lake  Basin. — 
Trans.  A.  I.  M.  E.,  vol.  33,  pp.  46-50  (1902). 

4.  Block-Faulting  and  Its  Relation  to  Ore  Deposition. — Min.  and  Sci.  Press, 
vol.  92,  pp.  54-55  (1906). 

JENNINGS,  E.  P. 

1.  The  Copper  Deposits  of  the  Kaibab  Plateau,  Arizona. — Trans.  A.  I.  M.  E., 
vol.  34,  pp.  839-841  (1903). 

2.  The  Genesis  of  the  Copper  Deposits  of  Yerington,  Nevada. — Can.  3Jin. 
Jour.,  new  ser.,  vol.  1,  pp.  365-366  (1907). 

JOHANSSON,  H.—Geol.   For.  i  Stock.  Forhand.,  vol.  28,  pp.  .516-538  (1906)  ;  vol. 

29,  pp.  143-186  (1907). 
JOHNSON,  J.  E.,  JR. 

The  Origin  of  the  Oriskany  Limonites. — E.  and  M.  Jour.,  vol.  76,  pp.  231- 

232  (1903). 
JOHNSON,  J.  P. 

1.  The  Ore  Deposits  of  South  Africa.— Part  I— Base  Metals  (190S).     61  pp. 

2.  The  Auriferous  Conglomerates  of  the  Witwatersrand  and  the  Antimony 
Deposits  of  the  Murchison  Kange  (London,  1908). 

JONES,  F.  A. 

The  Placers  of  Santa  F6  County,  New  Mexico.  —Min.  World,  vol.  25,  p.  425 

(1906). 
JONES,  S.  P. 

Gold  Deposits  of  Georgia.   (2d  rept.  )—Bull.  19,  Geol.  Sur.  Ga.  (1909).    283  pp 

JULIEN,  A.   A. 

1.  On  the  Part  played  by  Humus  Acids  in  Ore  Deposits,  Wall  Rock,  Gossan^ 
etc.— Proc.  Am.  Assoc.  Adv.  Sci.,  pp.  382,  385  (1879). 

2.  The  Genesis  of  the  Crystalline  Iron  Ores. — E.  and  M.  Jour.,  vol.  37,  pp. 
81-83  (1884). 

KATTEKFELD. 

tfber  die  Platina  Production  Russlands. — Bery-  u.   Hiltt.  ZeiL,   vol.   45,  pp. 
68-69  (1885). 

KAY,  G.  F. 

Nickel  Deposits  of  Nickel   Mountain,  Oregon.—  Bull.  315,  U.S.  G.  S.,  pp. 

120-127  (1907). 
KECK,  R. 

Genesis  of  Ore  Deposits.—^,  and  M.  Jour.,  vol.  35,  pp.  3-4  (  1883). 
KEDZIE,  G.  E. 

The  Bedded  Ore- Deposits  of  Red  Mountain  Mining  District,  Ouray  County  > 

Colorado.— Trans  A.  I.  M.  E.,  vol.  16,  pp.  570-581  (1887-88). 
KEELE,  JOSEPH. 

The  Duncan  Creek  Mining  District.— Can.  Geol.  Sur.  Sum.  Rept.  for  1904,  pp. 

18-42  (1905). 
KEILHACK,  K. 

1.  Spaltenbildung.—  Zeit.  f.  prak.  Geol.,  vol.  3,  p.  254  (1895). 

2.  Lehrbuch  der  praktischen  Geologic  (Stuttgart,  1896).     638  pp. 


ALPHABETICAL    LIST    OF    AUTHORS.  875 

• 
KELLOGG,  L.  O. 

Sketch  of  the  Geology  and  Ore   Deposits  of  the  Cochise   Mining   District, 

Cochise  County,  Arizona. — Econ.  GeoL,  vol.  1,  pp.  651-659  (1906). 
KEMP,  J.  F. 

1.  The  Literature  of  Ore  Deposits. — Sch.  Min.  Quar.,  vol.  10,   pp.   54,   116, 
326  (1889);  vol.  11,  p.  359  (1890);  vol.  12,  p.  218  (1891). 

2.  The  Precipitation  of  Metallic  Sulphides  by  Natural  Gas  — E.  and  M.  Jour., 
vol.  50,  p.  689  (1890). 

3.  On  the  Filling  of  Mineral  Veins.—  Sch.  Min.  Quar.,  vol.  13,  p.  20  (Oct., 
1891). 

4.  The  Classification  of  Ore  Deposits. — Sch.   Min.  Quar.,  vol.  14,  pp.  8-24 
(1893). 

5.  The  Ore  Deposits  at  Franklin  Furnace  and  Ogdensburg,  New  Jersey. — 
Proc.  N.  Y.  Acad.  Sci.,  pp.  76-96  (1894). 

6.  The  Development  of  Views  on  the  Origin  of  Ores. — Min.  Ind.,  vol.  2,  pp. 
835-840  (1893). 

7.  The  Nickel-Mine  at  Lancaster  Gap,  Pennsylvania,  and  the  Pyrrhotite 
Deposits  at  Anthony's  Nose  on  the  Hudson.  —  Trans.  A.  I.  M.  E.,  vol.  24, 
pp.  620-633  (1894). 

8.  An  Outline  of  the  Views  Held  To-day  on  the  Origin  of  Ores. — Min.  Ind., 
vol.  4,  pp.  755-766  (1895). 

9.  The  Geology  of  the  Magnetites  near  Port  Henry,  N.  Y.,  and  Especially 
those  of  Mineville.— Trans.  A.  I.  M.  E.,  vol.  27,  pp.  146-203  (1897). 

10.  Geological  Occurrence  and  Associates  of  the  Telluride  Gold  Ores. — Min. 
Ind.,  vol.  6,  pp.  295-320  (1898). 

11.  The  Titaniferous  Iron  Ores  of  the  Adirondacks.— 19th  Ann.  Eept.,  U.  S. 
O.  S.,  part  3,  pp.  377-422  (1898). 

12.  A  Brief  Keview  of  the  Titaniferous  Magnetites.—  Sch.  Min.  Quar.,  vol.  20, 
pp.  323-356  (July,  1899)  ;  pp.  56-65  (Nov.,  1899). 

13.  The  Deposits  of  Copper-Ores  at  Ducktown,  Tennessee. — Trans.  A.  L  M.  E., 
vol.  31,  pp.  244-265  (1901). 

14.  The  Kole  of   Igneous  Hocks  in  the  Formation  of  Veins. — Trans.  A.  L 
M.  E.,  vol.  31,  pp.  169-198  (1901). 

15.  The  Geological  Relations  and  Distribution  of  Platinum  and  Associated 
Metals.—  Bull.  193,  U.  S.  G.  S.  (1902),  95pp.;   Min.  Ind.,  vol.  10,  p.  540 
(1902)  ;  E.  and  M.  Jour.,  vol.  73,  pp.  512-513  (1902). 

16.  Igneous  Kocks  and  Circulating  Waters  as  Factors  in  Ore-Deposition. — 
Trans.  A.  I.  M.  E.,  vol.  33,  pp.  699-714  (1902). 

17.  Keview  of  the  General  Literature  on  Ore  Deposits. — Min.  Ind.,  vol.  12, 
pp.  385-395  (1903). 

18.  The  Formation  of  Veins.— M in.  Mag.  (J.),  vol.  10,  pp.  89-93  (1904). 

19.  A  Keview  of  the  Literature  on  Ore  Deposits  in  1904  and  1905. — Min.  Ind., 
vol.13  (1904). 

20.  The   Copper- Deposits  at  San   Jose,  Tamaulipas,  Mexico. — Trans.  A.   I. 
M.  E.,  vol.  36,  pp.  178-203  (1905). 

21.  The  Ore  Deposits  of  the  United  States  and  Canada  (New  York  and  Lon- 
don, 1906).     3d  ed.  ;  481  pp. 

22.  Literature  on   Ore-Deposits   in   1906. — Min.   Ind.,  vol.  15,   pp.  781-789 
(1906). 

23.  Secondary  Enrichment  in  Ore-Deposits  of  Copper. — Econ.    GeoL,  vol.  1, 
pp.  11-25  (1906). 

24.  The  Problem  of  the  Metalliferous  Veins.—  Econ.   Geol,  vol.  1,  pp.  207- 
232  (1906). 

25.  Some  New  Points  in  the  Geology  of  Copper  Ores. — Jour.  Can.  Min.  Inst., 
new  ser.,  vol.  1,  pp.  274-275  (1907)  ;  E.  and  M.  Jour.,  vol.  83,  pp.  1192- 
1193  (1907)  ;  Min.  and  Sci.  Press,  vol.  94,  pp.  402-403  (1907). 

26.  Ore  Deposits  at  the  Contacts  of  Intrusive  Kocks  and  Limestones ;  and 
their  Significance  as  Kegards  the  General  Formation  of  Veins.  —Econ.  Geol. , 
vol.  2,  pp.  1-13  (1907)  ;   Compt.  Rend.  Cong.  Geol.  Int.,  10th  sess.,  pp.  519- 
531  (Mexico,  1906). 

27.  Garnet  Zones.—  Mm.  and  Sci.  Press,  vol.  92,  pp.  220-221  (Mar.  31,  1906). 

28.  Waters,  Meteoric  and  Magmatic. — Min.  and  Sci.  Press,  vol.  96,  pp.  705-708 
(June  20,  27,  1908). 

29.  "  What  is  an  Ore?"—  Jour.  Can.  Min.  Inst.,vol.  12,  pp.  356-370  (1909). 

30.  "What  is  an  Ore  ?"—  Min.  and  Sci.  Press,  vol.  98,  pp.  419-423  (Mar.  20, 
1909). 

31.  The  Iron  Ores  of  the  Iron  Springs  District,  Utah. — Econ.    Geol,   vol.  4, 
pp.  782-791  (1909). 


876  ALPHABETICAL    LIST    OF    AUTHORS. 

• 

KEMP,  J.  F. ,  and  GUNTHER,  C.  G. 

The  White    Knob  Copper-Deposits,  Mackay,  Idaho.— Trans.  A.  I.  M.  E., 

vol.  38,  pp.  269-296  (1907). 
KEMPTON,  C.  W. 

The  Tin-Deposits  of  Durango,  Mexico.— Trans.  A.  I.  M.  E.,  vol.  25,  pp.  997-98 

(1895). 
KENDALL,  J.  D. 

The  Iron  Ores  of  Great  Britain  and  Ireland  (London,  1893).     224  pp. 
KENNEDY,  WILLIAM. 

Iron  Ores  of  East  Texas.— Trans.  A.  I.  M.  E.,  vol.   24,  pp.  258-288  (1894). 
KERR,  W.  C. 

The  Gold-Gravels  of  North  Carolina.— Tram  A.  I.  M.  E.,  vol.  8,  pp.  462- 

466  (1879-80). 
KESSLER,  L. 

The  Gold  Mines  of  the  Hand  and  the  Determination  of  Their  Value  (Lon- 
don, 1904).     135pp. 
KEYES,  C.  R. 

1.  Origin  and  Classification  of  Ore-Deposits. — Trans.  A.L  M.  E.,  vol.  30,  pp. 
323-356  (1900). 

2.  Ore  Formation  on  the  Hypothesis  of  Concentration  through  Surface  De- 
composition.— Am.  GeoL,  vol.  27,  pp.  355-362  (1901). 

3.  Criteria  of  Downward  Sulphide  Enrichment. — Econ.  GeoL,  vol.  5,  pp.  558- 
564  (1910). 

4.  Cerargyritic  Ores:    Their  Genesis  and  Geology. — Econ.  GeoL,  vol.  2,  pp. 
774-780  (1907). 

5.  Genesis  of  the  Lake  Valley,  New  Mexico,  Silver-Deposits. — Trans.  A.  L 
M.  E.,  vol.  39,  pp.  139-169  (1908). 

6.  Porphyry  Coppers.  -Sail.  25,  Min.  Met.  Soc.  Am.  (1910). 

7.  Garnet  Contact- Deposits  of  Copper  and  the  Depths  at  which  They  are 
Formed.—  Econ.  GeoL,  vol.  4,  pp.  365-372  (1909). 

KEYES,  W.  S. 

The  Eureka  Lode,  of  Eureka,  Eastern  Nevada.— Trans.  A.  L  M.  E.,  vol.  6, 
pp.  344-371  (1877-78). 

KlMBALL,  J.  P. 

1.  Genesis  of  Iron-Ores  by  Isomorphous  and  Pseudomorphous  Replacement 
of  Limestone.— Am.  Jour.  Ski.,  3dser.,  vol.  42,  pp.  231-241  (1891). 

2.  The  Iron-Ore  Range  of  the  Santiago  District  of  Cuba. — Trans.  A.  L  M.  E., 
vol.  13,  pp.  613-634  (1884-85). 

KING,  F.  H. 

Principles  and  Conditions  of  the  Movements  of  Ground  Water. — 19^  Ann. 
EepL,  U.  S.  G.  S.,  part  2,  pp.  59-294  (1898). 

KlRBY,  E.   B. 

The  Ore  Deposits  of  Rossland,  British  Columbia. — Jour.  Can.  Min.  List.,  vol. 

7,  pp.  47-69  (1904). 
KJERULF. 

Udsigt  over  det  sydlige  Norges  Geologi  (Kristiania,  1879). 
KLEINSCHMIDT,  J.  L. 

Gedankeniiber  Erzvorkommen.—  Berg-  u.  Hutt.  Zeit.,  p.  413  (1887). 

KLEMENT,  C. 

Expose*  de  quelques  vues  ge"nerale  sur  la  formation  des  gites  metalliferes. — 
Bull.  Soc.  Beige  de  GeoL,  vol.  11,  pp.  179-184  ;  vol.  12,  pp.  95-100,  121-126 
(1897-98). 
KLOCKMANN,  F. 

1.  Lehrbuch  der  Mineralogie  (1892)  ;  new  edition  (1900). 

2.  Das  Erzlager  des  Rammelsberges.—  Zeit.  d.  D.  GeoL  Gesel.,vol.  45,  pp.  281- 
284  (1893). 

3.  Uber    kontaktmetamorphe   Magnetitlagerstiitten,  ihre    Bildung  und   sys- 
tematische  Stellung.-«-Ze^./.  prak.  GeoL,  vol.  12,  pp.  73-85  (1904). 


ALPHABETICAL    LIST    OF    AUTHORS.  877 

KLOCKMANN,  F. — Continued. 

4.  tiber  den  Einfluss  der  Metamorphose  auf  die  Mineralische  Zusammen- 
setzung  der  Kieslagerstatten. — Zeit.   f.   prak.    GeoL,  vol.    12,  pp.  153-160 
(1904). 
KNETT,  J. 

Schwefel  und  Pyrite  als  Absatzvon  Karlsbader  Thermal wasser. — Neues  Jahrb. 

f.  Min.,  vol.  2,  pp.  81-84  (1899). 
KNIGHT,  C.  W. 

Notes  on  Some  Deposits  in  the  East  Ontario  Gold  Belt. — Jour.  Can.  Min.  Inst., 

vol.  7,  pp.  210-244  (1904). 
KNIGHT,  F.  C. 

A  Suspected  New  Mineral  from  Cripple  Creek. — Proc.  Col.  Sci.  Soc. ,  vol.  5, 

pp.  66-71  (1894-96). 
KNOPF,  ADOLPH. 

1.  Geology  of  the  Seward  Peninsula  Tin  Deposits,  Alaska. — Bull.  358,  U.  S. 
G.  S.  (1908).     71  pp. 

2.  Notes  on  the  Foothill  Copper  Belt  of  the  Sierra  Nevada. — Bull.  Dept.  GeoL 
Univ.  Col.,  vol.  4,  No.  17,  pp.  411-423  (1906). 

3.  Some  Features  of  the  Alaska  Tin  Deposits. — Econ.  GeoL,  vol.  4,  pp.  214- 
223  (1909). 

KNOX,  H.  H. 

An  Instance  of  Secondary  Impoverishment. — Trans.  Inst.  Min.  and  Met. ,  vol. 

18,  pp.  273-290  (1908-09). 
KNOX,  N.  B. 

Dredging  and  Valuing  Dredging-Ground  in  Oroville,  California. — Can.  Min. 
Rev.,  vol.  22,  pp.  211-213  (1903). 

K5BRICH,  B. 

Magnetische  Erscheinungen  an  Bauxiten. — Zeit.  f.  prak.   GeoL,  vol.    13,  pp. 

23-36  (1905). 
KOENIG,  G.  A.,  and  STOCKDEB,  MORITZ. 

On  the  Occurrence  of  Lustrous  Coal  with  Native  Silver  in  a  Vein  in  Porphyry, 
in  Ouray  County,  Colorado.— Trans.  A.  I.  M.  E.,  vol.  9,  pp.  650-656 
(1880-81). 

KOHLER,   G. 

1.  Lehrbuch  der  Bergbaukunde  (Leipzig,  1884). 

2.  Die  Storungen  der  Gange,  Flotze  und  Lager   (Leipzig,  1886).     Transla- 
tion by  W.  B.  Phillips  :  Irregularities  of  Lodes,  Veins,  and  Beds. — E.  and 
M.  Jour.,  vol.  43,  p.  454  ;  vol.  44,  p.  4  (1887). 

3.  Beitriige  zur  Kenntniss  der  Erdbewegungen  und  Storungen  der  Lagerstat- 
ten.—  Berg-  u.  Hiltt.  Zeit.,  vol.  56,  pp.  217-2^9,  261-263,  341-345  (1897). 

KOHLER,    E. 

Adsorptionsprozesse  als  Factoren  der  Lagerstiittenbildung  und  Lithogenesis. — 
Zeit.  f.  prak.  GeoL,  vol.  11,  pp.  49-59  (1903). 

KOHLER,   EUGEN. 

Die  neueren  Quellen-und  Grundwassertheorien  (Kondensationstheorien). — 

Zeit.  f.  prak.  GeoL,  vol.  18,  pp.  23-29  (1910). 
KONIG,  F. 

Die  Vertheilung  des  Wassers  iiber,  auf,  und  in,  der  Erde,  und  die  daraus  sich 

ergebende   Entstehung  des  Grundwassers    und   seiner  Quellen,  mit  einer 

Kritik  der  Bisherigen  Quellentheorien  (Jena,  1901). 

K5NIGSBERGER,  J. 

Die  Minerallagerstatten  im  biotit  protogin  des  Aar  Massives. — Neues  Jahrb. 
f.  Min.,  vol.  14,  pp.  43-49  (1901). 

KOSMANN. 

tiber  die   Bildung   Magnetischer  Eisenoxyde  und    Eisenhydroxyde.—  Ess- 

Gluck.,  vol.  4  (1893).     3pp. 
KOTO,  B. 

On  the  Cause  of  the  Great  Earthquake  in  Central  Japan.—  Jour.  Coll.  Sci.  Imp. 

Univ.  Jap.,  vol.  5,  part  4  (Tokyo,  1893). 
KRAHMANN,  MAX. 

1.  Fortschritte  der  Praktischen  Geologic  (Berlin,  1903).     2  vols.,  410  pp. 


878  ALPHABETICAL    LIST    OF    AUTHORS. 

KRAHMANN,  MAX.— Continued. 

2.  Lagerstatten-Schatzungen  im  Anschluss  an  eine  Beurteilung  der  Xachhaltig- 
keit   des    Eisenerzbergbaues  an  der   Lahn. — Zeit.  f.  prak.   Geol.,   vol.   12, 
pp.  329-348  (1904). 

3.  Der  deutsche   Erzbergbau.— Zeit.    f.  prak.    Geol.,  vol.   13,    pp.   265-304 
(1905). 

KRAUSE,  P.  R. 

IJber  den  Einfluss  der  Eruptivgesteine  auf  die  Erzfiihrungder  Witwatersrand- 
Conglomerate  und  der  im  dolomitischen  Kalkgebirge  von  Lydenbnrg  auf- 
tretenden  Quartzflotze,  nebst  einer  Kurzen  Schilderung  der  Grubenbezirke 
von  Pilgrimsrest  und  De  Kaap  (Transvaal). — Zeit.  f.  prak.  Geol., vol.  5,  pp. 
12-25  (1897). 

KRECKE,  F. 

Sind  die  Roteiaensteinlager  des  nassuaischen  Devon  primiire  oder  sekundare 
Bildungen?— Zeit.f.  prak.  Geol,  vol.  12,  pp.  348-355  (1904). 

KRUSCH,  PAUL. 

1.  tiber  die  Veranderungen  der  Erzgange  in  der  Tiefe. — Zeit.  f.  prak.  Geol., 
vol.  8,  pp.  313-322  (1900). 

2.  Bilder  von  den  Blei   und  Zink  Lagerstatten  in  Kaibl. — K.    K.   Ackerb. 
Minist.  (Wien,  1903). 

3.  Uber  die  Zusammensetzung  der  Westfalischen  Spaltenwiisser. — Zeit.  f.prak. 
Geol.,  vol.  12,  pp.  252-254  (1904). 

4.  Die  Einteilung  der  Erze  mit  besonderer  Beriicksichtigung  der  Leiterze 
sekundarer  und  primarer  Teufen. — Zeit.  f.  prak.  Geol.,  vol.  15,  pp.  129-139 
(19U7). 

5.  Die  Untersuchung  und  Bewertung  von  Erzlagerstatten. — (Stuttgart,  1907. ) 
517  pp. 

6.  Uber  primare  und  sekundare  Metasomatische  Prozesseauf  Erzlagerstatten. — 
Zeit.  f.prak.  Geol.,  vol.  18,  pp.  165-180  (1910). 

KUNTZ,  J. 

1.  Copper  Ore  in  Southwest  Africa.— Trans.  Geol.  Soc.  So.  Af.,  vol.  7,  pt.  2, 
pp.  70-76  (1904). 

2.  The  Hand  Conglomerates  :  How  they  were  formed. — Trans.  Geol.  Soc.  So- 
Africa,  vol.  1,  pt.  6,  pp.  113-122  (1896). 

KYN ASTON,  H.,  and  MELLOR,  E.  T. 

The  Geology  of  the  Waterberg  Tin-Fields.—  Mines  Dept.  Trans.,  Mem.  4  (1909). 
124  pp. 

LACHMANN,  E.  • 

Neue  ostungarische  Bauxitkorper  und  Bauxitbildung  uberhaupt. — Zeit.  f. 
prak.  Geol.,  vol.  16,  pp.  354-362  (1908). 

LACROIX,  A. 

1.  Sur  un  gitede  magnetite  en  relation  avec  le  granite  de  Querigut  (ariege). — 
Compt.  rend.  Acad.  Sci.,  vol.  12,  p.  6  (1890). 

2.  Sur  1' Origin e  de  1' Or  de  Madagascar. — Compt.  rend.   Acad.  Sci.,  vol.  132, 
pp.  180-182  (1901). 

3.  Notice  sur  les  Travaux  Scientifiques  de  M.  A.  Lacroix  (Paris,  1908). 

LAKE,  J.  V. 

The  Deposition  of  Alluvial  Gold. — Min.  Jour.,  vol.  73,  p.  11  (1903). 

LANE,  A.  C. 

1.  The  Theory  of  Copper  Deposition.—  Rept.  Mich.  St.  Geol.,  vol.  34,  pp.  240- 
250  (1903)  ;  Am,  Geol.,  vol.  34,  pp.  297-309  (1904). 

2.  The  Influence  of  Varying  Degrees  of  Superfusion  in  Magmatic  Differentia- 
tion.— Jour.  Can.  Min.  Inst.,  vol.  9,  pp.  210-217  (1906). 

3.  The  Formation  of  Lake  Superior  Copper. — Science,  new  ser.,  vol.  25,  p. 
589  (1907). 

4.  Mine  Waters.—  Proc.  Lake  Sup.  Min.  Inst.,  vol.  13,  pp.  63-152  (1908). 

5.  Mine  Waters  and  Their  Field  Assay.— Bull.  Geol.  Soc.  Am.,  vol.    19,  pp. 
501-512  (1908). 

6.  Mine  Waters.—  Jour.  Can.  Min.  Inst.,  vol.  12,  pp.  145-146  (1909). 


ALPHABETICAL    LIST    OF    AUTHORS.-  879 

LANG,  O. 

Titanhaltige  Magneteisenerze.--AStaW  u.  Eisen,  vol.  20,  pp.  377-382  (1900). 
LARSSEN,  PER. 

The  Chapin  Iron  Mine,  Lake  Superior. — Trans.   A.   I.   M.   E.,  vol.  16,  pp. 

119-129(1887-1888). 
LAUR,  M. 

1.  Du  Giaement  et  de  Texploitation  de  Tor  en  Californie. — Ann.  d.  Mines, 
ser.  6,  vol.  3.,  pp.  347-435  (1863). 

2.  Les  Bauxites  dans  le  Monde.— Compt.  rend.  Acad.  Sci.,  pp.  94-104,432- 
461  (1908). 

LAURENT. 

1.   Notes  sur  1' Industrie  de  1'or  et  du  Platine  dans  1'Oural. — Ann.  d.  Mines, 

ser.  8,  vol.  18,  pp.  537-579  (1890). 
LAWSON,  A.  C. 

1.  The  Post-Pleistocene  Diastrophism  of  the  Coast  of  Southern  California. — 
Bull  Dept.  Geol,  Univ.  CW.,vol.  1,  No.  4,  pp.  115-160  (1893). 

2.  The  Copper  Deposits  of  the  Robinson  Mining  District,  Nevada.—  Bull.  Dept. 
Geol,  Univ.  Col.,  vol.  4,  No.  14,  pp.  287-357  (1906). 

LECKIE,  R.  G. 

On  the  Nickel  Deposits  of  Norway. — Jour.   Can.    Min.   Inst.,  vol.  7  (1904). 

9pp. 
LE  CONTE,  JOSEPH. 

1.  Elements  of  Geology  (Edited  by  H.  L.  Fairchild,  New  lrork,1904).  649pp. 

2.  On  Mineral  Vein  Formation  in  Progress  at  Steamboat  Springs.  — Am.  Jour. 
Sci.,  3d  ser.,  vol.  25,  pp.  424-428  (1883). 

3.  Genesis  of  Metalliferous  Veins. — Am.  Jour.  Sci.,  3d  ser.,  vol.  26,  pp.  1-19 
(1883). 

4.  Discussion  of  Posepny' s  Paper,   "  The  Genesis  of  Ore-Deposits." — Trans. 
A.  I.  M.  E.,  vol.  24,  pp.  942-1006  (1894). 

5.  Origin  of  Jointed  Structure  in  Undisturbed  Clay  and  Marl  Deposits. — Am. 
Jour.  Sci.,  ser.  3,  vol.  23,  pp.  233-234  (1882). 

6.  The  Old  River  Beds  of  California.—  Am.  Jour.  Sci.',  3d  ser.,  vol.  19,  pp. 
176-190  (1880). 

LE  CONTE,  JOSEPH,  and  RISING,  W.  B. 

The  Phenomena  of  Metalliferous  Vein  Formation  now  in  Progress  at  Sulphur 

Bank,  Cal.—Am.  Jour.  Sci.,  3d  ser.,  vol.  24,  pp.  23-33  (July,  1882)  ;  vol. 

25,  pp.  424-428  (June,  1883). 
LEITH,  C.  K. 

1.  The  Mesabi  Iron-Bearing  District  of  Minnesota.—  Mon.  43,    U.  S.  G.  S. 
(1903).     316  pp. 

2.  A  Summary  of  Lake  Superior  Geology,  with  Special  Reference  to  Recent 
Studies  of  the  Iron- Bearing  Series.— Trans.  A.  L  M.  E.,  vol.   36,  pp.  101- 
154  (1905). 

3.  Rock  Cleavage.  —Bull,  239,  U.  S.  G.  S.,  153pp.  (1905). 

4.  Genesis  of  the  Lake  Superior  Iron  Ores. — Econ.  Geol,  vol.  1,  pp.  47-65 
(1906). 

5.  The  Geology  of  the  Cuyuna  Iron  Range,  Minnesota. — Econ.  Geol,  vol.  2, 
pp.  145-152  (1907). 

6.  The  Iron  Ores  of  Canada.— Can.  Min.  Jour.,  vol.  29.  pp.  370-374  (1908.) 

7.  The  Iron  Ores  of  Canada.—  Econ.  Geol,  vol.  3,  276-291  (1908). 

8.  Iron  Ores  of  Iron  Springs,  Utah.     Answer  to  Review  by  J.  F.  Kemp  on 
contact  metamorphism.—  Econ.  Geol,  vol.  5,  pp.  188-192  (1910). 

LEITH,  C.  K.,  and  HARDER,  E.  C.  . 

The  Iron  Ores  of  the  Iron  Springs  District,  Southern  Utah.—  Bull.  338,  U.  S. 

G.  S.     102pp.  (1908). 
LENHER,  VICTOR. 

Some  Observations  on  the  Tellurides.— Econ.  Geol,  vol.  4,  pp.  544-564  (1909)' 
LEONARD,  A.  G. 

1.  Origin  of  the  Iowa  Lead  and  Zinc  Deposits. — Am.  Geol,  vol.  16,  pp.  288- 
294  (1895). 

2.  Lead  and  Zinc  Deposits  of  Iowa.— Iowa  Geol  Sur.,  vol.  6,*pp.  11-66  (1897). 


880  ALPHABETICAL    LIST    OF    AUTHORS. 

LEV  AT,  DAVID. 

1.  L' Industrie  Aurif ere  (Paris,  1905).     878pp. 

2.  L'or  en  Siberie  orientale  (Paris,  1904).     2  vols.,  670  pp. 
LEVAT,  M.  D. 

Bassin  cuprifSre  du  Kovilou-Niari  Congo  fran9ais.—  Ann.  d.  Mines,  10th  ser., 

vol.  11,  pp.  5-65  (1907). 
LINCOLN,  F.  C. 

1.  Magmatic  Emanations. — Econ.  GeoL,  vol.  2,  pp.  258-274  (1907). 

2.  Certain  Natural  Associations  of  Gold.—  Econ.  GeoL,  vol.  6,  pp.  247-302 
(1911.). 

3.  Gold  Ores  of  Washington  and  Oregon. — E.  and  M.  Jour.,  vol.  92,  pp.  13- 
15  (1911). 

4.  Some  Gold  Deposits  of  the  Northwest. — E.  and  M.  Jour.,  vol.  92,  pp. 
408-410  (1911). 

LINDGREN,  WALDEMAR. 

1.  The  Silver  Mines  of  Calico,  California. — Trans.  A.  L  M.  E..  vol.  15,  pp. 
717-734  (1887). 

2.  Two  Neocene  Rivers  of  California. — Bull.  GeoL  Soc.  Am.,  vol.  4,  pp.  257- 
298  (1893). 

3.  Gold-silver  Mines  of  Ophir,  California.— 14th  Ann.  Rept.,  U.  S.   G.  S., 
Part  2,  pp.  243-284  (1894). 

4.  The  Auriferous  Veins  of  Meadow  Lake,  California. — Am.  Jour.  Sci.,  3d 
ser.,  vol.  46,  pp.  201-206  (1893). 

5.  An  Auriferous  Conglomerate  of  Jurassic  Age  from  the  Sierra  Nevada. — 
Am.  Jour.  Sci.,  3d  ser.,  vol.  48,  pp.  275-280  (1894). 

6.  Geological  Atlas  of  the  U.  S.     Sacramento  Folio  (No.  5)  (1894). 

7.  Characteristic  Features  of  California  Gold-Quartz  Veins.—  Bull.  GeoL  Soc. 
Am.,  vol.  6,  pp.  221-240  (1895). 

8.  The  Gold-quartz  Veins  of  Nevada  City  and  Grass  Valley  Districts,  Cali- 
fornia.— llth  Ann.  Rept.,  U.  S.  G.  S.,  Part  2,  pp.  1-262  (1896). 

9.  The  Mining  Districts  of  the  Idaho  Basin  and  the  Boise  Ridge,  Idaho. — 
ISth  Ann.  Rept.,  U.  S.  G.  S.,  Part  3,  pp.  617-744  (1897). 

10.  Orthoclase  as  Gangue  Mineral  in  a  Fissure  Vein. — Am.  Jour.  Sci.,  4th 
ser.,  yol.  5,  p.  418  (1898). 

11.  The  Gold  and  Silver  Veins  of  Silver  City,  De  Lamar,  and  other  Mining 
Districts  in  Idaho.— 20th  Ann.  Rept.,  U.  S.  G.  S.,  part  3,  pp.  65-256  (1899). 

12.  Metasomatic  Processes  in  Fissure  Veins.— Trans.  A.  I.  M.  E.,  vol.  30, 
pp.  578-692  (1900).      (Also  Special  Volume,   "Genesis  of  Ore-Deposits," 
pp.  498-612,  1902). 

13.  The  Gold  Belt  of  the  Blue  Mountains  of  Oregon.—  22d  Ann.  Rept.,  U.  S. 
G.  S.,  part  2,  pp.  551-776  (1901). 

14.  The  Character  and  Genesis  of  Certain  Contact-Deposits. — Trans.  A.  L  M- 
E.,  vol.  31,  pp.  226-244  (1901). 

15.  Tests  for  Gold  and  Silver  in  Shales  from  Western  Kansas.—  Bull.  202,  U. 
S.  G.  S.     21pp.  (1902). 

16.  The  Geological  Features  of  the  Gold  Production  of  North  America. — 
Trans.  A.  I.  M.  E.,  vol.  33,  pp.  790  845  (1902). 

17.  Characteristics  of  the  Gold  Quartz  Veins  in  Victoria. — E.  and  M.  Jour., 
vol.  79,  p.  458  (1905). 

18.  Neocene  Eivers  of  the  Sierra  Nevada.  —Bull.  213,  U.  S.  G.  S.,  pp.  64-65 
(1903). 

19.  The  Genesis  of  the  Copper  Deposits  of  Clifton-Morenci,  Arizona. — Trans. 
A.  I.  M.  E.,  vol.  35,  pp.  511-551  (1904). 

20a.  The  Copper  Deposits  of  the  Clifton-Morenci  District,  Arizona. — Prof. 
Paper  43,'  U.  S.  G.  S.  (1905).     395  pp. 

20.  A  Geological  Reconnaissance  across  the  Bitterroot  Range  and  the  Clear- 
water  Mountains  in  Montana  and  Idaho. — Prof.  Paper  27,  U.  S.   G.  S. 
(1904).      123pp. 

21.  The  Occurrence  of  Stibnite  at  Steamboat  Springs,  Nevada.  —  Trans.  A.  L 
M.  E.,  vol.  36,  pp.  27-31  (1905). 

22.  Occurrence  of  Albite  in  the  Bendigo  Veins. — Econ.  GeoL,  vol.  1,  pp.  163- 
166  (1906). 

23.  Metasomatic  Processes  in  the  Gold  Deposits  of  Western  Australia. — Econ. 
GeoL,  vol.  1.  pp.  530-544  (1906). 

24.  Ore-Deposition  and  Deep  Mining.— Ebon.  GeoL,  vol.  1,  pp.  34-46  (1906). 


ALPHABETICAL    LIST    OF    AUTHORS.  881 

LINDGREN,  WALDEMAR. — Continued. 

25.  The  Gold  Deposits  of  the  Dahlonega  (Ga. )  Mines.—  Bull.  293,  U.  S.  G. 
S.,  pp.  119-128  (1906). 

26.  The  Relation  of  Ore- Deposition  to  Physical  Conditions. — Econ.   GeoL, 
vol.  2,  pp.  105-127  (1907). 

27.  Present  Tendencies  in  the  Study  of  Ore-Deposits. — Econ.  GeoL,  vol.  2, 
pp.  743-762  (1907). 

28.  Metallogenetic  Epochs.— Can.  Min.  Jour.,  vol.  30,  pp.  430-434  (1909). 

29.  Metallogenetic  Epochs.—  Econ.  GeoL,  vol.  4,  pp.  409-420  (1909). 

30.  The  Localization  of  Values  in  Ore-Bodies  and  the  Occurrence  of  Shoots 
in  Metalliferous  Deposits.—  Econ.  GeoL,  vol.  4,  pp.  56-61  (1909). 

31.  The  Hot  Springs  at  Ojo  Caliente  and  Their  Deposits. — Econ.  GeoL,  vol. 
5,  pp.  22-27  (1910.) 

32.  Some  Modes  of  Deposition  of  Copper  Ores  in  Basic  Rocks.  — Econ.  GeoL , 
vol.  6,  pp.  687-700  (1911). 

33.  The  Nature  of  Replacement.—  Econ.  GeoL,  vol.  7,  pp.  521-535  (1912). 

34.  The  Tertiary  Gravels  of  the  Sierra  Nevada,  California.— Prof.  Paper  73, 
U.  S.  G.  S.  (1911). 

35.  Geologic  Introduction  to  the  Mining  Districts  of  the  Western  U.  S. — BulL 
507,  U.  S.  G.  S.,  pp.  1-43  (1912). 

36.  Chemistry  of  Copper  Deposits.—^,  and  M.  Jour.,  vol.  79,  p.  189  (1905). 
LINDGREN,  W.,  GRATON,  L.  C.,  and  GORDON,  C.  H. 

The    Ore  Deposits  of  New  Mexico.—  Prof.  Paper  68,    U.  S.   G.  S.  (1910). 

361  pp. 
LINDGREN,  WALDEMAR.  and  DRAKE,  N.  F. 

Nampa  Folio,    Idaho-Oregon.—  Atlas  of  the  U.  S.,  Folio  103,  U.  S.  G.  S. 
(1904). 
LINDGREN,  WALDEMAR,  and  KNOWLTON,  F.  H. 

The  Age  of  Auriferous  Gravels  of  the  Sierra  Nevada,  with  a  Report  of  the 

Flora  of  Independence  Hill.— Jour.  GeoL,  vol.  4,  pp.  881-906  (1896). 
LINDGREN,  WALDEMAR,  and  RANSOME,  F.  L. 

1.  The  Geological  Resurvey  of  the  Cripple  Creek  District,  Colorado. — BulL 
260,  U.  S.  G.  S.,  pp.  85-98  (1905). 

2.  The  Geology  and  Gold  Deposits  of  the  Cripple  Creek  District,  Colorado. — 
Prof.  Paper  54,  U.  S.  G.  S.  (1906).     516  pp. 

LINDOREN,  WALDEMAR,  and  TURNER,  H.  W. 

Geological  Atlas  of  the  U.  S.—Placerville  Folio  (No.  3)  (1894). 
LITSCHAUER,  L. 

Die  Vertheilung  der  Erze  in  den  Lagerstatten  der  metallischen  Mineralien. — 
Zeit.f.prak.  GeoL,  vol.  1,  pp.  174-182  (1893). 

LlVERSIDGE,  A. 

1.  On  the  Formation  of  Moss  Gold  and  Large  Nuggets. — Proc.   Roy.  Soc..t 
N.  S.  W.,  vol.  27,  p.  287  (1893)  ;  Rev.  in  Zeit.  f.  prak.  GeoL,  vol.  2,  pp.  401- 
402(1894). 

2.  The  Origin  of  Gold  Nuggets. — Austr.  Min.  Stand.,  vol.  13,  pp.  2554-2557 
(1897). 

3.  Gold  Nuggets  from  New  Guinea  Showing  a  Concentric  Structure. — Jour,  and 
Proc.  of  Roy.  Soc.  N.  S.  W.,  vol.  40,  p.  161  (1906). 

4.  Gold  in  Sea  \Vater.— Proc.  Roy.  Soc.  N.  S.  W.,  vol.  29,  pp.  335-350  (1895). 

5.  Distribution  of  Silver.—  Jour.  Am.  Chem.  Soc.,  vol.  71,  p.  298  (1897). 
LOCK,  A.  G. 

Gold  (London,  1882).     (Bibliography.) 
LODIN. 

Origine  de  certains  Gites  de  Blende  et  de  Calamine. — Compt.  rend.  Soc.  de  Vind. 

mm.,  pp.  210-215  (1905). 
LOEWINSON-LESSING,  F. 

1.  Uber  die  Magneteisenerzlagerstatte  des  Berges  Blagodatj  in  Ural. — GeoL 
Zentralb.,  vol.  12,  p.  170  (1909). 

2.  Uber  den  Fundort  des  Magneteisensteins  im  Berge  Wvssokaja  im  Ural. — 
GeoL  Zentralb.,  vol.  12,  p.  480  (1909). 

LOR  AM,  S.  H. 

Notes  on  the  Gold  District  of  Canutillo,  Chile,  S.  A. — Trans.  A.  L  M.  E.,  vol. 
35,  pp.  696-711  (1904). 


882  ALPHABETICAL    LIST    OF    AUTHORS. 

LOSSEN,  K.  A. 

Uber  ein  durch  Zufall  in  einer  Fensterscheibe  enstandenes  Torsion^paltenritz. 

— Jahrb.  d.  Kgl.  Pr.  Geol.  Landesanst.,  p.  336  (1886). 
LOTTI,  B. 

1.  La  ge"nese  des  giseraents  cupriferes  des  depots  ophiolitiques  tertiares  de 
1' Italic.  —Bull.  Soc.  Beige  de  GeoL,  vol.  3  (18b9). 

2.  I  Deposit!  dei  Minerali  Metalliferi  (Torino,  1903).     150  pp. 

3.  Die  Zinnober  und  Antimon  fuhrenden  Lagerstatten   Toscanas  und  ihre 
Beziehungen  zu  den  quartiiren  Eruptivgesteinen. — Zeit.f.  prak.  Geol..  vol.  9. 
pp.  41-46  (1901V 

4.  Geologische  Verhaltnisse  und  Genesis  der  Zinnoberlagerstatte  von  Corte- 
vecchia  am  Monte  Amiata.— £ei<.  /.  prak.  GeoL,  vol.  11,  pp.  423-427  (1903). 

5.  Die  geologischen  Verhaltnisse  der  Therraalquellen  im  toscanischen  Erzge- 
birge  (Catena  Metallifera).— Zeit.  f.  prak.  GeoL,  vol.  1,  pp.  372-378  (1893). 

LOTTNER,  E.  H. ,  and  SERLO,  A. 

Leitfaden  zur  Bergbaukunde  (Berlin,  1869-1872.     Also  1878). 
Louis,  HENRY. 

1.  On  the  Mode  of  Occurrence  of  Gold. — Mineralog.  Mag.  (London),  vol.  20,- 
No.  47,  p.  241  (1893). 

2.  The  Allotropism  of  Gold.— Trans.  A.  I.  M.  E.,vo\.  24,  pp.  182-186  (1894). 

3.  Grundsatze  der  Classification  der  Minerallagerstatten. — Zeit.  f.  prak.  GeoL, 
vol.  8,  pp.  275-278  (1900). 

4.  The  Occurrence  and  Treatment  of  Platinum  in  Kussia. — Min.  Ind.,  vol. 
6,  pp.  539-552  (1898). 

LOVEMAN,  H.  M. 

Geology  of  the  Miami  Copper  Mine. — Min.  and  Sci.  Press,  vol.  105,  pp.  146- 
148  (1912). 

LOVEWELL,  J.  T. 

Gold  in  Kansas  Shales.— Trans.  Kans.  Acad.  Sci.,  vol.  18,  pp.  129-137  (1903). 
LUNGWITZ,  E.  E. 

1.  Uber   die   Kegionalen  Veranderungen    der    Golderzlagerstatten. — Thesis, 
Leipzig  (1899). 

2.  Der  geologische  Zusammenhang  von  Vegetation  und  Goldlagerstatten. — 
Zeit.f.  prak.  GeoL,  vol.  8,  pp.  71-74  (1900). 

LYMAN,  B.  8. 

Geology  of  the  Low  Moor,  Virginia,  Iron-Ores. — Trans.  A.  I.  M.  E.,  vol.  14, 
pp.  801-809  (1886). 

MABSON,  R.  E. 

Mines  of  the  Transvaal  (London,  1906).     776  pp. 
MAC  A  LISTER,  D.  A. 

1.  Vertical  Distribution  of  the  Commercially  Valuable  Ores  of  Tin  in  the 
Camborne  Lodes.  —  Geol.  Sar.  Gt.  Brit.  (1903). 

2.  Geological  Aspect  of  the  Lodes  of  Cornwall. — Econ.  GeoL,  vol.  3,  pp.  363- 
380  (1908). 

MACALISTER,  D.  A.,  and  HILL,  J.  B. 

The  Geology  of  Falmouth  and  Trnro,  and  of  the  Mining  Districts  Camborne 
and  Redruth.— GeoL  Sur.  Eng.  and  Wales  (1906).     335  pp. 

MCCALLTE,  S.   W. 

1.  The  Iron  Ores  of  Georgia.— Butt.  IOA,  GeoL  Sur.  Ga.  (1900).     190  pp. 

2.  Fossil  Iron  Ores  of  Georgia.— Bull.  17,  GeoL  Sar.  Ga.  (1908).     199  pp. 
MCCARTY,  E.  T. 

Mining  in  the  Wollastonite  Ore-Deposits  of   the  Santa  Fe  Mine,  Chiapas, 
Mexico.— Trans.  Inst.  Min.  and  Met.,  vol.  4,  pp.  169-189  (1895-1896). 

McCONNELL,  K.  G. 

1.  .Report  on  Gold  Values  in  the  Klondike  High  Level  Gravels. — Can.  GeoL 
Sur.,  Bull.  979  (1907).     34  pp. 

2.  The  White  Horse  Copper  Belt,  Yukon  Territory.— Can.  Geol.  Sur.,  Bull 
1,050  (1909).     63  pp. 

3.  Klondike  District,  Yukon  Territory. — Can.  GeoL  Sur.,  Ann.  Rept.,  vol.  15 
(1903)  ;  Summ.  Rept.,  pt.  A  A,  pp.  34-42  (1904). 


ALPHABETICAL    LIST    OF    AUTHORS.  883 

MCDONNELL.  R.  G. — Continued. 

4.  Report  on  the  Klondike  Gold  Fields. — Can.  OeoL  Sur.,  Ann.  Rept.,  vol. 

14,  pt.  B.     71  pp.  (1905). 

5.  The  Kluana  Mining  District. — Can.  Geol.  Sur.,  Ann.  Rept.,  vol.  16  (1904); 
Summ.  Rept.,  pt.  A,  pp.  1-18  (1905). 

McCREATH,   A.   S. 

The  Iron  Ores  of  the  Valley  of  Virginia. — Tram.  A.  I.  M.  E.,  vol.  12,  pp. 
17-26  (1886). 

MACDONALD,  D.   F. 

Notes  on  the  Gold  Lodes  of  the  Carrville  District,  Trinity  County,  Califor- 
nia.—JS^/.  530,  U.  S.  G.  S.  (1912).     37  pp. 

MACFARLANE,  THOMAS. 

Silver  Islet.— Trans.  A.  I.  M.  E.,  vol.  8,  pp.  226-254  (1879). 

MADDREN,  A.  G. 

The  Ruby  Placer  District,  Alaska.—  Butt.  520,  U.  S.  G.  S.  (1912).     14  pp. 

McGEE,  W.  J. 

Note  on  Jointed  Structure. — Am.  Jour.  Sci.,  3d  ser.,  vol.  25,  pp.  152-153 
(1883). 

MACKELLAR,  PETER. 

The  Gold-Bearing  Veins  of  Bag  Bay,  near  Lake  of  the  Woods.— Tram.  A.  I. 
M.  E.,  vol.  29,  pp.  104-115  (1899). 

MACLAREN,  J.  M. 

1.  The  Occurrence  of  Gold  in  Great  Britain  and  Ireland. — Trans.  lust.  Min. 
Eng.,  vol.  25,  pp.  4/5-508  (1902-03). 

2.  Gold:  Its  Geological  Occurrence  and  Geographical  Distribution.     Pub. 
by  The  Mining  Journal.     London,  1908.     Reviewed  by  Ransome  in  Econ. 
Geol.,  vol.  4,  pp.  391-396  (1909). 

MADDREN,  A.  G. 

The  Innoko  Gold- Placer  District,  Alaska.—  Bull.  410,  U.   S.   G.  S.  (1910). 

87pp. 
MALCOLMSON,  J.  W. 

The  Sierra  Mojada,  Coahuila,  Mexico  and  Its  Ore- Deposits. — Trans.  A.  I.  M. 

E.,  vol.  32,  pp.  100-140  (1901). 
MALLET,  J.  W. 

On  the  Occurrence  of  Silver  in  the  Volcanic  Ashes  from  the  Eruption  of  Cota- 
paxi  of  July  22  and  23. — Proc.  Roy.  Soc.,  vol.  42;  also  Chem.  News,  vol. 
55,  p.  17  (1881). 
MALLERY,  W. 

Native  Gold  in  Igneous  Rocks.—  E.  and  M.  Jour.,  vol.  77,  p.  596  (1904). 
MAYNARD,  G.  W. 

The  Chromite  Deposits  on  Port  au  Port  Bay,  Newfoundland. — Trans.  A.  I.  M. 

E.,  vol.  27,  pp.  283-288  (1897). 
MEAD,  W.  J. 

The  Relation  of  Densitv,  Porosity,  and  Moisture  to  the  Specific  Volume  of 

Ores.—  Econ.  Geol.,  vol.  3,  pp.  319-325  (1908). 
MELL,  P.  H.,  JR. 

Auriferous  Slate  Deposits  of  the  Southern  Mining  Region. — Trans.  A.  I.  M. 

E.,  vol.  9,  pp.  399-402  (1881). 
MENDENHALL,  W.  C. 

1.  Reconnaissance  from  Fort    Hamlin  to    Kotzebue  Sound,   Alaska. — Prof. 
Paper  10,  U.  S.  G.  S.  (1902).     68pp. 

2.  A  Reconnaissance  in  the  Norton  Bay  Region,  Alaska,  in  1900.     Special 
Publication,  U.S.  G.  S.  (1901). 

3.  Geology  of  the  Central  Copper  River  Region,  Alaska. — Prof.  Paper  41, 
U.  S.  G.  S.  (1906).     133  pp. 

4.  The  Chistochina  Gold  Field,  Alaska.—  Bull.  213,    U.  S.   G.  S.,  pp.  71- 
75  (1903). 

5.  A  Phase  of  Ground  Water  Problems  in  the  West. — Econ.  Geol.,  vol.  4,  pp. 
35-45  (1909). 

MENDENHALL,  W.  C.,  and  SCHRADER,  F.  C. 

The  Mineral  Resources  of  the  Mount  Wrangell  District,  Alaska. — Prof.  Paper 

15,  U.  S.  G.  S.  (1903).     71  pp. 


884  ALPHABETICAL    LIST    OF    AUTHORS. 

MERENSKY,  HANS. 

1.  Neue  Zinnerzvorkommen  in  Transvaal. — Zeit.  f.  prak.  Geol.,  vol.  12,  pp. 
409-411  (1904). 

2.  Die  goldfiihrenden  Erzvorkommen  der  Murchison  Range  im  Nordostlichen 
Transvaal.—  Zeit.  f.  prak.  Geol,  vol.  13,  pp.  258-261  (1905)  ;  also  Trans. 
GeoL  Soc.  So.  Af.,  vol.  8,  pp.  42-46  (1905). 

3.  The  Kocks  belonging  to  the  Area  of  the  Buschveldt  Complex  in  which 
Tin  may  be  Expected.— Trans.  Geol.  Soc.  So.  Af.,  vol.  11  (1908). 

MERRILL,  G.  P. 

1.  An  Occurrence  of  Free  Gold  in  Granite. — Am.  Jour.  Sci.,  4th  ser.,  vol.  1, 
pp.  309-311  (1896). 

2.  The  Non- Metallic  Minerals,  Their  Occurrence  and  Uses. — Wiley  and  Son 
(1904).     414pp. 

MERRITT,  W.  H. 

The  Occurrence  of  Gold-Ore  in  the  Rainy  River  District,  Ontario,  Canada. — 
Trans.  A.  I.  M.  E.,  vol.  26,  pp.  853-863  (1896). 

MlETZSCHKE,  W. 

tiber  das  Verhalten  des  Guides  in  Pyriten  bei  deren  Verwitterung.  —  Bery. 

u.  Hutt.  Zeit.,  vol.  55,  p.  193  (1896). 
MILLER,  A.  M. 

The  Lead  and  Zinc-Bearing  Rocks  of  Central  Kentucky,  with  Notes  on  the 

Mineral  Veins.—  Bull.  2,  Geol.  Sur.  Ky.  (1905).     35  pp. 
MILLER,  W.  G. 

1.  The  Cobalt-Nickel  Arsenides  and  Silver  Deposits  of  Temiskaming. — Rept. 
Out.  Bu.  Mines,  vol.  16,  Part  11  (1907).     212  pp. 

2.  Notes  on   the    Cobalt   Area.—  E.    and  M.    Jour.,   vol.   92,   pp.    645-649 
(1911). 

MlRON,  F. 

Gisements  miniers;  stratification  et  composition  (Paris,  1903).     192  pp. 
MITCHELL,  D.  P. 

The  Peculiar  Ore-Deposit  of  the  East  Murchison  United  Gold-Mine,  Western 

Australia.— Trans.  A.  I.  M.  E.,  vol.  29,  pp.  556-562  (1899). 
MOFFIT,  F.  H. 

1.  Fairhaven  Gold  Placers,  Seward  Peninsula,  Alaska.—  Bull.  247,  U.  S.  G. 
S.  (1905).      85pp. 

2.  The  Kotzebue  Placer  Gold  Field  of  Seward  Peninsula,  Alaska.—  Bull. 
225,  U.  S.  G.  S.,  pp.  74-80  (1904). 

3.  The   Nome   Region,    [Alaska].—  Bull.    314,    U.  S.    G.    S.,   pp.  126-145 
(1907). 

4.  The  lower  Copper  River  Basin,  Alaska.—  Bull.  520,  U.  S.  G.  S.  (1912). 
19  pp. 

5.  Headwater  Regions  of  Gulkana  and  Susitna  Rivers,  Alaska. — Bull.  498, 
U.  S.  G.  S.  (1912).     82  pp. 

MOFFIT,  F.  H.,  and  KNOPF,  ADOLPH. 

Mineral  Resources  of  the  Nabesna- White  River  District,  Alaska.—  Bull.  417, 

U.  S.  G.  S.  (1910).     64  pp. 
MOFFIT,  F.  H.,  and  MADDREN,  A.  G. 

Mineral  Resources  of  the  Kotsina-Chitina  Region,  Alaska. — Bull.  374,  U.  S. 
G.  S.  (1909).     103  pp. 

MOISSENET,   L. 

Observations  on  the  Rich  Parts  of  the  Lodes  of  Cornwall ;   their  Form  and 
their  Relations  with  the  Directions  of  the  Stratigraphic  Systems  (London, 

1877). 

M5NCH. 

tiber  die  elektrische  Leitfahigkeit  von  Kupfer  sulphur,   Silber,   Blei,   und 
Schwarzen  Quecksilbersulphid. — Neues  Jahrb.  f.  Min.,  vol.  20,  pp.  365-435 
(1905). 
MONTGOMERY,  A. 

Some  Geological  Considerations  Affecting  Western  Australian  Ore  Deposits. 
—Trans.  Aust.  Tnst.  Min.  Eng.,  vol.  13,  pp.  160-193  (1909). 


ALPHABETICAL    LIST    OF    AUTHORS.  885 

MOORE,  CHARLES, 

Keport  on   Mineral   Veins  in  Carboniferous   Limestone,  and  their  Organic 

Contents. — Rept.  of  Brit.  Assoc.  Adv.  Sci.,  1869,  p.  360,  et  seq. 
MOREAU,  GEORGE. 

Etude  Industrielle  des  Gites  Metalliferes  (Paris,  1894).     453  pp. 
MORGAN,  P.  G. 

The  Geology  of  the  Greymouth  Subdivision,  No.  Westland.  —  Bull.  13  (New 

Ser.),  Geol.  Sur.  Branch  N.  Z.  Dept.  of  Mines  (1911).     159  pp. 
DE  MORGAN. 

1.  Note  sur  la  geologic  et  sur  P  Industrie  miniere  du  royaume  de  Perak  et  des 
pays  voisins—  Ann.  d.  Mines,  8th  ser.,  vol.  9,  pp.  368-442  (1886). 

M5RICKE,  W. 

1.  Betrachtungen  und  Beobachtungen  iiber  die  Entstehung  von  Goldlager- 
statten.—  Zeit.  f.  prak.  GeoL,  vol.  1,  pp.  143-148  (1893). 

2.  Uber  edle  Silbererzgiinge  in  Verbindung  mit  basischen  Eruptivgesteinen. 
— Zeit.  f.  prak.  GeoL,  vol.  3,  pp.  4-10  (1895). 

MOROZEWICZ,  J. 

1.  Die  Eisenerzlagerstatten  des  Magnetberges  im  siidlichen  Ural  und   ihre 
Genesis.— Tscher.  Min.  u.  Pet.  Mitt.,  vol.  23,  pp.  113-152  ;  225-262  (1904). 

2.  Experimentalle  Untersuchungen  iiber  die  Bildung  der  Minerale  im  Mag- 
ma. —  Tscher.  Min.  u.  Pet.  Mitt,  vol.  18,  pp.  1-90,  105-238  (1899). 

MORRIS,  H.  C. 

Hydro-Thermal  Activity  in  the  Veins  of  Wedekind,  Nevada. — E.  and  M. 
'Jour.,  vol.  76,  pp.  275-276   (1903). 

MOULAN,  PH. 

Origin  et  Formation  des  Minerals  de  Fer  (Bruxelles,  1904).     14S  pp. 

MULLER,  A. 

1.  Erzgange  (Basel,  1880). 

2.  Uber  die  Erzlagerstatten  der  umgegend  von  Berggiesshubel  (Leipzig,  1890). 

3.  Uber  die  Beziehung  zwischen  Mineralquellen  und  Erzgiingen  im  Nord- 
lichen  Bohmen  und  in  Sachsen  ;  von  Cotta's  Gangstudien,  III.  (Freiberg, 
1869). 

MULLER,  H. 

1.  Beitrage  zur  Kentniss  der  Mineralquellen  und  Stollenwtisser  Freiberger 
Gruben.  —  Jahrb.  f.  Berg-u.  Hutt.  in  Konig.  Sachs.  (1885). 

2.  Die  Erzgange  des  Freiberges  Bergreviers  (Leipzig,  1901).     350  pp. 

3.  Erzlagerstatten  bei  Freiberg,  Cotta's  Gangstudien,  1850,  vol.  1,  pp.  209-248 
(1850). 

MUNROE,  H.  S. 

List  of  Books  on  Mining.—  Sch.  Min.  Quar.,  vol.  10,  pp.  176-184  (1889). 
MUNSTER,  HERMANN. 

Die  Brauneisenerzlagerstiitten  des  Seen-  undOhmtals  am  Nord rand  des  Vogels- 
gebirges.—  Zeit.  f.  prak.  GeoL,  vol.  13,  pp.  242-258  (1905). 

MURCHISON,   R.  I. 

General  View  of  the  Conditions  under  which  Gold  is  Distributed. — Quar.  Jour. 
GeoL  Soc.,  vol.  8,  pp.  134-136  (1852). 

NASON,  F.  L. 

1.  Iron  Ores  of  Missouri.— GeoL  Sur.  of  Missouri,  vol.  2,  pp.  1-365  (1892). 

2.  The  Franklinite- Deposits  of  Mine  Hill,  Sussex  County,   New  Jersey. — 
Trans.  A.  I.  M.  E.,  vol.  24,  pp.  121-130  (1894). 

3.  The  Geological  Structure  of  the  Eingwood  Iron  Mines,  New  Jersey. — 
Trans.  A.  I.  M.  E.,  vol.  24,  pp.  505-521  (1894). 

4.  Some  Phenomena  of  the  Folding  of  Rock  Strata. — Econ.  GeoL,  vol.  4,  pp. 
421-437  (1909). 

NAUMANN,  C.  F. 

Lehrbuch  der  Geognosie,  Bd.  III.,  Lief  3.     (Unvollendet)  (1872). 
NAVARRO,  L.  F. 

Mas  sob  re  la  teoria  de  la  sustitucion  en  Almaden. — Act.  Soc.  EspaHola  d.  Hist. 

Nat.,  vol.  3,  2d  series  (1894). 
NECKER,  A.  L. 

On  the  Sublimation  Theory.  —Proc.  GeoL  Soc.  London,  vol.  1,  p.  392  (1826-33). 


886  ALPHABETICAL    LIST    OF    AUTHORS. 

NEUNIER,  S. 

Geologic  Experiment  ale  (Paris,  1904).     321  pp. 
NEWBERRY,  J.  S. 

1.  Report  on  the  Property  of  the  Stormont  Silver  Mining  Company,  No.  30, 
1880  ;  No.  21,  1881. 

2.  The  Genesis  of   our  Iron  Ores.—  E.  and  M.  Jour.,  vol.  31,  pp.  286-287; 
298-300  (1881). 

3.  Genesis  and   Distribution  of   Gold. — E.  and  M.  Jour. ,  vol.  32,  pp.  416- 
417,  433  (1881). 

4.  The  Origin  and  Classification  of  Ore-Deposits. — Sch.  Min.  Quar.,  vol.  1, 
pp.  87-104  (1880).   Also  E.  and  M.  Jour. ,  vol.  29,  pp.  421-422,  437-438  (1880). 

5.  The  Origin  and  Classification  of  Ore- Deposits. — Proc.  Am.  Assoc.  Adv.  Sci., 
vol.  32,  p.  243  (1883). 

6.  The  Deposition  of  Ores.—  E.  and  M.  Jour.,  vol.  38,  pp.  38-40  (1884). 

NEWBIGIN,  H.  T. 

1.  The  Siliceous  Iron  Ores  of  Northern  Norway. — Trans.  Inst.  Min.  Eng.,  vol. 

15,  pp.  154-171  (1897-98). 
NEWLAND,  D.  H. 

1.  Tin.—  Min.  Ind.,  vol.  12,  pp.  325-339  (1904). 

2.  On  the  Association  and  Origin  of  the  Nontitaniferous  Magnetites  in  the 
Adirondack  Region.—  Econ.  Geol.,  vol.  2,  pp.  763-773  (1907). 

3.  The  Clinton  Iron  Ore  Deposits  in  New  York  State.— Trans.  A.  I.  M.  E., 
vol.  40,  pp.  165-184  (1909). 

NEWLAND,  D.  H.,  and  HARTNAGEL,  C.  A. 

Iron  Ores  of  the  Clinton  Formation  in  New  York  State.—  Bull.  123,  New 

York  State  Miiseum  (1908).     76  pp. 
NEWLAND,  D.  H.,  and  KEMP,  J.  F. 

Geology  of  the  Adirondack  Magnetic  Iron  Ores. — Bull.  119,  New  York  State 
Museum  (1908).     184  pp. 

NICHOLAS,  WM. 

The  Origin  of  Gold  in  Certain  Victorian  Quartz  Reefs.  — E.  and  M.  Jour. , 

vol.  36,  pp.  367-368  (1883). 
NICHOLS,  H.  W.,  and  FARRINGTON,  O.  C. 

The  Ores  of  Colombia.—  Field  Col.  Mus.  Pub.  No.  33,  Geol.  ser.,  vol.  1,  No.  3 

(1899). 
NITZE,  H.  B.  C. 

1.  Notes  on  Some  of  the  Magnetites  of  Southwestern  Virginia  and  the  Con- 
tiguous Territory  of  North  Carolina. — Trans.  A.  I.   M.  E.,  vol.  20,    pp. 
174-188  (1891). 

2.  The  Magnetic  Iron-Ores  of  Ashe  County,  North  Carolina. — Trans.  A.  I. 
M.  E.,  vol.  21,  pp.  260-280  (1892). 

3.  Monazite.— 16th  Ann.  Rept.,  U.  S.  G.  S.,  part  4,  pp.  667-693  (1895). 

4.  Iron  Ores  of  North  Carolina.— Bull  1,  No.  Car.  Geol.  Sur.  (1893).    239pp. 

5.  Monazite  and  Monazite  Deposits  in  North  Carolina.     (Bibliography.) — 
Bull.  9,  No.  Car.  Geol.  Sur.  (1895).     47pp. 

NITZE,  H.  B.  C.,  and  HANNA,  G.  B. 

Gold  Deposits  of  North  Carolina.— Bull.  3,No.  Car.  Geol.  Sur.  (1896).     200  pp. 
NITZE,  H.  B.  C.,  and  PURINGTON,  C.  W. 

The  Kotchkar  Gold-Mines,  Ural  Mountains,  Russia. — Trans.  A.  I.  M.  E.,  vol. 

28,  pp.  24-33  (1898). 
NITZE,  H.  B.  C.,  and  WILKENS,  H.  A.  J. 

The  Present  Condition  of  Gold-Mining  in  the  Southern  Appalachian  States. — 
Trans.  A.  I.  M.  E.,  vol.  25,  pp.  661-796  (1895). 

NOVARESE,  V. 

Die  Erzlagerstatten  von  Brosso   and  Traversella  in  Piemont. — Zeit.  f.  prak. 
Geol,  vol.  10,  pp.  179-187  (1902). 

OCHSENITTS,  CARL. 

1.  tiber   unterirdische  Wasseransammlungen. — Zeit.  f.   prak.   Geol.,  vol.    1, 
pp.  36-40  (1893). 

2.  Sikin   als   Bildner  von  Erzlagerstatten. — Zeit.  d.  D.  Geol.  GeseL,  vol.  57, 
p.  567  (1905). 


ALPHABETICAL    LIST    OF    AUTHORS.  887 

ORDONEZ,  E. 

1.  Note  sur  les  gisements  d'or  du  Mexique  (Mexico,  1898). 

2.  Les  filons  Argentiferes  de  Pachuca. — Bull.  Soc.  Geol.  de  France,  vol.  26, 
pp.  244-258  (1898). 

3.  The  Mining   District  of   Pachuca,   Mexico, —  Trans.  A.  I.  M.  E.,vol.  32 
pp.  224-241  (1901). 

4.  A.  Brief  Review  of  the  Mining  Industry  of  Mexico. — Econ.  Geol ,  vol.  3,  pp. 
677-687  (1908). 

ORDONEZ,  E.,  and  AGUILERA,  J.  G. 

Bosquejo   geologico  de   Mexico.—  Bol.   Inst.    Geol.    Mex.,  Nos.  4,  5,  6,  pp. 

68-222  (1897). 
ORTON,  E. 

The  Trenton  Limestone  as  a  Source  of  Petroleum  and  Natural  Gas  in  Ohio 

and  Indiana.—  8th  Ann.  Rept.,  U.  S.  G.  S.,  Pt.  2,  pp.  483-662  (1889). 
O'  HARRA, 

The  Mineral  Wealth  of  the  Black  Hills.—  Bull  3,  Geol.  Sur.  S.  Dakota  (1902). 
136  pp. 

PACKARD,  R.  L. 

Genesis  of  Nickel  Ores.—  Min.  Res.,  U.  S.  G.  S.,  pp.  170-177  (1893). 
VON  PALFY,  M. 

Das  Goldvorkommen  im  Siebenbiirgischen  Erzgebirge  und   sein  Verhaltnis 
zum  Nebengestein   der  Giinge. — Zeit.  f.  prak.   Geol.,  vol.  15,   pp.   144-148 
(1907). 
PAGE,  DAVID. 

Economic  Geology  (London,  1874).     336  pp. 
PAIGE,  SIDNEY. 

Mineral  Resources  of  the  Llano-Burnet  Region,  Texas,  with  an  account  of 

the  Pre-Cambrian  Geology.— Bull.  450,  U.  S.  G.  S.,  p.  103  (1911). 
PAIGE,  S.,  EMMONS,  W.  H.,  and  LANEY,  F.  B. 

Copper.—  Bull.  470,  U.  S.  G.  S.  (1911).     47  pp. 
PALMER,  C. 

The  Geochemical  Interpretation  of  Water  Analyses.—  Bull.  479,  U.  S.  G.  S. 
(1911).  31pp. 

PARK,  JAMES. 

1.  The  Geology  and  Veins  of  the  Hauraki  Gold  Fields,  New  Zealand. — N* 
Z.  Inst.  Min.  Eng.  (1897).     105  pp. 

2.  On  the  Cause  of  Border  Segregation  in  Some  Igneous  Magmas. — Trans. 
Inst.  Min.  and  Met,  vol.  14,  pp.  537-541  (1904-1905). 

3.  Ore  Deposits  in  Relation  to  Thermal  Activity. — E.  and  M.  Jour.,  vol.  79, 
pp.  606-607  (1905). 

4.  A  Text-Book  of  Mining  Geologv  (London,  1906).     219  pp. 

5.  Magmatic  Segregation  in  its  Relation  to  the  Genesis  of  Certain  Ore-Bodies. 
—Trans.  N.  Z.  Inst.  Min.  Eng.,  vol.  38  ;  algo  N.  Z.  Mines  Rec.,  vol.  9,  pp. 
414-416  (1906). 

6:  Contact  Metamorphism  in  its  Relation  to  the  Genesis  of  Certain  Ore-De- 

rits. — Trans.  N.  Z.  Inst.  Min.  Eng.,  vol.  38  ;  also  N.  Z.  Mines  Rec.,  vol. 
yp.  476-477  (1906). 

7.  Thermal  Activity  in  its  Relation  to  the  Genesis  of  Certain  Metalliferous 
Veins.— Trans.  N.   Z.  Inst.  Min.  Eng.,  vol.  38;  also  N.  Z.  Mines  Rec.,  vol. 

.  9,  pp.  512-515  ;  vol.  10,  pp.  59-62  (1906). 

8.  Some   Principles   of  Concentration   in  River-Bed  Gravels. — Min.   Jour., 
vol.  84,  pp.  145-146  (1908). 

PARSONS,  H.  G. 

A  Handbook  to  Western  Australia  and  its  Goldfields  (London,  1894). 
PASLEY,  C.  S. 

The  Tin  Mines  of  Bolivia. — Trans.  Inst.  Min.  and  Met.,  vol.  7,  pp.   77-90 

(1908). 
PATERA. 

Zu  den  Beraerkungen  Sandbergers  iiber  die  Resultate  der  Untersuchungen 
von  Nebengestein  der  Pribramer  Erzgiinge. —  Verhand.  Geol.  Reichsanst.,  pp. 
86-88  (1888). 


888  ALPHABETICAL    LIST    OF    AUTHORS. 

PEARCE,  KICHARD. 

1.  On  Replacement  of  Walls.— Chem.  News,  vol.  ii.,  pp.  100-101  (1865). 

2.  Farther  Notes  on  Cripple  Creek  Ore.—  Proc.  Col.  Sci.  Soc..,  vol.  5,  pp.  11- 
16  (1894-1896). 

3.  The  Association  of  Gold  with  Other  Minerals  in  the  West. — Trans.  A.  L 
M.  E.,  vol.  18,  pp.  447-458  (1890). 

PEARCE. 

Nomenclature  of  Shoots. — Proc.  Aust.  Inst.  Min.  Eng.  (July,  1909). 
PENROSE,  K.  A.  F.,  JR. 

1.  Manganese  ;  Its  Uses,  Ores,  and  Deposits. — Ark.   Geol  Sur.     Ann.  Rept. 
for  1890,  vol.   1.  (1892).     642pp. 

2.  The  Superficial  Alteration  of  Ore  Deposits.—  Jour.   Geol,  vol.  2.  pp.  288- 
317  (1894). 

3.  Tin  Deposits  of  the  Malay  Peninsula.—  Jour.  Geol,  vol.  11,  pp.  135-154 
(1903). 

4.  Some  Causes  of  Ore  Shoots.—  Econ.  Geol,  vol.  5,  pp.  97-133  (1910). 
PENROSE,  K.,  and  CROSS,  W. 

Geology  and  Mining  Industries  of  Cripple  Creek  District,  Colo. — 17th  Ann. 

Rept.,  U.  S.  G.  S.,  Pt.  2,  pp.  263-403  (1896). 
PHALEN,  W.  C. 

1.  Origin  and  Occurrence  of  Certain  Iron  Ores  of  Northeastern  Kentucky. — 
Econ.  Geol.,  vol.  1,  pp.  660-669  (1906). 

2.  Potash — Occurrence  of  Potash  Salts  in  the  Bitterns  of  the  Eastern  United 
States.— Butt.  530,  U.  S.  G.  S.  (1911).     19  pp. 

PHILLIPS,  J.  A. 

1.  The  Rocks  of  the  Mining  Districts  of  Cornwall  and  Their  Relation  to  Met- 
alliferous Deposits. — Quar.  Jour.  Geol.  Soc.,  vol.  31,  pp.  319-345  (1875). 

2.  A  Contribution  to  the  History  of  Mineral  Veins. — Quar.  Jour.  Geol.  Soc., 
vol.  35,  pp.  390-396  (1879). 

3.  Connection  of  Certain  Phenomena  with  the  Origin  of  Mineral  Veins. — 
Phil.  Mag.,  4th  ser.,  vol.  42,  pp.  401-413  (1871). 

4.  Notes  on  the  Chemical  Geology  of  the  Gold-Fields  of  California. — Phil. 
Mag.,  4th  ser.,  vol.  36,  p.  321  (1868). 

5.  A  Treatise  on  Ore  Deposits  (London,  1884). 
PHILLIPS,  J.  A.,  and  Louis,  HENRY. 

A  Treatise  on  Ore  Deposits,  2nd  edition  (London,  1896).     943  pp. 
PILZ,  RICHARD. 

Die  Bleierzlagerstatten  von  Mazarron  in  Spanien. — Zeil  f.  prak.  Geol.,  vol.  13, 
pp.  385-409  (1905). 

PlRSSON,  L.   V. 

Rocks  and  Rock  Minerals.     Wiley  and  Son  (1908).     414  pp. 
PITTMAN,  E.  F. 

1.  On  the  Geological  Occurrence  of  the  Broken  Hill  Ore  Deposits. — Geol. 
Sur.  N.  S.  W.,  vol.  3,  Part  2  (1892). 

2.  Tin  Deposits  of  New  South  Wales.— Geol.  Sur.  N.  S.  W.  (1889). 
PORTER,  E.  A.,  and  ELLSWORTH,  C.  E. 

Mining  and  Water  Supply  of  Fortymile,  Seventymile,  Circle  and  Fairbanks 

Districts,  Alaska,  1911.— Bull.  520,  U.  S.  G.  S.  (1912).     63  pp. 
POSEPNY,  FRANZ. 

1.  The  Genesis  of  Ore  Deposits. — American  Institute  of  Mining  Engineers.    806 
pages.     Special  Volume.     (Contains  other  papers  also. )     (1902.) 

2.  The  Genesis  of  Ore  Deposits.— Trans.  A.  L  M.  E.,  vol.  23,  pp.  197-369 
(1893). 

3.  Reply  to  the  Discussion  of  No.  2,  by  Becker,  Emmons,  et  al. — Trans.  A.  I. 
M.  E.,  vol.  24,  pp.  962-980  (1894). 

4.  Uber  die  Entstehung  von  Blei,  und  Zinklagerstatten  in  aufloslichen  Ge- 
steinen.—  Zeit.  f.  prak.  Geol.,  vol.  1,  pp.  398-401  (1893). 

5.  Tiber  die  Bewegungsrichtung  der  Untererdischen  Zirkullerenden  Fliissig- 
keiten. — Compt.  rend,  de  la  3,  sess.  du  Congres  Intern.     (Berlin,  1885). 

6.  Die  Golddistrikte  von  Berezov  und  Mias  am  Ural. — Archiv  f.  prak.  Geol, 
vol.  2,  pp.  499-598  (1895). 


ALPHABETICAL    LIST    OF    AUTHORS.  889 

POSEPNY,  FRANZ. — Continued. 

7.  Zur  Genesis  der  Metalseifen.     Ost.  Zeit.  f.  Berg-  u.  Hutt.,  vol.  35,  p.  325 
(1887). 

8.  Die  Goldvorkommen  Bohmens  und  der  Nachbarlander.  — Archiv  f.  prak. 
Geol,,  vol.  2,  pp.  1-499  (1895). 

9.  Setzt  das  Gold  in  die  Tiefe?—  Ost.  Zeit.  f.  Berg-  u.  Hutt.,  vol.  15,  p.  169 
(1867). 

POSEWITZ. 

1.   Die  Zinninseln  im  Indischen  Ozeane. — Mittheilungen  der  Kaiserlich  ungarish 

geologischen  Anstalt,  vol.  7,  pp.  155-182  (1885)  ;  vol.  8,  pp.  59-106  (1886). 
POWER,  F.  D. 

The  Classification  of  Valuable  Mineral  Deposits. — Trans.   Aust.   Inst.    Min. 

Eng.  (1892). 
PRATT,  J.  H. 

1.  The  Occurrence,   Origin  and  Chemical    Composition  of    Chrormte,   with 
Especial  Reference  to  the  North  Carolina  Deposits. — Trans.  A.  I.  M.  E., 
vol.  '29,  pp.  17-39  (1899). 

2.  Separation  of  Alumina  from  Molten  Magmas,  and  the  Formation  of  Corun- 
dum.— Am.  Jour.  Sci.,  4th  ser.,  vol.  8,  pp.  227-231  (1899). 

3.  On  the  Origin  of  Corundum  associated  with  the  Peridotites  in  North  Caro- 
lina.— Am.  Jour.  Sci.,  4th  ser.,  vol.  6,  pp.  49-65  (1898). 

4.  Corundum  and  Its  Occurrence  and  Distribution  in  the  United  States. — 
Bull.  269,  U.  S.  G.  S.  (1906). 

PRATT,  J.  H.,  and  STERRETT,  D.  B. 

The  Tin  Deposits  of  the  Carolinas.—  Bull.  19,  No.  Car.   Geol.  Sur.  (1904). 

64pp. 
PRESCOTT,  BASIL. 

The  Occurrence  and  Genesis  of  the  Magnetite  Ores  of  Shasta  County,  Califor- 
nia.— Econ.  Geol,  vol.  3,  pp.  465-480  (1908). 
PRESTWICH,  JOSEPH. 

Chemical,  Physical  and  Stratigraphical  Geology  (Oxford,  1886). 
PRICHARD,  W.  A. 

Observations  on  Mother  Lode  Gold-Deposits,  California. — Trans.  A.  I.  M.  E., 

vol.  34,  pp.  454-466  (1903). 
PRIME,  FREDERICK,  JR. 

On  the  Occurrence  of  the  Brown  Hematite  Deposits  of  the  Great  Valley. — 

Trans.  A.  I.  M.  E.}  vol.  3,  pp.  410-422  (1875). 
PRINDLE,  L.  M. 

1.  The  Gold  Placers  of  the  Fortymile,  Birch  Creek,  and  Fairbanks  Regions, 
Alaska.— Bull.  251,  U.  S.  G.  S.  (1905).     89  pp. 

2.  The  Yukon-Xanana  Region,   Alaska.—  Bull.  295,    U.  S.   G.  S.  (1906). 
27  pp. 

3.  The  Fortymile  Quadrangle,  Yukon-Tanana  Region,  Alaska. — Bull.  375, 
U.  S.  G.  S.  (1909).     52pp. 

PRINDLE,  L.  M.,  and  HESS,  F.  L. 

1.  The  Rampart  Gold  Placer  Region,  Alaska.—  Butt.  280,  U.  S.  G.  S.  (1906). 
54  pp. 

2.  The  Fairbanks  and  Rampart  Quadrangles,  Yukon-Tanana  Region,  Alaska. 
With  a  Section  on  the  Rampart  Placers.— Bull.  337,  U.  S.  G.  S.  (1908). 
102  pp. 

PRINDLE,  L.  M.,  and  KATZ,  F.  J. 

The  Fairbanks  Gold  Placer  Region,  Alaska.—  B  M.  379,  U.  S.   G.  S.,  pp. 

181-200  (1903). 
PRINDLE,  L.  M.,  and  MERTIE,  J.  B.,  JR. 

Gold  Placers  between  Woodchopper  and  Fourth  of  July  Creeks,  Upper  Yukon 

Valley,  Alaska.— Bull.  520,  U.  S.  G.  S.  (1912).     12  pp. 
PUMPELLY,  RAPHAEL. 

1.  Metasomatic  Development  of  the  Copper-Bearing  Rocks  of  Lake  Superior. 
— Proc.  Am.  Acad.  Arts  and  Sci. ,  1877-1878,  vol.  13,  pp.  253-310  (1878). 

2.  The  Paragenesis  and  Derivation  of  Copper  and  its  Associates  on  Lake  Supe- 
rior.— Am.  Jour.  Sci.,  3d  ser.,  vol.  2,  p.  33  (1891). 

3.  Ore  Deposits. — Johnson's  Encyclopaedia.     Edition  of  1877,  vol.  3,  pp.  974- 
981. 

56 


890  ALPHABETICAL    LIST    OF    AUTHORS. 

PURINGTON,  C.   W. 

1.  Preliminary  Report  on  the  Mining  Industries  of  the  Telluride  Quadrangle^ 
Colorado.— ISth  Ann.  Eept.,  U.  S.  G.  S.,  part  3,  pp.  745-848  (1897). 

2.  The  Platinum-Deposits  of  the  Tura  River-System,  Ural  Mountains,  Rus- 
sia.— Trans'.  A.  I.  M.  E.,  vol.  29,  pp.  3-16  (1899). 

3.  Observations  on  Gold  Deposits. — E.  and  M.  Jour.,  vol.  75,  pp.  854-855; 
893-894;  929-931  (1903). 

4.  The  Occurrence  of  Platinum  in  the  Ural  Mts. — E.  and  M.  Jour.,  vol.  77, 
pp.  720-722  (1904). 

5.  Ore  Horizons  in  the  Veins  of  the  San  Juan  Mountains. — Econ.  GeoL,  vol. 
1,  pp.  129-133  (1906). 

6.  Methods  and  Costs  of  Gravel  and  Placer  Mining  in  Alaska. — Bull.  263,  U. 
S.  G.  S.  (1905).     273  pp. 

7.  The  Camp  Bird  and  Smuggler   Union  Fissure  (Colorado). — E.  and  M. 
Jour.,  vol.  79,  pp.  1243-1244  (1905). 

PURINGTON,  C.  W.,  WOODS,  T.  H.,  and  DOVETON.  G.  D. 

The  Camp  Bird  Mine,  Ouray,  Colorado,  and  the  Mining  and  Milling  of  the 
Ore.— Trans.  A.  I.  M.  E.,  vol.  33,  pp.  499-550  (1902). 

QUENEAU,   A.   L. 

The  Gold  Sands  of  Cape  Nome  [Alaska].—  Eng.  Mag.,  vol.  23,  pp.  497-510 
(1902). 


RADFORD,  G.  K. 

Mining  for  Gold  in  the  Auriferous  Gravels  of  California,  U.  S.  A. — Trans. 

Inst.  Min.  Eng.,  vol.  17,  pp.  452-481  (1898-99). 
RAINER. 

Vorkommen  und  Gewinnung  des  platins  im  Ural. — Leoben  Jahrbuch,  L.,  pp. 

255-298  (1902). 
RAKLI,  GEORGES. 

1.  The  Lead  Mines  of  Balia,  Turkey.—  E.  and  M.  Jour.,  vol.  77,  p.  274  (1904). 
RANGEL,  VILLARELLO  and  BOSE. 

Los  Criaderos  de  fierre  del  cerro  Mercado,  Durango,  Mexico. — Bol.  16,  Inst. 

GeoL  de  Mex.  (1902). 
KANSOME,  F.  L. 

1.  A  Peculiar  Clastic  Dike  near  Ouray,  and  its  Associated  Deposit  of  Silver 
Ore.— Trans.  A.  L  M.  E.,  vol.  30,  pp.  227-236  (1900). 

la.  Geological  Atlas  of  the  U.  S.— Mother  Lode  Special  Folio,  No.  63  (1900). 

2.  A  Report  on  the  Economic  Geology  of  the  Silverton  Quadrangle,  Colorado. 
—Bull.  182,  U.  S.  G.  S.  (1901).     265  pp. 

3.  The  Ore  Deposits  of  the  Rico  Mountains,  Colorado. — 22d  Ann.   Rept.,   U. 
S.  G.  S.,  part  2,  pp.  229-397  (1901). 

4.  The  Geology  and  Copper  Deposits  of  Bisbee,  Arizona. — Trans.  A.  I  M.  E., 
vol.  34,  pp.  618-642  (1903). 

5.  Geology  of  the  Globe  Copper  District,  Arizona. — Prof.  Paper  12,  17.  S. 
G.  S.  (1903).     168  pp. 

6.  Geology  and  Ore  Deposits  of    the  Bisbee  Quadrangle,   Arizona. — Prof. 
Paper  21,   U.  S.  G.  S.  (1904).     168  pp. 

7.  The  Geographic  Distribution  of    Metalliferous   Ores  within  the  United 
States.—  Min.  Mag.  (J],  vol.  10,  pp.  7-14  (1904). 

8.  The  Directions  of  Movement  and   the   Nomenclature   of  Faults. — Econ. 
GeoL,  vol.  1,  pp.  773-783  (1906). 

9.  The  As'sociation  of  Alunite  with  Gold  in  the  Goldfield  District,  Nevada. — 
Econ.  GeoL,  vol.  2,  pp.  667-692  (1907). 

10.  Preliminary  Account  of  Goldfield.   Bullfrog,  and  other  Mining  Districts 
in  Southern  "Nevada.—  Bull.  303,  U.  S.  G.  S.,  pp.  7-83  (1907). 

11.  The  Relation  between  Certain  Ore-Bearing  Veins  and  Gangue-Filled  Fis- 
sures.—Econ.  GeoL,  vol.  3,  pp.  331-337  (1908). 

12.  A  Theory  of  Ore  Deposition.— Econ.  GeoL,  vol.  3,  pp.  420-425  (1908). 

13.  Notes  on  some  Mining  Districts  in  Humboldt  County,  Nevada. — Bull.  414, 
U.  S.  G.  S.  (1909).     75pp. 


ALPHABETICAL    LIST    OF    AUTHORS.  891 

RANSOME,  F.  L. — Continued. 

14.  The  Geology  and  Ore  Deposits  of  Goldfield,  Nevada.—  Prof.  Paper  66, 
U.  S.  G.  S.  (1909).     258  pp. 

15.  Criteria  of   Downward  Sulphide    Enrichment. — Econ.    GeoL,  vol.  5,  pp. 
205-220  (1910). 

16.  Geology  and  Ore  Deposits  of  the  Goldfield  District,  Nevada. — Econ.  GeoL, 
vol.  5,  pp.  301-311  ;  438-470  (1910). 

17.  The  Literature  of  Ore-deposits  in  1910.— Econ.  GeoL,  vol.  6,  pp.  325-339 
(1911). 

18.  Geology  and  Ore  Deposits  of  the  Breckenridge  District,  Colorado. — Prof. 
Paper  75,  U.  S.  G.  S.  (1911).     187  pp. 

19.  The  Turquoise  Copper  Mining  District,  Arizona.—  Bull.  530,  U.  S.  G.  S. 
(1912).      12pp. 

RANSOME,  F.  L. ,  and  CALKINS,  F.  C. 

The  Geology  and  Ore  Deposits  of  the  Coaur  d'Al^ne  District,  Idaho. — Prof. 

Paper  62,  U.  S.  G.  S.  (1908).     203  pp.  , 
RANSOME,  F.  L.,  EMMONS,  W.  H.,  and  GARREY,  G.  H. 

Geology  and  Ore  Deposits  of  the  Bullfrog  District,  Nevada. — Bulletin  407, 

U.  S.  G.  S.  (1910).     130pp. 
RAYMOND,  R.  W. 

1.  Mining  Statistics  for  1869. 

2.  Mineral  Resources  West  of  the  Rocky  Mts. — Report  of  the  Mining  Commis- 
sioner, 1870-1876.     7  volumes. 

3.  The  Geographical  Distribution  of  Mining  Districts  in  the  United  States. — 
Trans.  A.  I.  M.  E.,  vol.  1,  pp.  33-39  (1871-73). 

4.  Hoefer's  Method  of  Determining  Faults  in  Mineral  Veins. — Trans.  A.   I. 
M.  E.,  vol.  10,  pp.  456-465  (1882). 

5.  A  New  Classification  of  Economic  Geological  Deposits. — E.  and  M.  Jour., 
vol.  58,  pp.  412-413  (1894). 

6.  Recent  Contributions  to  the  Science  of  Ore-Deposits.     (A  general  review 
of  progress,   chiefly  of  historical  value). — Min.  Ind.,  vol.  9,  pp.  753-762 
(1900). 

READ,   T.  T. 

1.  The  Phase  Rule  and  Conceptions  of  Igneous  Magmas.     Their  Bearing  on 
Ore  Deposition.—  Econ.  GeoL,  vol.  1,  pp.  101-118  (1906). 

2.  The  Secondary  Enrichment  of  Copper-Iron  Sulphides. — Trans.  A.  L  M. 
E.,  vol.  37,  pp.  297-303  (1906). 

RECKNAGEL,  R. 

On  the  Origin  of  the  South  African  Tin  Deposits.-- Trans.   GeoL  Soc.  So. 

Af.,  vol.  12,  pp.  168-202  (1909). 
REDLICH,  K.  A. 

1.  Sedimenlaire  ou  Epigenetique  ?    Contribution  a  la  connaissance  des  Gites 
M6tallif£res  des  Alps  orientales.— Congres  Int.  des  Mines  (1905).     9  pp. 

2.  Die  Genesis  der  Pinolit-ma°:nesite,  Siderite  und  Ankerite  der  Ostalpen. — 
Tscher.  Min.  u.  Pet.  Mitt.,  vol.  26. 

REID,  J.  A. 

1.  The  Structure  and  Genesis  of  the  Comstock  Lode.—  Bull.  Dept.  GeoL,  Univ. 
CaL,  vol.  4,  pp.  177-199  (1905). 

2.  A  Sketch  of  the  Geology  and  Ore  Deposits  of  the  Cherry  Creek  District, 
Arizona.— Econ.  GeoL,  vol.  1,  pp.  417-436  (1906). 

3.  The  Ore-Deposits  of  Copperopolis,  Calaveras  County,  California. — Econ. 
GeoL,  vol.  2,  pp.  380-417  (1907). 

4.  Discussion  of  Ransome  8.—  Econ.  GeoL,  vol.  2,  pp.  298-308  (1907). 
REID,  H.  F. 

Proposed  Nomenclature  of  Faults.— Advance  Bull.   G.  S.  A.  (May,  1912). 

17pp. 
REYER.  E. 

1.  Theoretische  Geologic  (1888). 

2.  Zinn  (Berlin,  1881).     248  pp. 

3.  Zinn  in  Australien  und  Tasmanien. — Ost.  Zeit.  f.  Berg- u.  Hiitt.,  vol.  28, 
pp.  47-49,  61-63,  74-76,  85-87  (1880). 

VON  RlCHTOFEN,  F. 

Studien    an    den    ungarisch-siebenbiirgischen    Trachytgebirgen. — Jahrb.  der 
K.  K.  GeoL  Reichsanst,,  p.  275  (1860). 


892  ALPHABETICAL    LIST    OF    AUTHORS. 

EICKARD,  EDGAR. 

Tin  Deposits  of   the  York  Kegion,  Alaska. — E.  and  M.  Jour.,  vol.  75,  pp. 

30-31  (1903). 
EICKARD,  FORBES. 

1.  Notes  on  the  Vein-Formation  and  Mining  of  Gil  pin  County,  Colorado. — 
Trans.  A.  L  M.  E.,  vol.  28,  pp.  108-126  (1898). 

2.  Notes  on  Nome,  and  the  Outlook  for  Vein-Mining  in  the  District  (Alaska). 
—E.-and  M.  Jour.,  vol.  71,  pp.  275-276  (1901), 

EICKARD,  T.  A. 

1.  The  Mount  Morgan  Mine,  Queensland. — Trans.  A.  I.  M.  E.,  vol.  20,  pp. 
133-155  (1891). 

2.  The  Bendigo  Gold-Field.— Trans.  A.  I.  M.  E.,  vol.  20,  pp.  463-545  (1891). 

3.  The  Gold  Fields  of   Otago.— Tram*.  A.  L  M.  E.,  vol.   21,  pp.  411-442 
(1893). 

4.  The  Bendigo  Gold-Field  (Second  Paper)  ;   Ore  Deposits  other  than  Sad- 
dles.— Trans.  A.  L  M.  E.,  vol.  21,  pp.  686-713  (1893). 

5.  The  Origin  of  the  Gold-Bearing  Quartz  of  the  Bendigo  Eeefs,  Australia. — 
Trans.  A.  L  M.  E.}  vol.  22,  pp.  289-321  (1893). 

6.  The  Mines  of  the  Chalanches,  France.— Trans.  A.  L  M.  E.,  vol.  24,  pp. 
689--705  (1894). 

7.  The  Genesis  of  Ore-Deposits  (Discussion  of  Posepny's  Paper). — Trans. 
A.  L  M.  E.,  vol.  24,  pp.  942-956  (1894). 

8.  Vein- Walls.— Trans.  A.  L  M.  R,  vol.  26,  pp.  193-242  (1896). 

9.  The  Enterprise  Mine,  Eico,  Colorado.— Trans.  A.  L  M.  E.,  vol.  26,  pp. 
906-980  (1896. 

10.  The  Minerals  which  Accompany  Gold  and  their  Bearing  upon  the  Eieh- 
ness  of    Ore  Deposits. — Trans.   Inst.   Min.   and  Met.,  vol.   6,   pp.  194-214 
(1898). 

11.  The  Alluvial  Deposits  of  Western  Australia.— Trans.  A.  L  M.  E.,  vol.  28, 
pp.  490-537  (1898). 

12.  The  Telluride  Ores  of  Cripple  Creek  and  Kalgoorlie.— Trans.  A.  I.  M.  E., 
vol.  30,  pp.  708-719  (1900). 

13.  The  Indicator  Vein,   Ballarat,   Australia.— Trans.   A.   L  M.  E.,  vol.  30, 
pp.  1004-1020  (1900). 

14.  The   Formation  of  Bonanzas   in  the  Upper  Portions  of  Gold-Veins. — 
Trans.  A.  I.  M.  E.,  vol.  31,  pp.  198-220  (1901). 

15.  The  Lodes  of  Cripple  Creek.— Trans.  A.  L  M.  E.,  vol.  33,  pp.   578-618 
(1902). 

16.  The  Veins  of  Boulder  and  Kalgoorlie.— Trans.  A.  L  M.  E.,  vol.  33,  pp. 
567-577  (1902).'  • 

17.  Eecent  Progress  in  the  Study  of  Ore  Deposits. — E.  and  M.  Jour.,  vol.  73, 
pp.  106-107  (1902). 

18.  The  Copper  Mines  of  Lake  Superior  (1905).     164  pp. 

19.  The  Geological  Distribution  of  Gold.— Min.  andSci.  Press,  vol.  93,  pp.  477- 
480   (1906);   Mines  and  Minerals,  vol.  27,  pp.  256-257  (1907);  Rept.  Proc. 
Am.  Min.  Cong.,  9th  Ann.  Sess.,  pp.  226-283  (1907). 

20.  Waters,   Meteoric  and  Magmatic. — Min.  and  Sci.  Press.,  vol.  96,  pp.  872- 
875  (1908). 

21.  Geological  Distribution  of  the  Precious  Metals  in  Colorado,  1. — Min.  and 
Sci,  Press.,  vol.  100,  pp.  89-96  (1910). 

EICKARD,  T.  A.,  et  al. 

1.  Ore  Deposits:  A  Discussion.— E.  and  M.  Jour.  (1903).     90pp. 

2.  Water  in  Veins  :  A  Theory.— E.  and  M.  Jour.,  vol.  75,  pp.  402-403,  589- 
590,  624,  661,  776,  848  ;  vol.  76,  p.  117  (1903). 

ElCKETTS,  L.    D. 

Faulting  in  Veins.—  E.  and  M.  Jour.,  vol.  53,  pp.  565-566  (1892). 
EIES,  HEINRICH. 

Economic  Geology  with  Special  Eeference  to  the  United  States.     Eevised 
ed.  (New  York,  1910).     589  pp. 

ElMANN,  E. 

Magmatische  Ausscheidung  von  Zinkblende  in   Granit. — Zeit.  f.  prak.  Geol., 
vol.  18,  pp.  123-124  (1910). 


ALPHABETICAL    LIST    OF    AUTHORS.  893 

HITTER,  E.  A. 

1.  The  Evergreen  Copper-Deposit,  Colorado. — Trans.  A.  I.  M.  E.,  vol.  38, 
pp.  751-766  (1907). 

2.  Ore  Formation  in  the  Wonder  District,  Nevada. — E.  and  M.  Jour.,  vol. 
87,  pp.  289-292  (1909). 

ROBERTSON,  J.  D. 

The  Missouri  Lead  and  Zinc  Deposits. — Am.  GeoL,  vol.  15,  pp.  235-248  (1895). 

R5LKER,   C.   M. 

1.  The  Alluvial  Tin  Deposits  of  Siak,  Sumatra.— Trans.  A.  I.  M.  E.,  vol.  20, 
pp.  50-84  (1892). 

2.  The  vSilver  Sandstone  District  of  Utah.— Trans.  A.  I.  M.  E.,  vol.  9,  pp. 
21-33  (1880). 

3.  Note  on  an  Exhibition  of  Banded  Structure  in  a  Gold- Vein. — Trans.  A.  I. 
M.  E.,  vol.  14,  pp.  265-266  (1885). 

ROLLIER,  L. 

liber  das  Bohnerz  und  seine  Entstehungsweise. —  Verh.  d.  Naturf.  Geo.,  Zurich, 

1905,  pp.  150-162  ;  Abstract  Stahl  und  Eisen,  vol.  25,  p.  1270  (1905). 
ROSE. 

Reise  nach  dem  Ural,  vol.  1,  pp.  325-338  (1837)  ;  vol.  2,  pp.  386-401  (1842). 

ROSENBUSCH,  H. 

Uber  die  chemische  Beziehungen  der  Eruptivgesteine. — Tscher.  Min.  u.  Pet. 
Mitt.,  vol.  11,  pp.  144-178  (1890). 

ROTHWELL,  R.  P.  , 

The   Silver  Sandstone  Formation  of  Silver  Reef. — E.  and  M.  Jour.,  vol.  29, 

pp.  25,  48,  79  (1880). 
ROTH,  J. 

Allgemeine  und  Chemische  Geologic  (1879). 
RUHL,  OTTO.. 

Unconformity  and   Deposits. — Min.    and   Sci.    Press,  vol.   96,   pp.    778-780 
(1908). 

RUMBOLD,  W.   R. 

1.  The  Origin  of  the  Bolivian  Tin  Deposits. — Econ.   GeoL,  vol.  4,  pp.   321- 
364  (1909). 

2.  The  Tin  Deposits  of  the  Kinta  Valley,  Federated  Malay  States.— Trans. 
A.  I.  M.  E.,  vol.  37,  pp.  879-889  (1906). 

RUSSELL,  I.  C. 

A  Geological  Reconpaisance  in  Southern  Oregon. — kth  Ann.  Rept.,  U.  S.  G.  S., 
1882-83,  pp.  431-464  (1884). 

RUTLEDGE,  J.  J. 

The  Clinton  Iron  Ore  Deposits  in  Stone  Valley,  Huntingdon  County,  Penn- 
sylvania.—Trans.  A.  I.  M.  E.,  vol.  40,  pp.  134-164  (1909). 
RUTTMAN,  F.  S. 

Notes  on  the  Geology  of  the  Tilly  Foster  Ore- Body,  Putnam  County,  N.  Y.— 

Trans.  A.  1.  M.  E.,  vol.  15,  pp.  79-92  (1886). 
RYBA,  FRANZ. 

Beitrag  zur  Genesis  der  Chromeisenerzlagerstatte  bei  Kraubat  in  Obersteier- 
mark.—  Zeit.  f.  prak.  GeoL,  vol.  8,  pp.  337-341  (1900). 

SALES,  R.  H. 

1.  Superficial  Alteration  of  the  Butte  Veins. — Econ.  GeoL,  vol.  5,  pp.  15-21 
(1910). 

2.  Ore  shoots  at  Butte,  Montana.— Econ.  GeoL,  vol.  3,  pp.  326-331  (1908). 
SAMUELS,  L.  A. 

Origin  of  the  Bendigo  Saddle  Reefs  (Bendigo,  1893).     40  pp. 
SANDBERGER,  F. 

1.  Zur  Theorie  der  Bildung  der  Erzgiinge. — Berg-  u.  Hiltt.  Zeit.,  vol.  36,  pp. 
377-381,  389-392  (1877). 

2.  Uber  die  Bildung  von  Erzgiingen  mittelst  auslaugung  des  Nebengesteins. 
— Berg-  u.   Hiitt.   Zeit.,  vol.   39,  pp.   329-331,  337-339,   390-392.  402-405 
(1880). 

3.  Untersuchungen   uber  Erzgange.     2  vol.     (1883-1885).     Abstract  in  E. 
and  M.  Jour.,  vol.  37,  pp.  196-198,  218-219,  232-233  (1884). 


894  ALPHABETICAL    LIST    OF    AUTHORS. 

SANDBERGER,  F. — Continued. 

4.  Neue  Beweise  fur  die  Abstammung  der  Erze  aus  dem  Xebengestein. —  Ver- 

hand.  der  Wiirz.  Phys.  Med.  Gesel.,  1883  ;  Neu.es  Jahrb.  f.  Min.,  p.  291  (1878). 

•  5.  Theories  of  the  Formation  of  Mineral  Veins. — E.  and  M.  Jour.,  vol.  37, 

pp.  196-198,  218-219,  232-233  (1884). 
6.  Untersuchungen  an  den   Erzgangen    von    Pribram   in   Bohmen. — Sitz.  d. 

Wiirz.  Phys.  Med.  Gesel.  (18-6). 
SANDEMAN. 

The  Mineral  Kesources  of  Tasmania. — Trans.  Fed.  Inst.  Min.  Enq.,  vol.   18, 

pp.  24-41  (1899-1900). 
SASS,  C. 

Beobachtungen  von  Schwankungen  des  Grundvvassers. — Zeit.  f.  prak.   Geol.. 

pp.  297-300  (1901). 
SAWYER. 

The  Tarcquah  Goldfield,  Gold  Coast,  West  Africa.— Trans.  Fed.  Inst.  Min. 

Eng.,voL  22,  pp.  402-417  (1901-02). 
SAYTZEFF,  A. 

Die  Platinlagerstatten  am  Ural.     Tomsk,  1898.— Abstract  in  Zeit.  f.  prak. 
Geol.,  vol.  6,  pp.  395-398  (1898). 

SCHAEFFER,  C.   A. 

Notes  on  Tantalite  and  other  Minerals,  accompanying  the   Tin-Ore  in  the 
Black  Hills.— Trans.  A.  I.  M.  E.,  vol.  13,  pp.  231-233  (1884). 

SCHARTTZER,  E. 

Beitrage  zur  Kenntniss  der  chemigchen  Kon^stitution  und  der  Genese  der 
naturlichen  Eisensulfate.—  Zeit.  f.  Krist.,  vol.  43,  pp.  113-129  (1907). 

SCHEERER,  TH. 

Die  Gneuse  des    Sachsischen   Erzegebirges   und   verwandte   Gesteine,    uach 
ihrer  chemischen  Konstitution  und  Geologischen  Bedeutung. — Zeit.  d.  D. 
Geol.  Gesel.,  vol.  14.  pp.  23,  et  seq.  (1862). 
SCHIERL,  A. 

Einteilung  der  Erzlagerstatten  und  kurze  Darstellung  der  Theorien  iiber  die 
Entstehung  von  Erzgangen. — 22  Jahr.  d.  Landes-Oberrealschule  in   Mahr. 
Ostrau,  1904-05,  pp.  3-13. 
SCHMEISSER,  KARL. 

The  Gold  Fields  of  Australasia  (London,  1898).     254  pp. 
SCHMIDT,  ALBRECHT. 

Uber  Kupfer  und  die  Entstehung  der  Kupfererze. — Sera-  u.  Hiltt.  JRund.,  pp. 

85-90  (1910). 
SCHMIDT,  J.  C.  L. 

Theorie der  Verschiebung  Alterer  Gange  (Frankfurt,  1910). 
SCHMIDT  and  PREISWERK. 

Les  Mines  de  Fer  et  de  Cuivre  de  Cala. — Rev.  Univ.  d.  Mines,  4th  ser.,  vol.  11, 
p.  217  (1905). 

SCHMITZ,  E.  J. 

Copper-Ores  in  the  Permian  of  Texas.— Trans.  A.  I.  M.  E.,  vol.  26,  pp.  97- 

108  (1897). 
SCHOCH,  E.  R. 

The  Genesis  of  the  Tarkwa  Banket.—  E.  and  M.  Jour.,  vol.  79,  pp.  1235-1236 

(1905). 

SCHRADER,  F.   C. 

1.  Notes  on  the  Antelope  District,  Nevada.—  Bull.  530,  U.  S.  G.  S.  (1912). 
14  pp. 

2.  A  Reconnaissance  of  the  Jarbidge  Contact  and  Elk  Mountain  Mining  Dis- 
tricts, Elko  County,  Nevada.— Bw//.  497,  U.  S.  G.  S.  (1912).     162  pp. 

SCHRADER,  F.  C.,  and  BROOKS,  A.  H. 

1.  Preliminary  Report  on  the  Cape  Nome  Gold  Region,  Alaska. —  U.  S.  G.  S. 
(1900).     56  pp. 

2.  Some  Notes  of  the  Nome  Gold  Region  of  Alaska. — Trans.  A.  I.  M.  E.,  vol. 
30,  pp.  236-248  (1900). 

SCHRADER,  F.  C.,  and  HAWORTH,  ERASMUS. 

Economic  Geology  of  the    Independence  Quadrangle,    Kansas. — Bull.    296, 
U.  S  G.  S.  (19U6).     74  pp. 


ALPHABETICAL    LIST    OF    AUTHORS.  895 

SCHRADER,  F.  C.,  and  SPENCER,  A.  C. 

The  Geology  and  Mineral  Resources  of  a  Portion  of  the  Copper  River  District, 
Alaska.  —  U.  S.  G.  S.,  Special  Reports  on  Alaska  (1901).  94  pp. 

SCHRAUF,   A. 

Uber  Metacinnabarit  von  Idria  und  dessen  Paragenesis.  — Jahr.  d.  K,  K.  Geol. 
Reichsanst.,  vol.  41,  pp.  349-400  (1891). 

SCHROEDER. 

Uber  Zinnerzgange  des  Eibenstocker  Granitgebiets  und  die  Entstehung  der~ 
selben. — Sitzungsberichte  der  naturhistorischen  Gesellschofi  zu  Leipzig  (1883). 
Rev.  Neues  Jahrb.  f.  Min.,  vol.  1,  p.  268  (1887). 

SCHURTZ. 

Der  Seifenbergbau  in  Erzgebirge  und  die  Walensagen  (1890).    ( Cited  by  Ber- 

geat-Stelzner,  p.  1289.) 
SCHWA  RZ,  T.  E. 

1.  The  Ore- Deposits  of  Red  Mountain,  Ouray  County,  Colorado. — Trans.  A. 
I.  M.  E.,  vol.  18,  pp.  139-145  (1889). 

2.  Features  of  the  Occurrence  of  Ore  at  Red  Mountain,  Ouray,  Colorado. — 
Trans.  A.  I.  M.  E.,  vol.  36,  pp.  31-39  (1905). 

SCOTT,  H.  K. 

1.  The  Manganese  Ores  of  Brazil. — Jour.   Iron  and.   Steel  Imt.,  vol.  57,  pp. 
179-218  (1900). 

2.  The  Gold  Field  of  the  State  of  Minus  Geraes,  Brazil.— TVa MX.  A.  I.  M.  E., 
vol.  33,  pp.  406-444  (1902). 

SCRIVENOR,  J.    H. 

The  Origin  of  Tin  Deposits.—  Min.  Jour.,  vol.  85,  pp.  307,  340  (1909). 
SERLO,  ALBERT. 

Leitfaden  zur  Bergbaukunde.     Dritte  Aufl.,  vol.  1  (Berlin,  1878). 
SHARPLES,  S.  P. 

Note  on  Black  Band  Iron  Ore  in  West  Virginia. — Trans.  A.  7.  M.  E.,  vol. 

10,  pp.  80-81  (1&82». 
SHARWOOD,  W.  J. 

Notes  on  Tellurium-bearing  Gold  Ores.— Econ.  Geol.,  vol.  6,  pp.  22-36  (1911). 

SIMPSON,  J.  F. 

The  Relation  of  Copper  to  Pyrite  in  the  Lean  Copper  Ores  of  Butte,  Mon- 
tana.— Ecvn.  Geol.,  vol.  3,  pp.  628-63(3  (1908). 

SlNOEWALD,  J.   T.,  JR. 

1.  The  Erzgebirge  Tin  Deposits.—  Econ.  Geol,  vol.  5,  pp.  166-177,  265-272 
(1910). 

2.  The    Mount  Roudny   Gold  Deposits.— Econ.   Geol.,   vol.  5,  pp.    257-264 
(1910). 

SJOGREN,  A. 

Om  forekomstren  af  Tabergs  jernmalmsfindighet  i  Smaland. — Geol.    Fb'ren. 

Fohr.,  vol.  3,  pp.  42-62  (1876-7).     Rev.  in  Neues  Jahrb.  f.  Min.,  pp.  434- 

435  (1876). 
SJOGREN,  HJALMAR. 

1.  Beitrage  zur  kentnissder  Erzlagerstatten  von  Moraviczaund  Dognaeska  ira 
Banat   und  Vergleichung  derselben  mit  den  Schwedischen  Eisenerzlager- 
stlitten.—  Jahrb.  d.  K.  K.  Geol.  Reichsanst.,  vol.  36,  pp.  607-668  (1886). 

2.  Uber    die    Entstehung    der    schwedischen    Eisenerzlager. — Geol.    For.    i 
Stock.  Forhand.,   vol.  13,  p.  373  et  seq.  (1891)  ;  Rev.  in  Zeit.  f.  prak.  Geol., 
vol.  1,  pp.  434-437  (1893). 

3.  The  Geological  Relations  of  the  Scandinavian  Iron-Ores  — Trans.  A.  I.  M. 
E.,  vol.  38,  pp.  766-835  (1907).     Rev.  by  Leith  in  Econ.  Geol,  vol.  3,  pp. 
658-661  (1908). 

4    The  Localization  of  Values  in  Ore  Bodies  and  the  Occurrence  of  Shoots  in 

Metalliferous  Deposits.— Econ.  Geol.,  vol.  3,  pp  637-643  (1908). 
SKEWES,  EDWARD. 

The  Ore-Shoots  of  Cripple  Creek.— Trans.  A.  I.  M.  E.,  vol.  26,  pp.  553-579 
(1896). 


896  ALPHABETICAL    LIST    OF    AUTHORS. 

SLIGHTER,  C.  S. 

1.  Theoretical  Investigation  of  the  Motion  of   Ground- Waters. — 19th  Ann. 
Rept.,  U.  S.  G.  S.,  Part  2,  pp.  295-384  (1899). 

2.  The  Motions  of  Underground  Waters.— Prof.  Paper  67,  U.  S.  G.  S.,  Water 
Supply  and  Irrigation  (1902).     106  pp. 

SMITH,  A.  M. 

Geology  of  the  Kolar  Gold  Field. — Trans.  Inst.  Min.  and  Met,  vol.  13,  pp. 

151-180  (1903-1904). 
SMITH,  F.  C. 

1.  The  Potsdam  Gold-Ores  of  the  Black  Hills  of  South  Dakota.  —  Trans.  A.  L 
M.  E.,  vol.  27,  pp.  404-428  (1897). 

2.  Localization  of  Values  in  Ore  Bodies  and  Occurrence  of   "Shoots"   in 
Metalliferous  Deposits.—  Econ.  Geol.,  vol.  3,  pp.  224-229  (1908). 

SMITH,  GEORGE. 

1.  The  Ore-Deposits  of  the  Australian  Broken  Hill  Consols  Mine,  Broken 
Hill,  New  South  Wales.— Trans.  A.  I.  M.  E.,  vol.  26,  pp.  69-78  (1896). 

2.  The  Garnet  Formations  of  the  Chillagoe  Copper-Field,  North  Queensland, 
Australia.— Trans.  A.  I.  M.  E.,  vol.  34,  pp.  467-478  (1903). 

SMITH,  G.  O. 

Gold  Mining  in  Central  Washington.— Bull.  213,    U.  S.  G.  S.,  pp.  76-80 

(1903). 
SMITH,  G.  O.,  and  WILLIS,  BAILEY. 

The  Clealum  Iron-Ores,  Washington.— Trans.  A.  I.  M.  E.,  vol.  30, pp.  356-367 

(1900). 
SMITH,  P.  S. 

1.  The  Gray  Iron  Ores  of  Talladega  County,  Alabama.— Bull.  315,  U.  S.  G.S., 
pp.  161-184  (1908). 

2.  The  Alatna-Noatak    Region,    Alaska.—  Bull.    520,    U.  S.    G.   S.    (1912). 
12pp. 

SMITH,  P.  S.,  and  EAKIN,  H.  M. 

A  Geologic  Reconnaissance  in  Southeastern  Seward  Peninsula  and  the  Norton 

Bay-Nulato  Eegion,  Alaska.—  Bull.  449,  U.  S.  G.  S.  (1911).     146  pp. 
SMITH,  W.  N. 

Loon  Lake  Iron-Bearing  District. — Rept.  Ont.  Bu.  Mines,  vol.  14,  Pt.  1,  pp. 

254-260  (1905). 
SMITH,  W.  S.  T.,  and  SIEBENTHAL,  C.  E. 

Description  of  the  Joplin  District  [Missouri-Kansas]. — Folio  148,  U.  S.  G.  S. 
(1907).     20  pp. 
SMOCK,  J.  C. 

Geologic-Geographical  Distribution  of  the  Iron  Ores  of  the  Eastern  United 

States.— rl Vans.  A.  L  M.  E.,  vol.  12,  pp.  130-144  (1884). 
SMYTH,  C.  H.,  JR. 

1.  On  the  Clinton  Iron  Ore—  Am.  Jour.  Sci.,  3d  ser.,  vol.  43,  pp.  487-496 
(1892). 

2.  The  Genetic  Relations  of  Certain  Minerals  of  Northern   New  York. — 
Trans.  New  York  Acad.  Sci.,  vol.  15,  pp.  260-271  (1896). 

3.  Replacement  of  Quartz  by  Pyrite  and  Corrosion  of  Quartz  Pebbles. — Am. 
Jour.  Sci.,  4th  ser.,  vol.  19,  pp.  277-285  (1905). 

SMYTH,  H.  L. 

1.  The  Origin  and  Classification  of  Placers. — E.  and  M.  Jour.,  vol.  79,  pp. 

1045-1046,  1179-1180,  1228-1230  (1905). 
2.  The  Relations  Between  Gold  and  Pyrite. — Min.  and  Sci.  Press,  vol.  93,  pp. 

58-59  (1906). 
SMYTH,  H.  L.,  and  FINLAY,  J.  R. 

The   Geological   Structure  of  the  Western   Part  of  the  Vermilion   Range, 

Minnesota.  — Trans.  A.  I.  M.  E.,  vol.  25,  pp.  595-645  (1895). 
SOPER,  E.  K. 

The   Genesis  of  Ore  Deposits.—  E.  and  M.  Jour.,  vol.  92,  pp.  897-900,  947- 

949  (1911). 
SORBY,  H.  C. 

Microscopical  Structure  of  Crystals  Indicating  the  Origin  of  Minerals  and 
•      Rocks.— Quar.  Jour.  Geol.  Soc.,  vol.  14,  pp.  453-500  (1858). 


ALPHABETICAL    LIST    OF    AUTHORS.  897 

SOUDER,  HARRISON. 

Mineral  Deposits  of  Santiago,  Cuba.— Trans.  A.  I.  M.  E.,  vol.  35,  pp.  308- 

321  (1904). 
SPENCER,  A.  C. 

1.  Genesis  of  the  Magnetic  Deposits  in  Sussex  County,  New  Jersey. — Min. 
Mag.  (J),  vol.  10,  pp.  377-381  (1904). 

2.  The  Copper  Deposits  of  the  Encampment  District,  Wyoming. — Prof.  Paper 
25.  U.  £  G.  S.  (1904).     107pp. 

3.  The  Geology  of  the  Tread  well  Ore-Deposits,   Douglas  Island,  Alaska. — 
Tram.  A.  /.  M.  E.,  vol.  35,  pp.  473-511  (1904). 

4.  The  Magmatic  Origin  of  Vein-Forming  Waters  in  Southeastern  Alaska. — 
Trans.  A.  I.  M.  E.,  vol.  36,  pp.  364-372  (1905). 

5.  The  Origin  of  Vein-Filled  Openings  in  Southeastern  Alaska.  —  Trans.  A. 
I.  M.  E.,  vol.  36,  pp.  581-586  (1905). 

6.  The  Juneau  Gold  Belt,  Alaska.—  Bull.  287,  U.  S.  G.  S.  (19!  6).     161  pp. 

7.  Magnetite  and  Zinc  Ores   of  Franklin  Furnace  Quadrangle. — Folio  161. 
U.  S.  G.  S.  (1908). 

8.  The  Mine  Hill  and  Sterling  Hill  Zinc  Deposits  of  Sussex  County,  New 
Jersey. — Ann.  Rept.  of  State  Geologist  for  1908,  Geol.  Sur.  New  Jersey,  pp. 
23-52  (1909). 

9.  Magnetite  Deposits  of  the  Cornwall  Type  in  Pennsylvania. — Bull.  359, 
U.  S.  G.  S.  (1908).     102  pp. 

SPIREK,  V. 

Das  Zinnobererzvorkommen  am  Monte  Amiata. — Zeit.  f.  prak.  Geol.,  vol.  5, 

pp.  369-374  (1897). 
SPRING,  K. 

Einige  Beobachtungen  in  den  Platmwaschereien  von  Nischnji  Tagil. — Zeit. 

f.  prak.  Geol.,  vol.  13,  pp.  49-54  (1905). 
SPURR,  J.  E. 

1.  The  Iron  Ores  of  the  Mesabi  Range  (Minnesota). — Am.  Geol..  vol.  13,  pp. 
335-345  (1894). 

2.  The  Iron-Bearing  Kocks  of  the  Mesabi  Range  in  Minnesota. — Butt.  10, 
Geol.  and  Nat.  Hist.  Sur.  Minn.  (1894).      259  pp. 

3.  Economic  Geology  of  the  Mercur  Mining  District,  Utah. — 16^.4nn.  Rept.. 
U.  S.  G.  S.,  part  2,  pp.  343-455  (1895). 

4.  Geology  of  the  Yukon  Gold  District,  Alaska.—  18th  Ann.  Rept.,  U.  S.  G.  S., 
part  3,  pp.  87-392  (1897). 

5.  Geology  of  the  Aspen  Mining  District,  Colorado. — Mon.  31,  U.  S.  G.  S., 
(1898).     260  pp 

6.  The  Ore  Deposits  of  Monte  Cristo,  Washington.—  22d  Ann.  Rept.,    U.  S. 
G.  S.,  part  2,  pp.  777-865  (1901). 

7.  The  Original  Source  of  the  Lake  Superior  Iron  Ores. — Am.  Geol.,  vol. 
29,  pp.  335-349  (1902). 

8.  A  Consideration  of  Igneous  Rocks  and  their  Segregation  or  Differentiation 
as  Related  to  the  Occurrence  of  Ores.— Trans.  A.  I.  M.  E.,  vol.  33,  pp. 
288-340  (1902). 

9.  Relation  of  Rock  Segregation  to  Ore  Deposition. — E.  and  M.  Jour.,  vol. 
76,  p.  54-55  (1903). 

10.  In  Discussion  of  Lindgren  on  The  Geological  Features  of  the  Gold  Pro- 
duction of  North  America.— Trans.  A.  I.M.  E.,  vol.  33,  pp.  1081-1083  (1902). 

11.  The  Ore  Deposits  of  Tonopah,  Nevada  (preliminary  report). — Bull.  219, 
U.  S.  G.  S.  (1903).     34  pp.     Also  Bull.  215,  pp.  89-110  (1904). 

12.  Genetic  Relations  of  the  Western  Nevada  Ores.— Trans.  A.  I.  M.  E.,  vol. 
36,  pp.  372-402  (1905). 

13.  Geology  of  the  Tonopah  Mining  District.  Nevada. — Prof.  Paper  42,  U.  S. 
G.  S.  (1905).     295  pp. 

14.  Ore  Deposits  of  the  Silver  Peak  Quadrangle,  Nevada. — Prof.  Paper  55,  U.  S. 
G.  S.  (1906).     174  pp.     Also  E.  and  M.  Jour.,  vol.  77,  pp.  759-760  (1904). 

15.  The  Southern  Klondike  District,  Esmeralda  County,  Nevada.     A  Study 
in  Metalliferous  Quartz  Veins  of  Magmatic  Origin. — Econ.  Geol.,  vol.  1, 
pp.  369-382  (1906). 

16.  Geology  Applied  to  Mining  (New  York,  1907).     326  pp. 

17.  A  Theory  of  Ore-Deposition.—  Econ.  Geol.,  vol.  2,  pp.  781-795  (1907). 


898  ALPHABETICAL    LIST    OF    AUTHORS. 

SPUER,  J.  E. — Continued. 

18.  How  should  Faults  be  Named  and  Classified? — Econ.  GeoL,  vol.   2,  pp. 
601-602  (1907). 

19.  Ore-Deposition   at   Aspen,    Colorado. — Econ.    GeoL.  vol.  4,    pp.   301-320 
(1909). 

20.  Native  Gold  Original  in  Metamorphic  Gneisses  — E.  and  M.  Jour.,  vol.  77, 
pp.  198-199  (1904). 

SPURR,  J.  E.,  and  GARREY,  G.  H. 

1.  The  Idaho  Springs  Mining  District,  Colorado.— Bull.   285,    U.   S.  G.  S.. 
pp.  H5-40  (1905). 

2.  Ore  Deposits  of  the  Velardena  District,  Mexico. — Econ.  GeoL.  vol.  3.  pp. 
688-725  (1908). 

3.  Economic  Geology  of  the  Georgetown  Quadrangle,  together  with  the  Em- 
pi  re  District,  Colorado.— Pro/.  Paper  63,   U.  S.  G.  S.  (1908).     422pp. 

4.  Gold  in  the  Dioritic  Bock  from  Mashonaland. — E.  and  M.  Jour.,  vol.  76, 
p.  500  (1903). 

STAPPENBECK,  K. 

Ubersicht  iiber  die  nutzbaren  Lagerstatten  Argentiniens  und  der  Magelhaens- 

lander.—  Zeit.  f.  prak.  Geol.t\ol.  18.  pp.  67-81  (1910). 
STAPFF,  F.  M. 

Goldvorkomnisse  in  Schweden  und  Tornebohm's  geologische  Unter-uchung 

von  Falnngrube.—  Rev.  in  Zeit.  f.  prak.  GeoL,  vol.  2,  pp.  181-202  (1894). 
STEIDTMANN,  EDWARD. 

A  Graphic  Comparison  of  the  Alteration  of  Eocks  by  Weathering  with  their 

Alteration  by  Hot  Solutions.— Econ.  GeoL,  vol.  3,  pp.  381-409  (1908). 
STEINMANN,  G. 

Die   Entstehung  der   Kupfererzlagerstatte  von    Caro-Caro    und    verwandter 

Vorkommnisse  in  Bolivia.—  Rosenb.  Fests.,  pp.  335-368  (1906). 
STELZNER,  A.  W. 

1.  Die  Lateral  Secretions  Theorie  und  ihre  Bedeutung  fiir  das  Pribramer 
Ganggebiet.—  Berg-  u.  Hiltt.  der  K.  K.  Bergaka.,  vol.  37  (1889). 

2.  Beitrage  zur  Entstehung  der  Freiberger  Bleierz — und  der  erzgebirgischen 
Zinnerz-Gansre.—  Zeit.  f.  prak.  GeoL,  vol.  4,  pp.  377-412  (1896). 

3.  Die  Silver-Zinnerzlagerstatten  Bolivias.     Ein  Beitrag  znr  Naturgeschichte 
der  Zinnerzes.—  Zeit.  d.  D.  GeoL  GeseL,  vol.  49,  pp.  51-142  (1897). 

STEVENS,  BLAMEY. 

The  Laws  of  Fissures.— Trans.   A.   I.   M.  E.,  vol.  40,  pp.  475-491  (1909). 
STEVENS,  E.  A. 

Basaltic  Zones  as  Guides  to  Ore-Deposits   in   the  Cripple  Creek  District. — 

Trans.  A.  I.  M.  E.,  vol.  33,  pp.  686-698  (1902). 
STEVENS,  H.  J. 

The  Copper  Handbook  (annual). — Houghton,  Michigan. 
STIRLING,  JAMES. 

1.  Notes  on  some  Observations  of  Temperature,  etc.,  in  the  Deep  Mines  of 
Bendigo.— GeoL  Sur.   Victoria  (1897). 

2.  The  Geological  Ages  of  the  Gold  Deposits  of  Victoria. — Trans.  Fed.  Inst. 
Min.  Eng.,  vol.  20,  pp.  442-475  (1900-1901). 

STOKES,  H.  N. 

1.  On  Pyrite  and  Marcasite.—  Bull.  186,  U.  S.  G.  S.,  pp.  1-50  (1901). 

2.  Experiments  on  the  Solution,  Transportation  and    Deposition  of  Copper, 
Silver  and  Gold.—  Econ.  GeoL,  vol.  1,  pp.  644-650  (1906). 

3.  Experiments  on  the  Action  of  Various  Solutions  on  Pyrite  and  Marcasite. 
—Econ?  GeoL,  vol.  2,  pp.  14-23  (1907). 

STORMS,  W.  H. 

1.  Ancient  Gravel  Channels  of  Calaveras  County,  California. — Min.  and  Sci. 
Press,  vol.  91,  pp.  170-171  ;  192-193  (1905). 

2.  The  Genesis  and  Character  of  Ore  Deposits. — Min.  and  Sci.  Press,  vol.  88, 
pp.  193-194  (1904). 

STRAUSS,  L.  W. 

Quicksilver  at  Hnancavelica,  Peru. — Min.  and  Sci.  Press,  vol.  99,  pp.  561- 
566  (1909). 


ALPHABETICAL    LIST    OF    AUTHORS.  899 

* 

STREMME,  H. 

Zur  Kenntniss  der  wasserhaltigen  und  wasserfreien  Eisenoxydbildungen  in 

den  Sedimentgesteinen. — Zeit  f.  prak.  Geol.,  vol.  18,  pp.  18-23  (1910). 
STRETCH,  R.  H. 

Notes  on  the  White  Horse  Copper  Belt,  Yukon  Territory. — E.  and  M.  Jour., 

vol.  70,  pp.  277-278  (1900). 
STRUTT,  E.  J. 

On  the  Origin  of  Ga«es  Evolved  by  Mineral  Springs. — Proc.  Roy.  Soc.,  vol. 

79,  pp.  436-439  (1907). 
STDTZER,  O. 

1.  Die  Eisenerzlagerstatten  bei  Kiruna. — Zeit.f.  prak.  GW.,  vol.  14,  pp.  65-71 
(1906). 

2.  Alte  und  neue  geologische  Beobachtungen  an  den  Kieslagerstatten  Suli- 
telma-Roros  Norwegen. — Ost.  Zeit.  f.  Sera-  u.  Hiitt..  vol.  54,  pp.  567-572 
(1906). 

3.  Turmalin  fiihrende  Kobalterzgiinge. — Zeit.  f.  prak.  OeoL.  vol.  14,  pp.  294- 
298  (1906). 

4.  Die  Eisener/.lagerstatte  Gellivare  in  Nordschweden. — Zeit.  f.  prak.  OeoL. 
vol.  14,  pp.  137-140  (1906). 

5.  Uber  die   Enstelmng   und  Einleitunar  der  Eisenerzlagerstatten. — Zeit.  f. 
Berg-  Hiitt.  u.  Salinenw.,  vol.  54,  pp.  301-304  (1906). 

6.  Der  Stammbaum  der  Erzlagerstiitten. — 6st.  Zeit.  f.  Berq-  u.  Hiitt,  pp.  317- 
320  (1907). 

7.  Magmatische   Ausscheidungen   von   Bornit. — Zeit.   f.  prak.  OeoL,  vol.  15, 
pp  371-372  (1907). 

8.  The  Geology  and  Origin  of  the  Lapland  Iron  Ores. — Jour.  Iron  and  Steel 
Inst.,  vol.  74,  pp.  106-206  (1907). 

9.  Versuche  uber  das  Eindringen  schmelzflussiger  Metal'sulfide  in  Silikat- 
gesteine.—  Zeitf.  prak.  OeoL,  vol.  16,  pp.  119-122    1908). 

10.  Uber  Pegmatite  und  Erzinjektionen  nebst  einigen  Remerkungen  iiber  die 
Kieslagerstatten  Sulitelma-Roros.— Zeit.  f.  prak.  Geol ,  vol.  17,  pp.  130-135 
(1909). 

11.  Die  Kontaktmetaraorphen    Kupfererzlagerstatten    von  White   Horse   in 
Yukon  (Canada).—  Zeit.f.  prak.  GeoL,  vol.  17,  pp.  116-121  (1909). 

12.  Kontakraetamorphe   Erzlagerstatten. — Zeit.  f.   prak.   Geol.,  vol.   17,  pp. 
145-155  (1909). 

13.  Juvenile  Quellen.—  Int.  Kong.  Diisseldorf,  1910.     Abteil.  IV.,  Vortrag 
21,  pp.  1-8. 

SUE.-S,  EDOUARD. 

1.  Zukunft  des  Goldes  (1877). 

2.  Uber  Heisse   Quellen. — Gesdlschaft  Deut.   Naturforsch.    u.   Aert.    Verhand' 
lungen  (1902). 

3.  Hot  Springs.— .E,  and  M.  Jour.,  vol.  76,  pp.  52-53  (1902). 
SULLIVAN,  E.  C. 

1.  The  Chemistry  of  Ore- Deposition — Precipitation  of  Copper  by  Natural 
Silicates.—  Econ.  OeoL,  vol.  1,  pp.  67- 73  (1906). 

2.  The  Interaction  between  Minerals  and  Water  Solutions,  with  special  refer- 
ence to  geologic  phenomena.— B all.  312,  U.  S.  G.  S.  (1907).     69  pp. 

3.  Experiments  on  the  Separation  of  the  Constituents  of  a  Solution  by  Filtra- 
tion through  a  Mineral  Filter.— Econ.  GeoL,  vol.  3,  pp.  750-756  (1908). 

SUTHERLAND,  GEORGE. 

Earth  Currents  and  the  Occurrence  of  Gold. — Nature,   vol.   42,   pp.  464-465 
(1890). 

TARR,  R.  S. 

Economic  Geology  of  the  United  States  (New  York,  1894).     509  pp. 
TARR,  W.  A. 

Copper   in   the   Red   Beds  of  Oklahoma.—  Econ.  GeoL,  vol.  5,  pp.  221-226 

(1910). 
THOMAS,  H.  H.,  and  MACALISTER,  D.  A. 

The  Geology  of  Ore  Deports  (London,  1908).     416  pp. 


900  ALPHABETICAL    LIST    OF    AUTHORS. 

TOLMAN,  C.  F.,  JR. 

1.  How  Should  Faults  be  Named  and  Classified  t—Econ.  GeoL,  vol.  2,  pp.  506- 
511  (1907). 

2.  Secondary  Sulphide  Enrichment. — Min.  and  Sci.  Press,  vol.  106,  pp.  38- 
43,  141-145,  178-181  (1913). 

3.  The  Southern  Arizona  Copper  Fields. — Min.  and  Sci.  Press,  vol.  99,  pp. 
356-359,  390-393  (1909). 

4.  Disseminated  Chalcocite  Deposits  at  Kay,  Arizona. — Min.  and  Sci.  Press, 
vol.  99,  pp.  622-624  (1909). 

5.  The  Miami-Inspiration  Ore  Zone. — Min.  and  Sci.  Press,  vol.  99,  pp.  646- 
648  (1909). 

6.  Graphical  Solution  of  Fault  Problems. — Min.  and  Sci.  Press,  vol.  102,  pp. 
810-812  ;  vol.  103,  pp.  128-130  (1911). 

TOULA,  F. 

tiber  den  nuesten  Stand  der  Goldfrage  (Wien,  1899).     60  pp. 
TOWER,  G.  W.,  JR.,  and  SMITH,  G.  O. 

Geology  and  Mining  Industry  of  the  Tintic  District,  Utah. — 19th  Ann.  Rept., 

U.  S.  O.  S.,  Part  3,  pp.  601-767  (1898). 
TRENER,  G.  B. 

Diffusion   fester  Metalle  in  feste  Kristallinische   Gesteine.  —  Verhand.  GeoL 

Reichsanst.,  pp.  360-370,  372  (1905) 
TRUCHOT,  P. 

Les  Pyrites  (Paris,  1907).     348  pp. 
TRUSCOTT,  S.  J. 

The  Witwatersrand  Goldfields  (London,  1907).     517  pp. 
TRUSTEDT,  O. 

1.  tiber  die  Erzlagerstatten  von  Pitkaranta. — Compt.  rend.  d.    Congres  d.  nat. 
et  med.  du  nord,  pp.  7-12  VII.  1902.     Rev.  in  Zeit.  f.  prakt.  GeoL,  vol,  11,  p. 
317  (1903). 

2.  Die  Erzlagerstatten  von  Pitkaranta  am  Ladagoasee.—  Bull.  19,  Com.  GeoL 
de  Finlande  (1907).     333  pp. 

TSCHERNE,  M. 

Beitrage  zur  Paragenese  der  Mineralien  (Wien,  1892).     29  pp. 
TURNER,  H.  W. 

1.  Notes  on  the  Gold  Ores  of  California. — Am.  Jour.  Sci.,  3d  series,  vol.  47, 
pp.  467-473  (1894).     Vol.  49,  pp.  374-389  (1895). 

2.  Replacement  Ore  Deposits  of  the  Sierra  Nevadas. — Jour.  GeoL,  vol.  7,  pp. 
389^00  (1899). 

3.  The  Copper-Deposits  of  the  Sierra  Oscura,  New  Mexico. — Trans.  A.  I.  M. 
E,,  vol.  33,  pp.  678-681  (1902). 

4.  Notes  on  Contact-Metamorphic  Deposits  in  the  Sierra  Nevada  Mountains. 
— Trans.  A.  I.  M.  E.,  vol.  34,  pp.  666-668  (1903). 

5.  The  Cretaceous  Auriferous  Conglomerate  of  the  Cottonwood   Mining  Dis- 
trict, Siskiyou  County,  California. — E.  and  M.  Jour.,  vol.  76,  pp.  -653-654 
(1903). 

6.  The  Terlingua  Quicksilver  Deposits.—  Econ.   GeoL,  vol.   1,  pp.   265-281 
(1906). 

7.  The  Ore-Deposits  at  Mineral,  Idaho.— Econ.  GeoL,  vol.  3,  pp.  493-502  (1908. 
TWEL.VETREES,  W.  H. 

1.  The  Deep  Leads  of  Infra-Basaltic  Stanniferous  Gravels  of  the  Ringarrooma 
Valley  near  Derby.—  Mines  Dept.  Tasm.  (1900). 

2.  Report  on  the  Anchor  Tin  Mine  and  other  mines  of  the  Blue  Tier  District, 
Tasmania.—  M ines  Dept  Tasm.  (1902). 

3.  The  Lisle  Goldfield.—  Bull.  4,  Mines  Dept.  Tasm.  (1909).      46  pp. 
TWELTVETREES,  W.  H.,  and  PETTERED. 

On  the  Topaz  Quartz  Porphyry  or  Stanniferous  Dykes  of  Mt.  Bischoff. — Roy. 

Soc.  Tasm.  (Oct.  11,  1897). 
TYRRELL,  J.  B. 

1.  Vein  Formation  at  Cobalt,  Ontario.— Can.  Min.  Jour.,  vol.  28,  pp.  301-303 
(1907). 

2.  Concentration  of  Gold  in  the  Klondike.—  Econ.  GeoL,  vol.  2,  pp.  343-349 
(1907). 


ALPHABETICAL    LIST    OF    AUTHORS.  901 

ULRICH,  E.  O.,  and  SMITH,  W.  S.  T. 

The  Lead,  Zinc,  and  Fluorspar  Deposits  of  Western  Kentucky. — Prof.  Paper 

36,  U.  S.  O.  S.  (1905).     218  pp. 
UMPLEBY,  J.  B.,  CALKINS,  F.  C.,  and  JONAS,  E.  L.,  JR. 

Gold  and  Silver  in  Idaho.—  Butt.  530,  U.  S.  O.  S.  (1912).     23  pp. 
UPSENSKY. 

Die  Eisenerzlagerstiitten  im  Bogoslowskschen  Bergrevier. — Kev.  in  NeuesJahrb. 
f.  Min.,  vol.  2,  p.  235  (1903). 

VALE,  W.  H. 

The  Indicators  of  the  Daylesford  Gold  Mines,  Victoria.  —  Trans.  Austral.  Inst 

Min.  Eng.,  vol.  10,  pp.  340-352  (1905). 
VAN  HISE,  C.  K. 

1.  The  Iron  Ores  of  the  Lake  Superior  Region. — Trans.  Wis.  Acad.  ScL,  vol.  8 
pp.  219-227  (1892). 

2.  Principles  of  North  American  Pre-Cambrian  Geology. — 16th  Ann.  Rept., 
U.  8.  G.  S.,  part  1,  pp.  571-874  (1896). 

3.  Deformation  of  Rocks.— Jour.  Geol.,  vol.  4,  pp.  195-213  (1896). 

4.  Some  Principles  Controlling  the  Deposition  of  Ores. — Trans.  A.  I.  M.  E., 
vol.  30,  pp.  27-177  (1900).    Reprinted  in  Special  Volume,  Genesis  of  Ore- 
Deposits,  pp.  282-432  (1902). 

5.  The  Iron  Ore  Deposits  of  the  Lake  Superior  Region.— 21st  Ann.  Rept.,  U.  S. 
O.  #.,part  3,  pp.  305-434  (1900). 

6.  Some  Principles  Controlling  the  Deposition  of  Ores  (Discussion). — Tram. 
A.  I.  M.  K,  vol.  31,  pp.  284-303  (1901). 

7.  Metamorphism  of  Rocks  and  Rock  Flo  wage. — Bull.  Geol.  Soc.  Am.,  vol.  9, 
p.  269  (1897). 

8.  A  Treatise  on  Metamorphism  (The  Relation  of  Metamorphism  to  Ore-De- 
posits, Chap.  12).— Man.  47,  U.  S.  G.  S.  (1904).     1286  pp. 

VAN  HISE,  C.  R.,  and  BAYLEY,  W.  S. 

1.  Preliminary  Report  on  the  Marquette  Iron-Bearing  District  of  Michigan. — 
15th  Ann.  Rept.,  U.  S.  G.  S.,  pp.  477-650  (1895). 

2.  The  Marquette  Iron-Bearing  District  of  Michigan,  with  Atlas. — Mon.  28, 
U.S.  G.  S.  (1897).     608pp. 

VlLLANUEVA,   B.   F. 

Distrito  de  Real  de  Saltepec  (Mexico,  1888). 

VlLLARELLO,  J.  D. 

1.  Genesis  de  los  Yacimientos  Mercuriales  de   Palomas  y  Huitzuco. — Mem. 
Soc.  Cien.  Ant.  Alz.,  vol.  19,  pp.  95-136  (1903). 

2.  Distribucion  de  la  Riqueza  en  los  criaderos  Metaliferos  Primaries  Epige- 
neticos.—  Bol.  Soc.  Geol.  de  Mex.,  vol.  1,  pp.  175-206  (1905). 

VOGT,  J.  H.  L. 

1.  Bildung  von  Erzlagerstatten  durch  Differentiationsprocesse  in  basischen 
Eruptivmagmata.—  Zeit.  f.  prak.  Geol,  vol.   1,   pp.  4-11,    125-143,   257-284 
(1893). 

2.  Beitriige  zur  genetischen  Classification  (1894). 

3.  Uber  die  Sedimentation  der  Eisenerzlager  und  der  Eisenglimrnerschiefer. — 
Salten  og  Ranen,  pp.  214-224  (1891),  rev.  in  Zeit.  f.  prak.  Geol.,  vol.  2,  pp. 
30-34  (1894). 

4.  Uber  die  Kieslagerskatten  vom  Typus  Roros,  Vigsiiiis,  Sulitelma  in  Norwegen 
und  Rammelsberg  in  Deutschland. — Zeit.  f.  prak.  Geol.,  vol.  2,  pp.  41-50, 
117-134,  173-181  (1894). 

5.  Beitriige  zur  genetischen  classification  der  durch  magmatische  Differentia- 
tionsprocesse und  der  durch  Pneumatolyse  entstandenen  Erzvorkommen. — 
Zeit.f.  prak.  Geol.,  vol.  2,  pp.  381-399;  vol.  3,  pp.  145-156,  367-370,  444- 
459,  465-484  (1894-1895). 

6.  The  Formation  of  Eruptive  Ore  Deposits. — Min.  Ind.,  vol.  4,  pp.  743-754 
(1895). 

7.  Kan  norske  nikkelverk  konkurrere  med  de  canadiske  ? — Norsk  Teknisk  Tids. 
(1897).     6  pp. 

8.  Uber  die  relativ  Verbreitung  der  Elemente  besonders  der  Schwermetalle, 
und  iiber  die  Concentration  des  urspriinglich  fein  vertheilten  Metallgehaltes 
zu  Erzlagerstatten.  —  Zeit.f.  prak.  GeoL,  vol.  6,  pp.  225-238,  314-327,  377- 
392,  413-420  (1898)  ;  vol.  7,  pp.  10-16  (1899). 


902  ALPHABETICAL    LIST    OF    AUTHORS. 

VOGT,  J.  H.  L.— Continued. 

9.  Das  Huelva-Kiesfeld  in  Siid-Spanien  und  dem  angrenzenden  Theile  von 
Portugal.—  Zeit.  f.  prak.  Geol.,  vol.  7,  pp.  241-254  (1899). 

10.  Problems  in  the  Geology  of  Ore- Deposits. — Trans.  A.  L  M.  E.,  vol.  31,  pp. 
12o-169  (1901). 

11.  Weitere  Untersuchungen  iiber  die  Ausscheidungen  von  Titaneisenerzen 
in   basischen   Eruptivgesteinen. — Zeit.  f.  prak.  Geol.,  vol.  8,  pp.  233-242, 
370-382  (lyOO) ;  vol.  9,  pp.  9-19,  180-186,  289-296,  327-340  (1901). 

12.  Beitrage  zur  Kenntniss  der  Gesetze  der  Mineralbildung  in  Schmelzmassen 
und  in  den  neovulkanischen  Ergussgesteinen  (Kristiania,  1902). 

13.  Die  regional-metamorphosierten  Eisenerzlagerstatten  im  nordlichen  Nor- 
wegen._ Zeit.  f.  prak.  Geol.,  vol.  11,  pp.  24-28,  59-65  (1903). 

14.  Tiber  anchi-eutektische  und  anchi-mono-mineralische  Eruptivgesteine. — 
Norsk  geol.  Tids.,  vol.  1  (1905).     33  pp. 

15.  tiber  manganwiesenerz  und   iiber   das  Verhaltnis   zwischen   Eisen    und 
Mangan  in  den  See-  und  Wiesenerze. — Zeit.  f.  prak.  Geol.,  vol.  14,  pp.  217- 
233  (1906). 

16.  Uber  magmatische  Ausscheidungen  von  Eisenerz  im  Granit. — Zeit.  f.  prak. 
Geol.,  vol.  15,  pp.  86-89  (1907). 

17.  tiber  die  Rodsand-Titaneisenerzlagerstatten  in  Norwegen. — Zeit.  f.  prak. 
Geol.,  vol.  18,  pp.  59-67  (1910). 

VOGT,  J.  H.  L.,  BEYSCHLAG,  and  KRUSCH. 

Lehre  von  den  Erzlagerstatten. — First  two  volumes  issued  (1910). 
VOIT,  F.  W. 

1.  Ursprung  des  Goldes  in  den  Randconglomeraten. — Monatsb.  d.  D.  Geol. 
GeseL,  pp.  107-119  (1908). 

2.  A  Contribution  to  the  Geology  of  German  Southwest  Africa. — Trans.  Geol. 
Soc.  So.  Af.,  vol.  7,  Pt.  2,  pp.  77-94  (1904). 

WABNER,  K. 

Uber  die  Eintheilung  der  Minerallagerstiitten  nach  ihrer  Gestalt,  sowie  die 

Anwendung  und  die  Bedentung  der  Worte   Lager  und  Flotz. — Berg-  u. 

Hiitt.  Zeit.,  vol.  50,  pp.  1-3  (1891). 
WADSWORTH,  M.  E. 

1.  The  Theories  of  Ore  Deposits.—  Proc.  Bost.  Soc.  Nat.  Hist.,  vol.  23,  pp. 
197-208  (1888). 

2.  The  Lateral  Secretion  Theory  of  Ore  Deposits.— #.  and  M.  Jour.,  vol.  37, 
pp.  364-365  (1884). 

3.  Classification  of  ore  deposits.— Rept,  Mich.  State  Geol.,  1891-92,  p.  144. 

4.  The  Origin  and  Mode  of  Occurrence  of  the  Lake  Superior  Copper- De- 


posits.—Trans.  A.  I.  M.  E.,  vol.  27,  pp.  669-696  (1897). 
5.  On  the  Origin  of  the  Iron-Ores  of  the  Marquette  District',  Lake  Superior. — 
Proc.  Bost.  Soc.  Nat.  Hist.,  vol.  20,  pp.  470-480  (1881). 

WAIT,  C.  E. 

The  Antimony  Deposits  of  Arkansas. — Trans.  A.  L  M.  E.,  vol.  8,  pp.  42-52 

(1880). 
VON  WALDENSTEIN,  J.  W. 

Die  besonderen  Lagerstatten  der  nutzbarer  Fossilien.     2  vol.     (Vienna,  1824.) 

WALLACE,  J.  P. 

Ore  Deposits  for  the  Practical  Miner  (New  York,  1908).     347  pp. 

WALKER,  E. 

The  Copper  Sulphate  Deposits  at  Copaquire,  Chile. — E.  and  M.  Jour.,  vol. 

75,  p.  710  (1903). 
WALKER,  T.  L. 

1.  Geological  and  Petrographical   Studies  of  the  Sudbury  Nickel   District 
[Canada].— Quor.  Jour.  Geol.  Soc.,  vol.  53,  pp.  40-66  (1897). 

2.  Eeport  on  the  Tungsten  Ores  of  Canada.     (Bibliography.) — Bull.  25,  Mines 
Branch,  Can.  Dept.  of  Mines  (1909).     56  pp. 

WARD,  L.  K. 

1.  The  Mount  Farrell   Mining  Field.—  Butt.  3,  Dept.  Mines   Tasm.   (1908). 
120  pp. 

2.  The  Tin  Fields  of  North  Dimdas.  —  Bull.  6,  Dept.  Mines    Tasm.  (1909). 
166  pp. 


ALPHABETICAL    LIST    OF    AUTHORS.  903 

WASHBURNE,  CHESTER. 

1.  The  Distribution  of  Placer  Gold  in  Oregon. — Oregon  Univ.  Bull.,  New  Ser., 
vol.  1,  No.  4,  pp.  18-19  (1904). 

2.  Beach  Gold  and  its  Source. — Oregon  Univ.  Bull.,  New  Ser.,  vol.  1,  No.  4, 
pp.  19-21  (1904). 

WASHINGTON,  H.  S. 

1.  Chemical  Analyses  of  Igneous  Rocks,  Pub.  from  1884  to  1900,  with  a  criti- 
cal discussion  of  the  character  and  use  of  analyses. — Prof.  Paper  14,  U.  £ 
G.  S.  (1903).   ^  495  pp. 

2.  The  Distribution  of  the  Elements  in  Igneous  Rocks. — Trans.  A.  I.  M.  E. 
vol.  39,  pp.  735-764  (1908). 

WATSON,  T.  L. 

1.  Geological  Relations  of  the  Manganese  Ore-Deposits  of  Georgia.  —  Trans. 
A.  I.  M.  E.,  vol.  34,  pp.  207-254  (1903). 

2.  The  Lead  and  Zinc  Deposits  of  the  Virginia- Tennessee  Region. — Trans.  A. 
L  M.  E.,  vol.  36,  pp.  681-737  (1905). 

3.  Lead  and  Zinc   Deposits  of  Virginia. — Bull.  1,  Geol.  Ser.,  Virginia  Geol. 
Sur.  (1905).     156pp. 

4.  The  Occurrence  of  Nickel  in  Virginia. — Trans.  A.  I.  M.  E..  vol.  38,  pp. 
683-697  (1907). 

5.  A  Preliminary  Report  on  the  Manganese  Deposits  of  Georgia. — Bull.  14. 
Geol.  Sur.  Ga.  (1908).     195  pp. 

6.  The  Manganese-Ore  Deposits  of  Georgia. — Econ.  Geol.,  vol.  4,  pp.  46-55 
(1909). 

WATSON,  T.  L.,  and  HESS,  F.  L. 

Zirconiferous  Sandstone  near  Ashland.  Virginia. — Bull.  530,    U.   S.    G.  S* 

(1912).     9pp. 
WATT,  J.  A. 

Saddle  Reefs  at  Hargreaves.—  Rec.  Geol.  Sur.  N.  S.  W.,  vol.  5,  pt.  4,  p.  153 

(1898) ;  vol.  6,  pt.  2,  p.  83  (1899). 
WATTS,  VV.  L. 

Across    V'atna  Jokull,   or,  Science   in  Iceland,  pp.  101,  109,  119,   153-157 

(London,  1876). 
WEDDING,  H. 

Die  Eisenerze  der  Insel  Cuba. — Stahl  und  Eisen,  vol.  12,  pp.  545-550  (1892). 
WEED,  W.  H. 

1.  A  Gold-Bearing  Hot  Spring  Deposit. — Am.  Jour.  ScL,  3d  ser.,  vol.  42,  pp. 
166-169(1891) 

2.  Enrichment  of  Mineral  Veins  by  Later  Metallic  Sulphides.— Bull.  Geol. 
Soc.  Am.,  vol.  11,  pp.  179-206  (1900). 

3.  Mineral  Vein  Formation  at  Boulder  Hot  Springs,  Montana.— 21st  Ann. 
Rent.,  U.  S.  G.  S.,  part  2,  pp.  227-255  (1900). 

4.  Types  of  Copper  Deposits  in  the  Southern  United  States. — Trans.  A.  I.  M. 
E.,  vol.  30,  pp.  449-i04  (1900). 

5.  The  Enrichment  of  Gold  and  Silver  Veins.—  Trans.  A.  I.  M.  E.,  vol.  30, 
pp.  424-448  (1900). 

6.  Influence  of  Countrv-Rock  on  Mineral  Veins. — Trans.  A.  L  M.  E.,  voL 
31,  pp.  634-653  (1901). 

7.  The  El  Paso  Tin  Deposits.— Bull.  178,  U.  S.  G.  S.,  pp.  1-15  (1901). 

8.  The  Copper  Deposits  of  the  Eastern  United  States.— Bull.  260,  U.  S.  G.  &, 
pp.  217-220  (1905). 

9.  Notes  on  Certain  Mines  in  the  States  of  Chihuahua,  Sinaloa,  and  Sonora, 
Mexico.— Trans.  A.  I.  M.  E.,  vol.  32,  pp.  396-443  (1901). 

10.  Ore-Deposits  near  Igneous  Contacts. — Trans.  A.  L  M.  E ,  vol.  33,  pp. 
715-746  (1902). 

11.  Ore-Deposition  and  Vein-Enrichment  by  Ascending  Hot  Waters. — Trans. 
A.  L  M.  E.,  vol.  33,  pp.  747-754  (1902). 

12.  Copper  Deposits  of  New  Jersey.—  Ann.  R  pt.  Slate  Geologist,  1902,  Geol. 
Survey  of  New  Jersey,  pp.  125-139  (1903). 

13.  The  Genetic  Classification  of  Ore  Bodies  (Geol.  Soc.  Am.). — E.  and  M. 
Jour.,  vol.  75,  pp.  256-257  (1903).      (See  also  Rickard,  T.  A.,  et  a/.,  1.) 

14.  Ore  Deposits  at  Butte,  Montana.—  Bull.  213,  U.  S.   G.  S.,  pp.  170-180 
(1903). 


904  ALPHABETICAL    LIST    OF    AUTHORS. 

WEED,  W.  H. — Continued. 

15.  Occurrence  and  Distribution  of  Copper  in  the  United  States. — 3 fin.  Mag., 
(J),  vol.  10,  pp.  185-193  (1904). 

16.  Original  Native  Gold  in  Igneous  Rocks.— E.  and  M.  Jour.,  vol.  77,  pp. 
440-441  (1904). 

16a.  The  Copper  Mines  of  the  United  States  in  1905.—  Bull.  285,  U.  S.  G.  S., 
pp.  93-124  (1905). 

17.  Adsorption  in  Ore  Deposition. — E.  and  M.  Jour.,  vol.  79,  p.  364  (1905). 

18.  Mutual  Dibplncement  by  Intersecting  Veins. — E.  and  M.  Jour.,  vol.  83, 
pp.  1145-1146  (1907). 

19.  Copper  Mines  of  the  World  (New  York,  1908).     375  pp. 

20.  Geology  and  Ore  Deposits  of  Butte  District,  Montana. — Prof.  Paper  74, 
U.  S.  Q.  S.  (1912).     262pp. 

21.  Copper  Deposits  of  the  Appalachian  States.—  Bull.  455,    U.  S.    G.   S. 
(1911).    466pp. 

WEED,  W.  H.,  and  BARBELL,  JOSEPH. 

Geology  and  Ore-Deposits  of  the  Elkhorn  Mining  District,  Jefferson  County, 

Montana.—  22d  Ann.  Rept.,  U.  S.  G.  S.,  part  2,  pp.  399-549  (1901). 
WEED,  W.  H.,  and  PIRSSON,  L.  V. 

1.  Geology  of  the  Castle  Mountain  Mining  District,  Montana. — Bull.  139,  U. 
S.  G.  S.  (1896).      164pp. 

2.  Geology  and  Mineral  Resources  of  the  Judith  Mountains  of  Montana. — 
18th  Ann.  Rept.,  U.  S.  G.  S.,  part  3,  pp.  437-616  (1897). 

3.  Geology  of  the  Little  Belt  Mountains,  Montana. — 20th  Ann.  Rept.,  U.  S. 
G.  S.,  part  3,  pp.  257-581  (1899). 

4.  Occurrence  of  Sulphur,  Orpiment  and  Realgar  in  the  Yellowstone  Na- 
tional Park.—  Am.  Jour.  Sci.,  3d  ser.,  vol.  42,  pp.  401-405  (1891). 

WEED,  W.  H.,  and  WTATSON,  T.  L. 

The  Virginia  Copper  Deposits.  —Econ.  GeoL,  vol.  1,  pp.  309-330  (1906). 

WEEKS,  F.  B. 

Geology  and  Mineral  Resources  of  the  Osceola  Mining  District,  White  Pine 

County,  Nevada.—  Bull.  340,  U.  S.  G.  S.,pp.  117-133  (1908). 
WEIDMAN,  SAMUEL. 

The  Baraboo  Iron-Bearing  District  of  Wisconsin. — Bull.  13,  Wis.   GeoL  and 
Nat.  Hist.  Sur.  (1904).     190  pp. 

WEILL,  L. 

L'or  ;   proprie'te's   physiques  et  chemiques  ;  gisements  ;  extraction  ;  applica- 
tions ;  dosage  (Paris,  1896).     420  pp. 
WEINSCHENK,  E. 

Die  Nickelmagnetkieslagerstatten  imBezirk  St.  Blasien  in  siidlichen  Schwarz- 

wald.—  Zeit.  f.  prak.  GeoL,  vol.  15,  pp.  73-86  (1907). 
WEISKOPF,  A. 

Uber  Anreicherung  von  Eisenerzen. — Stahl  und  Eisen,  pp.  471-475,  532-535 
(1905). 

WELLS,  R.  C. 

The  Fractional  Precipitation  of  Sulphides.— Econ.  GeoL,  vol.  5,  p.  1-14  (1910). 

WELTON,  W.  S. 

Notes  on  Gold-Bearing  Gravels. — Trans.   Inst.  Min.  and  Met.,  vol.  8,   pp. 
519-534  (1899). 

WENDEBORN,  B.  A. 

Beziehung  der   Mineralabsonderungen  aus  Gesteinen  zu  Erzlagerstiitten. — 

Berg-  u.  Hiltt.  Zeit.,  vol.  63,  pp.  568-569  (1904). 
WENDT,  A.  F. 

1.  The  Iron  Mines  of  Putnam  County,  N.  Y.— Trans.  A.  L  M.  E.,  vol.  13, 
pp.  478-485  (1885). 

2.  The  Copper  Ores  of  the  Southwest.— Trans.  A.  I.  M.  E.,  vol.  15,  pp.  25- 
77  (1887). 

3.  The  Potosi,   Bolivia,   Silver-District.— Trans.  A.  I.  M.  E.,  vol.  19,  pp. 
74-107  (1891). 

WERNER,  A.  G. 

Neue  Theorie  von   der  Entstehnns:   der   Giinge,   mit  Anwendung  auf  den 
Bergbau,  besonrlers  den  freibergischen  (Freiberg,  1791). 


ALPHABETICAL    LIST    OF    AUTHORS.  905 

VAN  WERVEKE,  L. 

Bemerkungen  tiber  die  Zusammensetzung  und  die  Entstehung  der  lothring- 
isch,   luxemburgischen  oolithischen  Eisenerze  (Minetten). — Zeit.  f.  prak. 
GeoL,  vol.  9,  pp.  396-403  (1901). 
WHERRY,  E.  T. 

The  Newark  Copper  Deposits  of  Southeastern  Pennsylvania. — Econ.  GeoL, 

vol.  3,  pp.  726-738  (1908). 
WHITNEY,  J.  D. 

1.  The  Metallic  Wealth  of  the  United  States  (Philadelphia,  1854).     510  pp. 

2.  Remarks  on  the  changes  which  take  place  in  the  structure  and  composition 
of  mineral  veins  near  the  surface,  with  particular  reference  to  the  East  Ten- 
nessee Copper  Mines. — Am.  Jour.  Sci.,  2d  ser.,  vol.  20,  p.  53-57  (1855). 

3.  The  Auriferous  Gravels  of  the  Sierra  Nevada  of  California. — Mem.  Mus. 
Comp.  Zool.  Har.  Col.,  vol.  6  (1879-1880).     569  pp. 

WHITTLESEY,  C. 

On  the  Origin  of  Mineral  Veins. — Proc.  Am.  Assoc.  Adv.  Sci.,  vol.  25,  p.  213 

(1876). 
WILLIAMS,  ALBERT,  JR. 

1.  Popular  Fallacies  Regarding  Precious   Metal   Ore   Deposits. — 4th  Ann. 
Rept.,  U.  S.  G.  S.,  pp  257-271  (1884). 

2.  Why  Dip  is  more  likely  to  be  Regular  than  Strike  with  Fissure  Veins. — 
E.  and  M.  Jour.,  vol.  53,  p.  398  (1892). 

WILLIAMS,  E.  G. 

The  Manganese  Industry  of  the  Department  of  Panama,  Republic  of  Colom- 
bia.— Trans.  A.  I.  M.  E.,  vol.  33,  pp.  197-235  (1902). 
WILLIAMS,  S.  G. 

Applied  Geology  (New  York,  1886).     386  pp. 
WILLIS,  BAILEY. 

1.  The  Mechanics  of  Appalachian  Structure. — 13^  Ann.  Eept ,  U.S.  G.  S., 
Pt.  2,  pp.  211-281  (1892). 

2.  Studies  in  Structural  Geology. — Trans.  A.  I.  M.  E.,  vol.  21,  p.  551 ;  E.  and 
M.  Jour.,  vol.  54,  pp.  390-391  (1892). 

WlLLMOTT,  A,.   B. 

The  Origin  of  Deposits  of  Pyrites. — Jour.  Can.  Min.  Inst.,  vol.  10,  pp.  118- 

128  (1907)  ;  Can.  Min.  Jour.,  vol.  28,  No.  18,  pp.  500-503  (1907). 
WILTSEE,  ERNEST. 

Notes  on  the  Geology  of  the  Half  Moon  Mine,  Pioche,  Nevada. — Trans.  A. 
L  M.  E.,  vol.  21,  pp.  867-873  (1893). 

WlNCHELL,  A.   N. 

1.  The  Oxidation  of  Pyrites.— Econ.  GeoL,  vol.  2,  pp.  290-294  (1907). 

2.  A  Consideration  of  Igneous  Rocks  and  their  Segregation  or  Differentiation 
as  related  to  the  Occurrence  of  Ores.     Discussion  of  a  paper  by  J.  E.  Spurr. 
—Trans.  A.  L  M.  E.,  vol.  33,  pp.  288-340  (1902). 

WlNCHELL,  H.   V. 

1.  The  Mesabi  Iron-Range.— Trans.  A.  I.  M.  E.,  vol.  21,  pp   644-686  (1892). 

2.  The  Genesis  of  Ore- Deposits. — (Discussion  of  a  paper  by  Posepny  in  Trans. 
A.  I.  M.  E.,  vol.  23,  pp.  197-368);  Trans.  A.  L  M.  E.,  vol.  23,  pp.  591-597 
(1893). 

3.  The  Lake  Superior  Iron-Ore  Region. — Trans.  Fed.  Inst.  Min.  Eng.,  vol.  13, 
pp.  493-562  (1896-97). 

4.  Synthesis  of  Chalcocite  and  its  Genesis  at  Butte,  Montana. — Bull.  GeoL  Soc. 
Am.,  vol.  14,  pp.  269-276  (1903);   also  E.  and  M.  Jour.,  vol.  75,  pp.  782- 
784  (1903). 

5.  Genesis  of  Ores  in  the  Light  of  Modern  Theory. — E.  and  M.  Jour.,  vol.  84, 
pp.  1067-1070  (1907). 

6.  A  Theory  of  Ore-Deposition  — Min.  and  Sci.   Press,  vol.  96,  pp.  385-387 
(1908). 

7.  The  Localization  of  Values  in  Ore  Bodies  and  the  Occurrence  of  Shoots  in 
Metalliferous  Deposits.—  Econ.  GeoL,  vol.  3,  pp.  425-428  (1908). 

8.  The  Genesis  of  Ores.—  Min.  and  Sci.  Press,  vol.  95,  pp.  55-58  (1907). 

9.  Prospecting  in  the  North.—  Min.  Mag.  (E),  vol.  3,  pp.  436-438  (1910). 

57 


906  ALPHABETICAL    LIST    OF    AUTHORS. 

WINCHELL,  H.  V.,  and  GRANT,  IT.  S. 

Preliminary  Report  on  the  Rainy  Lake  Gold  Region  [Minnesota]. — 23e/  Ann. 

Rept.,  Geol.  and  Nat.  Hist.  Sur.  Minn.,  pp.  36-104  (1894). 
WINCHELL,  H.  V.,  and  JONES,  J.  T. 

The  Biwabik  Mine.— Trans.  A.  I.  M.  E.,  vol.  21,  pp.  951-961  (1893). 
WINCHELL,  H.V.,  and  WINCHELL,  N.  H. 

The  Iron  Ores  of  Minnesota — Bull.  6,  Minn.  Geol.  and  Nat.  Hist.  Sur.,  pp. 

1-429  (1892). 
WINCHELL,  N.  H. 

1.  The  Cuyuna  Iron  Range.—  Econ.  Geol,  vol.  2,  pp.  565-571  (1907). 

2.  Structure  of  the  Mesabi  Iron-Ore. — Proc.  Lake  Sup.  Min.  Insi.,  vol.  13,  pp. 
189-204  (1908). 

WlNKLER,  C. 

1.  Die  Relative  Seltenheit  der  Elemente  mit  Bezug  auf  deren  technische  Ver- 
wendung.— Zeit.  f.  Anyew.  Chem.,  pp.  93-98  (1899). 

2.  On   the    Possibility  of  the   Immigration  of   Metals   into   Eruptive  Rocks 
through  the  Agency  of  Carbon  Dioxide. — Ber.  d.  Math.  Phys.  K.  K.  Ak.  d. 
W.,  Leipzig,  p.  9  (1900). 

WINSLOW,  ARTHUR. 

1.  Notes  on  the  Lead  and  Zinc  Deposits  of  the  Mississippi  Valley  and  the 
Origin  of  the  Ores.—  Jour.  Geol.,  vol.  1,  pp.  612-619  (1893). 

2.  Lead  and  Zinc  Deposits  of  Missouri. — Trans.  A.  I.  M.  E.,  vol.  24,  pp.  634- 
689  (1894). 

3.  The  Disseminated  Lead  Ores  of  Southeastern  Missouri.—^//.  132,  U.  S.  G.  S. 
(1896).     31  pp. 

4.  The  Liberty  Bell  Gold-Mine,  Telluride,  Colorado.— Trans.  A.  I.  M.  E., 
vol.  29,  pp.  285-307  (1899). 

VON  WlSSENBACH. 

Gang  verhaltnisse  (1836). 

WOAKEB,   E.  R. 

Modern  Gold-Mining  in  the  Darien — Notes  on  the  Re-opening  of  the  Espirito 
Santo  Mine  at  Cana.— Trans.  A.  I.  M.  EJ,voL  29,  pp.  249-280  (1899). 

W8LBLING,  H. 

1.  Bildung  der  oxydischen  Eisenerzlager. — Stahl  und  Eisen,  vol.  29,  p.   1248 
(1909). 

2.  Zur  Bildung  von  Eisenglanz. — Gluckauf,  vol.  45,  pp.  1-5  (1909). 
WOOD,  G.  C. 

Determination  of  the  Specific  Electrical  Resistance  of  Coals,  Ores,  etc. — Trans. 

No.  Eng.  Inst.  Min.  and  Mech.  Eng.,  vol.  56,  pp.  27-37  (1906). 
WOOD,  J.  E.  T. 

1.  The  Great  Western  Tin  Deposits,  Heberton  (1881). 

2.  The  Tin  Deposits  of  the  Northern  Territory.— Geol.  Sur.  So.  Aust.  (1886). 
WOODMAN,  J.  E. 

1.  Studies  in  the  Gold-Bearing  Slates  of  Nova  Scotia.— Proc.  Boston  Soc.  NaL 
Hist.,  vol.  28,  pp  375-407  (1899). 

2.  Geology  of  the  Moose  River  Gold  District,  Halifax,  Nova  Scotia. — Proc. 
and  Trans.  Nov.  Scot.  Inst.  Sci.,  vol.  11,  pp.  18-88  (1905). 

3.  Report  on  the  Iron  Ore  Deposits  of  Nova  Scotia. — Bull.  20,  Mines  Branch^ 
Can.  Dept.  Mines  (1909).     226  pp. 

WOLFF. 

Das  Australische  Gold.— Zeit.  d.  D.  Geol.  Gesel,  vol.  29,  pp.  156-157  (1877). 
WRIGHT,  F.  E.,  and  LARSEN. 

Quartz  as  a  Geologic  Thermometer. — Am.  Jour.  Sci.,  4th  ser.,  vol.  27,  pp.  421- 

447  (1909). 
WRIGHT,  C.  W. 

1.  The  Porcupine  Placer  District,  Alaska.—  Bull.  236,  U.  S.  G.   S.   (1904). 
35pp. 

2.  The  Lead  and  Zinc  Mines  of  Monteponi. — Min.  Mag.  ( J),  vol.  12,  pp.  33- 
38  (1905). 

3.  The  Copper  Deposits  of  Kasaan  Peninsula,  Alaska. — Econ.  Geol.,  vol.  3, 
pp.  410-417  (1908). 


ALPHABETICAL    LIST    OF    AUTHORS.  907 

WRIGHT,  C.  W.  and  F.  E. 

Ketchikan  and  Wrangell  Mining  Districts,  Alaska.—  Bull.  347,  U.  S.  G.  S. 

(1908).     210pp. 
WRIGHT,  L.  T. 

Diffusion  as  a  Factor  in  Ore  Deposition. — Min.  and  Sci.  Press,  vol.  96,  pp.  844- 

845;  vol.  97,  p.  149  (1898). 
WUENSCH,  A.  F. 

The  Cause  of  Ore  Shoots  —Sci.  Mon.,  pp.  74-76  (1893). 

YEATES,  W.  S.,  McCALME,  S.  W.,  and  KING,  F.  P. 

A  Preliminary  Keport  on  a  Part  of  the  Gold  Deposits  of  Georgia. — Bull.  4  A, 
Oeol.  Sur.  Ga.  (1898).     542  pp. 
YEATMAN,  POPE. 

The  Braden  Copper  Company  [Chile].— E.  and  M.  Jour.,  vol.  92,  pp.  1128- 

1132,  1186-1188  (1911). 
YUNG,  M.  B.,  and  MCCAFFERY,  K.  S. 

Ore-Deposits  of  the  San  Pedro  District,  New  Mexico. — Trans.  A.  I.  M.  E..  vol. 

33,  pp.  350-363  (1902). 
YOUNG,  R  B. 

Notes  on  the  Auriferous  Conglomerates  of  the  Witwatersrand. — Trans.  Oeol. 
Soc.  So.  Af.,  vol.  10,  pp.  17-30  (1907). 

ZERRENER,  CARL. 

Manganerz-Bergbaue  in  Deutschland,  Frankreich,  und   Spanien   (Freiberg, 
1861).     186  pp. 

ZlMMERMANN,   C. 

1.  Die  Wiederausrichtung  vervorfener  Gange,  Lager  und  Flotse. — Dormstadt 
und  Leipsig,  pp.  49,  72,  80  (1828). 

2.  Uber  den  Magnetberg  Katschkanar  am  Ural. — Zeit.  d.  D.  Geol.  GeseL,  vol. 
1,  pp.  475-482  (1849). 

ZlRKEL. 

1.  Lehrbuch  der  Petrographie  (1893). 

2.  Bergaunnische  Mittheilungen  iiber Cornwall. — Zeit.  f.  Berg-,  Hutt. u.Salinenw., 
vol.  9,  pp.  248-261  (1861). 

ZlRKLER. 

Uber  die  gangverhaltnisse  der  Grube  Bergmannstrost  bei  Clausthal. — Gl'dckauf, 
vol.  33,  p.  84  (1897). 

ZlNCKEN. 

Die  Mineralschatze  des  Europaischen  Kusslands. — Berg-  u.  Hutt.  Zeit,  vol.  39, 
pp.  340-341  (1880). 


SUBJECT  INDEX. 


NOTE. — Authors'  names  are  alphabetically  arranged  unless  otherwise  stated. 
Numbers  after  authors'  names  refer  to  the  number  of  the  paper  in  the  list  of  papers. 
When  names  or  numbers  are  in  Italics  papers  are  not  written  in  English. 

ABBREVIATIONS. — Hist,  chiefly  of  historic  interest;  Rec.,  strongly  recommended 
as  of  value  in  the  understanding  of  ore-genesis  ;  E. ,  elementary  ;  D.,  of  no  especial 
importance;  Des. ,  mainly  descriptive  and  only  incidentally  concerned  with  questions 
of  ore-genesis  ;  Geol.,  dealing  with  geological  problems  which,  though  not  directly 
concerned  with  ore-deposits,  have  important  applications  to  the  subject;  Rev., 
review  or  reviewed.  The  abbreviations  "Rec.,"  "Des.,"  etc.,  are  attached  to 
only  a  few  of  the  more  general . papers.  Where  omitted  the  paper  is  usually  a 
valuable  one  in  that  particular  phase  of  the  discussion  where  it  is  cited. 


GENERAL  TREATISES  ON    METALLIFEROUS 
DEPOSITS. 


Beck,  8,  Rec.,  1909. 

9,  Rec..  1909. 

Bergeat-Stelzner,  Spec.  Rec.,  1906. 
Branner  and  Newsom,  1  (Syllabus),  Rec.,  1910. 
Bruhns,  D.,  1870. 
Burat,!,  Hist.,  1870. 
Campbell,  A.  C.,  1, 1880. 
Cfiarpentier,  1900. 
Cole,  1906. 
von  Cotta,  1,  Rec.  Hist.,  1861. 

2,  Translation  in  English  by  F.  Prime,  Hist., 

Rec.,  1870. 
de  la  Coux,  1896. 

Oumenge  and  Robettaz,  Gold  only,  1, 1898. 
Curie,  1,  Gold  only,  1905. 
d'Achiardi,  Rec.,  1883. 
de  Launay,  1,  Rec.,  1893. 

4,  Rec.,  1897. 

6,  Rec.,  1897. 

11,  Rec.,  1905. 
Fawns,  3,  Tin  only,  1907. 

Fuchs  and  de  Launay,  1,  Encyclopaedic,  2  vols., 
Rec.,  1893. 

2,  Second  Edition,  Rec.,  1912. 
Grimm,  Hist,,  1869. 

von  Groddeck,  1,  Hist.,  1879. 

3,  French  translation  of  1, 1884. 
Giinther,  S.,  Geol.,  1897. 

Gilrich,  1,  Rec.,  1899. 

Hancock,  E.,  1908. 

Hayes,  2,  Suggestions  for  field  observations  on 

ore-deposits,  pp.  66-70, 109-154, 1909. 
Kenwood, 2.  Hist.,  1871. 
Hunt,  T.  S..2,  1873. 
Johnson,  J.  P.,  1,  South  Africa,  1908. 
Keck,  1883. 


Keilhack,  2, 1896. 

Kemp,  21,  Rec.,  1906. 

Kohler,  G.,  1,  Rec.,  1884. 

Krahmann,  1,  1903. 

Krusch,    Vogt  and  Beyschlag,  see  Vogt,  Rec. 

1907. 

Lindgren,  36,  Rec.,  1913. 
Lotti,  2,  1903. 

Lottner  and  Serlo,  Hist.,  1872,  also  1878. 
Mabson,  Transvaal  only,  1906. 
Miron,  1903. 
Moreau,  1894. 
Mutter,  H.,  3,  1850. 
Neunier,  Exper.  geol.,  1904. 
Page,  1874. 
Park,  4, 1906. 

Phillips-Louis,  Rec.,  1896. 
Posepny,  1  and  2,  Spec.  Rec. ,  1893. 
Pumpelly,  3,  Rec.,  1877. 
Rickard,  T.  A.  (et  al.),  "  a  Discussion,"  Rec., 

1903. 

Rickard,  T.  A.,  7,  Rec.,  1902. 
Ries,  H.,  E.,  Rec.,  1910. 
Sandberger,  1,  Hist.,  Rec.,  1885. 
Spurr,  16,  Rec.,  1907. 
Tarr,  R.  S.,  D.,  1894. 
Thomas  and  MacAlister,  1909. 
Van  Hise,4,  Rec.,  1900. 
Vogt,  Krusch  and  Beyschlag,  2  vols.  published. 

others  in  press,  Rec.,  1910. 
Wadsworth,  1, 1888. 
Wallace,  D.,  1908. 
Werner,  Hist.,  1791. 
Whitney,  1,  Rec.,  1854. 
Williams,  S.  G. ,  1886. 
von  Wissenbach,~L8'24.. 


ASCENSION    THEORIES. 

(Also  called  Ascension  by  Infiltration,  Thermal  Theories,  etc.  See  also  under  : 
"Emanations  from  Igneous  Rocks,"  "  Pegmatitic  Ore- Deposits,"  "Ore-Solu- 
tions," "  Pneumatolysis,"  ' '  Magmatic  Differentiation,"  etc. ). 


Bancroft,  4,  pp.  245-268  (vol.  38),  1908. 

4,  pp .  809-817  (vol.  40) ,  1910. 
de  Beaumont,  1, 1850. 
Beck,  8,  pp.  420-432, 1909. 

9,  vol.  ii.,  pp.  51-70, 1909. 
Becker,  6,  pp.  438-450. 


Bergeat-Stelzner,  pp.  1202-1239, 1906. 
Bischof,  1,  pp.  904-912,  Analyses  of  metal-bear- 
ing springs.  1866. 
Daubree,  A.,  1,  pp.  227-256,  Relation  of  veins  to 

springs,  1858. 
2,  pp.  235-246,  1879. 


SUBJECT    INDEX. 


909 


de  Launay,  7,  pp.  85,  et  seq.,  1899. 

Emmons,  S.  F.,  3,  Argues  against  ascension, 

pp.  135-147, 1887. 
Gautier,  A,  1,  pp.  316-370,  1906. 
Hochstetter  and  Teller,  1878.     . 
Jenney,  3,  pp.  445-499,  1902. 
Kemp,  14,  pp.  169-198, 1901. 

16,  pp.  699-714,  1902. 

21,  pp.  39-44,  1906. 
Le  Conte  and  Rising,  Sulphur  Bank,  pp.  23- 

33,  1883. 

Le  Conte,  3,  pp.  942-1006,  1894. 
Mutter,  H.,  1,  pp.  261-309,  1885. 
Newberry,  5, 1883. 


Phillips,  5,  p.  321, 1868.  . 
Phillips-Louis,  p.  136, 1896. 
Posepuv,  2.  pp.  220-244  and  247-254,  1894. 

5.  Underground  waters,  pp.  71  and  38, 1885. 
:  Roth,  Analyses  of  min.  springs,  pp.  564  et  seq., 

118/9. 
Spurr,  17,  781-795,  1907. 
Stelzner,  2,  pp.  377-412,  1896. 
Suess,  g,  1902. 

Van  Hise,  8,  pp.  1072  et  seq.     General  discus- 
sion, 1904. 
Weed,  3,  pp.  227-255, 1900. 

(Other  references  will  be  found  under  the 
headings  mentioned  above.) 


CAVITIES    IN    ROCKS. 


GENERAL. 

Bancroft,  4,  Depth  of  formation  of,  pp   259- 

263,  1908. 

Beck,  8,  pp.  161-175,  also  607-610, 1909. 
Bergeat-Stelzner,  pp.  476-521,  1906. 
Bra'nner   and    Newsom,  pp.    24-30    (Syllabus 

only),  1900 
Chance,  8,  Depth  of  fracture  zone,  pp.  299-302, 

1908. 

Fuller,  2,  pp.  63-64, 1906. 
Heim,  1,  p.  44, 1878. 

Hoskins,  pp.  845-874,  Flow  and  fracture,  1896. 
Kemp,  21.  pp.  13-32, 1906. 
Louis,  1, 1893. 
Phillips-Louis,  pp.  67-85,  also  in  part,  86-187, 

1896. 

Posepny,  2,  pp.  207-210, 1893. 
Ransome,  2,  pp.  43-67,  1901. 
Ries.  pp.  323-325,  329-335,  1910. 
Spurr,  16,  pp.  148-196,  1907. 
Van  Hise,  2,  pp.  589-603,  Cleavage  and  fissility, 

pp.  633-668,  1896. 

4,  pp.  29-45,  Cavities  in  general,  1900. 
8,  General,  pp.  125-146.  155,  618,  1201;  Depth 

Of  openings,  pp.  159-191, 1006-1008, 1904 

PORE-SPACES. 

Buckley,  2,  pp.  225  etseq.,  1898. 

Fuller.  2,  p.  61, 1906. 

Mead,  1908. 

Slichter,  pp.  305  et  seq.,  1899. 

Van  Hise,  8,  pp.  123-146, 1904. 

AMYGDALOIDAL  CAVITIES. 

Van  Hise,  8,  pp.  127,  134, 1904. 

FISSUKES. 

Bancroft,  4,  pp.  2-i9-263,  1909. 
Beck,  8,  pp.  161-175, 1909. 
Becker,  4,  pp.  407-415,  Good  general  discus- 
sion. 1888. 

7,  p.  49, 1891 ;  8,  1893 ;  9, 1893  ;  10,  p.  130, 1894. 
13,  pp.  269-272,  fissures  in  schists,  18%. 

Bergeat-Stelzner,  pp.  476-478,  1007-1188, 1906. 

Brown,  A.  J.,  1874. 

Burnt,  pp.  32-61, 1870. 

Church,  1,  pp.  469-613, 637, 1892. 

Daubree,  A.,  2,  pp.  300-374,  1879. 

Daubree,  O.  A.,  1  and  2,  Excellent  papers  on 

fissures,  1879-1887. 
de  Launay,  11,  pp.  596-605, 1905. 
Emmons,  S.  F.,4,  p.  200, 1887. 
6, 1888. 

8,  p.  49, 1892-3. 
7,  p.  548,  1892. 

Fuller,  2,  pp.  63-64. 1906. 
Glenn,  1,  pp.  499-514, 1895. 
Heim,  1,  p.  44,  1878. 
Hofer,  4,  1899. 

Irving,  J.  D.,  Emmons, S.  F.  and  Jaggar.  T.  A., 
pp.  126-136,  Torsion  fissures,  1904. 


KeUhack,  1, 1895. 

Kemp,  21,  pp,  13-32,  1906. 

Kohler,  O.,  1,  1884. 

3,  1897. 

Koto,  Earthquake  fissures,  1893. 
Lindgren,  8,  Grass  Valley  fissures,  pp.  164-171, 

1896. 

9.  p.  647  et  seq.,  also  pp.  690-693, 1897. 
11,  at  Silver  City,  pp.  101-103, 1899. 
Lindgren  and  Ransome,  2,  Cripple  Creek— Has 
very  general  bearing  on  fissure  formation 
in  general,  pp.  153-168,  1906 
Lossen,  1,  Torsion  fissures,  p.  336,  1886. 
MiMer,  H.,  2,  Freiberg  fissures,  1901. 
Penrose  and  Cross,  Cripple  Creek,  pp.  139-150, 

1896. 

Phillips,  2,  Origin  of  veins,  1871. 
Phillips-Louis,  pp.  60-85,  1896. 
Posepny.  2,  pp.  207-210.  1893. 
Purihgton,  1,  764-781.  1897. 

7,  Camp  bird  region,  1905. 
Ransome,  1,  Termination  of  fissures  in  shales, 
1900. 

2,  pp.  43-67,  Excellent  discussion  of  origin 
of  Silverton  fissures  which  has  wide  appli- 
cation. 1901. 

3,  Rico  Mts.,  1901., 

Ransome  and    Calkins,  Cceur   d'Alene,   Ex. 

gen    discussion,  pp.  114-122,  also  134-135, 

1908. 

Ries,  pp.  329-335, 1910. 
Rickard,  9, 1896. 
Spencer,  5,  p.  586, 1905. 

6,  Juneau,  pp.  27-28, 1906. 
Spurr,  16,  pp.  148-196, 1907. 

6,  Monte  Cristo,  pp.  805-831, 1901. 
Spurr  and  Garrey,3,  Contains  many  admirable 

illustrations  of  different  types  of  fissures 

showing  their  irregularities  but  no  general 

discussion  of  fissure  formation,  1908. 
Stevens,  B.,  1,  pp.  475-491,  Laws  of   fissures. 

Chiefly  mathematical,  D.,  1909. 
Tarr.  R.  S.,  1,  Rifting  in  granite,  1891. 
Tower  and  Smith,  Tintic  fissures,  pp.  676-683, 

1898. 

Tyrrell,  1,  Cobalt  fissures,  1907. 
Van  Hise,  2,  pp.  672-678, 1896. 
Watts,  Whittlesey,  1876. 
Williams,  A.,  Jr.,  2,  Dip  and  strike,  1892. 
Winslow,  2,  pp.  670-673,  in  Mo.  limestone,  1894. 
(Many  other  references  on  fissures  might  be 
cited,  but  are  omitted  as  they  would  occupy 
undue  space.    References  to  them  are  avail- 
able in  all  the  general  treatises  mentioned  on 
page  908.) 

JOINTS. 

Becker,  7,  1893 ;  8, 1893  ;  9,  1894  ;  10,  1896  ;  19, 

1904. 

Crosby,  1, 1881 ;  2. 1882  ;  3, 1887  ;  4, 1893. 
Gilbert,  1,  p.  50, 1882  ;  '2, 1882. 
Herman,  p.  112, 1899. 
Le  Conte,  5,  p.  233,  1882. 


.,  I  McGee,  pp.  152.  476,  1883. 
!Tarr,  R.  S.,  1, 1894. 


910 


SUBJECT    INDEX. 


GASH-VEENS,    PITCHES    AND 
FLATS,  ETC. 

Bain,  2,  pp.  35-45,  53-66, 1906. 
Branner,  3, 1901. 

Chamberlin,  T.  C.,  3,  pp.  451-488, 1882. 
Grant,  3,  1905  ;  4,  pp.  64-79, 1906. 
Grant  and  Burchard,  1907. 

DOLOMIT I Z  ATION-C  AVITIES. 

Bain  and  Van  Rise,  pp.  208-212, 1901. 

de  Beaumont,  2,  pp.  174-177,  1836. 

Bischof,  2,  vol.  Ill  ,  pp.  169-170,  1859. 

Dana,  4th  ed..  p.  133,  1895. 

Harkness,  p.  101, 1859. 

Hunt,  1,  p.  92. 

Orton,  pp.  582-587,  619-620,- 641-643,  also  plate 

LX.,  1889. 

Pirsson,  pp.  307-309,  1908. 
Prestwich,  vol.  i.,  pp.  113-114,  1886. 
Spurr,  5,  pp.  206-216,  1898. 
Van  Hise,  8,  pp.  238-239,  798-808, 1904. 

SADDLE-REEFS. 

Faribault,  7  and  8,  Nova  Scotia,  1899,  1903. 

Jaquet,  4,  1894. 

Phillips-Louis,  pp.  155-160,  1896. 

Pittman,  2,  p.  45,  1892. 

Rickard,  T.  A.,  2,  pp.  463-529,  1891. 

Samuels,  Behdigo,  1893. 

Schmeisser,  1898. 

Watt,  1898,  p.  153,  also  1899,  p.  83. 


SOLUTION-CAVITIES. 

(A  few  references  only  are  given  on 
this  topic  as  the  literature  is  extremely 
voluminous. ) 

Curtis,  2,  pp.  94-96,  1884. 

Dana,  1895. 

Emmons,  S.  F.,  2,  pp.  566-569,  1886. 

Leonard,  1.  pp.  288-294, 1895. 

2,  pp.  30,  43,  61,  1897. 
Posepny,  2,  p.  207,  et  seq.,  1893. 
Winslow,  2,  pp.  670-673,  1894. 

(See  also  all  books  on  ore-deposits,  and  all 
text-books  of  geology.) 

CVVITIES  DUE  TO  FISSILITY, 
CLEAVAGE,  AND  METAMOR- 
PHISM. 

Becker,  10,  pp.  429-448,  1896  ;  19,  1904  ;   12,  pp. 

269-272,  1896. 

Le  Conte,  1,  pp.  189-196,  1904. 
Leith,  3, 1905. 
Van  Hise,  2,  pp.  633-668, 1896.    ' 

3,  1896;  7,  pp.  294-328,  Rock-flowage . 


CONTACT-METAMORPHIC    DEPOSITS. 


CHARACTER  AND  GENESIS. 

Barrell,  1,  1902- 

2.  pp.  116-150,  1907. 
Beck,  8,  pp    482-606,  1909. 

9,  vol.  i.,  pp.  98-168,  1909. 
Bergeat,  1,  Concepcion  del  Oro,  1910. 
Bergeat-Stdzner,  pp.  1131-1188  (metaso  m  a  t  i  c 

type),  1904-1906. 

Credner,  2,  Geol.,  pp.  288-298, 1903. 
Fakuchi.  General  for  Japanese  ore-deposits, 

1907. 

Gabert,  Erzgebirge,  1907. 
von  Groddeck,  1,  Hist.,  1879. 
Hastings,  4,  1908. 
Kemp,.  26,  1907. 

27, 1906. 

Kemp  and  Gunther,  1907. 
Keyes,  7, 1909. 
Kjerulf,  1879. 
Klockmann,  3, 1904. 
Leith,  6, 1908. 

7,  pp.  277-281,  1908. 

Lindgren,  14,  Excellent  general  paper.    Espe- 
cially Rec..  1901  ;  19, 1904  ;  20  a.,  1905. 
Lindgren,  Graton  and  Gordon,  pp.  51-55  (1910). 
Lindgren  and  Ransome,  2,  pp.  19-20,  123-164, 

176-177,  Rec.,  1905. 
Lotti,  2,  pp.  51-78,  1903. 
McCarty,  1896. 
Park,  6, 1906. 

Spencer,  8,  pp.  49-52,  1909. 
Spurr,  3,  pp.  395-398,  399-402,  1895. 

16,  pp.  16,  107,  108,  245,  1907. 
Stulzer,  5,  1906. 

12,  1909. 

Thomas  and  MacAlister,  pp.  349-358, 1909. 
Vogt.  5,  Vol.  iii.,  p.  154,  1895. 

8,  Vol.  vi..  p.  415^16, 1898. 

10,  pp.  137-140,  Rec.,  1901. 
Weed,  10, 1902. 

9,  pp.  404-406,  428-435, 1902. 


CHEMICAL  AND  PHYSICAL 
CHANGES  WHICH  OCCUR  DUR- 
ING THE  FORMATION  OF  CON- 
TACT-METAMORPHIC DEPOSITS 

Barrell,  1,  pp.  279-296, 1902. 

2,  pp.  116-150, 1907. 
Kemp,  20, 1905. 

26,  pp.  190-194, 1907 ;  27,  1906  ;  31,  1909. 
Leith  and  Harder,  pp  24-37,  75-89, 1908. 
Lindgren,  19,  pp.  511-551,  1904. 

20  a., pp.  19-20, 123-164, 176-177,  1905. 

CONTACT-DEPOSITS   OF   COPPER. 

Bergeat-Stelzner,  pp.  1131-1188,  Many  individual 
deposits  in  detail  with  references  to  foreign 
literature;  pp,  1148-49,  Maidanpek,  Med- 
norudiansk  ;  pp.  1175-1176  ;  Bogoslowsk,  p. 
1176 ;  1906. 

Blake,  13, 1903. 

Boutwell,4,  Bingham,  Utah,  pp.  511-580,  1905. 

Brewer.  2,  Vancouver,  1899. 

3,  ditto,  vol.  69,  pp.  465-466,  526  ;  vol.  70,  pp. 
34-35, 1900. 

4,  ditto.  1906. 
Crosby,  7, 1905. 
Emmons,  S.  F.,  19, 1910. 
Emmons,  W.  H.,  4,  19Q9. 
Kemp,  San  Jose',  Mexico,  20, 1905. 

Kemp  and  Gunther,  White  Knob,  Idaho,  1907. 
Lindgren,  11,  pp.  249-253,  Idaho,  1899. 
Lindgren,  Graton  and  Gordon,  pp.  51-55, 172- 

174,  184-185,  205-206,  220,  241-243,   292,  305, 

329-330,  New  Mexico,  1910. 
McConnell,  2,  Yukon,  1909. 
Schmidt  and  Prciswerk,  4,  p.  217,  Cala,  1905. 
Smith,  George,  2,  Australia,  1903. 
Spurr  and  Garrey,  2,  Velardefia,  Mexico,  1908. 
Stutzer,  11.  Alaska.  1909. 
Trilstedt,  1,  Finland,  1903. 
Weed,  9,  Jimenez,  Mexico,  pp.  404-405, 1901. 
General,  19,  pp.  74-77,  1908. 


SUBJECT    INDEX. 


911 


CONTACT-DEPOSITS  OF  GOLD 
AND  SILVER 

Barrell,  2,  1907. 

Bergeat-Stelzner,  pp.  1136-7,  Reichenstein,  1906. 

Hershey,  1,  1899. 

Spurr,  3,  Mercur,  Utah,  pp.  395-398,  1895. 

OF  COBALT. 

Bergeat-Stelzner,  Daschkessan,  p.  1179  ;  Tuna- 
berg,  p.  1168,  1906. 

SILVER  AND  LEAD. 

Berg,  2,  Balia-Maden,  Turkey,  1901. 
Bergeat-Stelzner,  Sala,  p.  1166  ;  Balia-Maden,  p. 

1180,  R^zbanya,  p.  1147,  1906. 
Clapp  and  Ball,  Eastern  U.  S.,  1909. 
Lindgren,  Graton  and  Gordon,  New  Mexico, 

1910. 

Posepny,  2,  286-289,  1893. 
Ralli,  Turkey,  1904. 

IRON. 

Beck,  2,  Schwarzenberg,  1902,  1904. 
8,  Banat,  p.  587  :  Berggieshubel,  p.  583  ;  Elba, 

p.  596  ;  Magnitnaia  p.  598  ;  Schmiedeberg, 

p.  586  ;  Schwarzen  Cruz,  p,  587  ;  Traversella 

and  Brosso,  p,  595,  1909. 
Berg,  1,  Schmiedeberg,  1892. 
Bergeat-Stelzner,  Banat,  p.  1141;  Berggieshiibel, 

p.  1139  :  Elba,  p.  1159  ;  Magnitnaia,  p.  1177  ; 

Schmiedeberg,  p.  1135  ;  Schwarzenberg,  p. 

1137  ;  Traversella  and  Brosso,  p.  1150  ;  Gala, 


pp.  1149-50  ;  Wyssokaia  and  Goroblagodat, 
Ural  Mts.,  pp.  1171-1175;  Katschkanar, 
Siberia,  p.  1179;  Cerro  Mercado,  Mexico, 


p.  1186. 
d'Achiardi,  1883. 
Dalmer,  1,  Schwarzenberg,  1900. 
Diller,  2,  Redding,  Cal.,  1903. 
Farrington,  Cerro  Mercado,  Mexico,  1904. 
Halavdts  and  Sjogren,  Banat,  Hungary,  1891. 
Hill,  1,  Mexico,  1893. 
Kemp,  31,  Iron  Springs,  Utah,  1909. 
Kimball,  2,  Cuba,  1885. 
Lacroix,  1,  Que>igut,  1890. 
Leith,  8,  Iron  Springs,  Utah,  1910. 
Leith  and  Harder.  Iron  Springs,  Utah,  1908. 
Lotti,  2,  Brosso  and  Traversella,  pp.  56-68,  1903. 


Loewinson-Lessing,  1,  Goro-blagodat,  1907. 

2,  Wyssokaia,  1909. 

Morozewicz,  1,  Magnitnaia,  Urals,  1904. 
Mutter,  A.,  2,  Berggieshubel,  1890. 
Novarese,  Brosso  and  Traversella,  1902. 
Prescott,  California,  1908. 
Rangel,  Villarello  and  Bdse,  1,  Cerro  Mercado, 

Mexico,  1902. 

Schmidt  and  Preiswerk,  p.  217,  Cala,  1905. 
Sjogren,  1,  Banat,  1886. 

2,  Sweden,  p.  373, 1891. 

3,  Sweden  (English),  pp.  766-835, 1907. 
Smith,  George,  2,  Chillagoe,  Australia,  1903. 
Souder,  Cuba,  1904. 

Triistedt,  1,  Pitkaranta,  Finnland,  1903. 
Vogt,  5,  Christiania,  pp.  154-155, 1895. 
Wedding,  Cuba,  1892. 

TIN. 

Claypole,  1892. 

Collier,  1,  Seward  Peninsula,  Alaska,  1902. 

2,  York  region,  1904. 

Fawns,  3,  pp.  159-164, 1st  Ed.,  1905. 
Fay,  pp.  664-682,  1907. 
Gabert,  Erzgebirge,  1907. 
Knopf,  1,  Alaska,  1908. 

3,  ditto,  1909. 

Merensky,  3,  Transvaal,  1908. 
Rickard,  Edgar,  1903. 

ZINC. 

Beck,  2,  Schwarzenberg,  1902-4. 

Blake,  8,  1894. 

Crosby,  7,  1905. 

Dalmer,  1,  Schwarzcberg,  1900. 

Lindgren,  Graton  and  Gordon,  pp.  220, 241-243, 

1910. 

Spencer,  7,  Franklin  Furnace,  1908. 
Spurr  and  Garrey,  2,  Velardefia,  Mexico,  1908. 
Trustedt,  1,  Pitkaranta,  Finnland,  1903. 

MISCELLANEOUS      CONTACT-ME- 
TAMOKPHIC   OCCURRENCES. 

Oanaval,  1, 1908. 

Gabert,  1907. 

Kjerulf,  1879. 

McCarty,  pp.  169-189,  Mexico,  1895. 

Ordonez,  1,  p.  233,  Mexico,  1898. 

Ordonez  and  Aguilera,  68-222, 1897. 

Upsensky,  1903. 


CLASSIFICATION    OF    ORE-DEPOSITS. 

(These  references  are  chronologically  arranged.) 


von  Waldenstein,  pp.  4-6,  Hist.,  1824. 

Fuchs,  pp.  81-86, 1846. 

Whitney,  1,  pp.  1-68, 1854. 

von  Cotta,  2,  p.  2, 1859  (also  later  editions). 

Lottner  and  Serlo,  pp.  3-32,  1869. 

Grimm,  pp.  14-15.  1869. 

Burnt,  pp.  9-12, 1870. 

von  Cotta  (Prime's  translation),  2,  1870. 

Pumpelly,  3,  Vol.  3,  pp.  974-981,  1877. 

von  Groddeck,  1,  p.  84,  1879. 

Newberry,  4, 1880. 

Geikie,  A.,  pp.  807-812, 1882. 

Le  Conte,  2, 1883. 

Kdhler,  G.,  1,  1884. 

Phillips,  6,  p.  3, 1884. 

von  Groddeck,  2, 1885. 

Emmons,  S.  F.,  2,  pp.  367-375,  1886. 

6,  pp.  805-808,  1888. 

Munroe,  (referred  to  in  Kemp  21,  Appendix  I.) 
Wabner,  1891. 

Wadsworth,  3,  p.  144,  1891. 
Power,  1892. 
Kemp,  4,  pp.  3-24,  1893. 
KLockmann,  1,  pp.  400-406,  New  Edition  of  1900, 

pp.  595-602.  1892-1900. 
Jenney,  1,  pp.  190-191,  1893. 
Posepny,  2,  1893. 
Crosby,  5,  1894. 
Raymond,  5,  1894. 


Vogt,  J.  H.  L.,2,  1894. 

Hastings.  2,  1895. 

Phillips-Louis,  pp.  3-10,  1896. 

Hofer,  3,  pp.  112-116,  1897. 
4,  pp.  173-176,  1899. 

Giirich,  1,  1899. 

Lindgren,  12,  by  metasomatic  minerals,  1900. 

Louis,  3,  1900. 

Van  Hise,  4,  1900. 

Keyes,  1,  pp.  323-356,  1900. 

Bergeat-Stelzner,  pp.  15-19,  1900. 

Lindgren,  13,  of  veins  of  the  Blue  Mts.,  Oregon, 
1901. 

Rickard,  et  al,  1  (Edited  by)  "  A  Discussion." 
Contains  many  valuable  papers  on  classi- 
fication and  genetic  subjects,  1903. 

Lotti,  2,  p.  28,  1903. 

Weed,  13,  pp.  256-257,  1903. 

Schierl,  1904. 

Van  Hise,  8,  p.  1005,  1904. 

Hille,  2,  of  gold  deposits,  1905. 

Foster,  pp.  3-18,  1905. 

Kemp,  21,  pp.  54-79,  also  pp.  447-462,  1906. 

Weed,  19,  of  copper  deposits,  pp.  69-81,  1908. 


16  a,  of  copper  deposits,  pp. 
Beck,  8,  pp.  2-4,  1909. 

9,  pp.  4-8,  1909. 
Adam,  J.  W.  H.,  1910. 
Ries,  1910. 


96-97,  1905. 


912 


SUBJECT    INDEX. 


DEFINITION  OF  THE  TERM  "ORE." 

(See  general  treatises  on  ore-deposits  on  p.  908  of  this  index.) 


Beck,  8,  p.  1, 1909. 
9,  pp.  1-2,  1909. 
Kemp,  29,  1909. 


Kemp,  30,  1909. 
Ries,  p.  305,  1910. 
Weed,  19,  p.  22, 1908. 


DEPTH,  INFLUENCE  OF,  ON  ORE-DEPOSITION. 

Changes  which  affect  the  continuation  and  occurrence  of  ore-deposits  in  depth 
maybe  due  to  secondary  causes,  for  which  see  under  "Superficial  Alteration," 
and  "Oxidation,"  or  to  primary  or  original  causes.  These  latter  are  (1)  Ex- 
istence of  fissures  or  cavities.  (2)  Effects  of  temperature  and  pressure  on  min- 
erals deposited,  i.  e.,  changes  in  primary  mineralogy  with  depth. ) 


GENERAL. 

de  La.unay,  1,  1893. 

8,  1900  ;  16,  1909. 
Emmons,  S.  F.,  12,  pp.  428-429,   Ouster  Co., 

Colo.,  1896. 
Gregory,  J.  W.,  1,  1901. 

2,  1904;  7,1906. 
Lindgren,  24,  1906. 
Posepny,  9,  1867. 
Van  Hise,  8,  pp.  1081-1138,  1904. 


DEPTH  TO  WHICH  CAVITIES  CAN 
EXTEND. 

Adams,  F.  D.,  3, 1912,  Rec. 
Bancroft,  4,  pp.  259-263,  1907. 
Beck,  8,  pp.  121-125,  1909. 
Bergeat-Stelzner,  pp.  476-479, 1906. 
Chance,  8,  pp.  299-302,  1908. 
Emmons,  S.  F.,  2,  at  Leadville,  p.  568,  1886. 
Fuller,  2,  pp.  63-64,  1906. 
Faribault,  7  and  8,  Nova  Scotia,  1899-1903. 
Heim,  pp.  89  etseq.,  107,  1878. 
Reyer,  1,  pp.  454-593,  1888. 
Van  Hise,  2,  pp.  589-603,  1896. 
8,  pp.  187-191,  1005-1013,  1904. 


CHANGES   IN    PRIMARY  MINER- 
ALOGY WITH  DEPTH. 

Beck,  8,  pp.  361-363,  1909. 
Bergeat-Stelzner,  pp.  992-995,  1906. 
de  Launay,  1,  1893. 

8,  1900. 

16,  1909. 
Gregory,  1, 1901. 

2,  1904  ;  7,  1906. 

Lindgren,  25,  pp.  123-125,  Applied    to    Dah- 
lonega  veins,  26,  Excellent  general  paper 
on  physical  conditions,  1907.    24,  1906. 
Sjogren,  4,  Changes  with  depth  in  Swedish 

ores,  1908. 

Spencer,  6,  Alaska,  1906. 
Spurr,  16,  pp.  295-299,  1907. 
Spurr  and  Garrey,  3,  Georgetown,  pp.  148-149, 
1908. 

1,  Idaho  Springs,  p.  40,  1905. 
Van  Hise,  8,  pp.  1072-1138,  1904. 
Vogt,  9,  Huelva,  1899. 

10,  pp.  158-164,1901. 
Williams,  A.,  Jr.,  1,  pp.  259-262,  1884. 
Weed,  3,  p.  249-252,  1900. 
Weed  and  Barrell,  1901. 

Zirkler,  p.  84,  Change  in  mineralogy  of  Claus- 
thal  veins,  1897. 


DESCENSION   THEORIES. 

(See  also  under  "  Sedimentary  ores  "  sub-head  :   "  Ores  supposed  to  be  derived 
from  disseminated  particles  deposited  in  sedimentary  rocks  during  deposition.") 


Beck,  8,  pp.  411-413,  1909. 

9,  vol.  II.,  pp.  41-43,  1909. 
Bergeat-Stelzner,  pp.  1192-1193,  1906. 
von  Beust,  1840. 
Bucking,  pp.  51-52,  1889. 


Emmons,  S.  F.,  3,  pp.  125-147,  1887. 
2,  Leadville,  pp.  379,  569-584, 1886. 
Hornung,  2, 1905. 
Krusch,  3,  1904. 
Moore,  1869. 
Werner,  Hist.,  1791. 


DETRITAL    DEPOSITS. 


GENERAL. 

Beck,  8,  pp.  611-660,  especially  651-656, 1909. 

9,  vol  II.,  pp.  417-491,  especially  pp.  477-484, 

1909. 

Bergeat-Stelzner,  pp.  1258-1297, 1906. 
Brooks,  8, 1906. 
Cohen,  1887. 
de  Launay,  14, 1907. 

15,  1908.' 
Emmons,  W.  H.,  5,  Relation  of  placers  to  lodes 

1909. 

Helmhacker,  2,  Altai,  1891. 
Hutchins,  2, 1907. 


Lake,  p.  11, 1903. 

Maclaren,  2,  pp.  80-99,  Excellent  general  sum- 
mary, 1908. 
Park,  8,  1908. 
Phillips-Louis,  pp.  20-28,  see  also  pp.  619-633 

and  648-649,  1896. 
Posepny,  7,  General  treatise,  1887. 

2,  pp.  331-342,  Excellent  general  review.  1893.     , 

6,  pp.  499-598,  1895. 
Smyth,  H.  L.,  1,  1905. 
Spurr,  16,  pp.  205-233, 1907. 
Thomas  and  MacAlister,  pp.  376-409,  1908. 
Welton,  1899. 


SUBJECT    INDEX. 


913 


DISTRIBUTION  OF  GOLD  IN  PLA- 
CERS, ORIGIN  OF  NUGGETS,  ETC. 

Beck,  8,  pp.  651-656,  1909. 
9,  vol.  it,  pp.  477-484,  1909. 

Brauns,  p.  406,  1896. 

Buttgenbach,  1. 

Chalmers,  Quebec,  1901. 

Cohen,  Exhaustive  discussion  on  origin  of  al- 
luvial gold,  1887. 

Crane,  W.  R.,  A  Treatise  on  Gold  and  Silver,  pp. 
159-171,  1908. 

Devereux,  Discusses  formation  of  nuggets, 
pp.  465-475,  1881. 

Eggleston,  Nuggets,  1881.  Also,  Sch.  Min.  Quar, 
vol.  7,  p.  101,  Good  general  discussion  of 
placers,  1885. 

Francois,  1840. 

Gordon,  1895. 

Harrison,  Fowler,  and  Anderson,  Gold  in  vege- 
tation, 1908. 

Knox,  N.  B.,  pp.  211-213,  1903. 

Lake,  p.  11, 1903. 

Lindgren,  13,  pp.  634-637, 1901. 

Liversidge,  1, 1893^. 

2,  Nuggets,  1897. 

3,  ditto,  1906. 

Lotti,  2,  pp.  121-123,  1903. 

Lungwitz,  2,  Gold  in  vegetation,  1900. 

Maclaren,  pp.  80-86,  Ex.  general  summary. 

1908. 

Murchison,  1851. 
Park,  4,  pp.  10-19,  1906. 

8,  1908. 

Phillips,  5, 1868.   Also,  Am.  Jour.  Sci.,  2nd  Sen, 

vol.  47,  p.  134. 
Phillips-Louis,  p.  631, 1896. 
Posepny,  7,  1887.    2,  pp.  336-339, 1893. 
Smyth,  H.  L.,  1,  1905. 
Spurr,  4,  pp.  366-379,  1897. 
Tyrrell,  J.  B.,  2.  Concentration  in  Klondike, 

1907. 

GOLD  PLACERS. 

Stream    Placers. 

Bancroft,  3,  Sonora,  Mexico,  1903. 
de  Batz,  Siberia,  1898. 
Becker,  14,  Alaska,  1897. 

12,  Southern  Appalachians,  1895. 
Bergeat-Stelzner,  pp.  1266-1275,  Bibliography  of 
literature  of  foreign  deposits,  only  a  few 
of  which  are  given  here,  1906. 
Blatchford,  West  Australia,  pp.  21-30,1899. 
Boutwell,  5,  Bingham,  pp.  331-360, 1905. 
Branner  and  Newsom,  p.  126,  1900. 
Brooks,  A.  H.,  3,  pp.  41-44,  Alaska,  1903. 

5,  ditto,  pp.  43-59,  1903. 

7,  Alaska,  pp.  18-31,  1905. 

9,  Kougarok,  Alaska,  1907. 

10,  Circle  Precinct,  Alaska.  1907. 

Brooks,  Richardson  and  Collier,  Alaska,  1901. 
Browne,  E.  R  ,  California,  1890.    Also  E.  and 

M.  Jour.,  vol.  58,  p.  101,  1895. 
Chalmers,  Quebec,  1901. 
Coleman,  1,  Ontario,  1901. 
Collier,  3,  N.  E.  Washington,  1907. 
Collier,  Hess  and  Smith,  Seward  Peninsula, 

Alaska,  1908. 

Credner,  1,  California,  1866. 
Cumenge  and  Robellaz,  1898. 
Devereux,  Fossil  placers,  Black  Hills,  1882. 
Egleston,  Sch.  Min,  Quar.,  vol.  7,  pp.  101-131, 

1885. 

Gale,  1,  Routt  Co.,  Colo,  1908. 
Gordon,  New  Zealand,  1895. 
Granger,  Guyanas,  1896. 
Hammond,  1,  California,  1881  ;  also,  Mint  Re- 

portfor  1881,  p.  616. 
Hanks,  Mint  Report,  1882,  p.  728. 
Harrison,    Fowler     and    Anderson,    British 

Guiana,  1908. 
Hill,  2,  Sonora.  Mexico,  1902. 


Irving,  Emmons,  and  Jaggar,  Fossil  placers, 
pp.  98-111,  181-184  ;  Recent  placers,  179-180, 
1904. 

Keele,  pp.  18-42,  Yukon,  1905. 

Kemp,  21,  California,  especially  pp.  353-362. 

Kerr,  North  Carolina,  1880. 
Knox,  N.  B.,1903. 
Laur,  1,  California,  1863. 
LeConte,  6,  California,  1880. 
Lawson,  1,  California,  1893. 
Levat,  D.,  2,  Siberia,  1904. 
Lindgren,  9,  Idaho  Springs,  especially  pp.  657- 
680,  718-719,  1897. 

2,  California,  1893. 

6,  California,  1894. 

18,  California,  1903. 


13,  especially  pp.  634-637,  1901. 
20,  Bitter  Root  Mis.,  pp. 


pp.  83-85,  88-S9,  91-96, 

97,  102-103,  108,  1904. 
34,  Excellent  general  pa,per  on  California 

gold  gravels,  1911. 
Lindgren  and  Drake,  Nampa,  1904, 
Lindgren,  Graton  and  Gordon,  New  Mexico, 

pp.  74-76,  1910. 
Lock,  A.  G.,  1882. 
Maclaren,  2,  pp.  78-100,  1908. 
McConnell,  Klondike,  1,  3,  4,  5,  1904-1907. 
McGillivray,  Mint  Report  for  1881,  p.  630. 
Mendenhall,  4,  Alaska,  1903. 

1,  Kotzebue,  Alaska,  1902. 

2,  Norton  Bay,  Alaska,  1901. 
Moffit,  1,  Fairhaven,  Alaska,  1905. 

2,  Kotzebue  dist.,  1904. 
Moffit  and  Maddren,  Alaska,  1909. 
Newberry,  3,  1881  :  also,  Sch.  Min.  Quar.,  vol.  3. 
Prindle,  1,  Forty-mile,  Alaska,  1905. 

2,  Yukon-Tanana,  1906. 

3,  Forty-mile,  Seventy-mile,  Alaska,  pp.34-  39, 
1909. 

Prindle  and  Hess,  1,  Rampart  region,  Alaska, 

1906. 

2,  Fairbanks,  Alaska,  pp.  64-96,  1908, 
Prindle  and  Katz,  Fairbanks,  Alaska,  1903. 
Purington,  6,  Alaska,  1905. 
Radford,  1,  California,  1899. 
Ransome,  la.,  California,  1900. 
Rickard,  T.  A.,  3,  New  Zealand,  pp.  428-442, 

1893. 

Smith,  G.  O.,  2,  pp.  76-78,  1903. 
Spencer,  6.  Juneau,  Alaska,  pp.  77-85,  1906. 
Spurr,  4,  pp.  317-379,  Yukon.  Alaska,  1897. 
Spurr  and  Garrey,  1,  pp.  36-37,  Idaho  Springs, 

1905. 

Storms,  1,  Ancient  Gravels  of  California,  1905. 
Turner,  1,  California,  1895. 
Tyrrell.  2,  Klondike,  1907. 
Washburne,  I,  Oregon,  1904. 
Whitney,  3,  California,  1879-80. 
Wright,  C.  W.,  1,  Porcupine,  Alaska,  1904. 


Fossil  Placers. 

AUSTRALASIA. 

Daintree,  1878. 

Posepny,  2,  General,  pp.  342-345, 1894. 

BLACK    HILLS. 

Carpenter,  pp.  571-573,  1889. 

Devereux,  pp.  465-473, 1882. 

Irving,  J.  D.,  4,  pp.  131-132, 1904. 

Irving,  J.  D.,  Emmons,  S.  F.,  and  Jaggar,  pp. 

98-111,  181-184, 1904. 
O'Harra,  pp.  32-37, 1902. 
Turner,  5, 1903. 

CALIFORNIA. 

Blake,  Mint  Rept.  for  1884,  p.  572. 
Bordeaux,  1902. 

Browne,  E.  R.,  1890.    Also',  12th  Rept.  Cal.  State 
Min.,  p.  202,  1894. 


914 


SUBJECT    INDEX. 


Cre.dner,  1,  1866. 

Diller,  3,  1907. 

Hammond,  1, 1890. 

Kemp,  21,  pp.  353-362,  1906. 

Laur,  1,  1863. 

Lavvson,  1, 1893. 

LeConte,  6, 1880. 

Lindgren,  5,  1894. 

2, 1893 ;  6, 1894  ;  18, 1903.  34.  Excellent  gene- 
ral paper,  1911.  Also,  Folio$  17, 18,  29,  31. 39 
and  66,  U.  S.  G.  S. 

Lindgren  and  Knowlton,  1896. 

Lindgren  and  Turner,  1894. 

McGillivray,  Mint  Report  for  1881,  p.  630. 

Ransome,  Folio  63,  U.  S.  G.  S.,  1900. 

Silliman,  Am.  Jour.  Sci.,  2nd  ser.,  vol.  40,  p.  1. 

Storms,  1, 1905. 

Turner,  5,  1903.    Also,  Am.  Geol.,  vol.  15.  pp. 
371-379,  1905. 

Whitney,  3, 1879-80. 


SOUTH   AFRICA. 

Beck,  5, 1906. 

Becker,  17, 18,  20,  1897, 1898,  1909. 

Czyszkowski,  1896. 

de  Lannay,  3,  1896. 

Denny,  1909. 

Gregory,  J.  W.,  10, 1907-8. 

12,  1909. 

Hammond,  2,  1901. 
Hatch,  2,  1903. 
Kessler,  1904. 
Krause,  1897. 
Mabson,  1906. 

Maclaren,  pp.  435-447,  1908. 
Phillips- Louis,  Gold  Coast,  pp.  729-731 ;  Trans- 
vaal, 731-740,  1896. 
Sawyer,  Gold  Coast,  Africa,  1902. 
Schoch,  ditto,  1905. 
Truscott,  1907. 
Vott.  1,  1908. 
Wolff,  Australia,  1877. 
Young,  R.  B.,  1907. 

Beach  Placers. 

Halla,  Nome,  1907. 

Mendenhall,  2,  1901. 

Moffit,  3,  Nome,  1907. 

Queneau,  Nome,  1902. 

Rickard,  F.,  2,  Nome,  1905. 

Schrader  and  Brooks,  1,  Nome,  1900. 

2,  Nome,  1900. 
Washburne,  2,  Oregon,  1904. 

JEolian  Placers. 

Rickard,  T.  A.,  11,  Australia,  pp.  490-537,  1898. 
Spurr,  14,   Auriferous  Sand  Dunes,  Nevada, 
pp.  30-31,  96-97,  1906. 


TIN  PLACERS. 

Barrow,  1908. 

Beck,  1,  Bangka  and  Billiton,  1898. 

8,  General,  pp.  625-635,  1909. 

9,  General,  vol.  ii.,  pp.  436-450,  1909. 
Bergeat-Stelzner,  pp.  1288-1294,  1906. 
Brooks,  1,  Alaska,  1901. 

2,  ditto,  pp.  267-271,  1901. 
4,  ditto,  pp.  92-93,  1903. 


David,  New  England  Dist.,  Australia,  1887. 

Doyle,  Malay  Peninsula,  1879. 

Farrell,  Katanga,  p.  752,  1908. 

Fawns,  3,  1907. 

von  Fircks,  Mt.  Bischoff,  1899. 

Gascuel,  France,  1905. 

Henwood,  3,  Cornwall,  Eng.,  1874. 

Hess  and  Graton,  General  paper  with  excel- 
lent bibliography,  1905. 

Ingails,  1,  Durango,  "Mexico,  Placers  only  in- 
cidentally mentioned,  1895. 

Kynaston  and  Mellor,  Waterberg,  Australia, 
pp.  80,  83,  83,  89,  114-115,  1909. 

MacAlister  and  Hill,  Cornwall,  Eng.,  pp.6, 11, 
15,  95-98,  1906. 

MacAlister,  2,  pp.  379-380,  1908. 

de  Morgan,  Bangka  and  Billiton,  1886. 

Penrose,  3,  Malay  Peninsula,  1903. 

Reyer,  ditto,  2, 1881. 
3,  Australia  and  Tasmania,  1880. 

Rolker,  1,  Sumatra,  1892. 

Rum  bold,  2,  Malay  States,  1906. 

Sandeman,  Tasmania,  1899-1900. 

Schurtz,  Erzgebirge,  1890. 

Twelvetrees,  1,  Tasmania,  1900. 

Wood,  1,  2,  Australia,  1881, 1886. 

PLATINUM  PLACERS. 

General. 

Beck.  8,  pp.  656-660,  1909. 

9,  vol.  ii.,  pp.  484-490,  1909. 
Berffeat-Stelzner,pp.  1284-12*8,  1906. 
Kemp,  15.    Complete  discussion  with  full  bib- 
liography, 1902. 

In  Individual  Localities. 

Bourdakoff  and  Hendrikoff,  Russia,  1896. 

Brock,  2,  British  Columbia,  1904. 

Day,  North  Am.,  1900. 

Day  and  Richards,  Black  Sands,  pp.  1226-1227, 

1905. 

Diller,  4,  Oregon,  1903. 
Homer,  Borneo,  1842. 

Howe,  Bibliography  for  years  1748-1896,  1898. 
Hussak,  1,  Brazil,  1906. 
Jaquet,  2,  Bookin  Hill,  Australia,  1893. 

3,  New  South  Wales,  1897. 
Katterfeld,  Russia,  1885. 
Kemp,  15,  General,  1902. 
Laurent,  Urals,  1890. 
Louis,  4,  Russia,  1898. 
Purington,  2,  Urals,  1899. 

4,  ditto,  1904. 
Rainer,  1,  1902. 

Rose,  Russia,  1837-1842. 
Saytzeff,  1,  Urals,  1898. 
Spring,  Russia,  1905. 
Zincken,  Russia,  1880. 

IRON  PLACERS. 

Beck,  8,  pp.  49-60,  82-111,  1909  ;  9,  pp.  363-415, 

vol.  ii.,  1909. 

Bergeat-Stelzner,  pp.  85-470, 1906. 
Hunt,  T.  S.,  Prog.  Rept.  Can.  Geol.  Sur.,  1866- 

69.    E,  p.  264,  F,  p.  269,  1869. 
Kemp,  21,  pp.  180-181,  1906. 
Smith,  E.  M.,  E.  and  M.  Jour.,  vol.  61,  p.  566, 

1896. 
Vogt,  17,  Norway,  1910. 


DISSEMINATED    METALS     ORIGINAL    IN    ROCKS. 

GENERAL.  IN  ERUPTIVE  ROCKS. 


Forchhammer,  1854-1855. 

Lincoln,  2,  Association   of  gold  with  rocks, 

pp.  247-302,  1911. 
Vogi,  8,  1898,  1899. 
Washington,  2,  pp.  735-764,  1908. 


Blake,  11,  Gold  in  granite,  1896. 

Brock,  1,  1904. 

Catharinet,  Bornite,  1905. 

Derby,  1,  Gold  in  pegmatite,  1902 

Emmons,  S.  F.,  Leadville,  2,  pp.  574-584,  1886. 


SUBJECT    INDEX. 


915 


Harrison,  Fowler  and  Anderson,  pp.  52,  78,  96, 
204-211,  see  also  review  in  Econ.  Geol.,  vol. 
4,  p.  493,  1908. 

Hdmhacker,  2,  1891. 

Hussak,  3,  1898. 

Lincoln,  2,  pp.  247-302,  1911. 

Maclaren,  2,  pp.  100-103,  1908. 

Mallery,  Oregon,  1904. 

Mallet,  In  volcanic  ash,  1881. 

Merrill,  1,  Gold  in  granite,  1896. 

Hitter,  1,  1908. 

Washington,  2,  1908. 

(See  also  under  "  Magmatic  differentiation 
of  native  metals.") 


IN  SEDIMENTARY    ROCKS. 

Chance,  3,  Gold  in  coal,  pp.  227-228,  1899. 
Itieulefait,  2,  1879. 
5,  Zinc  in  dolomite,  1883. 

4,  Manganese  in  dolomite,  1883. 

5,  do.,  1883. 

6,  Copper  and  Zinc,  1885. 
Kemp,  21,  ditto,  p.  397,  1906. 
Lincoln,  2,  pp.  265-270,  1911. 
Lindgren,  15,  Shales  in  Kansas,  1902. 
Lovewell,  Shales,  1903. 

IN  METAMORPHIC  ROCKS. 

DieiOefait,  1, 1878. 

2,  1879. 

Lacroix,  3,  p.  21,  1903. 
Sandberger,  1,  2,  3,  4,  5,  6,  1877-1886. 
Spurr  and  Garrey,  4  p.  500,  1903. 


Spurr  and  Garrey,  4, 
Stelzner,  1, 1889. 

ELECTRICAL   ACTION    IN    ORE-DEPOSITION. 


Barns,  1.  1884. 

Becker,  1,  pp.  309-367,  1882. 

Erhard,  1885. 

Fritsch,  1862. 

Kenwood,  1,  1843. 

Hunt,  pp.  385-396,  400,  1884. 

Kemp,  21,  pp.  52-53,  1906. 


Monch,  pp.  365-435,  1905. 
Phillips-Louis,  pp.  12-5-126, 1896. 
Smith,  George,  1,  p.  77,  1896. 
Sutherland,  1890. 
Whitney,  1,  pp.  65-66, 1854. 
Wood,  G.  C.,  1906. 


EMANATIONS    FROM    IGNEOUS    MAGMAS. 

(Ore-deposits  have  been  conceived  as  arising  from  igneous  magmas  as  a  source 
and  depositing  ores  under  three  different  conditions  :  ( 1 )  As  final  products  of  dif- 
ferentiation or  solidification  of  the  rock  mass,  more  or  less  extensively  mingled 
with  molten  eruptive  rock,  and  producing  pegmatite  veins  ;  (2)  As  solutions  not  ap- 
preciably mingled  with  molten  magma,  i.  e.t  as  pneumatolytic  vapors,  producing 
deposits  under  conditions  of  high  temperatures  and  pressures  usually  conceived  as 
produced  by  deep  burial.  When  such  vapors  act  on  limestones  contact-metamorphic 
deposits  are  produced  (which  see)  ;  (3)  As  solutions  emanating  from  the  magmas 
in  the  same  way,  but  migrating  to  greater  distances  from  them,  and  giving  rise 
both  to  hot  mineral  springs,  and  to  the  usual  types  of  ore-deposits,  veins,  replace- 
ments, etc.  Commonly  called  hydrothermal  deposits  ( Hyd-atogenetic] .  These  three 
headings  are  used  in  classifying  the  following  references. ) 


EMANATIONS  IN  GENERAL. 

Bancroft,  4,  vol.  38,  pp.  245-268,  1909. 
de  Beaumont,  1,  Hist.,  1850. 
Beck,  8,  pp.  424-132,  1909. 

9,  vol.  ii.,  pp.  55-70,  1909. 
Sergeat-Stelzner,  pp.  1213-1230,  1906. 
Brun,  1911. 

Buckley,  Econ.  Geol.,  vol.  iv,  pp.  178-186, 1909. 
Chamberlin,  R.  T.,  1,  Gases  in  rocks,  1909;  2, 

1908. 

Church,  Trans.  A.  I.  M.  E .  vol.  23,  p.  593. 
Clarke,  F.  W.,  2,  pp.  201-205 ;  248-276,  1908. 
Daubree,  A.,  1,  p.  236,  1858. 
de  Launay,  1,  1893. 
Emmons,  19,  Cananea,  pp.  352-356,  1910.    10, 

1893, 

Finch,  1904. 
Frazer,  5,  1904. 

Gautier,  A.,  Relation  of  thermal  waters  to  vul- 
canism,  1906. 

S,  1906;  3,  1906. 

4,  Gases  in  rocks,  1906. 
Graton,  1,  1906. 

2,  Shasta  Co.,  Cal.,  pp.  71-111, 1910. 
Gregory,  11,  Geology  of  the  inner  earth,  1908. 
Gudzent,  1910. 
Heusler,  Relations  of  ores  to  igneous  rocks, 

1901. 

Hochsletter  and  Teller,  1,  1878. 
Kemp,  14,1901. 

16,  1902  ;  18, 1904  ;  24,  1906  ;  28,  1908. 
Lincoln, 1, 1907. 


Lindgren  and  Ransome,  3,  Cripple  Creek,  pp. 
252-269  ;  gases  in  rocks,  pp.  225-231 ;  mag- 
matic origin  of  ores  advocated,  1906. 

Lotti,  5,  pp.  372-378,  Tuscany,  1893. 

Newberry,  4,  5,  6,  1880,  1883,  1884. 

Park,  3,  Relation  of  ores  and  thermal  activity, 
1905  ;  7, 1906. 

Pirsson,  pp.  189-190,  1908. 

Posepny,  2,  pp.  247-262,  1893. 

Ransome,  2,  pp.  132-141,  Silverton,  Colo,  1901. 
3,  Rico,  Colo.,  pp.  294-304,  Argues  against 
emanations,  1901. 

5,  pp.   128-132,   Against   magmatic  waters, 
Globe,  1903. 

6,  Bisbee,  pp.  146-160,  1904. 
10,  pp.  189-201,  Goldfield,  1907 
14,  Goldneld,  1910. 

Ransome  and  Calkins,  Coaur  d'Alene,  pp.  134- 

140,  1908. 
Rickard,  T.  A.,  7,  pp.  949-956,  1894. 

20,  1908. 

Rickard,  et  al,  2,  1903. 
Ries,  pp.  311-323,  1910. 
Spencer,  4,  S.  E.  Alaska,  1905. 

6,  Juneau  Veins,  1906. 
Spurr,  3,  Mercur,  pp.  396-401,  1895. 

8.  General,  1902. 

12, 1905. 

13,  Tonopah,  pp.  253-262.  1905. 

14,  Silver  Peak,  pp.  99-156,  1906. 

15,  Southern  Klondike,  pp.  369-38-2,  1906. 
17,  1907. 


916 


SUBJECT    INDEX. 


Spurr  and  Garrey,  3,  Georgetown,  pp.  157-158, 

169-171,1908. 
Stelzner,  2,  1896. 
Strutt,  Gases  in  rocks,  1907. 
Van  Hise,  6,  1901. 
Vogt,  1.,  Sulphides  of  Norway  and  Rammels- 

berg,  1894. 

9,  Rio  Tinto,  1899  ;  5,  1894. 

10,  pp.  130-158,  1901. 

Weed  and  Pirsson,  2,  Judith  Mts.,  pp.  594-598, 

1897. 

Winchell,  H.  V.,  2.  pp.  591-593, 1907. 
5, 1908  ;  6, 1908  ;  8, 1907. 


Magmatic  vs.  Meteoric  Waters. 

Clark,  2,  pp.  201-205, 1911. 
Darapsky,  1903. 
Daubree,  6.  A.,  1  and  2, 1887. 
Delkeskamp,  1904, 1905. 
Hague,  2, 1911. 
Henrich.F.,  1910. 
Kemp,  14,  1901. 

16,  1902  ;  18,  1904  ;  24,  1906  ;  28,  1908. 
Rickard,  T.  A.,  20, 1908  ;  5,  1893  ;  7,  pp.  949-956. 
Van  Hise,  4,  pp.  27-177, 1900. 

6,  pp.  284-303,  1901. 

8,  pp.  1052-1069,  1904. 
Vogt,  5, 1894. 

10, 1901. 


PEGMATITIC  OKE-DEPOSITS. 

Beck,  U,  1906. 

6, 1906  ;  7,  1909. 

Bergeat-Stelzner,  pp.  918-964, 1906. 
Brogger,  pp.  215-235,  1890. 
Catharinet,  Bornite  in  pegmatite,  1905. 
Crosby  and  Fuller,  Origin  of  pegmatites,  1897. 
Derby,  1,  Gold  in  pegmatite,  1902. 
Hastings,  5,  Origin  of  pegmatite,  1908  ;  1,  1905. 
Hussak,  3,  Gold  in  pegmatite,  1898. 
Kemp,  14,  pp.  182-183,  1901. 
Pirsson,  General  excellent  discussion,  pp.  174- 

180,  1908. 
Rickard,    et  al.,   1,   "A   discussion."     Many 

other  authors,  1903. 
Ritter,  1,  Sulphides  in  pegmatite,  1908. 
Spencer,  1, 1904. 

7,  1908. 

Spurr,  4,  pp.  297-316,  Esp.   308-316,  good  gen- 
eral discussion.    Yukon  veins,  1897. 

8,  General,  1902. 

9,  1903. 

12,  W.  Nevada  ores,  1905. 

14,  Excellent  general  discussion  on  pegma- 
titic  origin  of  veins,  pp.  99-156,  1906. 

15,  1906  :  16,  pp.  1-22, 1907  ;  17,  1907. 

Spurr  and  Garrey,  3,  pp.  157-158,  169-171,  1908. 
Stutzer,  10,  1909. 
Vogt,  5,  1894. 
6,  1895  ;  10, 1901. 


PNEUMATOLYSIS. 

Beck,  8,  pp.  421-424,  1909. 

Bergeat-Stelmer,  pp.  19,  24,  527,  920,  921,  1186, 
1213,  1906. 

Clarke,  2,  New  Edition,  pp.  606-610, 1911. 

Dolmer,  5,  1894. 

Phillips-Louis,  pp.  127-129, 173,  1896. 

Rickard,  etal.,1,"  Discussion,"  pp.  19-20  (Em- 
mons),  25-27  (Weed) ;  also  excellent  dis- 
cussion by  others,  1903. 

Scrivenor,  Origin  of  Tin  Ores,  1909. 

Thomas  and  MacAlister,  pp.  5,  72-115,  1908. 


Vogt,  1,  1893  ;  5,  1894. 

10,  1901. 
Vogt,  Beyschlag  and  Krusch,  pp.  165-167,  1910. 

(A  few  references  only  are  given  on  pneuma- 
tolysis,  as  the  process  is  not  generally  very 
sharply  distinguished  from  other  processes 
of  magmatic  emanation.  See  also  under 
Sublimation.) 

HYDROTHERMAL  EMANATIONS. 

(See  also  under  Mine  Waters,  p.  927  of  this 
bibliography.) 

Beck,  8,  pp.  424-432,  1909. 

9,  vol.  ii.,  pp.  55-70,  1909. 
Bergeat-Stelzner,  pp.  1213-1230,  1906. 
Chalon,  1, 1905. 
Chamberlin,  R.  T.,  1, 1909. 
Clarke,  F.  W.,  2,  New  Edition,  pp.  201-205,  283- 

286,  606-610,  1911. 
Darapsky,  1903. 
Daubree,  A.,  1,1858. 

2,  pp.  71-102,  1879. 

de  Lannay,  7,  1899 ;  1,  1893. 

Delkeskamp,  3,  4,  5,  6,  7,  8,  1903, 1908. 

Finch,  1904. 

Fink,  Deposition  of  specularite  by  thermal 

waters,  1906. 

Griffiths,  Quicksilver,  New  Zealand,  1910. 
Gudzent,  Radio  active  thermal  springs,  1910. 
Hague,  2, 1911. 
Hastings,  6, 1908. 
Headden,  Radium  springs,  1905. 
Henrich,  F.,  1910. 
Heusler,  1901. 
Hixon,  1,  1907;  2,  1908-9. 
Kemp,  14,  1901  ;  16,  1902:  17,  1903:  18,  1904;  19, 

1904  ;  22,  1906 ;  24,  1906  ;  26,  1907  ;  28, 1908. 
Kohler,  Eugen,  1910. 
Konig,  F.,  1901. 

Le  Conte,  2,  Steamboat  Springs,  1883. 
Le  Conte  and    Rising,  Sulphur   Bank,    Cal., 

1883. 

Lincoln,  1,  Excellent  general  summary,  1907. 
Lindgren,  11,  Gold  and  silver,  in  sinter,  1899. 
21,  Steamboat  Springs,  1905. 
31,  1910  ;  14,  pp.  240-242,  1901  ;  19,  pp.  219-223, 

1904  ;  27,  p.  749,  1907. 
Lindgren,  Graton  and  Gordon,  pp.  56,  71,  74, 

New  Mexico,  1910. 

Lindgren  and  Ransome,  3,  pp.  225-231, 1906. 
Lotti,  5,  pp.  372-378,  Tuscany,  1893. 
Morris,  1903. 
Mutter,  H.,  1,  Mineral    springs    in    Freiberg 

mines,  1885. 
Park.  3, 1905;  7,1906. 
Phillips-Louis,   pp.    115-119,   135-142,   793-795, 

1896. 
Phillips,  3,  1879. 

4,  1871. 

Rickard,  T.  A.,  7,  1894 ;  20,  1908. 
Rickard,  et  al.,  1,   "A  Discussion,"  pp.  27-29 

(Weed),  also  excellent  discussion  by  many 

writers,  1903;  2,1903. 
Spurr,  17,  1907. 
Strutt,  1907. 
Stutzer,  18,  1910. 
Suess,  £,  S,  1902. 

Thomas  and  MacAlister,  pp.  116-236,  1908. 
Van  Hise,  4,  pp.  47-51, 1900. 
6,  1901. 

8,  pp.  1052-1069,  1904. 
Vogt,  5,  1894-5  ;  10,  pp.  132-147,  1901. 
Weed,  1,  Gold-bearing  hot  springs,  1891. 

3,  1900  ;  13,  1903. 

Weed  and  Pirsson,  4, 1893. 

Winchell,  H.  V.,  5,  1907  ;  6,  1908 ;  8,  1907. 


SUBJECT    INDEX. 


917 


EXPERIMENTAL  DATA  APPLIED  TO  ORE- 
DEPOSITION. 


Aston,  1,  Alloys  and  magmas,  1909. 

Biddle,  Deposition  by  ferrous  salts,  1901. 

Browne,  D.  H.,  2,  Magmas  and  mattes,  1895. 
3,  ditto,  1906. 

Daubree,  A.,  2,  General,  Many  applications  on 
fissure  formation  and  synthesis  of  min- 
erals, 1879. 

Doelter,  1,  pp.  79-112,  Stability  of  minerals 
under  certain  temperatures  and  pressures, 

2,  Solubility  of  minerals,  1890. 
Fernekes,  Precipitation  of  copper,  1907. 
Gautier,  A.,  2,  Action  of  H2S  on  certain  oxides, 
1900. 

S,  Action  of  water  vapor  on  sulphides,  1906. 
Jenney,  2,  Reducing  agents  in  nature,  1902. 
Neunier,  General,  1904. 


Stokes,  1,  Pyrite  and  marcasite,  1901. 

2,  Solution  of  copper,  silver  and  gold,  1906. 

3,  Solution  of  pyrite  and  marcasite,  1907. 
ullivan,  1,  Precipitation  of  copper  bv  Sili- 


Sullivan, 

cates,  1906. 

2,  Reactions  of  water  solutions   and   min- 
erals, 1907. 

3,  Mineral  filters,  1908. 
Weed,  17,  Adsorption,  1905. 

Wells,  Fractional  precipitation  of  sulphides, 
1910. 

Winchell,  A.  N.,1,  Oxidation  of  pyrite,  1907. 

Winchell,  H.  V.,  3,  Synthesis  of  chalcocite, 
1903. 

Wright  and  Larsen,  Quartz  as  a  geologic  ther- 
mometer, 1909. 


FAULTS  AND  FAULTING. 


Barrell,  2,  at  Marysville,  Montana,  pp.  94-104. 

1907. 

de  la  Beche,  General,  pp.  283-348,  1839. 
Beck,  8,  pp.  138-163,  General,  1909. 

9,  vol.  ii.,  pp.  199-225,  General,  1909. 
Becker,  1,  pp.  156-187,  at  Comstock  lode,  1882. 
Bergeat-Stdzner,  General,  pp.  100,  487,  492,  496, 

501,  507,  1906. 

Burnt,  pp.  44-54,  General,  Hist.,  1870. 
Chamberlin,  T.  C.,  2,  General,  very  theoreti- 

cal, 1907. 

Chance,  1,  p.  11,  1883. 
Church,  2,  Causes  of,  1893. 

1,  In  Veins,  1892. 
von  Cotta,  1,  1861. 

2,  pp  29-32,  1870. 

Gushing,  Discussion  of  Ransom  e,  8,  1907. 
Daggett,  at  Berlin  Mine,  Nevada. 
Dana,  1,  1907. 
Dannenberg,  General,  1884. 
Daubree,  A.,  2,  pp.  289-378,  1879. 
Emmons,  S.  F.,  2,  especially  pp.  284-292.    Of 
general  application,  1886. 

6,  General,  815-829,  1888. 

7,  In  veins,  1892 

Evans,  Discussion  of  Ransome,  8,  1907. 

Fairchild,  ditto,  1907. 

Farish,  1,  at  Rico,  Colo.,  pp.  151-164,  1892. 

Farrell,  pp.  94-102,  1912. 

Freeland,  2,  Fault-  rules,  excellent    but    old 


Bibliography,  1893. 
Goupilliere,  vol.  I.,  pp.  68-86,  1883. 
von  Groddeck,  1,  pp.  18-27,  1879. 
Greenwell,  p.  116,  1889. 
Gunther,  2,  pp.  33-42,  1912. 
Heim,  1,  vol.  ii.,  General,  1878. 
Henwood,  1,  1843. 

2,  pp.  17,  31,  1871. 
Hofer,  1,  General,  1886. 

2,  Determination  of  faults,  1881. 


Jaggar,  Discussion  of  Ransome,  8, 1907. 

Jenney,  4,  Block-faulting,  1906. 

KoMer,  <?.,  2,  pp.  21-39,  1887. 

Moissenet,  pp.  50,  54,  71,  85,  1877. 

Park,  4,  Rules  for  finding  faults,  pp.  93-104, 

1906. 

Phillips-Louis,  pp.  11-21,  74-80,  1896. 
Prestwich,  vol.  I.,  pp.  252-256,  318-321,  1886. 
Ransome,  6,  at  Bisbee,  pp.  85-104, 1904. 
8,  Direction  of  movement  and  nomenclature 

of,  1906. 
14,  at  Goldfield,  pp.  83-85,  161-162,  196,  201, 

1909, 

5,  at  Globe,  pp.  9^106,  144-148,  1903. 
Ransome  and  Calkins,  at  Coaur  d'Algne,  pp. 

17,  18,  61-69,  73-76,  84,  107,  117,  120-121,  134. 

139,  142,  1908. 
Raymond,  4,  Hofer's  method,  discussion  of, 

1882. 

Reid,  H.  F.,  1912. 
Reid,  J.  A.,  1,  at  Comstock  lode,  1905 

4.  Discussion  of  Ransome,  9,  1907. 
Russell,  pp.  442,  450-453, 1884. 
Schmidt,  J.  C.  L.,  1910. 
Serif),  pp.  35-48,  1878. 

Spurr,  5,  at  Aspen,  Colo.,  much  of  general  ap- 
plication, pp.  58-72,  84-107, 117, 120-130, 145- 

146,  148-149,  244,  251-256, 1898. 
16,  General,  pp.  148-164, 1907. 
18,  Discussion  of  Ransome,  8, 1907. 
13,  Tonopah,  pp.  7,  21-22,  37-38,  47-82,  115- 

116,  141-142,  146,  149,  158-161,  164,  1905. 
Tolman,  1,  Discussion  of  Ransome,  8, 1907. 

6,  Graphical  solution  of  faults. 
Van  Hise,  2,  pp.  672-678,  1896. 
Weed,  18,  Mutual  displacement  of  veins,  1907. 
Whitney,  1,  p.  57, 1854. 
Willis,  1,  Appalachians,  1892. 
Zimmermann,  1,  pp.  49-72,  80, 1828. 


FISSURE-VEINS. 


GENERAL. 


Beck,  8,  pp.  111-431,  1909 ;  9,  pp.  169-540,  1909. 


Bergeat-Stdzner,  pp.  471-1006,  1906. 

Brown-  A.  J.,  1874. 

Emmons,  S.  F.,  4, 1887;  6,  1888. 

Kemp,  21,  pp.  39-53,  1906. 

Phillips-Louis,  pp.  69-150,  1896. 

Rickard,  T.  A.,  8,  Vein- walls,  1896, 

Ries,  pp.  329-335,  1910. 

Thomas  and  MacAlister,  pp.  116-236,  1908. 

Spurr,  16,  pp.  177-193, 1907. 

Vogt,  BeyscMag  and  Krusch,  Band  II.,  H.  2,  pp. 

1-209,  1912. 
Wallace,  J.  P.,  pp.  174-205,  1908. 


FISSURES. 

(See  also  under  "  Cavities  in  Rocks." ) 

Systems  of. 
(With  many  illustrations  of  vein  groups.) 

Beck,  8,  Map  of  Freiberg,  1909. 

9,  Map  of  Freiberg  veins,  1909. 
Brown,  R.  G.,  2,  at  Bowie,  Cal.,  1907. 
Bergeat-Stdzner,  pp.  618,  625,  654,  659,  766,  854, 

1906. 
Daubree,  A.,  2,  pp.  289-378, 1879. 


918 


SUBJECT    INDEX. 


Lindgren,  8,  pp.  164-170,  Grass  Valley,  1896. 
11,  pp.  101-103,  of  Central  Idaho,  1899. 
13,  pp.  600-601,  at  Blue  Mts.,  Oregon,  1901. 
Lindgren  and  Ransome,  '6,  at  Cripple  Creek, 

pp.  158-167,  ]  906. 
MacAlister  and  Hill,  p.  206,  at  Cornwall,  Eng- 

land, 1906. 

Muller,  H.  ,  2,  at  Freiberg,  Saxony,  1901. 
Ransome,  2,  at  Silverton,  pp.  43-67,  1901. 

3,  pp.  255-261,  290-293.  at  Rico,  Colo.,  1901.    ' 
Ransome  and  Calkins,  pp.  115-116,  at  Cceur 

d'Algne,  Idaho,  1908. 
Rickard,  T.  A.,  9,  Rico,  Colo.,  1896. 
Phillips-Louis,  pp.  80-85,  1896. 
Spurr,  11,  pp.  18-21,  at  Tonopah,  Nevada,  1903. 

16,  pp.  177-193,  1907. 
Tower  and  Smith,  at  Tintic,  Utah,  pp.  676-683, 

1898. 
Vogt,  Beyschlag  and  Krusch. 

Origin  of  Fissures. 

Beck,  8,  pp.  163-173  ;  9,  pp.  226-235,  1909. 
Becker,  4,  pp.  407-415,  At  Comstock  Lode,  1888. 

7,  1893  ;  8,  1893  ;  9,  1894. 
Bergeat-Stelzner,.  pp.  471-508,  1906. 
Beutlien,  Berg-  und  Hiitten,  Zeitung,  p.  165,  1891. 
Brown,  A.  J.,  1874. 
Crosby,  2,  1882  ;  3,  1887  ;  4,  1893. 
Daubree  A.,  Les  Eaux  Souterraines,  III,  1887. 
Daubree,  G.  A.,1  and  2,  1887. 
Emrnons,  S.  F.,  4,  pp.  193-208,  1887  ;  6,  pp.  810- 

839.  1888. 

Heim,  J,  p.  44,  1878. 
Keilhack,  1,  Review  of  longer  paper,  1895. 


Kemp,  21,  pp.  13-31,  Cavities  in  rocks,  1906. 

,  8, 
1897. 


, 
Lindgren,  8,  pp.  169-170,  Ib96  ;  11,  pp.  102-103, 


Lindgren  and  Ransome,  3,  pp.  167-168,  Cripple 

Creek  veins. 
Lossen,  1886. 
Margerie  and  Htim,  "  Die  Dislocation  der  Er- 

drinde,"  Zurich,  1888. 
Muller,  H.,  2,  of  Freiberg  fissures,  1901. 
Nason.  E.  and  M.  Jour.,  vol.  71,  pp.  177-179, 

209-210,  1901. 

Phillips-Louis,  pp.  80-85,  1896. 
Posepny,  Leoben  Jahrbuch,  vol.  22,  p.  233,  1874. 
Purington,  1,  pp.  771-781,  1897. 
Ransome,  2,  pp.  43-47,  Excellent  discussion  of 

general  application,  1901. 
Ransome  and  Calkins,  pp.  134-135,  1908. 
Spencer,  5,  of  S.  E.  Alaska  fissures,  pp.  581-586, 

1905  ;  6,  of  Juneau  fissures,  pp.  27-28,  1906. 
Spurr,  6,  pp.  806-828,  Relation  to  joints  (of 

general  import),  1901;  16,  pp.  177-184,  1907. 
Voyt,  Beyschlag  and  Krusch,  Band  II,  H.  1,  pp. 

1-11,  Excellent  general  discussion,  1912. 
Weed,  Science,  New  series,  vol.  20,  p.  761,  Dila- 

tion fissures,  1904. 
Werner,  Hist.,  1791. 
Whittlesey,  p.  213. 

Displacements,    Irregularities     and 
Relative  Ages  of  Fissures. 

(See  also  under  "  Faulting.") 
Beck,  8,  pp.  112-161,  1909. 

9,  pp.  172-184,  190-226,  1909. 
Bergeat-Stelzner  ,  pp.  492-520,  1906. 
Church,  1,  Faulting  in  veins,  1892 
Emmons,  S.  F.,  7,  p.  548,  1892. 
Freeland,  2,  1893. 
Gresly,  p.  517,  1892. 
Hofer,  4,  Age  of  veins,  1899. 
Klockmann,  Zeit.  f.  prak.  Qeol.,  vol.  1,  p.  466, 

1893. 

Kohler,  G.,  2,  1884. 
Lindgren,  9,  pp.  647-651,  1897. 
Park,  4,  pp.  59-77,  93-104,  1906. 
Phillips-Louis,  pp.  13-19,  60-84,  150-168,  1896. 
Ricketts,  p.  565,  1892. 
Spurr,  13,  pp.  96-206.  Tonopah,  1905. 

14,  pp.  36-96,  Silver  Peak. 

16,  p.  177-199  etseq.,  1907. 

Spurr  and  Garrey,  1,  pp.  39-40.    Faulting  at 
Idaho  Springs,  Colo.,  1905. 

3,  Rel.  age  of  Georgetown  Veins,  pp.  99-101, 
1908. 


Van  Hise,  2,  pp.  589-603,  633-C68,  669-678,  1896. 

8,  p.  1201,  1904. 
Weed,  18,  1907. 

Williams,  Albert,  Jr.,  2,  Dip  and  strike,  1892. 

Classification  of  Fissure-Veins. 

Beck.  8,  pp.  191-195. 1909,    9,  pp.  257-260,  1909. 
Bergeat-Sttlzner,  pp.  566-571, 1904-1906. 
Breithaupt,  "Die  Parageuesis  der  Mineralien," 

Freiberg,  1849. 

von  Cotta,  2,  pp.  478-500,  1870. 
von  Qroddeck,  1, 1879. 
Werner,  pp.  224-251, 1791. 

Structure  and  Arrangement  of  Mineral 

Contents  of  Fissure-Veins. 

(Paragenesis. ) 

Beck,  8,  pp.  173-193, 1909. 

9,  pp.  237-256,  1909. 
Bergeat-Stelzner,  pp.  530-541,  1906. 
Boutwell,  5,  pp.  158-160,  161, 1905. 
Breithaupt,  "Paragenesis,"  Freiberg,  1849. 
Cornu,  F.,  1,  of  Zeolites,  1907. 

Cornu  and  Lazerovic,  in  copper-ores  of  Servia, 

1908. 

Farish,  1, 1892. 
von  Qroddeck,  1,  p.  61, 1879. 
Hqfmann,  A.,  Kurze  Ubersicht  der  montangeolo- 

gischen  Verhaltnisse  des  Pribramer  Bergbaues, 

Filhrer  /.  d.  Exkurs.  IX.  Int.  Geol.  Kongr., 

Wein,  1903,  No.  1. 
Kemp,  21,  pp.  47-53, 1906. 
Klockmann,  Zeit.  f.  prak.  Geol.,  vol.  1,  p.  466. 

1893. 

Kohler,  G.,  2, 1887. 
Lindgren,  8,  pp.  128-144,  Grass  Valley  ores,  1896. 

13,  pp,  601-603.  in  Blue  Mt.  veins,  1901. 
Lindgren  and  Ransome,  3,  pp,  176-182,  Cripple 

Creek  lodes,  1906. 
Lindgren,  Graton,  and  Gordon,  New  Mexico 

ores,  pp.  58-59, 1910. 
Muller,  H.,  Uber  eine  merkw.  Druse  auf  einem 

Schneeberger  Kobaltgange.  Zeit.  d.  D.  GeoL 

Gesel.,  vol.  2,  pp.  14-18, 1850. 
Naumann-Zirkel,  Elemente  der  Mineralogie,  14th 

ed.,  pp.  166-174, 1901. 
Neubert,  Gang  geologische  Verhaltnisse  bei  Him- 

melsfurstFundgr.,Jahr.f.d.  Berg.  u.Huttenw. 

i.  Sachs.,  p.  663, 1881 ;  pp.  126-127, 1890. 
Posepny,  2,  pp.  217-220,  244-247,  254-262,  1894. 
Pumpelly,  2, 1891. 
Purington,  1,  pp.  796-802. 1897. 
Ransome,  2,  in  Silverton  lodes,  pp.  67-70,  87- 

93,  1901. 

3,  pp.  261  to  265,  Rico  lodes,  1901. 
Ransome  and  Calkins,  Cceur  d'Alene,  pp.  107. 

127-129,  1908. 
Reuss,  A.  E.,  Paragenese  der  auf  den  Erzgangen 

von    Pribram    einbrechenden    Mineralien ; 

Sitzber.  k.  k.  Akad.  d.  Wiss.,  Ivii,  pp.  13-76, 

1863. 
Rickard,  8,  pp.  193-241,  1896. 

9,  Scattered  discussion,  pp.  919-980, 1896. 
Rogers,  A.  F.,  Econ.  Geol.,  vol.  7,  pp.  638-646, 

1912. 

Rolker,  3,  in  Honduras  vein,  1885. 
Schraiif,  of  metacinnabarite,  1891. 
Simpson,  of  Butte  ores,  1908. 
Smyth,  H.  L  ,  2,  gold  and  pyrite,  1906. 
Spurr,  6,  Monte  Cristo  ores,  pp.  835-840, 1901. 
Tower  and  Smith,  Tintic.  p.  704, 1898.     - 
Tschermak,  Lehrbuch  der  Mineralogie,  1894. 
Tscherne,  General  discussion,  1892, 
Vogt,  Beyschlag,  and  Krusch,  pp.  93-114, 1909. 
von  Weissenbach,  G.  A.,  "  Abbildungen  merkw. 

GangverhdUnisse  aus  dem  sdchs.  Erzgebirger 

Leipzig,  1836. 

THE   FILLING   OF   MINERAL 
VEINS. 

(See  under  "  Sublimation,"  "  Injection," 
"  Ascension  Theories,"  "  Descension  Theo- 
ries," "  Lateral  Secretion ''  and  subhead  "  Hy- 
drothermal  Emanations  "  of  "  Emanations- 
from  Igneous  Magmas." 


SUBJECT    INDEX. 


919 


GEOGRAPHIC    DISTRIBUTION    OF    METALLIF- 
EROUS DEPOSITS. 


Bain,  4,  Relation  of  ores  to  paleogeography, 
1907. 

Becker,  3,  Relation  of  ores  to  zones   of  up- 
heaval, 1884. 

von  Cotta,  2,  pp.  -509-516,  1870. 

de  Launay,  9,  Theories  of  geographic  distri- 
bution applied  to  Africa,  1903. 
IS,  to  Italy,  1906. 

17,  to  Russia,  1909. 

18,  to  Asia,  1911. 


Ransome,  7,  Distribution  in  U.  S.,  1904. 

Raymond,  3,  U.  S.,  1871. 

Smock,  of  iron  in  the  Eastern  U.  P.,  1884. 

Spurr,  13,  Excellent  discussion  of  geographic 

distribution  in  general,  pp.  278-287, 1905. 
!  Spurr  and  Garrey,  3,  pp.  102-130,  General  dis- 
cussion of  distribution  in  Colorado,  1908. 

Weed,  19,  Copper  deposits  of  the  world,  1908. 


GEOLOGIC  AGE  OF  ORE-DEPOSITS. 


Aguilera,    Geologic   distribution    of  ores   in 

Mexico,  1901. 

von  Cotta,  2,  pp.  526-546,  1870. 
Kemp,  21,  pp.  445-447,  1906. 
Lindgren,  28,  Metallogenetic  epochs,  1909. 
29,  ditto,  1909. 

16,  Geologic  features  of  U.  S.  gold-produc- 
tion, 1902.  See  also,  Proc.,  5th  Int.  Min. 
Congress,  pp.  29-36, 1903. 


Lindgren  and  Knowlton,  Age  of  gold-placers 

California,  1896. 
Purington,  1,  Age  of  Telluride  ores,  pp.  824-825, 

Rickard,  T.  A.,  21,  of  Colorado  ores,  1910 ;  Gold, 

19,  1906-7, 

Ries,  Metallogenetic  epochs,  pp.  342-345, 1910.. 
Spurr,  3,  Mercur  ores,  pp.  437-439,  1895. 

10,  Discussion,  1903. 
Stirling,  2,  Victoria,  Australia,  1900-1901. 


LATERAL  SECRETION. 


Beck,  8,  pp.  413-420,  General,  1909. 
9,  General,  vol.  I.,  pp.  43-50,  Argued  for  cop- 
per in  basic  rocks,  vol.  I.,  pp.  342, 1909. 

Bergeat-Stelzner,  pp.  1193-1202,  General,  1906. 

Bischoff,  1,  2nd  Ed.,  pp.  1209,  2121-2126,  1863- 
1871. 

Carthaus,  Discussion  of  Sandberger,  1896. 

Clarke,  2,  New  Edition,  pp.  600-602,  1911. 

Delkeskamp,  2,  Significance  of  barite   veins, 
1902. 

Dieulefait,  1,  2,  3,  U,  5,  6,  Original  metals  in 
rocks,  1878-1885. 

Don,  Argument  against  in  New  Zealand  gold- 
ores,  1897. 

Emmons,  S.  F.,  2,  Applied  to  Leadville  ores, 
1886. 

Forchhammer ,   Presence  of  metals  in    rocks, 
1854-1855. 

Kemp,  21,  pp.  40-43, 1906. 

Mallet,  Silver  in  volcanic  ash,  1881. 


Patera,  Applied  to  Pribram,  1888. 
Phillips-Louis,  pp.  129-136,  Excellent  general 

discussion,  1896. 

Posepny,  2,  pp.  248-254,  1893 ;  5,  1885. 
Purington,  1,  Discussion  for  Telluride,  Colo., 

pp.  819-824,  1897. 
Robertson,  J.  D.,  Missouri  Qeol.  Sur.,  vol.  7.  pp. 

479-481,  1894. 
Sandberger,  1,  pp.  377-381,  389-392  et  seq.,  1877. 

2,  General,  1880. 

3,  voL  I.,  pp.  31-36,  vol.  II.,  pp.  159-245,  1883- 
1885. 

-4,  1883. 

5,  Theories  of  vein-formation,  1884. 

6,  Researches  at  Pribram,  Bohemia,  1886. 
Sehroeder,  in  connection  with  tin,  1883. 
Stelzner,  1,  Criticism  of  Sandberger's  theories, 

1889. 

Wadsworth,  2, 1884. 
Wendeborn,  1904. 


MAGMATIC  DIFFERENTIATION. 


GENERAL  DISCUSSION. 
Applied  to  Rocks. 

Becker,  15, 1897. 

16,  1897. 
Brogger,  1890. 

Clarke,  2,  New  Edition,  1911. 
Daly,  2,  1906. 
Gregory,  11, 1908. 
Harker,  1,  Rec.,  1907. 

2,  1909. 

Iddings,  1, 1909. 
Lane,  2,  1906. 
Morozewicz,  "2,  1899. 

Pirsson,  pp.  164-180,  Especially  Rec.,  1908. 
Rosenbusch,  1890. 
Zirkel,  1,  pp.  778-794,  1893. 

Applied  to  Ores. 

General. 
Beck,  8,  pp.  11-49, 1909. 

9,  vol.  I.,  pp.  17-97,  1909. 

Bergeat-Stelzner,  pp.  19-85,  with  full  bibliogra- 
phy, 1906. 
Garrison,  2, 1909. 
Gregory,  11, 1908. 
Kemp,  21,  pp.  59-67,  72,  1909  ;  E.  and  M.  Jour., 

vol.  76,  pp.  804-805, 1903. 
Lotti,  2,  pp.  18,  19,  29-50,  1903. 


Park,  2,  1905. 

5,  1906. 

Phillips- Louis,  pp.  179-184,  1896. 
Rickard,  et.  al.,  1,  Discussion  by  many  writers^ 

1903. 

Thomas  and  MacAlister,  pp.  21-71, 1908. 
Trener,  1905. 
Vogt,  1,  General,  1893. 

5,  Classification  of  types.    Oxides,  pp.  383- 
384,  sulphides,  pp.  394-395,  native  metals, 
pp.  395-399,  1894. 

6,  English,  excellent  review  of  subject,  1895. 

10,  (English),  p.  131, 1901. 

11,  Titaniferous  ores,  1900. 

12,  in  Effusive  rocks,  1902. 
U,  1905. 

16,  Magnetic  iron-ores  in  granite,  1907. 

17,  Rtfdsand  iron-ores,  1910. 

Vogt,  Beyschlag  and  Krusch,  General.     Vol.  J.v 
pp.  162-165,  vol.  II.,  pp.  239-344,  1910. 

OXIDIC  OKE-DEPOSITS. 
Chromium. 

Cirkel,  pp.  85-87, 1909. 
Glenn,  2,  1897-8. 
Hall  and  Humphreys,  2,  1908. 
Pratt,  1,  1899. 
Vogt,  5,  pp.  384-393,  1894. 

Vogt,  Krusch,  and  Beyschlag,  vol.  i,  pp.  241-246 
1910. 


920 


SUBJECT    INDEX. 


Corundum. 

Pratt,  2,  1899. 

3, 1898 ;  4,  1906.    See  also  vol.  i,  Nor.  Car. 
Geol.  Sur.,  pp.  331-357, 1905. 

Iron. 

Adams,  F.  D.,  1,1894. 
Beck,  9,  vol.  1,  pp.  28-67. 
de  Launay,  10,  1903. 
Henrickson,  1906. 
Kemp,  11,  pp.  417-419, 1898. 

12,1899. 
Lowinnson- Leasing,  1,  Ural  Mts.,  1907. 

«,  ditto,  1909. 
Newland,  2, 1907. 
Newland  and  Kemp,  1908. 
Sjogren,  1,  Taberg,  Smaland,  1886. 

2,  1891. 

3,  Scandinavian  iron-ores,  1907. 
Stutzer,  1,  Kiruna,  1906. 

8,  1907. 
Vogt,  11,  1901. 

16,  Iron-ore  in  granite,  1907. 

17,  Titaniferous  ore  in  Norway,  1910. 

Vogt,  Krusch,  and  Beyschlag,  vol.  i,  pp.  247-274, 

1910. 
Warren,  Cumberland,  R.  I.,  Am.  Jour.  Sci.,  4th 

ser.,  vol.  25, 1908. 

SULPHIDE  DEPOSITS. 

Adams,  F.  D.,  1,  General  discussion  of  nickel- 
bearing  sulphides.    Excellent,  1894. 

Austin,  Riddles,  Oregon,  Nickel,  1896. 

Barlow,  1,  Sudbury,  1904. 
2,  ditto,  1906. 

Bastin  and  Hill,  Econ.  Geol.,  vol.  vi,  pp.  465- 
472, 1911. 

Beck,  3,  Sohland,  Nickel,  1903. 

8,  pp.  12-48,  General,  1909. 

9,  vol.  I.,  pp.  67-97,  General,  1909. 
Bergeat-Stelzner,  pp.  41-63,il906  (with  full  refer- 
ences to  literature). 


Browne,  D.  H.,  3,  Sudbury  nickel,  1906. 
Catharinet,  Bornite,  1905. 
Chaper,  Caucusus  Mts.  copper,  1893. 
Coleman,  2,  Sudbury  nickel,  1905.    See  also, 
Butt.  Geol.  Soc.  Am.,  1904. 

4,  ditto,  1907. 

5,  Nickel,  1910. 

Dickson,  1,  Sudbury  nickel  (argument  against 

magmatic  differentiation),  1903. 
3,  ditto,  1906. 

Gamier,  "Mines  de  Nickel  de  Sudbury,"  Paris, 
1891. 

Hille,  1,  Atik-Okan  nickel,  1905. 

Kay,  nickel,  1907. 

Kemp,  7,  Nickel,  Penna.,  1894. 

Leckie,  Norwegian  nickel,  1904. 

Packard,  Summary  of  theories  of  origin  of 
nickel-ores,  1893. 

Eimann,  Zinc-blende,  1910. 

Ritter,  1,  Bornite  and  chalcopyrite,  1908.  See 
also  recent  paper  on  Econ.  Geol.,  by  U.  S. 
G.  S.  man,  on  same  deposit. 

Stutzer,  7,*Bornit,e,  1907. 

Vogt,  7,  Comparison  of  Norwegian  and  Cana- 
dian nickel-ores,  1897.  1,  pp.  125-143,  257- 
268, 1893  ;  4,  1894  ;  5,  pp.  381-399,  1895  ;  6  (in 
English),  1895. 

Vogt,  Krusch,  and  Beyschlag,  Band  1,  pp.  16-241, 
275-336,  1910,  also  Band  1,  H.  1,  pp.  162-164, 
1909. 

Walker,  1,  Sudbury  nickel-ores,  1897. 

Watson,  4,  pp.  683-698,  1907. 

Weinschenclc,  Nickel,  Germany,  1907. 

Comparison   with    Solidification    of 

Slags. 
Browne,  D.  H.,  2, 1895;  3, 1906. 

Native  Metals. 

See  under  "  Disseminated  Metals  Original 
in  Rocks;"  sub-head:  "Eruptive  Rocks." 


METASOMATISM. 

("See  under  l<  Replace oient.") 


MINERALOGY  OF  METALLIFEROUS  ORES. 

(A  few  of  these  papers  containing  chapters  especially  devoted  to  descriptive 
mineralogy  are  indicated  here. ) 

Bain,  2,  pp.  46-53,  Miss.  Valley  ores,  1906. 
Bain  and  Van  Hise,  Miss.  Valley  ores,  pp.  111- 

124,  1901. 

Barlow.  1,93-107,1904. 
Becker,  12,  Appalachian  gold-ores,  pp.  272-281, 

1895. 

14,  pp.  60-64,  Gold-ores  of  S.  Alaska,  1897. 
Bergeat-Stelzner,  pp.  527-530,  General,  1906. 
Boutwell,  5,  Bingham  ores,  pp.  103-122. 1905. 
Clarke,  F.  W.,  2,  General,  pp.  541-618,  1908. 

New  Edition,  pp.  599-680,  1911. 
Coleman,  2,  Sudbury,  pp.  159-163,  1905. 
Courtis,  Gold  quartz,  1890. 
Day  and  Richards,  of  Blacksands,  1905. 
Emmons,  W.  H.,  3,  General  paper  011  genesis 

of  minerals,  1908. 
Ermisch,  1905. 
Farrell,  "Practical  Field   Geology,"  Chap.  X, 

1912. 

Fermor,  2,  Manganese-ores,  1909. 
Frazer,  P.,  Jr.,  2,  Iron  oxides,  1878. 
Haber,  of  Lead  and  Zinc,  1894. 
Hastings,  4,  Magnetite  and  sulphides  asso- 
ciated, 1908. 

Hershey,  3,  Primary  chalcocite,  1908. 
Hillebrand  and  Schaller,  Mercury  minerals, 

1909. 


Irving,  J.  D.,  11,  Relations  of  mineralogy  to 
depth  of  ore-formation  at  Lake  City,  Colo., 
pp.  33-37,  Paragenesis,  46-51,  descriptive 
mineralogy,  51-64, 1911. 

Irving,  J.  D.,  Emmons,  S.  F.,  and  Jaggar,  pp. 
68,  82-88,  138-140, 165,  166,  Black  Hills  ores, 
1904. 

Jenney,  1,  Mississippi  Valley,  lead  and  zinc, 
pp.  198-200,  210-211,  1893. 

Kemp,  10,  of  Telluride  ores,  1898. 
13,  of  Ducktown  ores,  pp.  249-250,  1901. 

21,  General,  pp.  32-38,  1906. 

Knight,    F,  C.,   new  mineral    from    Cripple 

Creek,  1896. 
Konigsberger,  1901. 
Lenher,  of  Telluride  ores,  1909. 
Lincoln,  2,  pp.  275-301,  Association  of  gold 

with  minerals. 

Lindgren,  10,  Orthoclase  gangue,  1898. 
8,  pp.  114-144,  of  Grass  Valley  ores,  1896. 

22,  Albite,  Bendigo,  1906. 

Lindgren  and  Boutwell,  pp.  100-122,  of  Morenci 

ores,  1904. 

i  Lindgren  and  Ransome,  2,  Cripple  Creek  ores, 
pp.  114-129,  173-175,  185-188,  1905;  26,  Rela- 
tion of  mineralogy  to  physical  conditions 
of  ore-deposition,  1907. 


SUBJECT    INDEX. 


921 


Lindgren,  Graton  and  Gordon,  pp.  77-81,  50- 
53, 57,  63,  69,  77,  New  Mexico,  1910. 

Mietzschke,  Gold  in  pyrite,  1896. 

Moulan,  Iron  minerals,  1904. 

Pearce,  Richard,  3,  Association  of  gold  with 
minerals,  1890. 

Purington,  1,  Telluride  dist.,  pp.  781-799,  1897. 

Ransome,  2,  Silverton,  pp.  67-93,  1901. 
3,  Rico  Mts.,  pp.  248-254,  1901. 

5,  Globe,  pp.  110-125,  1903. 

6,  Bisbee,  pp.  120-135,  1904. 
9,  Alunite,  1907. 

14,  Goldfield,  pp.  108-134 ;  also  165-171,  1910. 

15,  Criteria  of  sulphide  enrichment,  1910. 
Ransome  and  Calkins,  Coaur  d'Alene,  pp.  90- 

103,  107-113,  1908. 
Ransome,  Emmons  and  Garrey,  Bullfrog,  pp. 

92-100,  1910. 
Rickard,   T.  A.,   10,  Minerals  accompanying 

gold, 1898. 
12,  Tellurides  of  Cripple  Creek   and  Kal- 

goorlie,  1900. 
Schaeffer,  Tantalite   minerals,    Black   Hills, 

1884. 


Kcharitzer,  Iron  sulphates,  1907. 
:  Smith  and  Siebenthal,  Joplin,  pp.  12-15, 1907. 
'•  Smyth,  C.  H.,  Jr.,  2,  Genetic  relations,  1896. 
Smyth,  H.  L.,  2,  Gold  and  pyrite,  1906. 
Spencer,  6,  pp.  33-37,  Treadwell  minerals,  1906. 
1  Spurr,  3,  Mercur,  pp.  389-394,  1895. 
13,  Tonopah,  pp.  86-92,  1905. 
16,  pp.  299-301, 1907. 

Spurr  and  Garrey,  1,  p.  38,  Idaho  Springs,  1905. 
3,  Georgetown,  pp.  99-101,  136-138,  147-148, 

1908. 

Tower  and  Smith,  Tintic,  pp.  683-704, 1898. 
Van  Hise,  8,   pp.   192-408,  Applies  chiefly  to 

rock-making  minerals,  1904. 
Vogt,  k,  of  various  European  sulphide  ores, 

1894. 
I  Vogt,  Beyschlag,  and  Krusch,  vol.  i,  pp.  60-93, 

1909. 
Weed,  19,  of  Copper-ores  in  general,  pp.  22-35, 

1908. 
Weed  and  Pirsson,  2,  Judith  Mts.,  pp.  589-592, 

1897. 

Weed  and  Barrell,  Elkhorn,  Mont.,  pp.  459- 
469,  1901. 


ORE-SHOOTS. 

(See  also  effects  of  wall-rock. ) 


GENERAL. 

Beck,  8,  pp.  382-395,  1909. 
9,  vol.  II.,  pp.  1-22,  1909. 

Bergeat-Stelzner,  pp.  987-1006,  General,  1906. 

von  Cotta,  2,  pp.  522-525,  1870. 

Crawford,  Bull.  Col.  Geol.  Sur.  No.  — ,  1913. 

Irving,  J.  D.,  7, 1908. 

Lindgren,  30, 1909. 

Lindgren  and  Ransome,  3,  pp.  205-216,  excel- 
lent general  discussion,  1905. 

Litschauer,  1893. 

Lotti,  2,  pp.  133-135,  1903. 

Pearce,  nomenclature,  1909. 

Penrose,  2,  1894  ;  4,  1910. 

Phillips-Louisy  pp.  93-97, 1896. 

Purington,  5,  1906. 

Sales,  2,  at  Butte,  Montana,  1908. 

Smith,  F.  C.,  2,  1908. 

Smith,  George,  1, 1896. 

Spurr,  16,  pp.  195-196,  1907. 

Van  Hise,  4.  pp.  166-172, 1900 ;  8,  pp.  1223-1230, 
1904. 

Villarello,  2,  1905. 

Weed,  E.  and  M.  Jour.,  vol.  76,  p.  193, 1903. 

Winchell,  H.  V.,  7, 1908. 

Wuensch,  1893. 


SHOOTS    AS    DESCRIBED    IN    IN- 
DIVIDUAL LOCALITIES. 

Lindgren,  8,  Grass  Valley,  pp.  158-163,  1896. 

13,  Blue  Mts.,  pp.  605-610,  1901. 
Lindgren,  Graton  and  Gordon,  New  Mexico. 

p.  70,  1910. 

Moissenet,  Cornwall,  1877. 
von  Pdlfy,  Erzgebirge,  1907. 
Ransome,  2,  Silverton,  Colo.,  pp.  96-101,  1901. 
3,  Rico,  pp.  299-303,  1901. 

14,  Goldfleld,  Nov.,  pp.  158-165,  1909. 
Ransome  and  Calkins,  Coeur  d'Alene,  pp.  122- 

130,  1908. 

Rickard,  T.  A.,  13,  Ballarat,  1900. 
Kjogren,  4,  in  Swedish  mines,  1908. 
Skewes,  Cripple  Creek,  1896. 
Spurr,  13,  Tonopah,  pp.  85,   119-122,  276-278, 

1905. 

Spurr  and  Garrey,  3,  pp.  159-161, 1906. 
Vogt,  9,  Rio  Tinto.  1899. 
Weed  and  Barrell,  Elkhorn,  Mont.,  477-495, 

1901. 


ORIGIN   OF    METALLIFEROUS    DEPOSITS. 

(For  the 
headings,  s 

phic  Deposits,"  "Processes  of  Deposi 
place  are  given  Historical  Resumes  of  Theories  of  origin  or  Summaries  of  Theories 
of  the  origin  of  particular  metals  and  those  portions  of  a  number  of  reports  which 
deal  with  the  Origin  of  Deposits  in  Particular  Districts  ;  also  Theoretical  Papers 
Dealing  with  the  Origin  of  Ore-Deposits  as  a  whole. ) 

HISTORICAL  RESUMES  OF  THEO- 


RIES   AND     LITERATURE 
ORE-DEPOSITS. 

Emmons,  S.  F.,  15, 1904. 
Kemp,  6,  1893. 

8, 1895. 

Klement,  1,  1897-8. 
Lindgren,  27,  1907. 
Ransome,  17, 1911. 
Raymond,  6,  1900. 
Rickard,  T.  A.,  17, 1902. 
Rickard  el.  al.,1,  pp.  3-17, 1903. 
Winchell,  H.  V.,  5,1907. 


OF 


SUMMARIES  OF  THEORIES  OF 
THE  ORIGIN  OF  PARTICULAR 
METALS. 

Bateman  and  Ferguson,  Tin,  Economic  Geology, 
vol.  7,  pp.  209-262. 

de  Launay,  16,  Gold,  1909. 

Demaret,  1,  Copper,  1900;  2,  Iron,  1903;  3,  Mer- 
cury, 1904  ;  ^  Manganese,  1905. 

Fawns,  3,  Tin,  1907. 

Gautier,  F.,  1901. 

Hess  and  Graton,  Tin,  Bibliography  and  geo- 
graphic distribution  only,  1905. 

Julien,  2,  Iron,  1884. 


58 


922 


SUBJECT    INDEX. 


Kemp,  10,  Tellurides,  1898. 

15,  Platinum,  1902. 
Leith,  6,  Iron,  1908. 

7,  ditto,  1908. 
Louis,  1,  Gold,  1893. 
Maclaren,  pp.  1-117,  Gold,  1908. 
Newberry,  2,  Iron,  1881. 

3,  Gold,  1881. 

Schmidt,  Albrecht,  1,  Copper,  1910. 
Scrivenor,  Tin,  1909. 
Stutzer,  5,  Iron,  1906. 

Van  Hise,  8,  Tellurides,  pp.  1120-1125, 1904. 
Weed,  19,  Copper,  pp.  53-68,  1908,  also  Bull.  260, 
U.  S.  G.  S.,  pp.  96-97, 1906. 

ORIGIN    OF    DEPOSITS   IN    PAR- 
TICULAR DISTRICTS. 

(Only  a  few  titles,  mainly  of  American 
localities,  are  included  under  this  heading. 
Further  references  may  be  easily  secured  in 
various  published  bibliographies.) 

Antimony. 

Haley,  Gore,  Nova  Scotia,  1909. 

Cinnabar. 

Lotti,  4,  Cortevecchia,  1903. 

3,  Tuscany,  1901. 
Becker,  4,  pp.  394^50, 1888. 

Chromium. 

Eyba,  Kraubat,  1900. 

Copper. 

Boutwell,  5,  pp.  162-211,  1905. 
Finlayson,  2,  Rio  Tinto,  1910. 
Hershey,  3,  California,  1908. 
Lane,  1,  Lake  Superior,  1903. 

3,  ditto,  1907. 

Lawson,  2,  Ely,  Nevada,  pp.  330-343, 1906. 
Lindgren,  19,  Clifton-Morenci,  1904  ;  32,  1911. 
Lindgren  and  Boutwell,  pp.  19,  20,  23-25,  96, 

218-223,  ditto,  1905. 
Lindgren,  Graton,  and  Gordon,  pp.  51,  56,  67, 

71,  78,  New  Mexico.  1910. 

Spencer,  2,  Encampment,  Wyo.,  pp.  56-60, 1904. 
Steinmann,  Caro-Caro,  1906. 
Van  Hise  and  Leith,  Mon.  Lit.,  U.  S.  6.  S.,  pp. 

580-591,  1911. 


Gold  and  Silver. 

Aston,  3,  Barkerville,  B.  C.,  1906. 

Becker,  2,  pp.  266-289,  Comstock  Lode,  1882. 

Boutwell,  6,  pp.  128-130, 1912. 

Denny,  Rand,  S.  Africa,  1908. 

Emmons,  S.  F.,  2,  pp.  539-584,  1886. 

Harrison,    Fowler,   and     Anderson.     British 
Guiana,  pp.  204-211, 1908. 

Hatch,  Rand,  S.  Africa,  1903. 

Hershey,  2,  Panama,  1899. 

Irving,  Emmons,  and  Jaggar,  Black  Hills,  pp. 
78^0,  154-157, 1904. 

Lacroix,  2,  Madagascar,  1901. 

Lindgren,  8,  pp.  172-184,  Grass  Valley,  Cal. , 
1896. 

Lindgren  and  Ransome,  3,  Cripple  Creek,  1906. 

Lotti,  1,  Italy,  1889. 

Purington,  1,  Telluride,  pp.  819-824,  1897. 

Ransome,  14,  Goldfield,  pp.  189-199,  1910. 
Rico,  pp.  294-302, 1901 ;  18,  Breckenridge,  pp. 
164-174,1911 ;  2,  Silverton,  pp.  132-143, 1901. 

Ransome,  Emmons  and  Garrey,  Bullfrog,  Ne- 
vada, pp.  101-103,  1910. 

Ransome  and  Calkins,  pp.  134-140, 1908. 

Reid,  J.  A.,  1,  pp.  177-199,  ditto,  1905. 

Rickard,  T.  A.,  5,  Bendigo,  1893. 


Spurr,  3,  Mercur,  pp.  395-402,  1895 ;  4,  Yukon 

veins,  pp.  297-316,  1897. 
6,  Monte  Cristo,  pp.  859-865,  1901. 

12,  Western  Nevada,  1906;  5,  Aspen,  pp.  224- 
236,  1898 ;  19,  ditto,  1909. 

13,  Tonopah,  pp.  253-261, 1905. 

14,  Silver  Peak,  Nevada,  1906. 

15,  Southern  Klondike,  pp.  369-382,  1906. 
Spurr  and  Garrey,  3,  pp.  159-161, 1908. 
Voit,  1,  Rand  Conglomerate,  1908. 

Weed  and  Barrell,  Elkhorn,  Mont  ,  pp.  496- 

503,  1901. 
Weed  and  Pirsson,  2,  Judith  Mts.,  Mont.,  pp. 

594-598, 1897  ;  1,  Castle  Mountains,  1896 ;  3, 

Little  Belt  Mts.,  1891. 

Iron. 

Eckel,  Burchard,  and  Butts,  Clinton  ore,  pp. 

26-39, 1910. 

Irving,  R.  D.,  3,  Lake  Superior,  1886. 
Leith,  1,  pp.  237-277,  1903. 
2,  Lake  Superior,  1906. 

4,  Genesis,  Lake  Sup.  ores,  1906. 
Phalen,  1,  Kentucky,  1906. 

Smyth,  C.  H.,  Jr.,  1,  Clinton  ore,  1892. 
Spurr,  1,  Mesabi,  1894. 

2,  ditto,  1894  ;  7,  Lake  Superior,  1902. 
Stutzer,  5,  1906. 
Van  Hise,  1,  Lake  Superior,  1892. 

5,  ditto,  pp.  323-330,  1900. 

Van  Hise  and  Leith,  Mon.  Lii.,  U.  S.  G.S.,  pp. 
499-571,  1911. 

Lead  and  Zinc. 

Bain,  2,  Upper  Mississippi  Valley,  pp.  124-142, 

'    1906. 

1,  Northwestern  Illinois,  pp.  44-50,  1905. 
Bain  and  Van  Hise,  pp.  203-215,  Ozark,  1901. 
Finlayson,  1,  Great  Britain,  1910. 
Leonard,  1,  Iowa,  1895. 
Smith,  W.S.  T.,  and  Siebenthal,  Joplin,  1907 

Nickel. 

Adams,  F.  D.,  1,  Sudbury,  1894. 
Austin,  Riddles,  Oregon,  1£96. 
Barlow,  2,  Sudbury,  1906. 

1,  ditto,  pp.  123-132.  1904. 
Konigsberger,    Quartz-adularia-zeolite  veins, 

Aar,  1901. 

Tin. 

Bateman  and  Ferguson,  1, 1912. 
MacAlister  and  Hill,  Cornwall,  1906. 
Recknagel,  South  Africa,  1909. 
Rumbold,  1,  Bolivia,  1909. 

2,  Kinta  Valley,  Malay  States,  1906. 


GENERAL  PAPERS  DEALING 
WITH  THE  GENESIS  OF  ORE- 
DEPOSITS  AS  A  WHOLE. 

A  dam,  J.  W.  H.,  1910. 

Beck,  8,  1909. 
9,  1909. 

Becker,  4,  pp.  442-450, 1888 ;  13,  Discussion  of 
Posepny,  1893. 

Bergeat-Stelzner,  pp.  11S8-1239,  Excellent  gen- 
eral discussion,  1906. 

Brough,  1901. 

Carpenter,  Proc.  Col.  Sci.  Soc.,vol.  7,  pp.  253- 
266, 1904. 

Chalon,  1,  1905. 
2,  1906. 

Clarke,  2,  pp.  541-618, 1908.  Also  New  Edition, 
pp.  599-613,  1911. 

von  Cotta,  2,  pp.  546-552, 1870. 

de  Launay,  1, 1893. 
k,  1897  ;  5,  1897  ;  6, 1897  ;  11, 1905. 

Demaret,  5,  1906. 


SUBJECT    INDEX. 


923 


Eckel,  Bibliography,  Jour.  GeoL,  vol.  11,  pp. 

71(5-719, 1903. 
Emmons,  S.  F.,  3,  1887. 

4,  Fissure  veins,  1887. 

9, 1893  ;  10, 1893.  See  also  Science,  New  Series, 

vol.  17,  pp.  541-542,  1903. 
Frazer,  5,  1904. 
Heusler,  1901. 
Jenney,  2, 1902  ;  3, 1902. 
Keck,  1883. 
Keilhack,  2,  1896. 
Kemp,  3,  1891. 

4,  1893 ;  6,  1893  ;  8,  1895. 

14,  Reply  to  Van  Hise,  1901. 

16,  2d  ditto,  1902. 

17,  1903  ;  19,  1904. 

21,  pp.  37-46,  1906  ;  24,  1906. 
26, 1907  ;  27, 1906 ;  28, 1908  ;  also,  Contributions 
to  Col.   Univ.   Geol.  Dept.,  vol.  10,  No.  86, 
1902. 

Keyes,  1, 1900. 
Kleinschmidt,  1887. 
Klement,  1898. 
Le  Conte,  3, 1883. 

4,  Discussion  of  Posepny,  1894. 
Lindgren,  14, 1901. 

26,  1907. 
Lotti,  2,  1903. 
Maclaren,  Min.  and  Sti.  Press,  vol.  85,  p.  281, 

1903. 
Newberry,  6,  1884. 

5,  1883. 


Phillips,  2,  1871. 

4, 1871 ;  3, 1879. 
Phillips-Louis,  pp.  121-150,  Excellent  general 

discussion  revised  up  to  1895,  1896. 
Posepny,  1, 1902. 

2, 1893. 

Pumpelly,  3,  General,  1877. 
Ransome,  17,  1911. 
Raymond,  6, 1900. 

Rickard,  T.  A.,  et  al.,  1,  "  A  Discussion."   Val- 
uable collection  of  papers,  1903. 

2,  1903. 
Rickard,  T.  A.,  20,  1908. 

7,  Discussion  of  Posepny,  1894  ;  5, 1893. 
Schierl,  1904. 

Spurr,  16,  pp.  9-22,  1907.    See  also,  E.  and  M. 
Jour.,  vol.  76,  pp.  54-55,  1902. 

17,  1907. 
Stutzer,  5. 1906. 
Van  Hise,  4, 1900. 

6,  1901. 

8,  pp.  1004-1243, 1904.    See  also,  Scientific  Am- 
erican Suppl.,  vol.  52,  pp.  21,  504,1901. 

Vogt,  10,  1901. 

Vogt,  Beyschlag  and  Krusch,  pp.  161-186,  Excel- 
lent general  discussion,  1910. 
Wadsworth,  1,  1888. 
Werner,  Hist,  1791. 
Whittlesey,  1, 1876. 
Winchell,  H.  V.,  5, 1907. 
6,  1908. 


OXIDATION. 

(See  under  "  Superficial  Alteration.") 


ORE-SOLUTIONS. 

(For  Effect  on  Wall  Kock,  see  under  "  Replacement." 


NATURE  AND   ORIGIN    OF   THE 
AGENT  OF  DEPOSITION. 

Beck,  8,  pp.  424-432,  1900. 

9,  vol.  II.,  pp.  55-70,  1906. 
Becker,  4,  pp.  444-445, 1888. 
Bergeat-Stelzner,  pp.  1213-1239,  1905. 
Bischof,  1,  2d  ed.,  vol.  III.,  pp.  904-912, 1866. 
Clarke,  F.  W.,  2,  New  Edition,  pp.  201-205, 599- 

610,  Excellent  general  discussion,  1911. 
Darapsky,  1903. 

Daubree,  A.,  2,  p.  180,  et  seq.,  1879. 
Daubree,  G.  A.,  1,  1887. 

2,  1887. 

de  Launay,  7,  pp.  85,  et  seq.,  1899. 
Delkeskamp,  3,  4,  5,  6,  7,  8, 1899-1908. 
Doelter,  2,  Solubility  of  minerals,  1890. 
Finch,  Origin  of  water,  1904. 
Griffiths,  Quicksilver   in    mineral  springs  of 

New  Zealand,  1910. 
Hague,  2, 1911. 

Headden,  Radium  Springs,  1905. 
Kemp,  14, 1901. 

16,  1902  ;  18,  1904 ;  24,  1906. 

21,  pp.  39-46,  1906;  27,  1906. 
Knelt,  1899. 
Konig,  .P.,  1901. 
Krusch,  3,  1904. 
Lane,  4,  5,   6,  1908-9. 
Le  Conte,  2,  1883. 

4,  pp.  996-1006,  1894. 

1,  pp.  253-260,  1904. 
Le  Conte  arid  Rising,  1882. 
Lindgren,  21,  Steamboat  Springs,  1905. 

31,  1910. 
Lindgren,  Graton  and  Gordon,  pp.  56,  71-74, 

New  Mexico,  1910. 
Lotti,  5,  pp.  372-378,  1893. 
Mutter,  1,  Mineral  springs  in  Freiberg  mines, 

1885. 

Phillips-Louis,   pp.    115-119,    134-142,    793-795, 
1896. 


Phillips,  3, 1871. 

4,  1871. 

6,  1884. 

Rickard,  et  al.,  "A  Discussion,"  many  valu- 
able discussions  are  scattered  through  this 
volume,  1903. 
Rickard,  T.  A.,  20, 1908. 
Roth,  vol.  I.,  pp.  564  et  seq.,  1879. 
Strutt,  1907. 
Stutzer,  IS,  1910. 
Suess,  2,  and  3, 1902. 
Van  Hise,  4,  1900. 

6,  1901. 

8,  pp.  1052-1139,  1904. 
Van  Hise  and  Leith,  Mon.  Lii.  U.  S.  G.  S.,  pp. 

580-591, 1911. 
Vogt,  5,  1894-5. 

8,  1899 ;  10,  1901. 

Vogt,  Krusch  and  Beyschlag,  vol.  1,  pp.  118-135, 
Excellent  discussion,  also  pp.  171-179, 1909. 
Weed,  1, 1891. 

3,  1900  ;  13,  1903. 
Weed  and  Pirsson,  4, 1893. 


PKOCESSES  OF  DEPOSITION  FROM 
SOLUTIONS. 

Bain  and  Van  Hise,  pp.  95-110,  Excellent  dis- 
cussion, 1901. 

Becker,  4,  Deposition  of  mercury,  pp.  331-353. 
419-450,  1888. 

Biddle,  Copper,  1901. 

Bischof,  1, 1863-1871. 

Carthaus,  1896. 

Clarke,  2,  pp.  603-609,  New  Edition,  1911. 

Doelter,  1, 1906  ;  g,  1890. 

Fernekes,  Copper,  1907. 

Gillette,  Osmosis,  1903. 

Jenney,  2,  By  reducing  agents,  1902 ;  discus- 
sion of  by  Church,  Trans.  A.  I.  M.  E.,  vol. 
33,  pp.  1065-1070,  1902. 


924 


SUBJECT    INDEX. 


Kemp,  18, 1904. 

Kohler,  E.,  adsorption,  1903. 

Konigsberger.  1901. 

Le  Conte.  1,  pp.  253-256,  1904. 

Lenher,  Tellurides,  1909. 

Lindgren,  24,  By  loss  of  temperature  and  pres- 
sure, 1906. 
31,  1910. 

Lotti,  4,  Cinnabar,  1903. 

Louis,  2,  Gold.  1894. 

Newberry,  6,  General,  18S4. 

Sharwood,  of  Tellurides,  1911. 

Smith,  G.  O.,  E.  and  M.  Jour.,  vol.  73,  p.  826, 
1902. 

Sorby,  Evidences   of  temperature   and  pres- 
sure of  quartz  formation.  1858. 

Steidtrnann,  Comparative   effect  of  surface- 
waters  and  mineralizers,  1908. 

Stokes,  1,  of  Pyrite  and  marcasite,  1901. 
2,  General,  1906  ;  3,  Pyrite  and  Marcasite,1907. 

Sullivan,  1,  of  Copper  by  silicates,  1906. 

2,  Reactions  between  solutions  and   min- 
erals, 1907. 

3,  Mineral  niters,  1908. 

Van  Hise,  4,  of  Copper  in  Lake  Superior,  pp. 

67-71,  84-91,  99-102,  1900. 
8,  By  ascending  solutions,  pp.  1081-1132,1904. 

Van  Hise  and  Leith,  Mon.  LiL,  U.  S.  G.  S.,  Pre- 
cipitation of  Copper,  pp.  589-590,  1911. 

Vogt,  Beyschlag,  and  Krusch,  vol.  I.,  pp.  118-135, 
Excellent  general  disdussion,  1909. 

PRECIPITATION    FROM    SOLUTION. 

(See  under  "Ore-Solutions.) 

PHYSICAL  CONDITIONS  OF  ORE-DEPOSITION. 

(See  under  *'  Ore-Solutions "  and  " Contact-Metamorphic  Deposits.") 

PRESSURE    AND    TEMPERATURE    IN 
ORE-DEPOSITION. 

(See  under  "  Ore-Solutions  "  and  " Contact-Metamorphic  Deposits.) 

REGIONAL  METAMORPHISM,  DEPOSITS  PRO- 
DUCED DURING,  AND  EFFECT  ON  PREVIOUSLY 
FORMED  DEPOSITS. 

(In  many  of  the  references  cited  here  the  relation  of  ore-deposition  to  regional 
metamorphism  is  not  definitely  stated. ) 


Weed,  17,  By  adsorption,  1905. 
11,  By  ascending  waters,  1902. 

Wells,  Fractional  precipitation  of  sulphides, 
1910. 

Wright  and  Larsen,  Quartz  as  an  indicator  of 
temperature  and  pressure  of  ore-deposi- 
tion, 1909. 

TEMPERATURES  AND  PRESSURES 
OF  ORE-SOLUTIONS  AND  THEIR 
EFFECT  ON  THE  RESULTING 
ORE-DEPOSITS. 

de  Launay,  8,  1900. 

Doelter,  1,  pp.  79-112, 1906. 

Emmoris,  W.  H.,  3,  Genetic  classification  of 
minerals,  1908. 

Komgscberger,  Temperature  and  pressure  of 
quartz  formation,  1901. 

Lindgren,  25,  in  veins  of  Dahlonega,  pp.  123- 

125, 1906. 

26,  Excellent  general  paper  on  physical  con- 
ditions of  deposition,  1907. 
24,  In  deep  deposits,  1906. 

Lindgren  and  Ransome,  Evidence  on  tempera- 
ture and  pressure  of  solutions,  1905. 
3,  pp.  181,  226,  1906. 

Wright  and  Larsen,  Quartz  formation,  1909. 


Abbott,  1907. 

Bastin,  Criteria  of  regional  metamorphism, 
Jour.  Geol.,  pp.  445-472,  1909. 

Beck,  8,  Ores  in  the  Crystalline  schists  (Rela- 
tions to  regional  metamorphism  some- 
what indefinite),  pp.  433-477, 1909. 
9,  vol.  II.,  pp.  71-131, 1909. 

Becker,  12,  Gold,  Southern  Appalachians,  1895. 

Sergeat-Stelzner,  pp.  86-470,  occasional  types 
described  on  these  pages  have  been  meta- 
morphosed, 1906. 


Blake,  W.  P.,  9,  Zinc,  1894. 

Dresser,  Copper,  1906.. 

Emmons,  W.  H.,  4.  1909. 

Fermor,  2,  Manganese,  1909. 

Henrich,  C.,  3,  Copper,  1895. 

Kemp,  5,  Zinc  and  manganese,  1893. 

Thomas  and  MacAlister,  pp.  371-358, 1908. 


REPLACEMENT. 


GENERAL  DISCUSSIONS. 

Bams,  2,  1884. 

Beck,  8,  pp.  392-407,  1909. 
9,  vol.  II.,  pp.  20-36,  1909. 

Becker,  4,  pp.  394-401.  Good  general  discus- 
sion, 1888. 

13,  Discussion  of  paper  by  Posepny,  pp.  602- 
604,  1894. 

Bergeat-Stelzner,  General,  pp.  1007-1188.  A  very 
extensive  series  of  bibliographic  refer- 
ences will  be  found  under  the  descriptions 
of  the  several  districts,  1906. 


Emmons,  S.  F.,  2,  pp.  563-569, 1886. 
10,  Discussion  of  Posepny,  p.  602,  1893. 
3,  pp.  125-135,  1887  ;  6,  scattered  discussion, 
1888  ;  9,  pp.  64, 85, 86, 1893 ;  also  Trans.  A.  I. 
M.E.,  vol.  x.,  p.  418, 1882. 
20,  In  fissure-veins  of  Butte,  1897. 
Irving,  J.  D.,  9,  General  paper  on  replacement, 

1911. 

Irving,  R.  D.,  and  Van  Hise.l,  pp.  413-422, 1890. 
Irving,  Emmons,  and  Jaggar,  In  Black  Hills 

ore-bodies,  South  Dakota,  1904. 
Kemp,  21,  pp.  44-46, 1906. 
14,  Discussion  of  Van  Hise,  1901. 


SUBJECT    INDEX. 


925 


Kimball,  J.  P.,  1, 1891. 

Krusch,  6, 1910. 

Lindgren, -12,  Metasomatic  processes  in  fissure 

veins,  1900. 
23,  1906. 
Lindgren  and  Boutwell,  pp.  123-126,  Brief  but 

excellent  general  discussion,  1905. 
Phillips-Louis,  pp.  143-150,  also  pp.  175-179,1896. 
Posepny,  It,  General  discussion    of  lead-  and 

zinc-deposits  in  soluble  rocks,  1893. 

2,  (in  English)  Excellent  general  paper,  pp. 
210-212,  283-304,  318-321,  1893. 

3,  Reply  to  discussion  of  2, 1894. 
Pumpelly,  1, 1878. 

Purington,  1,  Replacement  versus  impregna- 
tion, pp.  802-809,  1897. 

Rickard,  T.  A.,  7,  pp.  942-948,  Discussion  of 
Posepny,  No.  2, 1894. 

Spurr,  16,  p.  247, 1907. 

Thomas  and  MacAlister,  pp.  237-300, 1908. 

Vogt,  10,  pp.  147-158,  1901. 

Vogt,  Bey&chlag  and  Krusch,  vol.  i.,  pp.  4, 13,  40- 
42,  131,  170-171,  235,  1910. 

Wallace,  pp.  220-231,  1908. 

Winchell,  H.  V.,  2,  Discussion  of  paper  by 
Posepny  (2),  1893. 


CRITERIA    OF  REPLACEMENT. 

Becker,  13,  pp.  602-604, 1893. 
Irving,  J.  D.,  9.  10,  1911. 
Lindgren,  12,  pp.  595-597,  1900. 


REPLACEMENT  ADVOCATED  OR 
DISCUSSED  FOR  INDIVIDUAL 
OCCURRENCES. 

(A  few  references  only  are  given  here  ;  the 
literature  is  extremely  voluminous.  For  com- 
plete bibliography  of  metasomatic  deposits 
see  Bergeat-Stelzner,  pp.  1007-1138.) 

Abbott,  Ely,  Iron,  1907. 

Barrell,  2,  pp.  126-128, 129,  131, 144,  146,  1907. 
Bayley,  1,  Iron,  pp.  395-401, 1904. 
Becker,  4,  pp.  394-401.    Cinnabar  not  a  replace- 
ment, 1887. 
Blake,  1,  Lead,  silver,  1878. 

2,  Gold,  silver,  1882. 
Blow,  Leadville,  1889. 
Boutwell,  4,  Bingham,  pp.  549-564,566-570. 1905. 

5,  ditto,  pp.  168-172,  179, 180,  194-201,  1905. 
Carpenter,  Black  Hills,  pp.  582-583,  1889. 
Church,  4,  Comstock  lode,  1879. 
Curtis,  1,  Eureka,  pp.  244-250,  1884. 

2,  ditto,  pp.  93-106,  1884. 
Douglas,  Bisbee,  pp.  531-537,  1899. 


Emmons,  2,  Leadville,  pp.  565-569, 1886. 

5,  Butte,  pp.  56-58, 1888  ;  20,  Butte,  1897. 
14,  pp.  669-672,  Gold,  1901. 

Emmons  and  Irving,  Leadville,  1907. 
Ermisch,  Tuscany,  1905. 
Finlayson,  1, 1910. 

2,  Rio  Tinto,  1910. 

Irving,  Emmons  and'Jaggar,  Black  Hills,  pp. 

111-160,  1904. 

Irving  and  Van  Hise,  pp.  411-422. 
Lindgren,  9,  pp.  646-647,  1897,. 

13,  Blue  Mts.,  Oregon,  pp.  604-605,  1901. 
23,  Western  Australia,  1906. 

Lindgren  and  Boutwell,  Clifton,  Morenci,  pp. 

123-191,  1905. 
Lindgren  and  Ransome,  3,  Cripple  Creek,  pp. 

184-196,  1906. 
Lindgren,  Graton  and  Gordon,  Pre-Cambrian 

veins,  New  Mexico,  p.  59,  In  limestone,  pp. 

62-67,  In  veins,  p.  71,  1910. 
Malcolmson,  Sierra  Mojada,  pp.  108-131,  1901. 
Moffit  and  Maddren,  of  Greenstone  by  copper, 

pp.  48,  80-88,  1909. 
Navarro,  Almade'n,  Spain,  1894. 
Pumpelly,  1,  Lake  Superior  copper,  1877. 
Ransome,  5,  Globe,  Ariz.,  pp.  125-132,  1903. 

6,  Bisbee,  Ariz.,  pp.  146-154,  1904. 

14,  at  Goldfield,  Nev.,  pp.  176-186, 1909. 
Ransome  and  Calkins,  at  Coeur  d'Alene,  pp. 

112,  138-139,  1908. 
Raymond,  Trans.  A.  I.  M.  E.,  vol.  6,  pp.  371- 

393.  1877-1878. 

Rickard,  T.  A.,  1,  Mt.  Morgan,  pp.  145-150, 1891. 
Rutledge,  Clinton  iron-ores  of  Pennsylvania, 

1909. 

Smith,  F.  C.,  1,  Black  Hills,  1897. 
Smith,  W.  S.  T.,  and  Siebenthal,  p.  14,  Joplin 

jasperoid,  1907. 
Smyth,  C.  H.,  Jr.,  1,  Clinton  ores,  1892. 

3,  Replacement  of  quartz  by  pyrite,  1905. 
Spencer,  6,  Juneau,  pp.  24,  62  and  111,  114, 1906. 

9,  Cornwall  magnetites,  p.  13,  1908. 
Spurr,  5,  Dolomitization,  pp.  206-216,  Silicifi- 

cation  and  Ferration,  pp.  216-223,  Of  ore, 

pp.  232-236,  Aspen,  Colorado,  1898. 
6,  of  Igneous  rocks,  Monte  Cristo,  pp.  831- 

833,  1901. 
13,  of  Andesite  by  vein-matter  at  Tonopah, 

in  Rock-alteration  at  Tonopah,  pp.  207-252, 

1905. 
Spurr  and  Garrey,  3,  at  Georgetown,  Colo.,  pp. 

160-161, 1908. 

Tower  and  Smith,  at  Tintic,  pp.  705-708,  1898. 
Turner,  2,  in  Sierra  Nevada,  1899. 
Watson,  2,  Lead  and  zinc  of  Virginia,  p.  716, 

1905. 
Weed  and  Barrell,  at  Elkhorn,  Montana,  pp. 

496-501,  1901. 
Weed  and  Pirsson,  2,  Judith  Mts.,  pp.  592-598 

1897. 


SEDIMENTARY  PROCESSES  AS    ORE-BUILDERS. 


ORES  SUPPOSED  TO  BE  A  DIRECT 
RESULT  OF  SEDIMENTARY 
PROCESSES. 

Beck,  8,  pp.  49-111,  General,  1909. 

9,  vol.  II.,  pp.  331-416,  1909. 
Bergeat-Stelzner,  General,  pp.  85-470, 1906. 
Bowron,  2,  Alabama-Clinton  ores,  1905. 
Burchard,  Butts,  and    Eckel,  Clinton,  Birm- 
ingham, pp.  28-39.  Argument  against,  1910. 
Hopkins,  Iron,  Penna.,  1900. 
Hornung,  1,  Kupferschiefer,  1904. 
McCallie,  S.  W.,  1,  Iron,  Georgia,  1900. 

2,  Ditto,  1908. 

Newland,  3,  Clinton  ores  of  New  York,  1909. 
Newland  and  Hartnagel,  Clinton,  1908. 
Phalen,  1,  Kentucky,  Clinton,  1906. 
Phillips-Louis,  General ,  pp.  35-»66,  1896, 
Redlich,  1,  W.  Alps,  ores,  1906;  S,  1907. 
Rolker,  2,  Silver  sandstones,  1880. 


Rutledge,  Against  sedimentary  origin,  1909. 
Stremme,  Iron  in  sedimentary  rocks,  1910. 
Spurr,  16,  General,  1907. 
Van  Hise,  1,  1892. 

8,  General,  pp.  1037-1043,  1904, 
Van  Werveke,  Minettes  of  Luxembourg,  1901. 
Vogt,  3,  Criteria  for  recognition    of  sedimen- 
tary ores,  1891  and  1894. 
Wherry,  Sedimentary  copper,  1908. 


ORES  SUPPOSED  TO  BE  DERIVED 
BY  LATER  CONCENTRATION  OF 
SEDIMENTARY  PARTICLES  IN 
ROCKS. 

Abbott,  1,  Vermillion  Iron  Range,  1907. 
Adams,  G.  I.,  2,  pp.  39-62,  1904. 
Adiasseurch,    Siberian   copper-ores    in    sand-\ 
stone,  1907. 


926 


SUBJECT    INDEX. 


Bain,  3,  Comparison  of  sedi-genetic   and  ig- 

neo-genetic  ores,  1906. 

4,  Paleogeography   and    Mississippi  Valley 
ores,  1907. 

Ball,  and  Shaler,  Congo  copper,  1910. 

Hergeat-Stelzner,  bibliography  of  Mansfeld  cop- 
per-shales, pp.  391-417,  1906. 

Buckley  and  Buehler,  pp.  9.  13,  14,  15,  25,  26, 
78-85,  97-110,  Lead  and  7,inc,  1906. 

Boutwell,  1,  p.  200-210, 1905. 

Buttgenbach,  2,  Congo,  1904. 

Chamberlin,  T.  C.,  3,  Lead-ores,  Wisconsin, 
pp.  377-568,  1882. 

Clarke,  2,  p.  611,  1908.  New  Edition,  Discus- 
sion of  Source  of  the  Metals,  pp.  600-680, 
1911. 

Emmons,  S.  F.,  16,  pp.  221-232,  1905. 

Emmons,  W.  H.,  1,  pp.  125-128,  1906. 

Farrell,  Congo,  1908. 


Fleck  and  'Haldane,  Vanadium,   pp.  47-115, 

1905-1906. 
Gale,  2,  Idaho,  1909. 

3,  Carnotite.  1908. 

4,  pp.  110-117,  Carnotite,  1900. 
Giirich,  2,  Copper,  Bohemia,  1893. 
Hewett,  1909. 

Hillebrand,  3,  Patronite,  p  141, 1907. 

Hillebrand  arid  Ransome,  Carnotite,  1900. 

Jennings,  1,  1903. 

Kemp,  21,  p.  333,  1906. 

Lindgren,  Graton  and  Gordon,  New  Mexico, 

pp,  76-79,  1910. 

Newberry,  1,  Silvers.  S.,  1880-1887. 
Rolker,  2,  Silver  in  S.  S.,  1880. 
Roth  well,  pp,  25,  48,  79,  Silver  sandstone,  1880. 
Schmitz,  Copper,  Texas,  1897. 
Spurr,  1.  2,  1894. 
Steinmann,  pp.  335-368, 1906. 
Tarr,  W.  A.,  Oklahoma  copper  in  S.  S.,  1910. 
1  Turner,  3,  New  Mexico,  1902. 


SUBLIMATION. 

(See   also  under  sub-head    "  Pneumatolysis"    of   "Emanations   from    Igneous 
Magmas.") 


Beck,  8,  pp.  421-424,  1909. 

9,  vol.  2.  pp.  52-55,  1909. 
Becker. 
Bergeat,  3, 1899. 

4,  ditto,  1899, 

Bergeat-Stelzner,  pp,  1208-1213,  1906. 
Clarke,  2,  pp.  248-276, 1908. 


Duroclier,  Artificial  production  of  minerals  in 

the  dry  way,  1851-1856. 
Necker,  General,  1833. 
Phillips-Louis,  pp.  127-129,  General,  1896. 
von  Richtofen,  p.  275,   Hungarian  propvlites, 

gold, 1860. 


SUPERFICIAL   ALTERATION. 

(The  superficial  alteration  of  ores  is  brought  about  by  atmospheric  waters  which 
seep  downward  from  the  surface.  These  produce,  first,  a  zone  of  oxidation,  and, 
second,  a  zone  of  secondary  sulphide  enrichment.  References  are,  therefore,  given 
under  the  following  heads  :  (1)  Ground- water  and  its  Movement,  (2)  Oxidation. 
(3)  Secondary  Sulphide  Enrichment.) 

GROUND- WATER  AND  ITS  MOVE- 
MENT. 

Daubrte,  G.  A.,  1, 1887. 

2,  1887. 

deLaunay,  7, 1899;  5, 1897. 
Finch,  1904. 
Finlayson,  4, 1910. 
Fuller,  2,  Excellent  general  summary,  1906  ;  1, 

General  bibliography  from  1879-1904. 
Kemp,  14,  pp.  184-195,  1901. 

16,  1902. 

King,  Excellent  general  discussion,  1898. 
Mendenhall,  5,  Relating  especially  to  Los  An- 
geles, 1909. 
Ochsenius,  1,  1893. 
Posepny,  2,  pp.  212-247, 1893. 
Ransome,  2,  p.  141,  1901. 
Ries,  General,  pp.  293-301,  311-316,  1910. 
Sass,  1,  Oscillations  of  ground-water  level,  1901. 
Slichter,  1,  Motion  of  ground-water  (mathe- 
matical treatment),  1899. 

2,  ditto,  Excellent  discussion,  1902. 
Spurr,  16,  General,  pp.  237-242,  1907. 
UMig,  Motion  of  ground-water,  1893. 
Van  Hise,  4,  General  discussion,  1900. 

6,  1901. 

8,  General,  pp.  65-119,  circulation  and  work 
of,  120-159,  1052-1024,  1904. 

OXIDATION. 

Beck,  8,  pp.  363-378, 1909. 

9,  vol.  II.,  pp.  308-327,  1909. 
Biddle,  1901. 

Buehler  and  Gottschalk,  Experimental,  1910. 
Butler,  At  Leadville,  Econ.  GeoL,  vol.  viii.  pp. 

1-18, 1913. 

Chance,  6,  Iron  sulphides,  1908. 
9,  1908. 


Chautard  and  Lemoine,  Laterization,  1908. 
Cornu,  2,  1909. 

Curtis,  1,  Eureka,  pp.  51,  et  seq.,  1884. 
deLaunay,  5,  1897. 

8,  1900. 

Dodler,  2,  Solubility  of  minerals,  1890. 
Eckel,  Burchard  and  Butts,  pp.  28-39,  1910. 
Emmens,  1,  1892. 
Emmons,  S.  F.,  1,  Chemical,  1882. 

13,  1900. 
Emmons,  W.  H.,  5,  1909. 

7,  Manganese  in  ores  and  its  effect  in  oxida- 
tion of  gold-veins,  1911. 

Gregory,  1,  1901. 

2,  1904;  7,  1906. 

Hoover,  Western  Australia,  1898. 
Julien,  1,  1879. 
Kemp,  23,  Copper.  1906. 
Keyes,  4,  Silver  chlorides,  1901. 

5i  ditto,  1908. 
Kruscfi,  4,  Criteria,  1907. 
Lindgren  and  Graton,  pp.  55-56,  59,  70. 
Litschciuer,  1893. 

Phillips-Louis,  pp.  97-99,  106-107,  1896. 
Penrose,  2,  1894. 
Rickard,  T.   A.,  14,  Bonanzas  in  gold-veins, 

1901. 

Scharitzer,  1907. 

Spurr  and  Garrey,  3,  pp.  148-149, 1907. 
Stokes,  2,  Chemical,  1906. 
Thomas  and  MacAlister,  pp.  362-375,  1908. 
Van  Hise,  4,  pp.  99-150,  1900. 

8,  pp.  461-472,  1904. 

Walker,  E.,  Copper  sulphate,  1903. 
Weed,  5,  Chemical,  1907. 

19,  pp.  43-52,  in  copper  deposits,  1908. 
Weifikopf,  Iron,  1905. 
Whitney,  2.  1855. 
Winchell,  A.  N.,  1,  Oxidation  of  pyrite.  1907. 


SUBJECT    INDEX. 


927 


SECONDAKY  SULPHIDE  ENRICH- 
MENT. 

Bain   and  Van  Hise,  Chemical,  pp.  103-106, 

Bancroft,  2,  1903. 
4,  General,  1909. 

Bastin,  Replacement  in  sulphide  enrichment 
Econ.  GeoL,  vol.  viii.,  pp.  51-63,  1913 

Beck,  8,  pp.  378-382,  Extensive  discussion, 
chemical,  1909 ;  9,  vol.  2,  pp.  308-220,  Ex- 
cellent general  discussion,  1909. 

Bergeat-Stelzner,  pp.  541-564,  Excellent  general 
discussion,  1906. 

Bout  well,  5,  pp.  212-217,  218-223,  228-230,  1905. 

Brock,  Min.  Mag.  (R.),  vol.  4,  pp.  203-204, 1911 ; 
Effect  of  climate  on  secondary  enrich- 
ment, discussion  of  Winchell,  1911. 

Burgess,  E.  and'M.  Jour.,  vol.  76,  p.  153,  1903. 

Church,  E.  and  M.  Jour.,  vol.  80,  p.  695,  1905. 

de  Launay,  5,  1897. 
6,  1900. 

Emmons,  S.  F.,  13,  1900  ;  20, 1897. 

Emmons,  W.  H.,  pp.  615-617,  618-627,  7,  Man- 
ganese and  gold,  1911;  Effect  of  climate 
on,  Min.  Mag.  (R).  vol.  iv,  p.  116  ;  8, 1908. 

Farrell,  J.  H.,  Chapter  XI,  1912. 

Finlayson,  4, 1910-11. 

Foote,  1910. 

Fuchs  and  de  Launay,  vol.  ii,  pp.  230-234, 1893. 

Gautier,  1, 1906  ;  3.  1906  ;  1, 1906  ;  5, 1909. 

Graton  and  Murdoch.  Excellent  discussion  on 
copper.  Advance  Bull.  A.  I.  M.  E.  at  Feb. 
Meeting,  1913. 

Gregory,  J.  W.,  1,  1901. 
2,  1904  ;  6,  1906  ;  13,  1910. 

Gunther,  2,  Chapter  X.  1912. 

Herrick,  Min.  and  Sci.  Press,  vol.  87,  pp  1-97 
1903. 

Hill,  E.  and  M.  Jour.,  vol.  80,  pp.  645-646,  1905 

Kemp,  23,  Copper,  1905. 
25,  1907. 
21,  pp.  49-52,  1906. 

Keyes,  3, 1910. 

Krusch,  4,  Criteria,  1907  ;  1, 1900. 

Lazerovic,  Zeit.f.  prak.  Geol.  vol.  19.  pp.  321-327 ; 
vol.  20,  pp.  337-371,  1911,  1912. 


Lindgren,  19,  pp.  511-550,  by  replacement,  1904 ; 

36.  Copper,  1905  ;  20  a,  pp.  177-208,  1905 ;  26, 

190/ . 

Lindgren  and  Graton.  pp.  315-317,  1910. 
Lotti,  2,  pp.  133-135,  1903. 
MacAlister  and  Hill,  Extensive  discussion  of 

secondary  alteration  at  Cornwall,  Eng., 


pp.  187-194, 1906. 
cla 


Maclaren,  of  gold,  pp.  79-86,  100-105,  111-115, 

1908. 

Moffit  and  Maddren,  pp.  52-54, 1909 
Penrose,  2,  1894. 
Purington,  E.  and  M.  Jour.,  vol.  75,  pp.  472-473, 

1903. 
Ransome,  2,  pp.  138-141.  1901 ;  5,  pp.  128-132, 

1903  ;  6,  pp.  132-160, 1904  ;  15,  Criteria,  1910  ; 

Discussion  of,  Econ.  GeoL,  vol.  5,  pp.  81-89  ; 

479-480,488-491;  558-564;  681-682. 
Read,  T.  T.,  2,  1906. 

Rickard,  T.  A., 14,  Bonanzas  in  gold-veins,  1901. 
Ries,  pp.  338-340,  1910. 
Sales,  1,  1910. 
Simpson,  1908. 
Spurr,  16,  pp.  265-293,  1907;   E.  and  M.  Jour., 

vol.  80,  pp.  597-598,  1905. 
Spurr  and  Garrey,  3,  p.  143, 1908. 
Starbird,  E.  and  M.  Jour.,  vol.  75,  pp.  702-703, 

Stokes,  1,  Pyrite  and  marcasite,  1901. 

2,  Chemical,  1906  ;  3, 1907. 
Thomas  and  MacAlister,  pp.  359-375,  1908. 
Tolman,  2, 1913;  3,  1909;  4, 1909  ;  5,  with  bib- 
liography, 1909. 
Van  Hise,  4,  pp.  104-138, 1900. 

8,  pp.  1139-1193,  1904. 

Weed,  2,  Excellent  general  discussion,  orig- 
inal paper,  1900. 

5,  ditto,  1900. 

14,  At  Butte.  Mont.  pp.  176-179,  1903 ;  also 
Bull.  Geol.  Soc.  Am.,  vol.  15,  pp.  179-206, 1900. 

19,  In  copper-ores,  pp.  43-52,  1908. 
Weed  and  Barrell,  p.  503,  1901. 
Wells,  Chemical,  1910. 
Winchell,  H.  V.,  4,  Chemical,  copper,  1903. 

8,  Effect  of  climate  on,  1910. 

9,  ditto,  1911. 


UNDERGROUND    WATERS. 


BIBLIOGRAPHY  OF. 

Clarke,  2,  p.  170,  1908 ;  2nd  ed.,  pp.  204-205, 
1911. 

Fuller,  1,  For  years  1879-1904, 1905. 

Slichter,  1,  pp.  381-384,  Contains  many  refer- 
ences which  for  lack  of  space  are  not 
here  repeated,  1899. 

MINE-WATERS. 

Becker,  1,  Analyses  and  temperature  of  water 
of  Comstock  lode,  p.  152,  1882  ;  4,  pp.  258- 
261,  346-350. 

Bergeat-Stelzner,  pp.  555-560,  General  discussion, 
analyses,  1906. 

Buckley,  1,  Analyses,  pp.  231 ;  Analyses  of,  p. 
249,  1909. 

Don,  Assays  for  gold  in,  pp.  601-605,  1897. 

Fernekes,  Analyses  Lake  Sup.  copper-mine 
waters,  1907. 

Kemp,  21,  Analyses  and  brief  general  dis- 
cussion, pp.  29-31,  1906. 

Krusch,  S,  1904. 

Lane,  3,  Lake  Superior  copper-mine  waters, 
1907. 

4,  ditto,  1908. 

5,  Field  analyses  of  mine-waters,  1908. 

6,  1909. 

Lindgren,  8,  pp.  120-124, 1896. 

Mulle.r,  H.,  1,  1885. 

Posepny,  2,  pp.  220-247,  Excellent  general  dis- 
cussion, 1893. 

Spurr,  13,  pp.  105-108  ;  23. 

Spurr  and  Garrey,  3,  pp.  125-126,  Georgetown, 
1908. 


GENERAL  DISCUSSIONS  ON  UN- 
DERGROUND WATERS. 

Bain  and  Van  Hise,  Excellent  general  dis- 
cussion, pp.  95-110,  1901. 

Blake,  12,  Deposition  by  vadose  waters  in 
Arizona,  1901, 

Chamberlin,  T.  C.,  1,  Artesian  water-supply, 
1885. 

Clarke,  F.  W.,  2,  pp.  139-171,  Mainly  chemi- 
cal, 1908 ;  Juvenile  vs.  meteoric 'water,  2. 
pp.  201-205,  2nd  edition,  1911. 

Darapsky,  Juvenile  vs.  meteoric  waters,  1903. 

Daubree,  G.  A,,  1,  Subterranean  waters  in  an- 
cient epochs,  1887. 

2,  Subterranean  waters  of  the  present  day, 
1887. 

de  Launay,  7,  1899. 

Delkeskamp,  3,  Genesis  of  thermal  waters,  1899. 
4,  1904. 

6,  Juvenile  vs.  vadose  springs,  1905. 

7,  Juvenile  and  vadose  carbonic  acid,  1906. 

8,  Progress   in    the    sciences   of   mineral 
springs,  1908. 

Don,  Genesis  of  gold-ores  (in  relation  to  min- 
eral waters),  1897. 

Finch,  Excellent  discussion  oh  depth  of 
ground-water,  1904. 

Fuller,  2,  Excellent  paper,  1906. 

Gautier,  A.,  1,  Excellent  general   paper  on 

magmatic  water,  1906. 
2,  General,  1906. 

4,  General,  1906. 

5.  1909. 

Griffiths,  Quicksilver,  New  Zealand,  1910. 
Gudzent,  Radio-activity  of  thermal  waters,1910 


928 


SUBJECT    INDEX. 


Hague,  2,  Origin  thermal  waters,  1911. 
Henrich,  F.,  1910. 

Kemp,  14,  pp.  184-194,  Excellent  general  dis- 
cussion, 1901. 

16,  Excellent  general  discussion,  1902. 
King,  F.  H.,  Excellent   general   discussion, 

1898. 

Krusch,  3,  Westphalian  vein- waters,  1904. 
Lindgren,  31,  Deposition  of  sulphides  by  hot 

springs,  1910. 

21,  Steamboat  Springs,  1905. 
Le  Conte,  2,  Ditto,  1883. 

4,  Sulphur  Bank,  Cal.,  1894. 
Mendenhall,  5,  General  problems  in  ground-  j 

water  near  Los  Angeles,  Cal.,  1894. 
Mutter,   H.,  1,    Mineral   springs   in    Freiberg 

mines,  1885. 

Ochsenius,  1,  General,  1893. 
Posepny,  2,  Excellent  general  discussion,  pp. 

212-247,  1893. 

Rickard,  et  al.,  2,  water  in  veins,  1903. 
Eickard,  T.    A.,  20,  Meteoric  vs.    magmatic 

waters,  1908. 


Hies,  General,  pp.  293-301,  311-316,1910. 

Sass,  1,  Oscillations  of  ground-water  level, 
1901. 

Slichter,  1,  Motion  of  ground -water,  mathe- 
matical, 1899.  See  also  Water  Sup.  and 
Irr.  Bull.  U.  S.  O.  S.,  Nos.  67  and  140, 1902-5. 

2,  ditto,  1902. 

Spurr,  16,  General,  pp.  235-242,  1907. 
Stutzer,  13,  Juvenile  springs,  1910. 
Suess,  2,  Hot  Springs,  1902. 

3,  English  translation  of  2, 1902. 
Thorkellson,  Hot  Springs,  Iceland,  1910. 
Ulilig,  General  discussion  on   motion  of  un- 
derground waters,  1894. 

Van  Hise,  4,  Excellent  general  discussion, 
1900. 

6,  Discussion  with  Kemp  regarding  under- 
ground circulation,  1900. 

8,  Chemistry  and  physics  of,  pp.  65-119:  cir- 
culation and  work  of.  pp.  123-159  ;  circula- 
tion of  ore-solutions,  pp.  1017-1029  ;  mete- 
oric origin  of  waters,  pp.  1065-1069, 1904. 


WALL   ROCK. 


INFLUENCE    OF   ON    ORE- 
DEPOSITION. 


(For  influence  of  wall-rock  on  fissure  formation  see  u  Fissures,"  sub-head  under 
Cavities  in  Rocks."     These  references  apply  only  to  mineral  contents.) 


Beck,  8,  pp  384-395, 1909. 

9,  pp.  16-20,  1909. 
Bergeat-Stelzner,  pp.  608,  718,  especially  pp.  995- 

1006,  1906. 
Boutwell,  5,  pp.  180-183, 1905. 

6,  p.  119, 1912. 

von  Cotta,  2,  pp.  516-525,  1870. 
Denckmann,  Ramsbecker,  1908. 
Fairbanks,  2.  1893. 
Foster,  p.  12,  1900. 
Irving,  J.  D.,  7, 1908. 
Jenney,  2,  Reducing  agents,  1902. 
Kemp,  21,  pp.  42-44,  1906. 
Lindgren,  12,  The  relations  between  wall  rocks 
and  deposition  are  discussed  in  some  de- 
tail, 1900. 

3,  p.  279, 1894. 

13,  pp.  612-613,  1901. 

Lindgren  and  Ransome,  3,  pp.  159-160,  208-209, 
1906. 


Mutter,  H.,  3,  Freiberg  veins,  1850. 

2,  p.  296, 1901. 

Phillips-Louis,  pp.  108-112,  General,  1896. 
Purington.  1,  Telluride,  1897  ;  5,  1906. 
Ransome,  14,  Goldfield,  1909. 
18,  pp.  165-166, 1911. 

3,  pp.  299-302,  1901. 

Ransome  and  Calkins,  pp.  104-107,  139,  1908. 
Rickard,  T.  A.,  13,  1900. 

8,  9, 1896. 

Scheerer,  Erzgebirge,  1 862. 
Smith,  W.  S.  T.,  U.  S.  G.  S.  Prof.  Paper  36,  pp. 

148-149,  1905. 

Spurr  and  Garrey,  1,  pp.  160-161,  1905. 
3,  pp.  234-237,  1908  :  6,  pp.  828-830,  859, 1901  ; 

12,  pp.  396-401,  1905. 
Van  Hise,  4,  pp.  88-91,  1900 ;  8,  pp.  1086-1088, 

1229,1904. 
Weed,  6,  General,  1901. 


INDEX. 


[NOTE. — In  this  Index  the  names  of  authors  of  papers  are  printed  in  small  capitals, 
and  the  titles  of  papers  in  italics.  Eeferences  to  papers  expressly  treating  of  the  sub- 
ject named  are  likewise  in  italics ;  and  casual  notices,  giving  but  little  information, 
are  usually  indicated  by  bracketed  page  numbers.] 


A.,  C.  F. :  silver  sandstones  of  Utah,  324. 
Absorption  process  in  contact-metamorph- 

isin,  579. 

Accident  mine,  Cripple  Creek,  Colo.,  [420]. 
Acidity  in  mine-waters:  cause,  174. 
Adams,  F.  D. :  origin  of  nickel-ores,  482.  . 
Age  of  igneous  rocks :  determination,  67. 
Agency  of  Manganese  in  the  Superficial  Al- 
teration   and    Secondary    Enrichment    of 

Gold- Deposits  in  the  United  States  (EM- 

MONS),  xxviii,  759-828. 
Aguilera,  J.  G. :  mineral  deposits  of  Mex- 
ico, [367]. 
Aguilera  and  Ordonez ;  rocks  of  San  Jose, 

Tamaulipas,  Mexico,  565. 
Ajax  mine,  Cripple  Creek,  Colo.,  [419]. 
Alaska,   Forty-Mile  district ;   dike-rocks, 

272. 
igneous  rocks,  261,  262,  263. 

gold-production,  436. 

Napoleon  creek  placers:  origin,  300. 

Panhandle  region  :  geology,  583. 
Alaskite :  crystallization  process,  609. 

definition,  272,  604. 

occurrence  and  composition,  273. 

Silver  Peak,  Nev.,  623. 
Albite :  crystallization  from  magmas,  609. 

in  veins  of  Juneau  district,  Alaska,  588. 
Alfreiua  mine,  Cananea,  Mexico,  [378]. 
Algoma  district,  Ontario,  nickel-deposits, 

463. 
Algonkian  ;  Lake  Superior  region,  637. 

rocks  included  in,  69. 
Algonkian  rocks;  classification,  69. 

distribution,  69. 
Alkaline  earths:  in  mine-waters,  768. 

solutions;  solvent  capacity,  30. 
Allen,  E.  T. :    composition   of  gravel  at 

Steamboat  Springs,  Nevada,  631. 
Allotropism  of  Gold  (Louis),  xv,  105-109. 
Alteration :  agents,  113. 

antimony-deposits,  134. 

bismuth-deposits,  134. 

copper-deposits,  128-131. 

Arizona:  climatic  effect,  129. 
process,  129. 

depth  of,  118.  . 
factors  controlling,  120. 

gold-deposits,  132-133. 

in  fissure-veins,  532. 

lead-deposits,  131. 

manganese-deposits,  127. 

mercury-deposits,  134. 

method  and  chemical  effects,  113. 

molybdenum-deposits,  135. 

physical  effects,  116. 


Alteration :  silver-deposits,  131. 

Silver  Cliff,  Colo.,  155. 
sulphides    to    oxides,    carbonates,   and 

chlorides,  2. 

superficial :  ore-deposits,  xv. 
tin-deposits,  133-134. 
varying  depths  from  surface,  121. 
wall-rocks,  Tonopah,  Nev.,  595. 
zinc-deposits,  131-132. 
Alteration-products:  classification,  123. 

technical  names,  112. 
Alumina:  in  mine- waters,  768. 

quantity  in  igneous  rocks,  732. 
Amalgamation :  gold,  107. 
Analyses:  analcite-tinguaite,  566. 
basalt,  567. 
camptonite,  566. 
deep  water  from  Geyser  mine,  Silver 

Cliff,  Colo,  152. 
diorite-porphyry,  564. 
eruptive  rocks,  705. 
gabbro,  563. 
limestone,  568. 
mine-timbers,  180. 
minerals  isolated  from  rocks    of  New 

Zealand,  167. 
nephelite-syenite,  562. 
nickel-bearing  mineral,  472,  473. 
non-magnetic  residue  from  pyrrhotites, 

472. 
ore  from  Geyser  mine,  Silver  Cliff,  Colo., 

147. 

radioactive  water,  709. 
sinter,  629. 
sinters  from  Geyser  mine,  Silver  Cliff, 

Colo ,  149. 
spring  waters,  706. 

vadose    country-rock ;     Ballarat    gold- 
field,  Victoria,  187. 
Lake  Wakatipu,  N.  Z.,  189. 
Ohinemuri  district,  N.  Z.,  190. 
Otago,  N.  Z.,  188. 
Walhalla  gold-field,  Victoria,  186. 
vadose  water  from  Geyser  mine,  Silver 

Cliff,  Colo.,  151. 
volcanic  gas,  388. 
water,  152,  630. 
wood  for  gold,  198. 
Anchoria-Leland  mine,    Cripple    Creek, 

Colo.,  [420]. 

Andesite :  Tonopah,  Nev.,  591. 
Andradite :  San  Jose,  Tamaulipas,  Mexico. 

572. 

Animikie  iron-range :  Lake  Superior  re- 
gion, 651. 
Annie  Laurie  gold-mine,  Utah,  [827]. 


930 


INDEX. 


Anthon,  E.  F. :  affinity  of  metals  for  sul- 
phur, xli. 
Anthracite,   graphitic;    association   with 

silver-lead  ores,  317. 

Auti  mony :  in  silver-ore,  Silver  Cliff,  Colo., 
141,  147. 

reducing  power,  353,  358. 

relations  to  igneous  rocks,  754. 
Antimony-deposits:  alteration,  134. 
Apatite:  in  magnetite:  Kiirunavaara,  677. 
Apollo    gold-mine,  Unga    Island :     gold- 
production,  440. 

Apparatus  for  examining  mine-waters,180. 
Aqueous  solutions:  ore-deposition,  29. 
Archean  :  Lake  Superior  region,  637. 

rocks  included  in,  68. 

Silver  Cliff,  Colo.,  139,  145. 
Areal  distribution  of  mining-districts,  325. 
Argall,  Philip  :  origin  of  Sudbury  nickel- 
ores,  483. 
Arid  regions:  alteration  of  ore-deposits, 

136. 

Arizona :  Clifton  copper-deposits,  401, 517- 
556. 

gold-production,  440. 
Arsenic  :  reducing  power,  353,  358. 

relations  to  igneous  rocks,  754. 
Arsenopyrite :  in  contact-inetatnorphic  de- 
posits of  Sacriflcio  mountain,  Durango, 
Mex.,  402. 

reducing  power,  353,  358. 
Arseuopyrite  type  of  ore-deposits,  372. 
Ascending  meteoric  waters :  cause,  242. 
Ascension-theory  of  ore-deposition,  xiii, 
12,  14,  15,  201. 

objections  to,  160. 
Ashburner,  C.  A. :  charcoal  in  anthracite,  j 

319. 

Assays:  for  determination  of  fineness  of  i 
gold,  182. 

for  gold  in  California  rocks,  301. 

marine  sediments,  197. 

silver,  [17]. 

Sudbury,  Ontario,  ores,  464. 

vadose  and  deep  vein-gold,  184. 

methods,  185. 
Atacamite:  occurrence  at  Jerome,  Ariz., 

136. 

Augite:  separation  from  "hornblende,  166.  | 
Auric  compounds  :  formation,  107. 
Auriferous  lodes:  origin,  201. 
Aurylic  compounds:  formation,  107. 
AUSTIN,  W.  L. :  Discussion  on  Ore-Deposits 
near  Igneous  Contacts,  396-402. 

DiNCussion  on  The  Geological  Features  of  i 
the  Gold- Production  of  North  America,  I 
447-449. 

contortion  in  wollastonite,  577. 
Austin  district,  Nevada,  ore-deposits,  617. 

Backstrom :  genesis  of  iron-ores  of  Norr- 
botten,  Sweden,  678. 

Ball,  Spurr,  and  Garrey:  silver-lead  de- 
posits, Georgetown  and  Silver  Plume, 
Colo.,  [816]. 

Ball  Mountain  fault,  Leadville,  Colo.,  48. 

Ballarat  gold-field,  Victoria  :  vadose  coun- 
try-rock :  analyses,  187. 

BANCROFT,  G.  J. :  The  Formation  and  En- 
richment of  Ore-Bearing  Veins,  xxvii,  696- 
719;  Supplementary  Paper,  720-728. 


Banded  structure  in  ore-bearing  rock  ;  ori- 
gin, 56. 

Banuack,  Mont.,  gold-deposits,  381. 
Baraboo  iron-range,  Wisconsin  :  origin  of 

ores,  651,  652. 

Baric  chloride:  precipitant  for  gold,  194. 
Barite;  distribution  in  Missouri,  89. 
Barite-deposits :  Virginia,  834. 
Barium  :  distribution  in  igneous  rocks,  748. 

quantity  in  igneous  rocks,  733. 
Barlow,  A.  E, ;  geology  of  Sudbury,  Onta- 
rio, nickel-deposits,  479. 
Barrell,  Joseph  :  contact-effects  in  Elkhorn 

district,  576. 
contact-rnetamorphism,  374,  392,  524. 

physical  effects,  385. 
rocks  of  Elkhorn  district :  composition, 

383. 

Barus,  Carl :  compression  of  water,  244. 
Barysphere :  metals  in,  714. 
Baryta:  tests  for:  in  rocks  at  Leadville, 

Colo.,  16-17. 

Basalt:  San  Jose,  Tamaulipas,  Mexico,  567. 
Basaltic  rocks :    Cripple    Creek   district, 

Colo.,  411. 

Bassick  mine,  Silver  Cliff  district,Colo., 158. 
example  of  chimney-deposits,  58,  59. 
locus  of  ore-bodies,  24. 
BATESON,  C.  E.  W. :   The  Mojave  Mining- 
District,  California  [Trans.,  xxxvii,  160- 
177],  Notice,  832. 
Batesville,     Ark. :      manganese-deposits : 

concentration,  128. 
Bauxite :  origin,  135. 
Bayley,  W.  S. :  absorption-phenomena  at 

Pigeon  Bay,  Minn.,  579. 
Beck,  Richard :  gold-bearing  granite,  367. 
nickel-ores,  origin,  485. 
ore-deposits,  [218]. 
genesis,  [253]. 
Berggiesshiibel,  378. 

BECKER,  G.  F. :  Biographical  Notice  of 
Samuel  Franklin  Emmons,  xxix-xlvii. 
The  Torsional  Theory  of  Joints,  xiii,  92- 
104:  Discussion  (HowE),  101;  (RAY- 
MOND), 101-102 ;  (BECKER),  103,  104 ; 
(Bo  YD),  103. 

Discussion  on  The  Genesis  of  Certain  Au- 
riferous Lodes,  207-208. 
bitumen  associated  with  quicksilver,345. 
Comstock  lode,  60. 
production,  803. 
quartz,  801. 
replacement,  xl. 
source  of  ore-materials,  [164]. 
Comstock  rocks,  erosion,  85. 
convection  currents  in  magmas,  260. 
deposition  of  sulphides  by  hot  ascend- 
ing waters,  629. 
investigations  of  country -rocks,  Washoe, 

23. 

"  linked  veins,"  221. 
minerals  in  Appalachian  gold-deposits, 

809. 
natural  solvents  of  precious  metals,  xiv, 

[203]. 

osmosis  in  ore-formation,  [xxiv]. 
quicksilver-deposits,  [207]. 

genesis,  79. 

vein-formation  at  Clear  Lake,  Cal.,  and 
Steamboat  Springs,  Nev.,  xiv. 


INDEX. 


931 


"  Bedded  vein  ":  definition,  36. 

Bedding:  agency  in  producing  water- 
channels,  33. 

Bell,  Eobert:  origin  of  nickeliferous  pyr- 
rhotite,  481. 

Bel  mont  district,Nevada :  ore-deposits,617. 

Ben  Eaton  mine,  Silver  Cliff  region,  Colo., 
157. 

Beudigo  gold-field,  Victoria  :  assays,  185. 

Beresite  at  Belmont,  Nevada,  278. 

Berggiesshiibel,  Saxony,  ore-deposits,  378. 

BERKEY,  C.  P.,  and  HASTINGS,  J.  B. :  The 
Geology  and  Petrography  of  the  Goldfield 
Mining- District,  Nevada  [Trans.,  xxxvii, 
140-159],  Notice,  832. 

Berner's  Bay,  Alaska  :  gold-deposits,  811. 

Beryllium:  distribution  in  igneous  rocks, 
746. 

Bibliography:     Science     of    Ore-Deposits, 
(IRVING,  SMITH,  FERGUSON), 837-928. 
Scientific  Publications  of  S.  F.  Emmons, 
xlii-xlvii. 

Bibra:  metals  in  ashes  of  marine  plants, 
[256]. 

Big  Seven  mine,  Neihart,  Mont.,  220. 

Bischof,  G. :  derivation  of  vein-materials, 

22. 

metals  in  water  of  springs,  [708]. 
ores  in  sedimentary  rocks,  256. 
transformation  of  potassium  feldspar  to 
albite,  587. 

Bisilicates :  metal-content,  203-204. 

Bismuth :  relations  to  igneous  rocks,  754. 

Bismuth-deposits:  alteration,  134. 

Bispberg  mine,  Sweden:  origin  of  iron- 
ores,  670. 

Bitumen :    association  with  ore-deposits, 

345. 
reducing  power,  305,  350,  357. 

Bituminous  coal :  reducing  power,  351,  357. 

Bituminous  shales  ;  association  with  ore- 
deposits,  327. 

Black  Hills,  S.  Dak. :  fissures  conducting 
ore-bearing  solutions,  700. 
gold-deposits,  810. 

Blair  mines,  Silver  Peak  quadrangle,  Ne- 
vada, 621,  622,  624. 

BLAKE,  W.  P. :  Discussion  on  The  Genesis 

of  Certain  Auriferous  Lodes,  211-212. 
petroleum    associated   with    zinc-   and 
lead-ores,  344. 

Blende:  deposition  from  mine- waters,  330. 
mode  of  occurrence  in  Missouri,  327. 
reducing  power,  358. 

Blezard  (Dominion)  mine,  Blezard  town- 
ship, Sudbury  district,  Ontario,  499. 

Block  8  of  State  laud  mine,  Cripple  Creek, 
Colo.,  42-2. 

Blue  limestone,  Leadville,  Colo. :  geologic 

horizon,  18. 
ore-bodies  in,  7,  13. 
receptacle  of  ore-materials,  7,  16. 

Bluebird  granite,  223,  224. 

Bodie,  Cal. :  gold-deposits,  823. 

BOEHMER,  MAX  :  Some  Practical  Sugges- 
tions Concerning  the  Genesis  of  Ore-De- 
posits  [Trans.,  xxxiv,  449-453],  Notice, 
829-830. 

Bog  iron-deposits :  Gunnison  region,  Colo.,  | 

32. 
Red  mountain,  Colo.,  32. 


Bog-ore:  Scandinavia,  694. 

Boiler-scale:  examination  for  gold,  178- 

179. 

Bonanzas :  occurrence,  453. 
Bo  rax -deposits:  formation,  115. 

United  States  (KEYES),  835. 
Bornite :  reducing  power,  358. 
Boron  :  distribution  in  igneous  rocks,  748. 
Boundary  district,  B.  C. :  copper-deposits, 

374. 

BOUTWELL,  J.  M. :   Genesis  of  the  Ore-De- 
posits at  Bingham,  Utah  [Trans.,  xxxvi, 

541-580],  Notice,  831. 
BOYD,  C.  E. :  Discussion  on  The  Torsional 

Theory  of  Joints,  103. 
Breccia :  in  fissures,  45. 

in  fissure-veins :  origin,  46. 

Silver  Cliff,  Colo.,  143. 
Brecciation  in  country-rock :  effect  on  ore- 
deposits,  118. 
Breithaupt :  derivation  of  vein-materials, 

22. 

British  Columbia :  Boundary  district :  cop- 
per-deposits, 374. 

gold-production,  436. 

Eossland  :   pyrrhotite-deposits,  462,  486. 
British  Guiana:  gold-quartz  veins,  281. 
Brock,  E.  W. :   copper-deposits  of  Boun- 
dary district,  375. 

pyrrhotite-deposits,  Eossland,  B.  C.,  486. 
Brogger,  W.  C. :  contact-metamorphic  phe- 
nomena, 525. 

igneous  rocks  of  Christiania  region,  692. 

origin  of  igneous  rocks,  [260]. 
Brokaw,  A.  D. :  experiments  on  solution 

of  gold,  763,  773,  776. 
Bromine  :  solvent  of  gold,  173. 
BROWN,  E.  G. :  The  Vein  System  of  the  Stan- 
dard Mine,  Bodie,  Cal.  [Trans.,  xxxviii, 

343-357],  Notice,  833. 

Browne,  D.  H. :   magnetic  separation   of 
nickel-ores,  467. 

nickel-ores  of  Sudbury,  470,  483. 
Browne,  Eoss  E. :  association  of  gold  with 

slate  in  California,  211. 
Brun,  Albert:  experiments  on  lavas,  725. 

gases  in  lavas,  [767]. 
Buehler  and  Gottschalk:  role  of  pyrite, 

766. 
Bull-Domingo  mine,  Silver  Cliff  district, 

Colo.,  24,  58,  158. 

Bullfrog,  Nev. :  geology  and  ore-deposits, 
600. 

gold-deposits,  827. 
Bullion-Beck  mine,  Tintic  district,  Utah, 

335,  336. 

Buusen,  E. :  volcanic  gases,  723. 
Burns  mine,  Cripple  Creek,  Colo.,  422. 
Bush,  E.  E. :  origin  of  Sudbury  nickel- 
ores,  483. 

Butte,  Mont. :  copper-deposits:  alteration, 
130. 

genesis,  76. 

vein-formation,  55,  220. 
Butte  granite,  223,  224. 

Cable     mine,     Philipsburg     quadrangle, 
Mont.,  [762],  814. 

character  of  gold-enrichment,  762. 
Cadmium  :  distribution  in  igneous  rocks, 

753. 


932 


INDEX. 


Calcium  :  in  mine-waters,  768. 

Calcium  disulphide  :  reducing  power,  358. 

California :  assays  for  gold,  301. 
gold  production,  436. 

California  metal lographic  province,  619. 

California  region  :  geologic  history,  583. 

Cambrian:  Silver  Peak  quadrangle,  Ne- 
vada, 604. 

Camp  Bird  gold-mine,  Ouray,  Colo.,  [787], 
[818]. 

Camptonite :  San  Jose,  Tamaulipas,  Mex- 
ico, 566. 

Cananea,  Sonora,  Mex. :  copper-deposits, 

376,  396. 
volcanic  action,  715. 

Cananea  mountains:  physiographic  fea- 
tures, 376. 

Carbon  :  mode  of  occurrence,  315. 
protective  action,  311. 
reducing  action,  305. 
reducing  power,  307. 

Carbon  dioxide:   occurrence  in  New  Al- 

maden  quicksilver  mine,  363. 
r6le  in  formation  of  ore-deposits,  312. 

Carbon  monoxide :  reducing  power,  358. 

Carbonaceous  matter :  influence  on  forma- 
tion of  ore,  231. 

Carbonate  fault,  Leadville,  Colo.,  48. 

Carbonate  Queen  mine,  Cripple  Creek, 
Colo.,  419. 

Carbonates :  in  mine- waters,  768. 

Carbonic  acid  gas :  in  subterranean  water : 

Silver  Cliff,  Colo.,  148. 
role  in  formation  of  ore-deposits,  312. 
stability,  313. 

Carboniferous  rocks :  relation  to  Cambrian 
country-rock  in  Ozark  region,  Mo.,  88. 

Carlyle,  W.  A. :  gold-quartz  veins  in  Slo- 
can  district,  B.  C.,  280. 

Cam  Marth,  Cornwall :  banded  ore-depos- 
its, 57. 

Catalytic  action  :  definition,  309. 

Caves  :  formation  by  solution,  6. 

Leadville,  Colo. :  formation  subsequent 
•  to  ore-deposits,  4. 
receptacles  for  ore-bodies,  7-8. 

Cavities:  ore-deposition  in,  87. 

Cazin,  F.  M.  F. :  origin  of  copper-  and  sil- 
ver-ores in  Triassic  sand-rock,  [326]. 

Cerium  :  distribution  in  igneous  rocks, 
749. 

Chalcocite:  chemical  relations  with  py- 

rite,  798. 
in  diorite,  90. 
oxidation,  534. 
reducing  power,  358. 

Chalcocitization  :  vertical  relation  to  deep- 
seated  enrichment  of  gold,  798. 

Chalcopyrite :  formation,  310. 

in  Geyser  mine,  Silver  Cliff,  Colo.,  146. 

reducing  power,  358. 

relation  to,  pyrrhotite,  513. 

San  Jose,  Tamaulipas,  Mexico,  574. 

Chalcopyrite  type  of  ore-deposits,  372. 

Chamberlin  and  Salisbury  :  gases  in  vol- 
canic emanations.  723. 
specific  gravity  of  earth,  715. 

Chamberlin,  K.  T. :  gases  in  rocks,  [767]. 

Chamberlin,  T.  C. :  succession  of  ores  in 
lead-  and  zinc-deposits  of  Wisconsin, 
[407]. 


!  Chance,  H.  M. :  coal  carrying  gold,  321. 
Channels: ,  conducting   ore-bearing   solu- 
tions. 700. 
for  circulating  waters  in  earth's  crust, 

30. 

in  rock-masses  :  closing  of,  699. 
Chapeau  de  fer  (gossan) :  definition,  112. 
Character  and  Genesis  of  Certain  Contact- 
Deposits  [Lindgren],  xix. 
Charcoal   in    Geyser  shaft,   Silver    Cliff, 

Colo.,  143.     ' 

native  :  deoxidizing  agency,  319. 
Charters  Towers,  Queensland :  rocks,  163. 
Chemical  changes  (rocks  and  ore-depos- 
its) :  see  Alterations. 
Chemical  composition  of  beds :  factor  in 

ore-deposition,  36. 

Chemical  forces:  role  in  solution  and  de- 
position, 30. 

Chemistry    of    Ore-Deposition    (JENNEY), 
xxii,    305-363;     Discussion    (CHURCH), 
359-363. 
Cherokee  limestone,  Missouri :  character 

and  composition,  334. 
Chile :  copper-deposits,  130. 
Chimney-deposits:  definition,  58. 

examples,  58. 

China:  gold-quartz  veins,  282. 
Chloride  ores:  distribution,  [768]. 

occurrence,  136. 
Chlorides :   copper :   effect  in  solution  of 

gold,  77H,  781. 
in  mine-waters,  766. 
Chlorine:    agency    in    transportation    of 

metals,  722. 

amount  necessary  for  solution  of  gold 
in  presence  of  manganese  compounds, 
784. 
distribution,  767. 

in  igneous  rocks,  751. 
in  mine-waters,  766,  779. 
in  natural  waters :  map,  New  England 

and  New  York,  769. 
in  volcanic  emanations,  723. 
nascent :  agency  in  solution  of  gold,  777. 
quantity  in  igneous  rocks,  734. 
solvent  of  gold,  174. 
with  manganese  compounds:  solubility 

of  gold  in,  784. 
Christiania  regi on ,  Norway:  igneous  rocks : 

classification,  692. 

Christmas  mine,  Cripple  Creek,  Colo.,  422. 
Christy,  S.  B. :   bitumen  associated  with 

quicksilver,  345. 
Chromium:  distribution  in  igneous  rocks, 

750. 

in  basic  rocks,  285. 
in  igneous  rocks,  267. 
quantity  in  igneous  rocks,  733. 
CHURCH,  JOHN  A. :  Discussion  on  Geolog- 
ical Distribution  of  Useful  Metals  in  the 
United  States,  83-86. 

Discussion  on  The  Chemistry  of  Ore-Depo- 
sition, 359-363. 

deposition  of  ores  in  limestone,  341. 
Circulation  :  meteoric  waters.  242,  243. 
ore-bearing  solutions:    factors  control- 
ling, 791. 

Clarke,  F.  W. :  average  composition  of  ig- 
neous rocks,  [734]. 
chlorine-content  of  igneous  rocks,  [767]. 


INDEX. 


933 


Clarke,  F.   W. :   formula  of  vesuvianite, 

[572]. 

manganese  in  igneous  rocks,  [794]. 

reactions  produced  by  hot  waters,  [726]. 

relative  proportion  of  elements  in 
earth's  crust,  [293], 

rock-analyses,  [767],  [794]. 
Classification  :  Algonkian  rocks,  69. 

genetic :    Clifton-Morenci    ore-deposits, 
556. 

ore-deposits,  286,  366. 

products  of  alteration,  123. 

rock -fractures,  40. 
Cleavage-planes :  cause,  41. 

definition,  101. 
CLEKC,  F.  L. :   The  Ore-Deposits  of  the  Jop- 

lin    Region,    Missouri    [Trans.,    xxxviii, 

320-343],  Notice,  833-834. 
Clifton-Morenci  district,  Arizona  :   depth 
of  oxidized  zone,  545. 

distribution  of  ores,  540. 

fluid  inclusions,  545. 

genesis  of  ores,  551. 

genetic  classification  of  deposits,  556. 

geology,  519. 

groundwater  conditions,  544. 
Climatic  conditions :  effect  on  alteration, 

120. 

Coal,  bituminous:   association  with   ore- 
deposits,  320. 
Coast-sediments :    examination   for  gold, 

196. 
Cobalt:  in  igneous  rocks,  269,  752. 

in  Sudbury  pyrrhotites,  466. 

presence  in  pyrrhotite,  461. 

quantity  in  igneous  rocks,  733. 
Colorado :  Cripple  Creek  district :  ore-de- 
posits, 411. 

gold-production,  437,  441. 

pre-Mesozoic  gold-deposits,  447. 

relation  of  rain-fall,  run  off,  and  evapo- 
ration, 698. 

Eico :  mineral  veins,  226. 

San  Juan  region:  vein-system,  290. 
Colorados  (gossan) :  definition,  112. 
Cornagrnatic  region  :  definition,  738. 
Comb-structure :  veins,  10. 
Compression-fissures :  Butte,  Mont.,  55. 
Compression-fractures :  characteristics,  45. 
Compression -joints  :  definition,  41,  50. 
Comstock,  T.  B. :  genesis  of  Red  Mountain 
deposits,  31. 

The    Geology  and    Vein-Structure    of 
Southwestern  Colorado,  [31]. 

vein-system  of  San  Juan  region,  Colo., 

290. 
Comstock  district :  comparison  with  Tono- 

pah,  Nev.,  601. 

Comstock  lode,  Nevada :  genesis  of  ores, 
ix,  x,  19,  85,  803. 

gold -production,  440. 

production  of  silver  and  gold,  and  rela- 
tion of  ores,  801,  802. 

structural  features,  60. 
Comstock  vein  :  extent,  11. 

structure,  10. 
Concentration  :  gold  :  in  oxidized  zone,797. 

iron-deposits  :  Lake  Superior,  125.    . 

natural :  minerals,  255. 

ore-metals,  300. 
Concentration -process :  ore-deposits,  29. 


Consanguinity  :  in  rOcks,  738. 
Contact-deposits :   character  and  genesis, 

xix. 

examples,  38. 
formation,  230. 
miners'  use  of  term,  37. 
Contact-metamorphic  deposits,  432. 
distribution,  396. 
genesis,  387,  392. 
geographic  distribution,  373. 
Contact-metamorphic  effects  :  variability, 

578. 

Contact-metamorphic  ore-deposits :  char- 
acter, 371. 

Contact-metamorphic  zones,  371. 
Contact-metamorphism  :  Bannack,  Mont., 

382. 

Clifton-Morenci  district,  Arizona,  522. 
effects,  385. 

Elkhorn  district,  Montana,  576. 
hydrothermal,  529. 
origin,  262. 

San  Jose,  Tamaulipas,  Mexico,  567. 
western  Nevada,  617. 
Contact-planes :  definition,  37. 
Contour-mapping :  introduction,  xxy.ii. 
Contraction  hypothesis,  42. 
Contraction-planes  :  origin  and  extent,  35. 

relation  to  ore-deposition,  35. 
Copper  :  deposition  from  sea-water,  258. 
distribution  in  igneous  rocks,  752. 
in  basic  rocks,  285. 
in  igneous  rocks,  270. 
in  mine-waters,  770,  781. 
in  nature  :  detection,  77. 
quantity  in  igneous  rocks,  733. 
reducing  power,  358. 
Copper  chlorides:  effect  on  solubility  of 

gold,  773,  781. 
i  Copper  Cliff  mine,  Sudbury,  Ontario,  456. 

501. 

photomicrographs  of  ore,  489,  494. 
i  Copper-deposits:  alteration,  114,  128-131. 
Appalachians  :  genesis,  76. 
Arizona :  Bisbee,  829. 
Clifton,  401. 
Clifton-Morenci  (LINDGREN),XXV,  517- 

556. 

classification,  521. 
climatic  effects,  122. 
Jerome,  136. 

superficial  alteration,  128. 
Australia:     Chillagoe     district,    North 

Queensland,  830. 
Cananea  type,  374. 
Chile,  130. 

climatic  effects,,  122. 
Colorado :  Evergreen,  835. 
concentration,  76. 
genesis.  75-77. 
Idaho :  Mackay,  833. 
kind  of  rock  in  which  found,  77. 
Lake  Superior  district,  76. 
Mansfeld,  Harz  mountains,  36. 
Mexico :  Cauauea,  396. 
Michigan  :  climatic  effects,  121. 
Montana:  Butte  City:  alteration,  130. 

genesis,  76. 
San  Jose,    Tamaulipas,   Mexico   (KEMP), 

xxv-xxvi,  557-581. 
source  of  material,  75. 


934 


INDEX. 


Copper-deposits:  Tasmania:  climatic   ef- 
fects, 122. 

Tennessee  :  Ducktown  :  alteration,  130. 
Copper-iron  sulphides  :  secondary  enrich- 
ment, 832. 
Copper-veins  :  Butte,  Mont.,  224,  225,  403. 

Virgilina,  Va.,  220. 

Coriolanus  mine,  Cripple  Creek,  Colo.,  419. 
Cornwall,  England  :  veins  :  structure,  10, 

225. 

Coronadite,  Clifton-Morenci  district,  Ari- 
zona, 519. 
Coronado  lode,   Clifton-Moreuci  district, 

Arizona,  543. 

Coronado  quartzite,  Cliftou-Morenci  dis- 
trict, Arizona,  519. 
Correlation  of  the  elements,  743. 
Correlation  table :  pre-Cambrian  series  of 

the  Lake  Superior  region,  634. 
Cotta,  B. :  derivation  of  vein-materials,  22. 

Treatise  on  Ore-Deposits,  [viii],  316. 
Country-rock  :  auriferous  lodes  :  examina- 
tion, 183. 

Colorado :  Custer  county :  assays  for  sil- 
ver, 161. 

Leadville :  investigations,  23. 
Silver  Cliff:  assays  for  silver,  161. 

investigations,  23. 
Ten-Mile  :  investigations,  23. 
Influence  on  Mineral  Veins  (WEED),  216- 

234. 

influence  on  vein-filling,  222,  223. 
Nevada  :  Washoe  :  investigations,  23. 
New  Zealand  :  classes,  212. 
of  ore-deposits  :  decay,  117. 
sheeting,  46,  47. 
vadose  region   of  Walhalla  gold-field, 

Victoria,  186. 

Covellite  :  reducing  power,  358. 
Cracks  :  in  glass :  produced  by  torsioual 

strain,  51. 
Creighton  mine,  Sudbury,  Ontario,  502. 

photomicrographs  of  ore,  490-492. 
Cretaceous  gold-deposits,  435-438. 
Cretaceous  rocks,  Tamaulipas,  Mexico,561. 
Cripple  Creek  and  Silver  Cliff  ore-depos- 
its compared,  158. 

Cripple  Creek   district,    Colorado :    gold- 
production,  441. 
ore-deposits,  411,  819. 
rocks,  718. 

underground-water  conditions,  699. 
CROSBY,  W.  O. :  Ore-Deposits  of  the  Eastern 
Gold-Belt  of  North    Carolina  [Trans., 
xxxviii,  849-856],  Notice,  834-835. 
origin  of  cross-joints,  44. 
torsional  hypothesis,  [95]. 
Crosby  and  Fuller  :   origin  of  pegmatite, 

275. 
Cross,   Whitman :    absence    of   steam   in 

Kilauea,  390. 
Democrat  and  Ben  Eaton  mines,  Colo., 

[157]. 
Cross-joints  :  definition,  40. 

origin,  44. 

Crown  Point- Belcher  bonanza,  361. 
Crowning  Glorv  gold-mine,  Silver  Peak, 

Nev.,  621,  [813]. 
cross-section,  625. 
Crushed  zones  :  ore-deposits,  57. 
Crystalline  rocks  :  see  Rocks. 


Crystallization  :  in  igneous  rocks  :  order, 

261,  263. 
in  magmas  :  order,  585. 

Cupric  chlorides  :  see  Chlorides,  copper. 

Cupric  salts  :  efficiency  in  promoting  solu- 
tion of  gold,  782. 

Curtis,  J.  S. :  ore-deposits  of  Eureka  dis- 
trict, Nev.,  7,  58. 

Curve :  gold  in  vadose  country-rock,  Wal- 
halla, Victoria,  192. 

Custer  county  :  country-rock  :  assays,  161. 

Dacite  :  Tonopah,  Nev.,  593. 
Dacite-porphyry :  percentage  composition, 

565. 
DAGGETT,  ELLSWORTH  :  The  Extraordinary 

Faulting    at    the     Berlin    mine,    Nevada 

[Trans.,  xxxviii,  297-309],  Notice,  833. 
Daintree,   Eichard  :   auriferous  rocks  of 

Queensland,  282. 

Daunemora  mine,  Sweden  :  diagram,  661. 
Dart  Eiver  :  auriferous  lode,  North  Gipps- 

land,  Victoria :  assays,  184. 
Daubree,  A. :   classification  of  rock  frac- 
tures, 40. 

experiments  on  glass.  51. 

genesis  of  titaniferous  albite  veins,  587. 

movement  in  rocks,  92,  93,  94. 

production  of  joints,  94. 

subterranean  waters,  29. 

synthetic  experiments,  [2]. 

torsion  experiments  on  glass  plates,  95. 
Dawson,   G.  M. :    quartz-veins  associated 

with  granite,  279. 

Dead  Pine  mine,  Cripple  Creek.  Colo.,  419. 
Deadwood  mine,  Cripple  Creek,  Colo.,  422. 
Death  valley  :  borax-deposits,  [835]. 
Decomposition  of  volcanic  rocks,  727. 
Deep  mines  :  dryness,  241. 
Deformation  :  modes,  92. 
DE  KALB,  COURTENAY  :    Geology  of   the 
Exposed   Treasure  Lode,  Mojave,   Cali- 
fornia [Trans.,  xxxvii,  310-319],  No- 
tice, 834. 

gold-deposits  of  Exposed  Treasure  mine, 

Cal.,  824. 
De  la  Beche:  mineral  veins  of  Corn  wall,226. 

mineral  veins  of  Derbyshire,  229. 

vein-formation,  220. 
Delamar  district,  Idaho  :  comparison  with 

Tonopah,  Nev.,  601. 

Delamar  gold-mine,  Nevada,  [794],  [828], 
De  Launay,  L. :  distribution  of  rare  ele- 
ments, 745. 

genesis  of  iron-ores,  678. 

genesis  of  ore-deposits,  [253]. 
Del  Mar,  Alexander :  gold-resources  of  the 

world,  425. 

Delmonico  mine,  Cripple  Creek,  Colo. ,422. 
Democrat  mine,  Silver  Cliff  region,  Colo., 

157. 
Depth  of  alteration  of  ore-deposits  in  un- 

glaciated  regions,  122. 
Derby,  O.  A. :  Brazilian  gold- veins,  [239]. 
Derbyshire  lead -mines,  229. 
Descending  solutions:    agency  at   Lead- 
ville, Colo.,  12. 
Descending  waters  :  agency  in  formation 

of  iron-deposits,  69-71. 
Detection  and  Estimation  of  Small  Quantities 
of  Gold  and  Silver  (WAGONER),  829. 


INDEX. 


935 


Deville,  C.  St.  C.:  juvenile  waters,  [xxxviij. 

volcanic  gases,  723. 
Diaclase  :  rocks,  92. 
Diaclases :  definition,  40. 
Diamond  swindle  :  Vermilion  Creek  Basin, 

Wyoming,  [xxxiii]. 

DICKSON,  C.  W. :  The  Ore-Deposits  of  Sud- 
bury, Ontario,  xxiv-xxv,  455-516. 
Differentiation  :  igneous  magmas,  67. 
Dikes  (see  also   Intrusions) :    Forty-Mile 
district,  Alaska,  272. 

San  Jose,  Taniaulipas,  Mexico,  565. 
Dillon  mine,  Cripple  Creek,  Colo.,  419. 
Diopside  :  San  Jose,  Tamaulipas,  Mexico, 

570. 

Diorite  :  source  of  nickel-ores,  90. 
Diorite-porphyry  :  San  Jose,  Tamaulipas, 

Mexico,  563! 
Distribution  of  the  Elements  in  Igneous  Rocks 

(WASHINGTON),  xxviii,  729-758. 
"Distributive"  faults,  221. 
Doctor- Jack    Pot   mine,    Cripple    Creek, 

Colo.,  423. 

Doelter  :  preparation  of  pyrrhotite,  460. 
Dolcoath  mine,  Cornwall,  225. 
Dolcoath  mine,  Montana,  [383]. 
Dolomite  :  disintegration,  336. 

unaltered  :   distribution  on  Fryer  hill, 

Leadville,  Colo.,  13. 

DON,  JOHN  R. :  The  Genesis  of  Certain  Au- 
riferous Lodes,  xvi,  162-215  ;  Discus- 
sion (LE  CONTE),  202 ;  (EMMONS),  202- 
206;  (BECKER),  207-208;  (WINSLOW), 
208-211;  (BLAKE),  211-212;  (DON), 
212-215. 

analyses    of    Australian    mine-waters, 
[779]. 

chlorine  as  solvent  of  gold,  763. 

genesis  of  auriferous  lodes,  696. 

method  of   determining   gold   in   sea- 
water,  194. 

solution  of  gold,  763,  771,  773. 
Douglas,   James:   secondary  enrichment, 

xli. 
Drinkwater  mine,  Silver  Peak,  Nev.,  621. 

cross-section,  625. 
Dryuess  of  deep  mines,  241,  698. 
Ducktown,  Tenn.,  copper-deposits,  510. 

alteration,  130. 

Dunderland,  Norway,  iron-ores,  690. 
Dustiness  of  mines:  explanation,  698. 
Duty  of  a  reducing  ageut :  definition,  347. 
Dynamic   disturbance   of  earth's    crust : 

periodicity,  43. 

Dynamic  movements:    effect    on    water- 
channels,  34. 

Eakins,  L.  G. :  assays  for  silver,  161. 
Earthquakes:    relation    to    rock-flowage, 
712. 

theory,  44. 
Earth's  axis :  shifting  as  explanation  of 

stress,  715. 
East  Tennessee  mine :  photomicrographs 

of  ore,  494. 

Edgemout,  Nev.,  gold-deposits,  815. 
Edison,   T.  A. :     magnetic    separation  of 

nickel-ores,  467. 
Egleston,  T. :    petroleum  associated  with 

quicksilver,  344. 
Eisener  Hut  (gossan) :  definition,  112. 


Elba  Island  :  iron-ores,  8-9. 
Elements :  correlation,  743. 

distribution  in  igneous  rocks,  754. 
rare:  distribution,  745. 
Elenita  mine,  Cananea,  Mexico,  398. 
Elisa  mine,  Cananea,  Mexico,  398. 
Elk  mountains,  Gunnisou  county,  Colo. : 

fissure-faulting,  49. 
Elkhorn  district,  Montana  :  ore-deposits, 

382. 

Elkton  mine,  Cripple  Creek,  Colo.,  420. 
Ellis,  H.  E. :  coal  carrying  gold,  321. 
Elsie  mine,  Snider  township,  Sudbury  dis- 
trict, Ontario,  500. 
photomicrographs  of  ore,  489-490. 
Emma  mine,  Tintic  district,  Utah,  362. 
Emmens,    S.    H. :    nickel-minerals    from 

Sudbury,  457. 

EMMONS,  SAMUEL  FRANKLIN  :  Biograph- 
ical Notice  (BECKER),  xxxi-xlix. 
List  of  Scientific  Publications,  xliv-xlix. 
Introduction,  vii-xxviii. 
The  Genesis  of  Certain  'Ore-Deposits,  xi, 

1-25. 

Geological  Distribution  of  the  Useful  Met- 
als in  the  United  States,  xii,  65-83 ; 
Discussion  (CHURCH),  83-86:  (WIN- 
SLOW),  86-89;  (EMMONS),  89-90; 
(MERRITT),  90-91. 
Some  Mines  of  Rosita  and  Silver  Cliff, 

Colorado,  xvi,  139-161. 
Structural     Relations     of     Ore-Deposits 

[Trans.,  xvi,  804],  xii,  26-64. 
Discussion  on  The  Genesis  of  Certain  Au- 
riferous Lodes,  202-206. 
association    of  gold    with    manganese, 

[787]. 

chlorine  in  natural  water,  768. 
copper-deposits   of    Boundary  district, 

British  Columbia,  374,  375. 
Delamar  mine,  Nev.,  828. 
genesis  of  certain  ore-deposits,  [27]. 
genesis  of  Leadville  ore-deposits,  xxxvi. 
gold-deposits  of  Black  Hills,  [Sll]. 
increase  in  production  of  gold,  425. 
investigations  of  country-rocks,  Lead- 
ville, 23. 

manganese  as  indication  of  rich  ore,  787. 
manganiferous  gold-ore,   Leadville, 

Colo.,  816. 
manganiferous  silver-ore  at  Leadville, 

Colo.,  800. 
non-mineral-bearing  fissures,  Leadville, 

Colo.,  49. 

origin  of  Sudbury  nickel-ores,  486. 
secondary  enrichment  of  ore-deposits^ 

[696],  [761],  [811]. 
silver-ores  of  Aspen,  Colo.,  332. 
Theories  of  Ore-Deposition  Historically 

Considered,  [viii]. 
veins  of  Butte,  Mont.,  55. 
Emmons,  S.  F.,  and  Irving,  J.  D. :   Down- 
town District,  xxxviii. 
Emmons,  Irving,  and    Jaggar :    gold-de- 
posits, Black  Hills,  S.  D.,  [810]. 
EMMONS,  W.  H. :  The  Agency  of  Manganese 
in  the  Superficial  Alteration  and  Second- 
ary Enrichment  of  Gold-Deposits  in  the 
United  States,  xxviii,  759-828. 
gold-deposits,  Edgemont,  Nev.,  [815]. 
Midas,  Gold  Circle  district,  Nev., [827]. 


936 


INDEX. 


Emmons,  W.  H.,  and  Garrey,  G.  H. :  gold- 
deposits,  Manhattan,  Nev.,  [827] . 

Enargite:  in  Butte,Mout.,ore-deposits,403. 
reducing  power,  354,  358. 

Enrichment  of  ore-deposits  :   see  Ore-de- 
posits. 

Enrichment  theory,  408. 

Eruptions:    ejecting  metalliferous    mag- 
mas, 716. 

kinds  of  magmas  ejected,  715. 
of  igneous  material ;  source,  43. 

Eruptive  activity :  association  with  ore- 
deposition,  21. 

Eruptive  rocks  :  see  Eocks. 

Eruptive  theory :  ore-deposits,  8. 

Erzgebirge,  Freiberg,   Saxony :   vein-sys- 
tem, 52. 

Eureka  district,  Nev. :  ore-deposits,  58. 
genesis,  7. 

Evergreen   Copper-Deposits,   Colorado  (EiT- 
TER),  835. 

Exposed  Treasure  lode,  Mojave,  Cal.:  geol- 
ogy, 834. 

gold-deposits,  823. 
relations  of  ores,  804. 

Extraordinary  Faulting  at  the  Berlin  mine, 
Nevada  (DAGGETT),  833. 

Fahlcrantz,  A.  E. :  iron-ores,  Sweden,  666. 
Faltenverwerfungen  (fold-faults) :  defini- 
tion, 41. 

Faulting  (see  also  Fissures) :  character  of 
movement,  102. 

determined  by  stresses,  104. 

horizontal :  Mt.  Guyot,  Colo.,  64. 

illustrated  by  torsion  experiments,  99. 

in  Cambrian  rocks  of  Missouri,  88. 

in  Mississippian  rocks  of  Missouri  :  ab- 
sence, 88. 

Leadville,  Colo.,  [3] . 

Nevada,  Berlin  mine,  833. 

Ontario  mine,  Utah,  62. 

Queen  of  the  West  mine,  Colo.,  62-64. 
Fault-fissure    deposits:    Ontario    mine, 

Utah,  60. 
Fault-planes :  effect  on  water-channels,  34. 

Leadville,  Colo. :  lack  of  ore-deposits,  10. 
Faults  (see  also  Fissures  and  Fold-faults) : 
extent,  39. 

lack  of  uniformity  in  nomenclature,  40. 
FAY,  A.   H. :    Geology  and  Mining  of  the 

Tin-Deposits   of  Cape  Prince  of   Wales, 

Alaska  [Trans.,  xxxviii,  664-682J,  Notice, 

833. 
Features  of  the  Occurrence  of  Ore  at  Red 

Mountain,  Our  ay  County,  CWo^ScHWARz), 

831. 
FERGUSON,  H.  G.,  IRVING,  J.  D.,  SMITH, 

H.  D. :  Bibliography  of  the  Science  of  Ore- 
Deposits,  837-928. 

Ferric  chloride  :  solvent  of  gold,  173. 
Ferric  salts  :  efficiency  in  solution  of  gold. 

781. 

Ferric  sulphate  :  solvent  of  gold,  173. 
Ferrous  sulphate  :  precipitant  of  gold,  784. 

reducing  power,  355,  356,  358. 
Filter  for  sea- water  in  testing  for  gold,  198. 
Finlay,  G,  I. :  analysis  of  analcite-tingua- 
ite,  566. 

analysis  of  basalt,  567. 

analysis  of  camptonite,  566. 


Finlay,  G.  I. :  analysis  of  diorite-porphyry, 

564. 

eruptive    rocks   of   San    Carlos   range, 

Mexico,  558. 

Fiulay,  J.  E. :  analyses  of  gabbro,  563. 
Fissure-faults  :  definition,  41. 

examples  :  Gunnison  county,  Colo.,  49. 

San  Juan  region,  Colo.,  50. 
Fissure-planes  :  repeated  movements,  59. 
Fissure-systems : 

Clifton-Morenci  district,  Arizona,  539. 

Conrad  Hill,  Davidson  county,  N.  C. : 
character  and  origin,  103. 

origin,  60. 

simultaneous  production,  104. 
Fissure-veins:  extent  in  depth,  11. 

gold-bearing,  427. 

relations  of  length  and  depth,  11. 

so-called  :  formation,  10. 

walls,  54. 
Fissures  (see  also  faults)  : 

conducting  ore-bearing  solutions,  700. 

extent,  53. 

limiting  depth,  44. 

relation  of  walls,  713. 

structural  features  characterizing,  45. 
Fissuring  :  relation  to  ore-bodies,  339. 
Flowage-zone :    effect  on  open   channels, 

699. 
Fluid-inclusions :  Clifton-Morenci  district, 

Arizona,  545. 
Fluorine  :  distribution  in  igneous  rocks, 

751. 
Fold-fault :  definition,  41. 

examples,  Leadville,  Colo.,  48. 

typical  form  :  origin,  47. 
Foliation-planes :  cause,  41. 
Forchharnmer :  metals  in  ashes  of  marine 

plants,  [256]. 
Formation  and  Enrichment  of  Ore-Searing 

Veins  (BANCROFT),  696-719  ;  Supplemen- 
tary Paper  (BANCROFT),  720-728. 
Formulae  for  reducing  power  of  minerals, 

348. 

Fossil  remains  :  replaced  by  ore,  87. 
Foster,  C.  Le  Neve:  veins  of  Cornwall,  10. 
Fouque,  F.  A. :  volcanic  gases,  388. 
Fracture :  causes,  41. 

copper-steel :  character,  101. 
Fracture-system  :  Ontario  mine,  Utah,  61. 
Free  Coinage  mine,  Cripple  Creek,  Colo., 

422. 
Freelaud,  F.  T. :  sulphide  ores,  Leadville, 

Colo.,  3. 

Freiberg,  Saxony :  vein-system,  52. 
Frood   mine,  McKim  township,  Sudbury 

district,  Ontario,  500. 
Fryer  hill,  Leadville,  Colo.:  ore-deposits,  13. 
Fumaroles:  gases  from,  389. 

sublimation  products  :  composition,  390. 
Fumarolic  deposits,  368. 
Fumarolic  origin  of  ore-deposits,  240. 
Furnace  canyon  :  borax  deposits,  [835]. 
Furstenburg :  Wenzal  vein  :  varying  with 

country-rock,  227. 
Fusion,  region  of:  depth,  22. 

Gabbro :  Tamaulipas,  Mexico.  563. 
Galena  :  effect  of  pyrite  on  solubility,  [766], 

occurrence  in  shale,  Missouri,  330. 

reducing  power,  358. 


INDEX. 


937 


Garnet :  San  Jose,  Tamaulipas,  Mexico,  570. 

Gar  net- Formations  of  Chillagoe  Copper  Field, 
North  Queensland,  Australia  (SMITH),  830. 

Garrey,  Ball,  and  Spurr :  silver-lead  de- 
posits of  Georgetown  and  Silver  Plume, 
Colo.,  [816]. 

Garrey,  Emmons,  and  Ransome  :  gold-de- 
posits, Bullfrog  district,  Nev.,  [827]. 

Garrey.  G.  H.,  and  Emmous,  W.  H.  :  gold- 
deposits,  Manhattan,  Nev.,  [827]. 

Garrey,  G.  H.,  and  Spurr,  J.  E.  :  ore-de- 
posits of  Georgetown,  Colo.,  [816],  [817]. 

Gas-content  of  rocks,  767. 

Gautier,  Arrnand:  gase&occluded  in  rocks, 
[390],  [767]. 

Geikie,  A. :  origin  of  igneous  rocks,  [260]. 
volcanic  gases,  388. 

Gellivare  iron-deposits,  Norrbotten, 
Sweden,  671. 

Genesis:    Auriferous    Lodes    (DON),   xvi, 

162-215. 

copper-deposits,  75-77. 
gold-  and  silver-deposits,  80-81. 
iron-deposits,  69-71. 
Lake  Valley,  New   Mexico,  Silver-Deposits, 

(KEYES),  835. 

lead-  and  zinc-deposits,  77-79. 

manganese-deposits,  74-75. 

nickel  deposits,  75. 

Ore-Deposits  (  EMMONS),  xi,  1-25. 

Ore-Deposits  at  Bingham,     Utah  '( BOUT- 
WELL).  831. 

quicksilver-deposits,  79. 

Sudbury,  Ontario,  nickel-ores,  477. 

Touopah  ores,  598. 
•Genetic  Relations  of  the    Western  Nevada 

Ores  (SPURR),  xxvi,  590-620. 
Geologic  history:  California  region,  583. 
Geological  Distribution  of  the  Useful  Metals  in 

the   United  States  (  EMMONS/,  xii,  65-83, 

89-90  ;  Discussion,  83-91. 
Geological  maps : 

central  Sweden,  658. 

Lake  Superior  region,  636. 

Norrbotten,  Sweden,  ore-province,  673. 

San  Jose  district,  Tamaulipas,  Mexico, 

560. 

Geology  and  Copper-Deposits  of  Bisbee.  Ari- 
zona (RANSOME),  829. 
Geology  and  Mining  of  the   Tin-Deposits  of 

Cape  Prince  of  Wales,  Alaska  (FAY),  833. 
Geology  and  Petrography   of    the    Goldjield 

Mining- District,   Nevada  (HASTINGS  and 

BERKEY),  832. 

Geology:    Clifton-Morenci    district,    Ari- 
zona, 518. 

Exposed    Treasure   Lode,     Mojave,    Cali- 
fornia (DE  KALB),  834. 

Lake  Superior  iron-bearing  and  copper- 
bearing  series,  633. 

Rossland,  B.  C.,  pyrrhotite-deposits,  48. 

South  Island,  New  Zealand,  162. 

Sudbury,  Ontario,  nickel-deposits,  479, 
481. 

Treadwell   Ore- Deposits,    Douglas  Island, 
Alaska  (SPENCER),  830. 

Virginia  Barite- Deposits  (WATSON),  834. 
Georgetown,   Colo. :    silver-lead  deposits, 

816. 

Georgetown  quadrangle,  Colo. :  gold-de- 
posits, 817. 


Gertrude  mine,  Creighton  township,  Sud- 
bury district,  Ontario,  504. 
photomicrographs  of  ore,  491-492. 
Geyser:  definition,  32. 
Geyser  shaft :  Silver  Cliff,  Colo. :  section, 

144. 

Geyser  gold-mine,  Silver  Cliff,  Colo.,  xvi. 
analyses  of  ore,  147. 
analyses  of  water,  151,  152. 
country-rocks,  143. 
deep  deposits,  142. 
exploration-work,  143. 
nitrate-content  of  waters,  768,  778. 
ore-bodies,  145. 
vein-materials,  146. 
water-courses,  147. 
Gilbert,  G.  K. :    temperature  of  thermal 

waters,  245. 
GILLETTE,  H.  P. :  Osmosis  as  a  Factor  in 

Ore- Formation,  xxiv,  450-454. 
Glaciation  :  control  of  depth  of  alteration, 

121. 

Glaciers  in  the  United  States :  first  dis- 
covery, xxxi. 

Glass  cracked  by  torsional  strain,  51. 
Glass  plates :  torsional  experiments,  95. 
God  iva  mountain  ore-bearing  beds,  338. 
Gogebic    district :    locus   of  ore-deposits, 

646. 
Gold :    allotropic    forms :    behavior  with 

mercury,  107. 
conditions  produciug,-108. 
-   conversion  to  ordinary  form,  108. 
Allotropism  (Louis),  105-109. 
amalgamation,  107. 
association  :  with  carbonaceous  slates  in 

California,  211. 
with  coal,  321. 
with  manganese  oxides,  786. 
with  platinum  in  Urals,  289. 
with  pyrites,  132. 
with  sulphides,  203. 
chemical  properties,  107. 
concentration  in  oxidized  zone,  797. 
contact-metamorphic  deposits,  432. 
criteria     for     determining     secondary 

origin,  792. 
crystallization,  105. 

deep-seated  enrichment :    vertical  rela- 
tion to  chalcocitization,  798. 
determination  of  small  amounts  in  sea- 
water,  829. 

difference  between    placer-   and   vein- 
gold,  182. 

distribution  in  igneous  rocks,  752. 
experiments  in  solution  and  deposition, 

[763],  771. 

fineness :  variation,  182. 
forms  from  precipitation,  105. 
free:  in  undecomposed  rocks,  208,  214. 
general  diffusion,  209. 
geologic  age  of  deposition,  429. 
in  assays  of  California  rocks,  301. 
in  coal  from  Wyoming,  211. 
in  country-rock,  210. 
in  country-rock  at  deep  levels,  Walhalla, 

Victoria ;  curve,  193. 
in  diorite,  90. 
in  igneous  rocks,  271. 
in  mine-waters:  evidence  for,  178. 
search  for,  179. 


59 


938 


INDEX. 


Gold  :  in  sea-water,  191,  192. 

determinations,  195. 

methods  of  detecting,  193. 
in  siliceous  igneous  rocks,  286. 
in  vadose  country-rock,  Walhalla,  Vic- 
toria :  curve,  192. 
mode  of  occurrence,  108,  724. 
native  :  deposition  by  primary  processes, 

793. 

natural  solvents,  173. 
occurrence  in  sulphides,  New  Zealand, 

170. 

origin  in  stratified  deposits,  191. 
placer-deposits,  133. 
precipitation,  784. 

by  black  shales,  331. 

from  sea-water,  194. 
experiments,  198,  199. 

in  marine  sediments,  196. 

reagents,  108. 

relative  fineness  of  vadose  and  deep  vein- 
gold,  184. 
Crustiness,"  109. 
solution :  reactions,  777. 

and  re-precipitation,  206. 

in  vadose  waters,  177. 
source,  201. 

in  pyrite,  203. 
specific  gravities,  106. 
tests  for :  in  rocks  at  Leadville,  Colo.,  16. 
transfer  in  cold  solutions,  785. 
varieties,  105.  ' 
Witwatersrand,  Transvaal :  action  with 

reagents,  109. 

Gold  Circle,  Nev. :  gold-deposits,  827. 
Gold  Coin  gold-mine,  Cripple  Creek,  Colo., 

419,  [821]. 

Gold-concentrations:  occurrence,  271. 
Gold-content  of  sea-water:  amount,  206. 
Gold-deposits    (see    also    Gold-silver    de- 
posits) : 
Agency  of  Manganese  in   Alteration  and 

Enrichment,  759-828. 
Alabama,  [810J. 
Alaska:  Berner's  Bay,  811. 

Treadwell  mines,  811. 
alteration,  132-133. 
Appalachian,  806. 

association  with  eruptive  rocks,  80. 
Bannack  type,  381. 
California,  Bodie,  823. 

Mojave:  Exposed  Treasure  mine,  823. 

-Mother  Lode  district,  811,  830. 

Nevada  City  and  Grass  Valley  district, 
812. 

Ophir  district,  813. 
classification  according  to  age,  433. 
classification  (Lindgreu's),  [763],  [806]. 
Colorado :  Cripple  Creek,  159,  819. 

Georgetown  quadrangle,  817. 

Leadville,  815. 

Mt.  Guyot,  near  Breckenridge,  64. 

San  Juan,  818. 

Summit  district,  822. 
concentration,  80. 

in  oxidized  zone,  797. 
Cretaceous,  435,  806. 
formation,  172. 

greater  richness  in  vadose  region,  171. 
Homestake  type  in  South  Dakota,  806. 
Idaho,  [815]. 


Gold-deposits :   Montana,  Granite   moun- 
tain, 122. 

other  districts,  815. 
Philipsburg,  [762],  814. 
Nevada  :  Bullfrog  district,  827. 
Delamar  mine,  828. 
Edgemont,  815. 
Gold  Circle  district,  827. 
Goldfield,  825. 
Manhattan,  826. 
Silver  Peak,  813. 
Tonopah,  68. 
Ontario,  445. 
Pre-Cambrian,  434. 
South  Carolina:  Haile  mine,  806. 
South  Dakota:  Black  Hills,  810. 
Southern  Appalachian  districts,  809. 
Tertiary,  807. 

United  States  :  superficial  alteration  and 
secondary  enrichment  by  ageney  of 
manganese,  759. 
Utah  :  Annie  Laurie  mine,  827. 
Golden  Cyele  mine,  Cripple  Creek,  Colo.r 

422. 
Goldfield  district,  Nevada:   geology  and 

ore-deposits,  599. 
geology  and  petrography,  832. 
gold-deposits,  825. 

Gold  Ledge,  Mercur,  Utah  :  origin,  290. 
Gold-mine  waters  :  salts  in,  764. 
Gold-mines  (see  also  Gold-silver  mines) : 
Alaska  :  Treadwell,  Douglas  Island,  811. 
California :  Exposed  Treasure,  Mojave, 

804,  823. 

Colorado :  Camp  Bird,  Ouray,  [787],  [818]. 
Geyser,  Silver  Cliff,  [766]. 
Gold  Coin,  Cripple  Creek,  [821] 
Pharmacist,  Cripple  Creek,  [819]. 
Summit,  Cripple  Creek,  [819]. 
Tomboy,  Silverton,  [787],  [818]. 
Montana:  Cable,  Philipsburg,  [762], [814]. 
Granite-Bimetallic,  Philipsburg, [762], 

[814]. 
Nevada :   Crowning  Glory,  Silver  Peak, 

[8.13]. 

Delamar,  [794],  [828]. 
Drinkwater,  Silver  Peak,  [813]. 
South  Carolina:    Haile,  [794],  [810]. 
Utah:  Annie  Laurie,  [827], 
Gold    Mountain,  Nev. :  geology  and  ore- 
deposits,  599. 

Gold-ores  :  in  contact-deposits,  380. 
Gold-production  :  future  status,  442.  445. 
increase:  causes,  442. 
North  America,  442-444. 

The  Geological  Features:  (LiNDGREN),. 

xxiii-xxiv,  424-444. 
Tertiary  deposits,  438. 
unit  of  measurement,  433. 
Victoria,  171. 

Gold-provinces  of  the  United  States,  806. 
Gold-quartz  veins:  connection  with  basic 

igneous  rocks.  284. 

genetic   connection   with    siliceous    ig- 
neous rocks,  279. 
Gold-silver  and  silver-gold  ores  :  vertical 

relations,  in  deposits,  799. 
Gold-silver  deposits : 
California :  Bodie,  823. 
Mojave,  823. 
Ophir  district,  813. 


INDEX. 


939 


Gold-silver    deposits    Montana :    Philips- 
burg,  [762],  [814]. 

Nevada:   Gold   Hill    group,    Comstock 
lode,  [804.] 

Gold-silver    mines   (see  also    Silver-gold 

mines): 
Nevada:    Gold    Hill    group,   Comstock 

lode,  [804]. 
Yellow  Jacket,  Comstock  lode,  [804]. 

Gonzalo,  Joaquin  :  copper  -  deposits  of 
Huelva,  xli. 

Gooch  and  Whitfield :  arsenic  in  hot- 
springs  waters,  [404]. 

Gossan  :  appearance,  112. 
definition,  112. 

Gossan-ores:  Appalachians,  73. 

Gottlob  vein,  Freiberg,  Saxony,  218. 

Gottschalk  and  Buehler:  effect  of  pyrite 
on  solubility  of  galena,  [766]. 

Grabill,  L.  E.:  charcoal  in  the  Bassick 
mine,  319. 

Grand  Central  mine,  Tintic  district,  Utah, 
335,  337. 

Grangesberg,  Sweden :  map,  662. 

Grangesberg  iron-deposits,  Sweden,  671. 

Granite :  New  Zealand  :  samples  for  anal- 
ysis, 163. 
solution  by  acids,  726. 

Granite-Bimetallic  gold-mine :  Philips- 
burg  quadrangle,  Mont.,  814. 

Granite-Bimetallic  lode :  Philipsburg 
quadrangle,  Mont. :  character  of  gold- 
enrichment,  762. 

Granite  mine,  Cripple  Creek,  Colo.,  419. 

Granite  Mountain,  Montana,  gold-depos- 
its :  depth  of  alteration,  122. 

Granitic  rocks :  origin,  608. 

Graphite :  occurrence.  315. 

Grarberg  mines,  Sweden :  origin  of  iron- 
ores,  670. 

Grass  Valley,  Cal.:  gold-deposits,  812. 

Graton,  L.  C.:  enrichment  of  gold-depos-  ! 

its,  Haile  mine,  S.  C.,  [810]. 
gold-deposits  of  central  and   southern 

North  Carolina,  [835]. 
minerals  in  Appalachian  gold-deposits, 
809. 

Gravity  :  influence  in  magmatic  differen- 
tiation, 72. 

Great  Gulch  ores :  genetic  relations,  612. 

Groddeck,  A.  von  :  nature  of  veins,  26. 
Kristiania  type  of  contact-deposits,  372. 
ores  in  sedimentary  rocks,  256. 
replacement  ores,  xxxix. 

Grossularite :  San  Jose,  Tamaulipas,  Mex- 
ico, 572. 

Ground-water :  in  mines,  248. 
in  lithosphere,  698. 

Guadalupe  mine,  Chihuahua,  Mex.:  vein-  I 
formation,  218. 

Gunnison  region,  Colo.:  bog-iron  deposits,  i 

32. 
walls  of  fissure-veins,  55. 

GUNTHER,  C.  G.,  and  KEMP,  J.  F.:     The  ; 
White     Knob     Copper- Deposits,  Mackay, 
Idaho  [Trans.,  xxxviii,  269-296],  Notice, 
833. 

Gyrnpie,  Queensland  :  rocks,  163. 

Gypsum-deposits :  alteration,  114. 
expansion  in  formation,  116. 
formation,  116. 


Habermehl:    composition  of  pvrrhotite, 

459. 
Hague  and   King :  genesis  of  Comstock 

lode,  x. 
Haile  gold-mine,  South   Carolina,  [794], 

[806],  [810]. 

Hall,  C.  W. :  origin  of  pegmatite,  275. 
Hallowell,  J.  K. :  ore-deposits  in  Gunnison 

region,  Colo.,  32. 
Halogens  :  agency  in  transferring  metals, 

728. 

Haloid  compounds  in  ore-deposits :  forma- 
tion in  arid  regions,  135. 
Harker,  Albert :  average  composition  of 
igneous  rocks,  [734]. 

contact-effects  in  Westmoreland,  575. 
HASTINGS,  J.  B. :  Are  the  Quarts-  Veins  of 
.  Silver  Peak,  Nevada,  the  Result  of  Mag- 
matic Segregation?,  xxvi,  621-628. 
HASTINGS,  J.  B.,  and  BEEKEY,  C.  P. :  The 

Geology  and  Petrography  of  the  Goldfield 

Mining- District,  Nevada  [Trans.,  xxxvii, 

140-159],  Notice,  832. 
Hausmann :  iron-ores  of  Taberg,  Smaland, 

681. 
Hawes :  contact-metamorphic  phenomena, 

525. 

Headden,  W.  P. :  deposition  of  basic  sul- 
phate, 710. 

Heat :  role  in  ore-deposition,  2. 
Heim,  A. :  classification  of  rock-fractures. 
41. 

limiting  depth  of  fissures,  44. 
Hematite  :   Grant  county,  N.  M. :  origin. 
127. 

transformation  to  and  from  magnetite, 

670,  671. 
i  Henrich,  F. :   decomposition  of  volcanic 

rocks,  727. 

|  Hill,  E.  T. :  Cretaceous  rocks  of  Tamau- 
lipas, Mexico,  561. 

origin  of  Mexican  iron-deposits,  127. 
Hillebrand,  W.  F.  :  analyses  :  sinters,  149. 
water  from  Geyser  mine,  151.  152. 

elements  in  igneous  rocks,  732. 
Hills,  E.  C. :    formation  of  ore-deposits, 
[233]. 

gold-deposits,  Summit  district,  Colo.,822. 
Hillside  mine,  Cripple  Creek,  Colo.,  420. 
Hinge-faults  :  definition,  103. 
Hoefer  :  ores  in  sedimentary  rocks,  256. 
Hoefer's  Method  of  Determining  Faults 

in  Mineral  Veins,  [101]. 
Hogbom  :   iron-ores  of  Norrbotten,  Swe- 
den, 678,  679. 

Hogborn  mines,  Sweden  :  plan,  668. 
Horn-silver :  in  Exposed  Treasure  mine, 
Mojave,  Cal.,  [804]. 

in  mines  on  Comstock  lode,  Nev.,  [804]. 

theories  of  formation,  800. 
Hornblende  :   in  rocks  of  New  Zealand, 
Victoria,  and  Queensland  :  analyses, 
167-168. 

separation  from  augite,  166. 

separation  from  rocks  for  examination, 
165. 

separation  from  syenite,  165. 
Hot  springs  :  decrease  in  flow,  704. 

explanation,  597. 
HOWE,  H.  M. :   Discussion  on  The  Torsional 

Theory  of  Joints,  101. 


940 


INDEX. 


Huanatajayite :  occurrence,  136. 
Humboldt  mine,  Eosita,  Colo. :    locus  of 

ore-bodies,  24. 

Humus  acid  :  reducing  power,  351,  357. 
Hunt,  T.  S. :   classification  of  crystalline 

rocks,  68. 

Huronian  rocks :  Lake  Superior  region,  69. 
Hussak,  E. :    auriferous    quartz-vein    in 

Brazil,  276. 

Hutton,  F.  W. :    geology  of  Otago,  New 
Zealand,  [162J. 

source  of  ore-materials  of  Thames  dis- 
trict, N.  Z.,  164. 
Hydration,  depth  of,  119. 
Hydrocarbons :  classification,  308. 

protective  action,  311. 

reducing  action,  305. 
Hydrogen  :  reducing  power,  307. 
Hydrothermal  metamorphism,  529. 

Idaho  :  gold-production,  437,  440. 
Iddings,  J.  P. :  consanguinity  of  rocks,  738. 
contact  metamorphic  effects,  384. 
formation  of  veins,  [394]. 
origin  of  igneous  rocks,  261. 
Igneous  activity  :  periods,  429. 
Igneous  contacts:  relation  to  ore-deposi- 
tion, 365. 

Igneous  rocks  (see  also  Eocks) : 
Igneous  Bocks  and  Circulating  Waters  as 
Factors  in  Ore- Deposition  (KEMP),  xxi- 
xxii,  235-250. 

Segregation  or  Differentiation  as  Related  to 
the  Occurrence  of  Ores  (SPURR),  xxii, 
251-303 ;  Discussion  (WiNCHELL),  303- 
304. 

Ilmenite  :  in  eruptive  rocks,  70. 
Immortal  mine,  Silver  Cliff,  Colo.,  [140]. 
Independence  mine,  Cripple  Creek,  Colo., 

419. 

India :  Tfavancore  :  quartz-reefs,  282. 
Indian  Queen  mine,  Birch  Creek,  Beaver- 
head  county,  Montana,  [374]. 
Influence  of  Country  Bock  on  Mineral  Veins 

(WEED),  xxi. 
Intrusions :  effects  on  circulating  waters, 

247. 

effect  on  water-channels,  34. 
Ontario  mine,  Utah,  60-62. 
source  of  ore-materials,  20. 
Iodine :  solvent  of  gold,  173. 
Iron :  concentration,  255. 
in  basic  rocks,  285. 
in  igneous  rocks,  266,  267. 
in  mine-waters,  770,  781. 
reducing  power,  358. 
Iron  and  manganese:  in  rocks:  chemical 

relations,  795. 
relative  amounts  in   vadose   and  deep 

waters,  153. 

Iron-deposits :  alteration,  114,  124. 
Appalachian   region :     mode  of   occur- 
rence, 117. 
origin,  71. 

surface-action,  125-126. 
bog :  Colorado,  32. 
conditions  favoring  formation,  73. 
contact  deposits   in  Christiania  region, 

692. 

contraction  in  formation,  117. 
Elba  Island,  8-9. 


Iron-deposits :     eruptive-origin    theory 

abandoned,  8. 
formed    by   magmatic    segregation    in 

basic  eruptions,  680. 
genesis,  9,  69-71,  124. 
keratophyre  type,  ,672. 
lake-  and  bog-ores,  694. 
Lake  Superior  region,  637. 

character,  647. 

mode  of  concentration,  641. 

origin   and  development,   29,   69-71, 

124,  642,  654. 

magnetic :  Pennsylvania,  73. 
Marquette  region,  Mich.:  origin,  71. 
Mesabi  range,  Minn.:  origin,  125. 
Missouri :  genesis,  87. 

Iron  Mountain  :  87,  126. 

Pilot  Knob,  87. 
of  metamorphosed  Canibro-Silurian 

schists,  689. 
Ovifak,  Greenland,  72. 
relations  to  eruptives,  72-73. 
Scandinavian:     The  Geological   Relations 

of  (SJOGREN),  xxvi,  657-695. 
Styria:  surface-action,  126. 
Sweden  :  central :  types  and  origin,  659. 

Norrbotten  :  structure,  676. 

genesis,  677. 

Sweden  and  Norway :  lake  region,  127. 
Texas :  origin,  127. 

eastern:  surface-alteration,  126. 
titauiferous :    map    of   distribution    in 

Scandinavia,  682. 
types :  derivation,  73. 

examples:  73. 

Iron  fault,  Leadville,  Colo.,  48. 
Iron  Mountain,  Mo. :  ores  :  occurrence,  87. 
Irving,  J.  D. :  classification  of  Algonkian 

rocks,  '69. 
genesis  of  Lake  Superior  iron-deposits, 

29. 

iron  ores:  origin,  70. 
minerals  of  gold-deposits,    Homestake 

belt,  Black  Hills,  S-  D.,810. 
Irving,  J.  D.,  and  Emmons,  S.  F. :  Down- 
town District,  xxxviii. 
Irving,  Emmons,  and  Jaggar  :  gold-depos- 
its, Black  Hills,  S.  D.  [810]. 
IRVING,  J.  D.,  SMITH,  H.  D.,  FERGUSOX, 
H.  G. :  Bibliography  of  the  Science  of  Ore- 
Deposits,  837-928. 
Isabella  mine,  Cripple  Creek,  Colo.,  422. 

Jackson,  D,  D.:  chlorine  in  waters,  767. 
Jacque  mountain,  Ten-mile  district,  Colo.: 

structural  features,  62. 
Jaggar,  Emmons,  and  Irving  :  gold-depos- 
its, Black  Hills,  S.  D.,  [810]. 
JENNEY,  W.  P.:  The  Chemistry  of  Ore-De- 
position, xxii,  305-363. 
formation  of  solid  oxidized  hydro-car- 
bons, 308. 

genesis  of  Missouri  lead-  and  zinc-depos- 
its, 78. 
lead-  and  zinc-deposits  of  the  Mississippi 

Valley,  306. 

Jerome,  Ariz;:  copper-deposits,  136. 
Jimenez  copper-mine,  Chihuahua,  Mexico, 

[374]. 

Joass    and    Cameron :    Sutherland    gold- 
fields  of  Scotland,  281. 


INDEX. 


941 


Joints  :  definition,  40.  101,  103. 

ore-bearing:  Silver  Cliff.  Colo.,  141. 

origin  and  extent,  35,  93. 

phenomena,  92. 

relation  to  ore-deposition,  35. 

Torsional  Theory  (BECKER),  92-104. 
Joplin  region,  Missouri  :  ore-deposits,  833. 
Josie  mine,  Eossland  district,  B.  C.,  509. 
Judd,  J.  W.:  chlorine  in  volcanic  emana- 
tions. 723. 

disintegration  of  volcanic  rocks,  727. 
Judson,    J.    N.:    magnetic  separation   of 

nickel-ores,  467. 
Juvenile  waters  :  origin,  xx. 

Kaolinization,  depth  of,  119. 

Kawich   district,   Nevada :    geology   and 

ore-deposits,  600. 
Keck,   Rudolph  :    association   of  organic 

matter  with  ore-deposits,  344. 
KEMP,  J.  F.:  Igneous  Rocks  and  Circulating 
Waters  aft   Factors  in    Ore-Deposition, 
xxi,  235-250. 

The    Copper-Deposits  at   Fan    Jose,    Ta- 
maulipas,  Mexico,  xxv-xxvi,  557-581. 
Ducktown,  Tenn.,  copper-deposits,  810. 
genesis  of  ore-deposits,  [253]. 
igneous  rocks  a  source  of  vein-materi- 
als, 222. 

metals  in  eruptive  rocks,  [707]. 
metals  in  igneous  rocks,  295. 
order  of  formation  of  minerals  in  crys- 
talline rocks,  263. 
origin  of  pegmatites,  276. 
origin  of  Sudhury  nickel-ores,  483. 
role  of  igneous  rocks,  384. 
R6le  of  the  Igneous  Rocks  in  the  Formation 

of  Veins,  xix.  696. 

secondary  enrichment  in  copper-depos- 
its, [761]. 

silica  in  the  Sierras,  280. 
Silver-Islet  mine,  231. 
vein-system  of  San  Juan  region,  Colo., 

290/ 

KEMP,  J.  F.,  and .  GUNTHER,  C.  G.:  The 
White  Knob  Copper- Deposits,  Mackay, 
Idaho  [Trans.,  xxxviii,  269-296],  Notice, 
833. 

Keweenawan  rocks,  Lake  Superior  re- 
gion, 69. 

KEYES,  C.  E.:  Borax- Deposits  of  the  United 
States  [Trans.,  xl,  674-710],"  Notice,  835. 
Genesis  of  the  Lake  Valley,  New  Mexico, 
Silver-Deposits    [Trans.,    xxxix,    139- 
169],  Notice,  835. 
chlorine  in  arid  regions.  768. 
Keystone  mine,  Silver  Cliff,  Colo.,  [140]. 
Kiirunavaara  iron-ore  deposits,  Sweden, 

672. 
Kimball,  J.  P.:  replacement  of  limestones 

by  iron-ores,  70. 
King,  Clarence:  genesis  of  Butte,  Mont., 

deposits,  404. 
horn-silver,  803. 

manganese  in  Comstock  lode,  802. 
meridional   zones  of   mineral -deposits, 

.[81]. 

views  as  to  genesis  of  ore-deposits,  x. 
King  and   Hague :    genesis  of  Comstock 

lode,  x. 
King,  William  :  joints.  93. 


Kinta  Valley,   Federated   Malay   States: 
tin-deposits,  832, 

Klein's  solution  :  ad  vantages,- 166. 

Klockmann :    contact-metamorphic    phe- 
nomena, 525,  527. 

Knaffl,   Ludwig :  amalgamation   of  gold, 
107. 

Knopf,   Adolph :    gold-deposits,    Berner's 
Bay  district,  Alaska,  811. 

Kceuig,  G.  A.,  and  Stockder,  M.:  occur- 
rence of  coal  with  silver,  321. 

Kohler,  E.:  adsorption  process,  536- 

Kohlrausch :    solubilities  of  silver-salts, 
800. 

Kolecki,  Theodore :  contour  sketch-maps, 
[xxxii]. 

Kootenay  volcanic  group,  495. 

Kristiania  type  of  contact    ore-deposits, 

372. 
permanence  in  depth,  393. 

Laccolith:  San  Jose,  Tamaulipas,  Mexico, 

563. 

Lacroix,  A.:  metals  in  fumaroles,  721. 
Lake  Superior  iron-ores  :  character,  647. 
Lake  Superior  region  :  Algonkian  rocks, 

69. 

development  of  rocks,  648. 
geological  map,  636. 
iron-deposits,  69. 
genesis,  29. 

mode  of  concentration,  641. 
origin  and  development,  642,  650, 

654. 

time  of  concentration,  649. 
topographic  relations,  650. 
pre-Cambrian  series,  634. 
Lake  Wakatipu,  New   Zealand :    vadose 

country-rock  :  analyses,  189. 
Lapparent,  A.  de :  solution-theory  of  ore- 
deposition,  2. 

Lassaigne  :  solubility  of  manganese,  [796]. 
Lateral  migration  :  manganese  salts,  794. 
Lateral-secretion  theory :  ore-genesis,  xiii, 
23-24,  82,  83,  160,  171,  201,  204,  210,  213. 
Lava  :  experiments  on,  725. 

gaseous  content,  767. 

Lava  streams  :  Vesuvius :  steam  from,  701. 
Law  of  areal  distribution  of  mining-dis- 
tricts, 325. 

Law  of  replacement,  9. 
Lead  :  distribution  in  igneous  rocks,  753. 
tests  for :  in  rocks  at  Leadville,  Colo., 

16-17. 
Lead-deposits :  alteration,  131. 

Australia :     Chillagoe    district,    North 

Queensland,  830. 
Cornmern,  Eifel  district,  36. 
genesis,  77-79.       f 
source  of  material,  77. 
Virginia-Tennessee  region,  831. 
Lead-  and  zinc-deposits  :  association  with 

eruptives,  78. 
Missouri  :  occurrence  in  Carboniferous 

rocks,  88. 

occurrence  in  Franklin  county,  89. 
Missouri  region  :  genesis,  78. 
Virginia- Tennessee  Region  (WATSON), 831- 

832. 

Lead  oxides  :  agency  in  solution  of  gold, 
780. 


942 


INDEX. 


Leaders :  definition,  51. 
Leadville,  Colo. :  investigations  of  coun- 
try-rocks, 23. 

ore-deposits  :  character,  27,  38. 
genesis,  xi,  5. 
investigation,  26. 
original  depth,  7. 
sulphide  origin,  3. 
silver-,  lead-,  and  gold-deposits,  815. 
silver-lead  deposits:  aqueous  origin,  2. 
LE  CONTE,   JOSEPH  :    Discussion   on    The 
Genesis  of  Certain  Auriferous  Lodes,  202. 
association  of  eruptive  activity  with  ore- 
deposition,  21. 

chlorine  as  solvent  of  gold,  763. 
genesis  of  metalliferous  veins,  14-15. 
mis-statement  of  Emmons's  views  on 

Leadville  ores,  4. 
Ledoux,  A.  R. :   coutact-metamorphism  in 

Boundary  district,  375. 
Lehner,   Victor:    lead    oxide:    effect  on 

solubility  of  gold,  [780]. 
LEITH,  C.  K. :  A  Summary  of  Lake  Superior 
Geology  with  Special  Reference  to  Recent 
Studies  of  the  Iron-Bearing  Series,  xxvi, 
633-656. 

Leptoclases :  definition,  40. 
Levack  township  deposits,  Sudbury  dis- 
trict, Ontario,  507. 
Levigation  theory  :  ore-deposits,  14. 
Lignite :  association  with  ore-deposits,  322. 

reducing  power,  351,  357. 
Limburgite :  Cripple  Creek  district,  Colo., 

412. 

Lime :  quantity  in  igneous  rocks,  732. 
Limestone  :  analyses,  334,  335,  337,  338. 
Chlorine-content,  766. 
oxidation,  535. 
relation  to  ore-deposits,  333. 
Sail  Jose,  Tamaulipas,  Mexico,  568. 
Limonite  :  eastern  Texas:  origin,  126. 
Limonites  :  origin,  124 
LINCOLN,  F.  C. :    The  Promontorio  Silver- 
Mine,  Durango,  Mexico  [Trans.,  xxxviii,  j 
734-746],  Notice,  834. 

LINDGREN,  WALDEMAR  :    The  Genesis  of  \ 
the  Copper- Deposits  of  Clifton-Morenci,  j 
Arizona,  xxv,  517-556. 
The  Geological  Features  of  the  Gold-Pro- 
duction of  North  America,  xxiii-xxiv, 
424-444 
The   Occurrence  of  Stibnite  at  Steamboat 

Springs,  Nevada,  xxvi,  629-632. 
andradite  at  Clifton-Morenci,  Arizona, 

[572]. 

Annie  Laurie  gold-mine,  Utah,  827. 
auriferous  quartz-vein  in  Brazil,  276. 
Character  and  Genesis  of  Certain  Contact- 
Deposits,  [xixj. 

contact-deposits,  236,  237,  [372]. 
contact-metamorphic  deposits,  528. 
contact  metamorphism,  371. 
copper-deposits,     Clifton-Morenci     dis- 
trict, Arizona,  [788]. 
formation  of  metalliferous  veins,  369. 
garnetization  at  Clifton-Morenci,  Ariz., 

579. 

genesis  of  ore-deposits,  [253]. 
gold-deposits  :  classification,  [763],  807. 
Nevada  City  and  Grass  Valley,  Cal., 
812. 


LINDGREN,  WALDEMAR: 

gold-deposits:  Ophir  district,  Cal.,  813. 
southern     Appalachians :     associated 
minerals,  [809]. 

hypothesis  of  igneous  emanations,  582. 

magmatic  differentiation,  722. 

rnagmatic  origin  of  ore-deposits,  619. 

metallogenetic  epochs,  806. 

metals  in  gneiss,  [707]. 

Metasomatic  Processes    in   Fissure- Veins, 
[xviii]. 

metasomatic  replacement,    [223],    225, 
232. 

metasomatism,  xl. 

osmosis  in  ore-formation,  [xxiv]. 

primary  pyrites,  204. 

relation  of  ore-deposition   to   physical 
conditions,  763. 

telluride  ores,  380. 

vein-forming  waters,  586. 
Lindgren,  W.,  and  Eansome,  F.  L. :  gold- 
deposits,  Cripple  Creek,  Colo.,  819. 
List  of  Scientific  Publications  of  Samuel  F. 

Emmons,  xlii-xlvii. 
Lithium:  distribution  in  igneous  rocks.746. 

quantity  in  igneous  rocks,  734. 
Lithoclases:  definition,  40. 
Liversidge,  A.:  gold  in  sea-water,  193. 

gold  in  solution,  177. 

origin  of  nuggets,  [182]. 
Lodes :  metalliferous :  suceessive  zones  in 

depth, 789. 

Lofstrad :  iron-ores  of  Norrbotten,  Swe- 
den, 678. 
Lone    Mountain    ores,   Nevada:    genetic 

relations,  614. 
Longfellow     limestone,     Clifton-Morenci 

district,  Arizona,  519,  523. 
Lossen  :  quotation  from  Groddeek,  26. 
Lotti,  B.:  studies  of  Elba  iron-ores,  9. 
Louis,  HENRY  :  The  Allotropism  of  Gold, 
xv.,  105-109. 

mode  of  occurrence  of  gold,  108. 

ore-deposits  in  Permian  of  Nova  Scotia, 

[327]. 
Lucky  Guss  mine,   Cripple  Creek,   Colo., 

422. 
Luossavara  iron-ore  deposits,  Sweden,  673. 

McCaskey,  H.  D.:  gold-deposits,  Alabama, 

[810]. 

McCaughey,  W.  J.:  experiments  on  solu- 
tion of  gold,  763,  771,  772,  776,  798. 
McDerniott,  W.:    association  of  graphite 

and  silver  in  Silver-Islet  mine,  317. 
McLaughlin,  E.  P.:  gold-deposits,  Bodie, 

Cal.,  [823]. 
McTighe,   T.   J.:  magnetic  separation  of 

nickel-ores,  467. 

Macetown  gold-district,  N.  Z.:  assays,  184. 
Magmas  :  action  during  cooling,  725. 

differentiation  phenomena,  687. 

kinds  ejected  in  eruptions,  715. 

relations  to  ore-bodies,  717. 

temperature,  724. 

water  in,  702. 
Magmatic    differentiation :     ore-deposits, 

67,  84,  205,  274. 
Magmatic  Origin  of  Vein-Forming  Waters  in 

Southeastern    Alaska   (SPENCER),    xxvi, 

582-589. 


INDEX. 


943 


Magmatic  segregation,  288. 

as  working  hypothesis,  292. 

effect  on  ore-deposits,  300. 
Magmatic  waters :  origin,  xx. 

role,  584. 

Magnesia:  quantity  in  igneous  rocks,  732. 
Magnesium  :  in  mine-waters,  768. 
Magnetic  iron-ore  deposits,  Pennsylvania, 

73. 
Magnetite:  in  eruptive  rocks, 70. 

in  rnagmas,  72. 

in  rocks  of  New  Zealand  and  Victoria:  j 
analyses,  167, 

reducing  power,  358. 

San  Jose,  Tamaulipas,  Mexico,  573. 

transformation  to  and  from  hematite, 

670,  671. 

Magnetite-deposits :  Colorado :  genesis,  74. 
Malaguti :  metals  in  ashes  of  marine  plants, 

[256]. 

Malaguti    and    Durocher:  silver  in  sea- 
water,  191. 

Mallet,  J.  W.:  silver  in  volcanic  ash,  721, 
Malm,   J.   L.:  chlorination   treatment  of 

ores,  722. 
Mammoth   mine,   Tintic  district,    Utah, 

335,  337. 

Manganese :  Agency  in  Superficial  Altera- 
tion and  Secondary  Enrichment  of  Gold- 
Deposits,  759-828. 

chemical  relations  with  iron  in  rocks,795. 

chemistry  of,  780. 

concentration,  255. 

distribution  in  igneous  rocks,  751. 

effect  on  solubility  of  gold,  778. 

experiments  on  solution,  795. 

in  igneous  rocks,  267. 

in  mine-waters,  770,  781. 

occurrence  in  gold-deposits,  779. 

quantity  in  igneous  rocks,  733. 

use  in  chlorination  process,  762. 
Manganese  and  iron,  relative  amounts  in 

vadose  and  deep  waters,  153. 
Manganese-deposits :   alteration,  127-128. 

Batesville,  Ark.,  128. 
Manganese-ore  :  bog  :  formation,  128. 

southern  Appalachians,  74. 
Manganese  oxides :  association  with  gold- 
deposits,  786. 

occurrence  in  mining-districts,  174. 

reactions  in  dissolving  gold,  778. 
Manganese-salts :   lateral  migration  from 

country-rock,  794. 

Manganite  :  association  with  gold,  793. 
Manhattan,  Nev.  :  gold-deposits,  826. 
Matiipori   formation,  South  Island,  New 

Zealand,  162. 
Map :    New    England    and    New    York : 

iiormal  chlorine,  769. 
Marble  :    San  Jose,  Tamaulipas,  Mexico, 

569. 

Marcasite  :  reducing  power,  352,  357,  358. 
Marquette  region,  Michigan:  iron-depos- 
its :  origin,  71. 

vertical  section,  639. 

Marsh-gas :  association  with  ore-deposits, 
345. 

reducing  power,  350,  357. 
Martinique:  volcanic  gas:  analysis,  388. 
May  Belle  Tunnel   mine,  Cripple  Creek, 

Colo.,  419. 


Melville,  W.  H. :  analysis  of  sinter,  629. 
Mendenhall,  W.  C. :  gold  in  aplite  dikes, 

Alaska,  280, 
Mercury  (see  also  Quicksilver)  : 

relations  to  igneous  rocks,  753. 
MERRITT,  W.  H. :  Discussion  on  Geological 

Distribution  of  Useful  Metals  in  the  United 
States,  90-91. 

origin  of  Sudbury  nickel-ores,  483. 
Mesabi  ore-deposit :  vertical  section,  640. 
Mesozoic  gold-belt,  435-438. 
Metalliferous  lodes  :    successive  zones  in 

depth,  789. 
Metalliferous  province  :  definition,  293. 

relation  to  petrographic  province,  293, 

297. 

Metallographic  province  of  California,  619. 
Metallographic  province  of  Nevada,  619. 
Metals :      distribution     in     sedimentary 
rocks,  254. 

in  detrital  rocks,  257. 
Metamorphism    (see  also  Contact-meta- 
morphism)  : 

effects,  68. 

hydrothermal,  529. 

Sudbury  district,  Ontario,  514. 
Metasomatic  interchange  :  definition,  3. 
Metasomatic  processes,  232. 

in  Fissure- Veins  (LiNDGREN),  xviii. 
Metasomatic   replacement :    explanation, 
453. 

Tintic  district,  Utah,  342. 
Metasomatism :  definition,  xl. 

in  Leadville  ore-deposits,  2. 

in  Scandinavian  iron-ores,  xxvii. 
Metastibnite :  Steamboat  Springs,  Nevada, 

632. 

Meteoric  hypothesis  :  inadequacy  for  ore- 
deposition  on  Pacific  coast,  589, 
Meteoric  waters  :  circulation,  240. 

role  in  formation  of  ore-deposits,  xix. 
Mexico :   gold  production,  435,  436,  438, 
439. 

Cananea  copper-deposits,  376.  396. 

Chihuahua:  Guadalupe  mine,  218. 

San  Jose  :  ore-deposits,  237. 
Mica :  in  rocks  of  New  Zealand  and  Vic- 
toria:  analyses,  167-168. 

separation  from  rocks  for  examination, 

164. 
Michel-Levy,    A.  :     contact-metamorphic 

phenomena,  525. 
Microcline  :  crystallization  from  magmas, 

609. 

Midget  mine,  Cripple  Creek,  Colo.,  420. 
Mike  fault,  Leadville,  Colo.,  48. 
MILLER,  W.  G. :  Discussion  on  The  Geolog- 
ical  Features  of  the   Gold- Production  of 

North  America,  445-446. 
Millerite  :  Sudbury,  Ontario,  456. 
Mineral-bearing    currents :    direction   of 

flow,  37. 

Mineral  ridge,  Tonopah,  Nev. :    mineral 
veins.  607. 

rocks,  604. 

silver-ores  :  genetic  relations,  613. 
Mineral  vein  :  genesis,  430. 
Mineral  veins :   Influence  of  Country-Rock 
on  (WEED),  216-234. 

near  igneous  contacts,  394. 
Mineral  zone,  western  America,  298. 


944 


INDEX. 


Mineralization  :  due  to  rich  solutions,  700. 

of  veins :  rapidity,  700. 

source  of  ores,  710. 
Mineralized    veins :    product  of  expiring 

vulcanisrn,  698. 

Mineralizing  agents:  distribution   in  ig- 
neous rocks,  755. 

Mineralizing  process  :  Tonopah,  Nev.,  594. 
Mineralizing  solutions:  source:  Tonopah, 

Nev.,  596. 

Minerals:   isolated    from    rocks    of    New 
Zealand  :  analyses,  167. 

isolation  for  examination,  164. 

of  secondary  origin,  791. 

reducing  power,  347,  357. 

segregation  in  magmas,  264. 

separation  from  rocks  by  solutions,  165. 
Mines  (see  also  Gold-mines  :  Silver-mines, 
etc.)  : 

of  Rosita    and    Silver     Cliff,      Colorado 
(EMMONS),  139-161. 

scarcity  of  commercially  valuable,  696. 
Mine-timbers  :  examination  for  gold,  180. 
Mine-waters  :  acidity:  cause,  174. 

average  of  analyses,  765. 

composition,  764. 

examination :    apparatus    and    results, 
180-181. 

vadose  :  acidity,  175. 

examination  for  free  acid  and  ferric 

salts,  176, 
Mining-districts :  areal  distribution,  325. 

review,  805. 

Mint  mine,  Cripple  Creek,  Colo  ,  420. 
Mirabel  mine,  Lake  county,  Cal.:  quick- 
silver, 79, 

Mississippi  valley  zinc-and  lead-ores,  335. 
Missouri :  lead-and  zinc-deposits,  327. 

Sedalia:  coal   associated    with    blende, 
320. 

Versailles:  coal  associated  with  blende, 

320. 
Mitchener   mine,    Drury  township,  Sud- 

bury  district,  Ontario,  505. 
Mizpah  silver-gold  mine,  Tonopah,  Nev., 

[825].  ^ 
Modoc  limestone,  Clifton-Morenci  district, 

Arizona,  519,  523. 
Modoc  porphyry,  224. 

Moissan,  H.:  analysis  of  volcanic  gas,  388. 
Mojave  desert :  borax-deposits,  [835]. 
Mojave  Mining-District,   California  (BATE- 
SON),  832. 

Molybdenite :  San  Jose,  Tamaulipas,  Mex- 
ico, 573. 

Molybdenum  :     distribution    in    igneous 
rocks,  750. 

in  siliceous  rocks,  285. 
Molybdenum-deposits:  alteration,  135. 
Mongolia :  Ku  Shau  Tzu :  ore-deposition, 

359. 
Montana  :  Bannack  gold-deposits,  381. 

Butte :     copper-veins,     224,     225,     403. 
silver- veins,  223. 
vein-formation,  220. 

Elkhorn   district  :    ore-deposits,    [239], 
382. 

gold-production,  437. 

gold-quartz  veins,  280. 

Jefferson   county  :  Lump   Gulch  silver- 
gold-veins  :  genesis,  408. 


Montana:   Madison  county :   ore-deposits 
produced    by    successive    concentra- 
tions, 303-304. 
mrneral  veins,  228-229. 
Neihart:  mineral  veins,  227,  228. 

silver-lead  mines,  219. 
Monument  mine,  Cripple  Creek,  Colo.,  419. 
Moon-Anchor  mine,  Cripple  Creek,  Colo., 

420. 

i  Moonlight  mine,  Cripple  Creek,  Colo.,  420. 
Morenci  shale,    Clifton-Morenci  district, 

Arizona,  519,  523. 

Morencite,  Clifton-Morenci  district,  Ari- 
zona. 519. 

Mosquito  fault,  Leadville,  Colo.,  48. 
Mosquito  range,  Leadville,  Colo.:  faulting, 

48. 

uplift.  16. 
Mother  Lode  district,  Cal.:   gold-deposits, 

811. 

;  Mounds  :  deposits  from  springs,  32. 
Mount  Guyot,  near  Breckenridge,  Colo.: 

horizontal  faulting,  64. 
Mount   Hood  :  ascent  by  Arnold  Hague, 

fxxxil. 
Mount   Nickel   mine,  Blezard  township, 

Sudbury  district,  Ontario,  497. 
photomicrographs  of  ore,  487-488. 
Mount     Eainier :    ascent     by     Emmons, 

[xxxi]. 

Mount  Shasta:  ascent  by  King  and  Em- 
mons, [xxxi]. 

Mountain-building:  periodicity,  43. 
Mountain  View  mine,  Silver  Cliff,  Colo., 

[140]. 

'Movements:     repeated:     along    fissure- 
planes,  59. 
Mullan,  John  :  Report  on  the  Construction 

of  a  Militarv  Road,  1863,  [xxxii]. 
Miinster  :  gold  in  sea- water,  [193]. 
Murchison,  R.  I. :  age  of  auriferous  rocks, 

258. 

horizon  of  irold,  [ix]. 
1  Murray,  A.  R.    F. :    auriferous   rocks   of 

Victoria,  163. 
Murray  mine,  McKim  township,  Sudbury 

district,  Ontario,  500. 

Muscovite :  crystallization  from  magmas, 
609. 

Nason,   F.  L. :    genesis  of  iron-deposits, 

Missouri,  87. 

|  National  mine,  Cripple  Creek,  Colo.,  420. 
|  Natural  gas  :  confinement,  313. 
I  Natural  water-channels  :  causes,  33. 
Neihart,  Mont.  :  silver-lead  mines,  219. 

veins,  227,  228. 

I  Nelson  granite,  Rossland,  B.  C.,  495. 
Nenthorn  gold-field,  Otago,  N.  Z. :  assays, 

184. 
Nepheline-basalt :  Cripple  Creek  district, 

Colo.,  411. 
Nephelite-syenite:  analysis,  562. 

Tamaulipas,  Mexico,  562. 
Nevada  :  Belmont :  dike-rocks,  277. 
gold-production,  440. 
metallographic  province,  619. 
silver-mining  industry,  299. 
Tonopah  :  geology,  591. 

mineral  veins,  593. 
Nevada  City,  Cal. :  gold-deposits,  812. 


INDEX. 


945 


New  Brunswick  :  pyrrhotite,  462. 

New   Mexico :    San   Pedro :    ore-deposits, 

[238]. 

New  Zealand  :  South  Island  :  geology.  162. 
Newberry,  Cosmo  :  source  of  gold,  178. 
Newberry,  J.  S. :  age  of  lignitic  sandstone 
at  Silver  Reef,  Utah,  [322]. 

criticism  of  Emmons's  views  answered, 
4,  19. 

genesisof  Appalachian  iron-deposits,  [36] 

selenium   in   Silver   Reef,  Utah,  sand- 
stones, 325. 

theory  of  formation  of  solution-cham- 
bers, 6. 

Newberry's  theory  of  ore-genesis:   criti- 
cism, 6,  21,  24. 
Nickel :  associates  in  rocks,  75. 

distribution  in  igneous  rocks,  751. 

in  basic  rocks,  285,  295. 

in  igneous  rocks,  268. 

in  Sudbury  pyrrhotites,  466. 

occurrence,  316. 

quantity  in  igneous  rocks,  733. 

relation  to  pyrrhotite,  455,  461. 

Virginia,  834. 

Nickel-deposits :    characteristic   features. 
511. 

genesis,  75. 

Sudbury,  Ont.,  90-91. 
Nickel-ores  :  classification,  477. 

concentration -experiments,  470. 
Nickel  Plate  mine,  British  Columbia,  383. 
Nickeliferous  pyrrhotite  :  magnetic  sepa- 
ration, 466. 

theories  of  origin,  481. 
Niter-deposits :  formation,  115. 
Nitrates :  in  mine- waters,  768. 

reactions  in  dissolving  gold,  776. 
Norite  :  Sudbury,  Ontario,  480. 
Norrbotten,  Sweden,  iron-ores,  672. 
Norway :     island    of    Bommel  :     igneous 
rocks,  281. 

titaniferous  iron-ore  :  concentration  in 

magmas,  72. 
Nova  Scotia  :  pyrrhotite,  462. 

Observations  on  Mother-  Lode  Gold- Deposits, 
California  (PRICHARD),  H30. 

Occurrence  of  Nickel  in  Virginia  (WATSON), 
834. 

Occurrence  of  Stibnite  at  Steamboat  Springs, 
Nevada  (LlNDGRBN),  xxvi,  629-632. 

Ocher-deposits  :  Cartersville  district,  Bar- 
tow  county,  Ga.,  830. 

Oddie  rhyolite,  Tonopah,  Nov.,  593. 

Ohinemuri  district,  N.  Z. ;  vadose  country- 
rock  :  analyses,  190. 

Ontario  :  gold-deposits,  445. 
pyrrhotite,  462. 

Ontario  mine,  Utah  :  structural  features 
of  deposit,  60-62. 

Ophir  district,  Cal.  :  gold-deposits,  813. 

Ore-bearing  solutions  :  source,  11. 

Ore-bodies :     association   with    eruptive 

rocks,  697. 

limited  to  certain  magmas,  716. 
mode  of  formation,  720. 
mode  of  occurrence,  Lead  ville,  Colo.,  13. 
Queen  of  the  West  mine,  Colo.,  63. 
relations  to  vein-walls:  Gunnison  region, 
Colo.,  56. 


Ore-currents  :  descent  from  above,  2. 
Ore-deposition  :  aqueous  solution,  29. 
ascending  theory,  12,  14,  15. 
association  with  eruptive  activity,  21. 
by  Ascending  Hot  Waters  (WEED),  xxiii, 

403-410. 

by  thermal  springs,  406. 
causes,  37,  342. 
character  of  receptacles,  30. 
Chemistry,  305-363. 
conditions,  24-25,  35,  37. 
determining  factors,  24. 
differential,  362. 
Igneous  Rocks  and  Circulating  Waters  as 

Factors  (KEMP),  xxi,  235-250. 
Ku  Shau  Tzu,  Mongolia,  359. 
lateral  secretion  theory,  23-24. 
process,  342. 

processes  :  western  Nevada,  616. 
Principles  Controlling  (  VAN  HISE),  xvii. 
selective  hypothesis,  614. 
variation  in  parts  of  an  ore-body,  361. 
Ore-deposits  (see  also  names  of  metals) : 
Alaska,  Tread  well,  830. 
along  bedding-planes,  35. 
along  contact-planes,  37. 
along  planes  of  rock-fracture,  39. 
alteration  in  situ,  123. 
ascending  theory,  201. 
bibliography,  837-928. 
classification,  286. 
climatic  effects  on,  120-121. 
concentration,  83. 
Cripple  Creek  District,  Colorado  :  Basaltic 

Zones  as  Guides  (STEVENS),  xxiii,  411- 

423. 

definition,  111. 
depth    of    alteration   in   uuglaciated 

regions,  122. 
Eastern     Gold-Belt    of    North     Carolina 

(CROSBY),  834-835. 
Enrichment    of    Gold    and    Silver    Veins 

(WEED),  xviii. 
formation :    influence  of   cai'bonaceous 

matter,  231. 

from  meteoric  waters,  369. 
fumarolic  origin,  240. 
Genesis  (EMMONS),  xi,  1-25,  300. 
genetic  classification.  366. 
haloid  compounds :   formation  in  arid 

regions,  135. 
in  limestone  :  depth,  7. 

form,  5. 

Joplin  Region,  Missouri  (CLERC),  833-834. 
Kristiania  type  :  permanence  in  depth, 

393. 

lateral -secretion  theory,  82,  83.  201. 
Leadville,  Colo. :  investigation,  26. 
levigation  theory,  14. 
magmatic  differentiation,  83. 
materials :    source   and    concentration, 

159. 
Montana :  Butte,  55. 

produced    by    successive    concentra- 
tions, 303-304. 
Near    Igneous    Contacts   (WEED),    xxiii, 

364-402. 
occurrence,  53. 

of  contact-metamorphie  origin,  369. 
of  fumarolic  origin,  368. 
of  gas-aqueous  origin,  368. 


946 


INDEX. 


Ore-deposits:  of  igneous  origin,  366. 

of  igneous-emanation  origin,  368,  370. 

open-cavity  theory,  4. 

origin  in  depth,  84. 

pneuraatolytic  origin,  240. 

primary  or  original,  28. 

receptacles:  assumptions  regarding,  3. 

Ked  Mountain,  Colo.,  21-32. 

relation  to  igneous  rocks,  253. 

relations    to    petrographic     provinces : 
practical  considerations,  755. 

replacement  theory  :  application,  8. 

rich  :  factors  determining  location,  790. 

secondary     concentration  :       Sudbury, 
Ont.,  90. 

secondary    enrichment,    761,    791,   810 
et  seq. 

selective  concentration,  79. 

Silver  Cliff,  Colo.:  genesis,  155. 

solfataric  origin,  85. 

source  and  concentration  (summary),  82. 

source  of  materials,  15,  111. 

status  of  investigations,  81. 

Structural  Relations  (EMMOXS),  xii,  26-64. 

Sudbury,   Ontario  (DiCKSON),  xxiv-xxv, 
455-516. 

Superficial  Alteration  (PENROSE), 110-138. 

sulphide  secondary  enrichment,  xvii. 

Utah,  Bingham,  831. 
Ore-Formation  :  Osmosis  a  Factor  in  (GiL- 

LETTE),  xxiv,  450-454. 
Ore-genesis:  ascension  theory,  xiii. 

lateral  secretion  theory,  xiii. 
Ore-materials:  migration,  123. 
Ore-minerals:  source  in  eruptive  rocks,  2. 
Ore-regions :  association  with  ores  of  ig- 
neous activity,  253. 
Ore-segregation:  definition,  252. 
Ore-zone:  Cripple  Creek,  Colo.:  structure, 

413,  414. 
Ores  (see  also  names  of  metals) : 

deposition  contemporaneous  with  sedi- 
ments, 256. 

derivation  from  magmas,  237. 
Oregon  :  gold-production,  436. 
Origin  of  Vein-filled  Openings  in  Southeast- 
ern Alaska  (SPENCER),  83. 
Orphan  Belle  mine, Cripple  Creek, Colo.,422 
Osmosis  as  a  Factor  in  Or e- Formation  ^(  GIL- 
LETTE), xxiv,  450-454. 
Osmotic  pressure  :  law,  451. 
Osmotic  separation   of  metal-bearing  so- 
lutions, 207. 
Otago,  New  Zealand  :  vadose  country-rock: 

analyses,  188. 
Otaso  harbor  :    sediments  :     examination 

for  gold,  196. 

Oversight  mine,  Cananea,  Mexico,  398. 
Ovifak,  Greenland  :  iron -ore  deposit,  72. 
Owyhee   mines,   Idaho :  gold-production, 

440. 

Oxidation  :  limiting  depth,  118. 
Oxidized  ores,  581. 

Pachuca     district,     Mexico:    comparison 

with  Tonopah,  Nev.,  601. 
Pacos  (gossan) :  definition,  112. 
Paraclase  :  rocks,  92. 
Paraclases :  definition,  40. 
Paragenesis    of    minerals :    Clifton-Mor- 

euci  district,  Arizona,  536. 


Paris  mine,  Silver  Peak  district,  Nevada, 

627. 
Park,  James:  gold  in  sea- water,  [192]. 

source  of  ore-materials  of  Thames  dis- 
trict, N.  Z.,  164. 

Pearce,  Richard :  analyses  of  gold-ores. 
[820]. 

experiments  in  solution  of  gold,  [763]. 
[773). 

veins  of  Cornwall,  10. 
Pearceite  ores,  Neihart,  Montana,  genesis, 

404. 

Pegmatite  veins.  239. 
Pegmatites:  definition,  275. 
Penfield,  S.   L.:  pentlandite   in    Sudbury 

ores,  470. 

Penokee-Gogebic  ore-deposit:  vertical  sec- 
tion, 639. 

PENROSE,  R.  A.  F.,  JR.:  The  Superficial  Al- 
teration of  Ore- Deposits,  xv.  110-138, 
[761]. 

chemical  relations  of  iron    and    man- 
ganese in  rocks,  [795]. 

distribution  of  chloride  ores,  [768]. 

fissures  at  Cripple  Creek,  Colo.,  221. 

formation   of  silver   chlorides   in    arid 
countries,  801. 

manganese  in   gold-deposits  of  Cripple 

Creek,  Colo.,  819. 
Pentlandite:  formula,  474-475. 

Lillehammer,  Norway,  474. 

Sudbury,  Ontario,  456,  474. 
Permeability   of  rocks   under    heat    and 

pressure,  29. 
Persberg,    Sweden :    iron-deposits :    map, 

667. 
Petrographic  provinces,  737. 

distribution,  295-299. 

in  the  United  States,  740. 

of  foreign  countries,  741. 

persistence,  291. 
Petrographic  pi'ovinces  and  ore-deposits: 

practical  considerations,  755. 
Petroleum:  associated  with   ore-deposits, 
344. 

oxvgenation,  308. 

reducing  power,  350,  357. 
;  Pharmacist    gold-mine,     Cripple    Creek, 

Colo.,  422,  [819]. 

Philips:    deposition   of  copper    from  sea- 
water,  258. 

Philipsburg,  Mont.:  gold-deposits,  814. 
Phillips,   J.  A.:  banded  structure  in    ore- 
deposits,  57. 

ore-deposits  in  vadose  region,  171. 

Treatise  on  Ore-Deposits,  [5,  12]. 
Phillips  and  Lewis:  ore-deposits,  [282]. 

pegmatite-dikes     at     Timbarra,    New 

South  Wales,  276. 

Phosphate-deposits:  formation,  114-115. 
Phosphates:  in  mine-waters,  770. 
Phosphorus  :  distribution  in  igneous  rocks, 
749. 

in  Lake  Superior  iron-ores,  652. 

quantity  in  igneous  rocks,  733. 
Piesoclases :  definition,  40. 
Pilot  fault,  Leadville,  Colo.,  48. 
Pilot  Knob.  Mo.,  iron-ores  :  occurrence,  87. 
Pirsson,  L.  V.:  radial  dikes.  394. 
Placer-deposits   (see   also    Gold-deposits), 

133,  134. 


INDEX. 


947 


Placers :  distribution  in  western  America, 
435. 

relation   to  manganiferous  gold-depos- 
its, 805. 

Plant- remains,  Jasper  county,  Mo.,  329. 
Plasticity  of  rock -masses,  44. 
Platinum:  association  with  gold  in  Urals, 
289. 

distribution  in  igneous  rocks,  753. 

in  basic  rocks,  285. 

in  igneous  rocks,  269. 
Plication  of  rock  masses,  44. 
Pneumatolysis  :  definition,  205. 
Pneumatolytic  origin  of  ore-deposits,  240. 
Pneumatolytic  vapors :  action,  388. 
Pocatello  mine,  Mineral  ridge,  Nev.,  613. 
Pointer  mine,  Cripple  Creek,  Colo.,  420. 
Pontgibaud,    France:    silver-lead    veins, 

226. 
Porphyry  :  in  Norbotten  ore-fields,  675. 

percolation  by  water,  13. 

white :  Leadville,  Colo.:  condition  and 

composition,  18. 

Leadville,  Colo.:  source  of  ore-materi- 
als, 18. 

Porphyry  Dike  mine,  Rimini,  Mont.,  221. 
Portland  mine,  Cripple  Creek,  Colo.,  419. 
Posepny,    Franz :  Genesis    of  Ore-Depos- 
its, v,  vii,  xiii,  86,  171,  696. 

gold  in  stratified  formations,  200. 

metals  in  water  of  springs,  [70d]. 

origin  of  Sudbury  nickel-ores,  485. 
Potash  :  quantity  in  igneous  rocks,  732. 
Pre-Cambrian  gold-deposits,  434. 

production,  435. 

Pre-Cambriau  series  of  the  Lake    Supe- 
rior region,  634. 
Precious  metals :    greater  abundance  in 

vadose  region  :  cause,  206. 
Precipitation  :  circumstances  favoring,  30. 

of  mineral  solutions:  causes,  37. 

ore-materials  :  conditions  favoring,  35. 
Pressure  :  in  relation  to  jointing,  94, 

r61e  in  ore-deposition,  2. 
PRICHARD,  W.  A.:  Observations  on  Mother- 
Lode    Gold-Deposits,    California  [Trans., 

xxx iv,  454-466],  Notice,  830. 
Prime,  F.:  on  Appalachian  iron-ores,  36. 
Principles  Controlling  Ore- Deposition  (VAN 

HISE),  xvii. 
Promontorio  Silver-Mine,   Durango,  Mexico 

(LINCOLN),  834. 
Prophylitic  veins  :  definition,  438. 

gold-production,  441. 
Puerticitos  mine,  Cananea,  Mexico,  378, 

398. 

Pumpelly,   R.:   copper  of  Lake  Superior 
region,  xxxviii. 

genesis  of  copper-deposits  in  Lake  Su- 
perior region,  76. 

Purington,   C.    W. :    ore-deposits    of   San 
Juan  region,  Colo.,  818. 

source  of  useful  metals,  716. 
Pyrite  :  as   primary  constituent  of  rocks, 
203,  212. 

behavior  with  carbonate  solutions,  409. 

chemical     reactions    with     chalcocite, 
[799]. 

crystallization  from  magmas,  609. 

effect  on  solubility  of  galena  [766]. 

in  eruptive  rocks,  70. 


Pyrite:  precipitating-agency,  232. 

reducing  action,  405. 

reducing  power,  352,  357,  358. 
Pyrolusite:  association  with  gold,  793. 
Pyroxenes :  in   rocks   of    New   Zealand : 

analyses,  167. 
Pyrrhotite:  analyses,  460. 

composition  and  formula,  458,  475. 

Deadwood,  S.  D.,  316. 

in  diorite,  90. 

origin,  460. 

relation  to  chalcopyrite,  513. 

reducing  power,  355,  358. 
Pyrrhotite-deposits  :  Rossland,  B.  C.,  486. 
Pyrrhotites  :  associated  minerals,  478. 

classification,  477. 

geological  relations,  477. 

Quartz:  crystallization  from  magmas,  609. 

Quartz-porphyry  :  Cripple  Creek  district, 
Colo.,  412. 

Quartz-veins  :  origin,  275. 

origin  as  magmatic  segregations,  275. 

Quarts- Veins  of  Silver-Peak,  Nevada  (HAST- 
INGS), xxvi.  621-628. 

Quebec :  pyrrhotite,  462. 

Queensland  :  gold-quartz  veins,  282. 

Queen   of  the  West  mine,  Ten-mile  dis- 
trict, Colo.:  structural  conditions,  62. 

Quicksilver,  associated  with    petroleum, 
344. 

Quicksilver-deposits :  alteration,  134. 
genesis,  79. 
Mirabel  mine,  Lake  county,  Cal.,  79. 

Racine    Boy    claim:   Silver    Cliff,    Colo., 

[140], 

Radioactive  water:  analyses,  709. 
Rainfall    run-off,  and  evaporation  :   rela- 
tion in  Colorado,  698. 

Rainy   River   district,   Ontario:   gold-de- 
posits, 445. 

RANSOME,  F.  L.:     The  Geology  and  Copper- 
Deposits    of   Bisbee,  Arizona    [Trans., 
xxxiv,  618-642].  Notice,  829. 
association    of   gold   with    manganese, 

[781]. 

gold-deposits,  Goldfield,  Nev.,  825. 
gold-deposits,  Mother  Lode  district,  Cal., 

811. 

gold-deposits,  San  Juan  region,  Colo., 818. 
manganese  as  indication  of  rich  ore,  787. 
Ransome,  F.  L.,  and  Lindgren,  W.:  gold- 
deposits,  Cripple  Creek,  Colo.,  819. 
Raven  mine,  Cripple  Creek,  Colo.,  420. 
RAYMOND,  R.  W.:  Preface,  v. 

Discussion  on   The   Torsional   Theory   of 

Joints,  101-103. 

charcoal  between  lava  flows,  319. 
Geological  Distribution  of  Mining  Dis- 
tricts in  the  United  States,  [65]. 
gold-deposits,    Summit   district,    Colo., 

[823]. 

King's    meridional    zones    of  mineral- 
deposits,  [81], 

origin  of  ore-deposits,  [242]. 
Reports  on  Mines  and  Mining  West  of 

the  Rocky  Mountains,  [764]. 
READ,  T.  T.:  'The  Secondary  Enrichment  of 
Copper-Iron  Sulphides    [Trans.,    xxx  vii, 
297-303],  Notice,  832. 


948 


INDEX. 


Real  del  Monte  district,  Mexico :  compari- 
son with  Tonopah,  Nev.,  601. 
Receptacles    for    ore-deposition :    charac- 
ter, 30. 
Recrystallization   process:  San  Jose,  Ta- 

maulipas,  Mexico,  575. 
Red  Cliff  region,  Colo.:  ore-deposits,  36. 
Red  Mountain,  Ouray  county,    Colo.:  oc- 
currence of  ore,  831. 

ore-deposits,  31-32. 
Red   Spruce  mine,   Cripple   Creek,    Colo., 

429. 
Reducing  action  of  volatile  hydrocarbons, 

346. 

Reducing  power  of  minerals,  347,  357. 
Reid,  J.   A.:  analyses    of  vadose    waters : 
Com  stock  lode,  802. 

silver-content  of  mine-waters,  800. 
Repeated  movements  along  fissure-planes, 

59. 
Replacement-deposits :  Rocky  mountains, 

10. 

Replacement     iron-deposits :     Appalach- 
ians, 36. 

Replacement-theory  :  ore-deposits,  8,  9. 
Rhodochrosite  :  reducing  power,  358. 
Rhyolite:    near  Silver   Cliff,   Colo.,    139, 

143,  157. 

Rhyolite-dacite:  Tonopah,  Nev.,  592. 
Richthofen,  F.  von  :  genesis  of  Comstock 
lode,  ix,  85. 

mineralization    of  the   Comstock   lode, 
598. 

Natural     Classification      of     Eruptive 
Rocks,  [ix]. 

production  of  Comstock  lode,  803. 

proportion  of  gold   to   silver   in   Com- 
stock lode,  802. 

Rickard,  T.   A.:  bonanzas   in    gold-veins, 
[797]. 

formation  of  bonanzas,  761. 

mineral  veins   varying  with    country- 
rock,  226 

ore-deposits  of  Rico,  Colo.,  [3301. 

origin    of  ores   of    Bendigo  reefs,   Aus- 
tralia, [208]. 

reduction  of  ore-bodies  by  black  shale, 
331,  332. 

solution  of  gold,  773. 

vein-structure,  221. 

vertical  distribution  of  ores,  [407]. 
Rico,  Colo.,  veins,  226. 
RITTER,  E.  A.:  The   Evergreen    Copper-De- 
posits,Color  ado  [Trans.,  xxxviii,  751-765], 

Notice,  835. 
Robertson  :  analyses  of  rocks  of  Missouri, 

[209]. 
Rock-flowage:  locus  and  conditions,  711. 

relation  to  earthquakes,  712. 
Rock-fracture  :  causes,  41. 

effect  on  water-channels,  34. 
Rock -fractures  :  character  and  extent,  39. 

classification,  40. 

complexity,  92. 

Rock-intrusions  (see  Intrusions). 
Rock -masses  :  plication  and  fracture,  44. 

rigidity  and  plasticity,  43. 
Rocks:    changes  due    to    contact    meta- 
morphism,  384. 

crystalline:  classification,  68. 
determination  of  age,  68. 


Rocks  :  eruptive  :  analyses,  705. 
emissions,  236. 
geological  age,  66. 

Leadville,  Colo.:  mode  of  eruption,  18. 
source  of  ore-materials,  15. 
tests  for  ore-materials,  16. 
source  of  vein-materials,  20-22. 
Tamaulipas,  Mexico,  561. 
gaseous  content,  767. 
igneous:  average  composition,  734. 
central  Sweden,  657. 

origin,  659. 
chlorine-content,  767. 
crystallization  :  order  in,  261. 
derivation  from  refusion  of  stratified 

rocks,  21. 

determination  of  age,  67. 
general  chemical  composition,  730,  734. 
geological  age,  66. 
origin,  67,  259. 
Role  in  the  Formation  of  Veins  (KEMP), 

xix. 

segregation  or  differentiation,  259. 
superficial :   lack  of  ore-materials,  20. 
influence  on  vein-structure,  217. 
New  Zealand  :  examination,  167-168. 
permeability  to  water,  29. 
Queensland  :  examination,  168. 
salts  in  waters  of  non-calcareous,  764. 
secular  decay,  112. 
sedimentary,  at  Leadville,   Colo.:  tests 

for  ore-materials,  16-17. 
distribution  of  metals,  254. 
stratified :    derivation     from     igneous 

rocks,  21. 

Victoria ;  examination,  168. 
Rock -segregation  :  unknown  finer  laws,265 
Rohn,   Oscar :  Bullfrog  and   Kawich  dis- 
tricts, Neyada,  600. 
Rolker,  Charles  M.:  ore-deposits  at  Lead- 

ville,  Colo.,  13.  18. 

Roscoe  and  Schorlemmer :  analysis  of  sea- 
water,  [195]. 
Rose,  G.:  forms  of  gold  from  precipitation, 

105. 

specific  gravities  of  gold,  106. 
Rosenbusch,     H.:      contact-metamorphic 

phenomena,  524. 

Rosita.  Colo.:  Mines  (EMMONB),  139-161. 
Rosslaud  monzonite,  Rossland,  B.  C.,  495. 
J  Rossland,  B.  C.:  pyrohotite-deposits,  486. 
Rotation  in  faulting.  102. 
Rothwell,  R.   P.:  charcoal  in  silver-bear- 
ing sandstones,  319. 
Silver  Reef  district,  Utah,  326. 
j  Rounding  of  rock-fragments:  origin,    46. 
RUMBOLD,  W.  R.:  The  South  African   Tin- 
Deposits  [Trans.,  xxxix,  783-789.],  No- 
tice. 832-833. 

The  Tin-Deposits  of  the  Kinta  Valley,  Fed- 
erated Malay    Nates    [Trans.,   xxxvii, 
879-889],  Notice,  832. 
Rupture  :  angle  of,  104. 
by  shear,  98. 
torsion al :  character,  99, 
Rupture-surfaces,      experimentally     pro- 
duced, 97. 

Russell,    Clarence :  compilation  of  analy- 
ses, 763,  765. 

Rutile :  occurrence    in   veins    of  Alaska, 
586,  587. 


INDEX. 


949 


Saline  deposits  :  formation,  115. 

Salisbury  mine,  Silver  Peak  district,  Ne- 
vada, 627. 

Salt :  in  sedimentary  rocks,  766. 

Sandberger,    F.:  derivation    of    vein-ma- 
terials, 22. 
genesis  of  ore-deposits,  14,  86,  204. 

Sandstone :  chlorine-content,  766. 

San   Jose  district,   Tamaulipas,    Mexico : 

geology,  559. 
geological  map,  560. 
ore-deposits,  237. 
situation,  559. 

San  Jose  deposits,  Tamaulipas,  Mexico  : 
map  showing  location,  558. 

San  Juan  region,  Colo.:  fissure-faulting,  50. 
gold-deposits,  818. 

Sankowsky,  Nicholas :  compilation  of  an- 
alyses, 763,  765. 

San  Pedro,  N.  M. :  ore-deposits,  [238] . 

Savant  lake,  Ontario  :    gold-deposits,  446. 

Saxony  :  Berggiesshiibel  ore-deposits,  378. 
Freiberg  :  Gottlob  vein,  218. 

Scandinavian  Iron-Ores,  The  Geological 
Relations  o/[Sj6GREN),  xxvi,  657-695. 

Scandinavian  lake-  and  bog-ores  :  distri- 
bution and  origin,  694. 

Scheerer:  amount  of  water  in  magmas, 
608. 

Schmitz,  E.  J.:  copper-ores  in  the  Per- 
mian of  Texas,  327. 

Schneider,  E.  A.:  experimental  tests  on 
colloidal  sulphides  of  gold,  [xxiv]. 

Schrader  and  Brooks:  quartz-veins  in 
Nome  region,  Alaska,  280. 

SCHWARZ,  T.  E.:  Features  of  the  Occurrence 
of  Ore  at  Red  Mountain,  Ouray  County, 
Colo.  [Trans.,  xxxvi,  31-39],  Notice,  831. 

Science  of  Ore-Deposits :  Bibliography 
(IRVING,  SMITH,  FERGUSON).  837-928. 

Scientific  method  of  study,  70. 

Scotland  :  Sutherland  gold-fields,  281. 

Secondary  concentration  :  ore-deposits,  74. 
Sudbury,  Ont.,  ore-deposits,  90. 

Secondary  enrichment :    Copper-Iron  Sul- 
phides (READ),  832. 
criteria  for  recognition,  791. 
gold-deposits,  761. 
of  metals,  785. 
ore-deposits,  326. 
sulphide  ores,  xl. 

Secular  contraction  of  earth's  crust,  42. 

Security-Geyser  mine  :  Silver  Cliff,  Colo., 
142. 

Sedimentation :  agency  in  producing 
water-channels,  33. 

Sediments  :  aggregate  thickness,  22. 

Segregation  of  igneous  rocks:  laws,  261. 

Segregation  of  rock  materials :  cause,  260. 

Selenium  :  mode  of  occurrence,  326. 
occurrence  in  Silver  Reef,  Utah,  sand- 
stones, 325. 
relations  to  igneous  rocks,  754. 

Selwyn,  A.  R.  C.:  auriferous  rocks  of  Vic- 
toria, 163. 

Se'narmont  :  synthetic  experiments.  [2]. 

Sentinel  mine,  Silver  Peak  district,  Ne- 
vada, 626. 

Serpentine  :  metamorphic  origin,  75. 

Sewell,  H.:  silver-ore  associated  with  coal, 
321. 


Shale :  oxidation,  536. 
Shaler,  N.  S.:  origin  of  limonites,  124. 
Shales :  chlorine-content,  766. 
Sheeting  of  country-rock,  46,  47. 
Shuler,   D.    P. :   magnetic    separation   of 

nickel-ores,  469. 
Siderite  :  reducing  power,  358. 
Silica  :  in  mine-waters,  770. 

quantity  in  igneous  rocks,  732. 
Silver  :  association  with  gold,  182. 

assays,  [17],  161. 

determination  of  small  amounts  in  sea- 
water,  829. 

distribution  in  igneous  rocks,  752. 

in  assays  of  California  rocks,  301. 

in  mine-waters,  800. 

in  rocks  of  New  Zealand,  170. 

in  sea-water,  191. 

native:  in  Lake  Superior  district,  76. 

precipitation  by  black  shales,  331. 

removal  by  solution,  116. 

salts:  reactions,  115. 

tests  for  :  in  rocks   at  Leadville,  Colo., 

16-17. 
Silver  City  district,   Iduho:   comparison 

with  Tonopah,  Nov.,  601. 
Silver  Cliff,   Colo.:  country-rock  :    assays 
for  silver,  161. 

investigations  of  country-rocks,  23. 

Mines  (EMMONS),  xvi,  139-161. 

mines  in  rhyolite  :    geology,  139. 

ore-deposits  :  genesis,  155. 

silver-mines :  production,  141. 

surface-deposits,  140. 

Silver  Cliff  and   Cripple  Creek  ore-depos- 
its compared,  158. 
Silver-deposits:  alteration,  131. 

association  with  eruptive  rocks,  80. 

Colorado:  Silver  Cliff  region,  157. 
Bassick  mine,  158. 
Ben  Eaton  mine,  157. 
Bull-Domingo  mine,  158. 
Democrat  mine,  157. 
genesis,  155. 
Summit  district,  [823]. 

concentration,  80. 

New  Mexico,  Lake  Valley  :  genesis,  835. 
Silver-gold  and  gold-silver  ores  :  vertical 

relations  in  deposits,  799. 
Silver-gold  deposits :  associated  minerals, 
825. 

Nevada:  Tonopah,  824, 
Silver-gold  mines    (see    also    Gold-silver 
mines) : 

Mizpah,  Tonopah,  Nev.,  [825]. 

Montana-Tonopah,      Tonapah,      Nev., 

[825]. 

Silver-gold  ores  :  Comstock  lode,  Nev.,  800. 
Silver-Islet  mine,  Lake  Superior,  231. 

gas-flows,  346. 

Silver-lead   deposits  :    Colorado :   George- 
town and  Silver  Plume,  816. 

in  dolomitic  limestone,  1. 
Silver-lead-gold  deposits:  Leadville,  Colo., 

815. 
Silver-lead    mines,   Neihart,  Mont.,    219, 

220. 
Silver     Ledge,    Mercur    district,     Utah: 

origin,  290. 
Silver-mine  :  Mexico,  Durango  (Promon- 

torio),  834. 


950 


INDEX. 


Silver-mine  waters  :  salts  in,  764. 

Silver-ore:  Leadville,  Colo.,  800. 

Mineral   ridge,    Nevada :  genetic  rela- 
tions, 613. 
mode  of  occurrence,  Silver  Cliff,   Colo., 

140. 

Neibart,  Mont.,  800. 
Silver  Cliff,  Colo.:  treatment,  141. 

Silver-ores  of  West :  origin,  136. 

Silver   Peak,   Nevada :  geology  and  ore- 
deposits,  622, 
gold-deposits,  813. 
ore  deposits :  origin,  628. 
Quartz-Veins  (HASTINGS),  xxvi, 621-628. 

Silver  Peak   quadrangle,    Nevada :  geol- 
ogy, 603. 
mineral  veins,  607.     • 

Silver  Eeef  ore-deposits,  36. 

Silver-salts  :  solubilities,  800. 

Silver-veins,  Butte,  Mont.,  223, 

Silvestri,  O.:  copper  in  volcanic  fumes, 
721. 

Similkameen  type  of  ore-deposits,  383. 

Sinter  :  analyses,  149,  629. 

Sinters:  Geyser  mine,  Silver  Cliff,  Colo., 
148. 

Sjogren,  A.:  iron -ores  of  Taberg,  Sma- 
land,  681. 

SJOGREN,  HJALMAE:  The  Geological  Re- 
lations of  the  Scandinavian  Iron-Ores, 
jxxvi,  657-695. 

Skarn :  definition,  657. 

Skolar  :  formation,  669. 

"Slickenside"-surfaces  :  fissures,  45. 

Slickensiding:  in  joints,  93. 

Smith,  Alexander  :  chemical  reactions  in 

solution  of  gold,  [777]. 
chemistry  of  manganese,  780. 

SMITH,  H.  D.,  IRVING,  J.  D.,  FERGUSON, 
H.  G. :  Bibliography  of  the  Science  of  Ore- 
Deposits,  837-928. 

SMITH,  GEORGE:  The  Garnet  Formations 
of  Chillagoe  Copper-Field,  North  Queens- 
land, Australia  [Trans.,  xxxiv,  467-478], 
Notice,  830. 

Smith,  J.  Alden  :  deposition  of  ores  by 
ascending  solutions,  12. 

Smyth,  R.  Brough :  gold-fields  of  Vic- 
toria, 171. 

Soda:  quantity  in  igneous  rocks,  732. 

Soda  mine,  Silver  Peak  district,  Nevada, 
627. 

Solfataras  :  source  of  ores,  84. 

Solution  chambers  :  formation,  5. 

Solutions:  role  in  ore-deposition,  2. 

Some  Practical  Suggestions  Concerning  the 
Genesis  of  Ore-Deposits  (BOEHMER),  829- 
830. 

Songbird  mine;  Silver  Cliff,  Colo.,  [140]. 

Sonstadt,  E.:  gold  in  sea- water,  192. 
methods  of  detecting  gold  in  sea-water, 
193. 

Sonstadt's  solution  :  disadvantages,  166. 

Soret's  principle  of  cooling  solution,  67. 

Soret's  principle  of  molecular  flow,  260. 

South  African  Tin-Deposits  (EUMBOLD), 
832-833. 

Southern  Klondike  district,  Nevada,  ore- 
deposits,  618. 

Spaltenverwerfungen  (fissure-faults)  -.def- 
inition, 41. 


SPENCER,  A.  C.:  Geology  of  the  Treadwell 
Ore-Deposits,  Treadwell  Island,  Alaska 
[Trans.,  xxxv,  473-510],  Notice.  830. 
The  Magmatic  Origin  of  Vein-Forming 
Waters  in  Southeastern  Alaska,  xxvi, 
582-589. 

The  Origin    of    Vein-Filled   Openings  in 
Southeastern    Alaska    [Trans.,   xxxvi, 
581-586],  Notice,  831. 
Treadwell  gold-mines,  Alaska,  [811]. 
Sperrylite:  in  diorite,  90. 

Sudbury  district,  Ontario,  463. 
Spherulites  :  Silver  Cliff,  Colo.,  140. 
Spring  waters :  analyses,  706. 
Springs  :  Nevada  region  :  source,  597. 

production,  33. 

SPURR,   J.   E.:  A   Consideration  of  Igneous 
Rocks  and  their  Segregation  or  Differen- 
tiation as  Related   to   the  Occurrence  of 
Ores,  xxii,  251-303. 
Genetic  Relations  of  the  Western  Nevada 

Ores,  xxvi,  590-620. 
convection  currents  in  magmas,  260. 
differentiation  in  igneous  rocks,  261. 
gold-deposits,  Silver  Peak,  Nov.,  [813]. 
magmatic  differentiation,  722. 
metallographic  provinces,  756. 
ore-deposits  of  Silver  Peak  quadrangle, 

621. 

silver-gold  deposits,  Tonopah,  [824]. 
Spurr  and  Garrey  :  ore-deposits  of  George- 
town, Colo.,  8i6,  817. 

Spurr,  Garrey,  and  Ball :  silver-lead  depos- 
its, Georgetown  and  Silver  Plume,  Colo., 
[816]. 

Stallberg  mines,  Sweden  :  plan,  664. 
Standard  mine,  Bodie,  Cal.:  vein-system, 

833. 

Steamboat  Springs,  Nevada  :    ore-deposi- 
tion, 86. 
stibnite  at,  629. 

Stelzner:  origin  of  ore-deposits,  [201]. 
Step-faults,  Leadville,  Colo.,  49. 
Sternbeck,    E.    von :    specific    gravity  of 

earth,  715. 

Stetefeldite,  Mineral  ridge,  Nevada,  614. 
STEVENS,  E.  A.:  Basaltic  Zones  as   Guides 
to  Ore-Deposits  in  the  Cripple  Creek  Dis- 
trict, Colorado,  xxiii,  411-423. 
Stevens,  Hazard  :  ascent   of  Mt.  Eainier, 

[xxxiii]. 
Stibnite  :  at  Steamboat  Springs,    Nevada, 

629,  631. 

reducing  power,  354,  358. 
Stobie  mine,  Blezard  township,  Sudbury 

district,  Ontario,  499. 
photomicrographs  of  ore,  487-488. 
Stokes,  H.  N.:  action  of  pyrite  and  mar- 

casite,  409. 
reaction   with    pyrite  in  production  of 

chalcocite,  799. 
solution  of  gold,  771,  772. 
Stratification  :  agency  in  producing  water- 
channels,  33. 

Stretch,  E.  H.  :  "compression-veins,"  221. 
mineral-veins   varying   with    country- 
rock,  225. 

vein-contents  and  country-rock,  233. 
Striations  :  fissures,  45. 
Stringers:  definition,  51. 
Strong  mine,  Cripple  Creek,  Colo.,  419. 


INDEX. 


951 


Strontium  :  distribution  in  igneous  rocks,  ] 
747. 

quantity  in  igneous  rocks,  733. 
Stutzer,  O.:  genesis   of  iron-ores   of  Nor- ! 

botten,  Sweden,  678. 

Styria :  iron-deposits:  surface-action,  126. 
Sublimation   theory  of  ore-deposition,  2, 

204. 

Substitution  theory:  ore-deposits,  8. 
Subterranean  water  :  limiting  depth,  44.    j 
Subterranean   waters  :  Geyser  mine,    Sil- 1 

ver  Cliff,  Colo.,  148. 
Sudbury  district,  Ontario :  metamorphism, 

514. 

Sudbury,  Ontario,  nickel-region  :    miner- 1 
als,  456. 

nickel-deposits,  90-91. 
geology,  479,  481. 

nickel-ores :  genesis,  477. 

Ore-Deposits  (DiCKSON),  xxiv-xxv,  455- 

516. 

Sudbury  mattes:  composition,  465. 
Sudbury  ores:  assays,  464. 

origin  :  microscopical  evidence,  497. 
Suess,    Eduard :      formation    of  mineral  ! 
veins  by  gaseous  emanations,  389. 

gold  resources  of  the  world,  425. 

hot  springs  of  Carlsbad  region,  369. 

ore-deposits  derived  from  igneous  ema- 
nations, [368]. 

origin  of  ore-deposits,  391. 
Sullivan,  E.  C.:  chemical  relations  of  iron 
and  manganese  in  rocks,  795. 

experimentation     on    copper-iron    sul- 
phides, 832. 

Sulphates  :   effect  on  solution  of  gold,  772, 
775. 

in  mine-waters,  766. 

solution  and  precipitation  of  mangan- 
ese by,  795. 

Sulphide  secondary  enrichment :   ore-de- 
posits, xvii. 
Sulphides  :  alteration,  2. 

deep :  formation,  183, 

in  rocks,  163. 

secondary:  definition,  183. 
Sulphur:  distribution  in  igneous  rocks,  750. 

quantity  in  igneous  rocks,  734. 

reducing  power,  307,  351,  357. 
Sulphuretted  hydrogen:  reducing  power, 

352,  357. 
Summary  of    Lake   Superior    Geology  with 

Special   Reference  to  Recent  Studies  of  the 

Iron-Bearing  Series  (LEITH),  xxvi,  633- 

656. 

Summit  district,  Colo.:  gold-deposits,  822. 
Summit  gold-mine,  Cripple  Greek,  Colo., 

[819]. 
Sunrise    gold-mine,     Macetown,    1ST.    Z.: 

assays,  184. 

Sunrise  mine:  Silver  Cliff,  Colo.,  [140]. 
Superficial  Alteration  of  Ore-Deposits  (PflN- 

KOSE),  xv. 

Surface-alteration  :  varying  depths,  121. 
Surface-waters  :  definition,  6. 

varying  action  on  ore-deposits,  116. 
Sutro,  A.:  genesis  of  Conistock  lode,  x. 
Svartvik  mines,  Sweden  :  section,  665. 
Sweden  :  map  of  ore-province,  658. 

titaniferous  iron-ore :  concentration  in 
magmas,  72. 


Swedish  iron-deposits  :  lake  region  :  con- 
centration, 127. 

Syenite  :  in  Norbotten  ore-fields,  675. 
treatment  for  isolation   of  hornblende, 
165. 

Synclases :  definition,  40. 

Taberg,  Sweden,  iron-district:  map,  683. 
Taberg   mines,   Sweden:    origin   of  iron- 
ores,  668. 

Telluride  type  of  ore-deposits,  372. 
Tellurium :    relations    to  igneous    rocks.. 
754. 

reducing  power,  358. 
Temperature:  increase  with  depth,  246. 

of  descending  column  of  water,  245. 

of  fluid  magmas,  724. 

rate  of  increase  in  earth's  crust,  713. 
Ten-Mile  district,  Colo.:  investigations  of 
country-rocks,  23. 

ore-deposits,  36. 
Tephrite :    Cripple  Creek   district,   Colo.: 

412. 

Tertiary  gold-deposits,  438-441. 
Tertiary  volcanic  rocks,  Tonopah,    Nev., 

591. 

Tetrahedrite  :  reducing  power,  358. 
Thames  district,  N.  Z. :  vadose  and  deep 

vein-gold :  assays,  185. 
Thermal  springs  :  ore-deposition,  406. 
Thompson   mine,    Cripple    Creek,    Colo., 

420. 

Thomsen,  J.:  chemical  properties  of  gold, 
107. 

forms  of  gold  from  precipitation,  105. 
Thorium  :   distribution  in  igneous  rocks, 

749. 

Thunder  Bay,  Canada,  silver- veins,  231. 
Tibbey,   B.:  hydrocarbon -gas   in    Illinois 

mine,  Montana,  346. 
Tiberg,  H.  V.,  iron-ores  of  Sweden,   665, 

669. 

Time  in  geologic  operations,  700. 
Tin  :  distribution  in  igneous  rocks,  753. 

in  siliceous  rocks,  285. 
Tin  chloride  test  for  gold,  194. 
Tin-deposits :    Alaska,    Cape     Prince    of 
Wales  :  geology  and  mining,  833. 

alteration,  133-134. 

Kinta    Valley,    Federated    Malay    States 

(EUMBOLD),  832. 

South  African,  832. 
Tin-veins :  occurrence,  287. 
Tiuguaite :  San  Jose,  Tamaulipas,  Mexico, 

565. 
Tipperary  Premier  gold-mine,  Macetown, 

N.  Z.:  assays,  184. 

Titaniferous    iron-ore :  concentration    in 
magmas,  72. 

Norway,  72. 

Sweden,  72. 
Titanium  :  distribution  in  igneous  rocks, 

749. 
Titanium   dioxide  :  quantity   in  igneous 

rocks,  733. 

Tomboy  gold-mine,  Silverton,  Colo.,  [818]. 
Tonopah,  Nevada:  geology,  591. 

mineral  veins,  593. 

silver-gold  deposits,  824. 
Topography  :  effect    on  depth  of   altera- 
tion, 120. 


952 


INDEX. 


Tornado  mine,  Cripple  Creek,  Colo.,  420. 
Tornebohm  :    iron-ores  of  Taberg,   Sma- 

land,  681. 
Torsion :  effects,  51. 

experiments  on  glass  plates,  95 

of  rock-masses,  45. 
Torsion-fractures  :  character,  95. 
Torsional  rupture :  character,  99. 
Torsional  Theory  of  Joints  (BECKER),  xiii, 

92-104. 

Tourmaline  :  occurrence  in  ores,  586. 
Toyabe  range,  Nevada:   ore-deposits,  617. 
Travers,  M.  W.:  origin  of  gas  in  mineral 

substances,  389. 
Tread  well     gold -silver     mine,     Douglas 

Island,  Alaska,  811, 
Treadwell   ore-deposits :  Alaska,  Douglas 

Island,  830. 
Tremolite  :  San  Jose,  Tamaulipas,  Mexico, 

569. 

Triumph  mine,  Cripple  Creek,  Colo.,  419. 
Tungsten  in  siliceous  rocks,  285. 
Tuollavaara  iron-ore   deposits :    Sweden, 

673. 

Turner,  A.  T. :  Sudbury  mattes,  465. 
Turner,  H.  W.:  field-work  in  Silver  Peak 
region,  Nevada,  604. 

quartz-veins  at  Silver  Peak,    Nevada, 
276. 

Ulrich,  G.  H.  F.:  auriferous  rocks  of  Vic- 
toria, 283. 

rocks  of  Otago  peninsula,  N.  Z.,  166. 
Uncle  Sam   mine,   Tintic  district,  Utah, 

339,  340,  343. 

Underground   water :  agency   in    forma- 
tion of  Lake   Superior  iron-ores,  644. 

circulation  :  factors,  237. 

derivation,  236. 

direction  of  flow,  14. 
Union  Belle  mine,  Cripple   Creek,  Colo., 

420. 

United  States  Geological  Survey  :  found- 
ing, [xxxiii]. 
Urals :  relations  of  gold    and    platinum, 

289. 
Uranium  :    distribution  in  igneous  rocks, 

749, 
Utah,  Dry  Canon,  Mono  silver-mine,  332. 

Mercur  district:  gold-production,  437. 
vein  system,  290. 

Silver  Eeef :  geologic  structure,  325. 
ore-deposits,  322. 
silver-ore  in  sandstone,  320. 

Tintic  district  ore-deposits,  335-340, 362. 

Vadose  country-rock  at  different  distances 
from  auriferous  lodes :  examination,  183. 

Vadose  region  :  greater  richness  of  gold- 
deposits,  171. 

Vadose  waters,  xiv. 

Valcalde    mines,    Silver     Peak    district, 

*    Nevada,  626. 

Vanadium  :  association  with  coal,  321. 
distribution  in  igneous  rocks,  750. 
in  basic  rocks,  285. 

Vanderbilt  mine,    Mineral    Eidge,  Nev., 
613. 

Vanderbilt  mine  :  Silver  Cliff,  Colo.,  [140]. 

Van  Diest,   E.   C.   and   P.   H.:  Eito  Seco 
gold-deposits,  Costilla  county,  Colo.,  447. 


Van  Hise,  C.  E.:  classification   of  Algon- 
kian  rocks,  69. 

critical  temperature  of  water,  713. 

development  of  rocks  of  Lake  Superior 
region,  648. 

fissures  at  Cripple  Creek,  Colo.,  221. 

formation    of    secondary     copper    sul- 
phides, 533. 

genesis  of  ore-deposits,  [252]. 

iron-ores :  origin,  70. 

magnetite  in  magmas,  72. 

meteoric  waters,  240. 

origin  of    iron-ores   of   Michigan   and 
Wisconsin,  124. 

origin  of  pegmatite,  275. 

principles  of  ore-deposition,  xvii,  [235], 
696,  [761]. 

zone  of  flowage,  699,  711. 

zone  of  fracture,  711. 
Veins:  comb-structure,  10. 

dependence  on  rock-structure,  217. 

derivation  of  mineral  contents,  14. 

frequency,  248. 

productive  :  explanation,  718. 

relation  to  trap  rocks,  20. 

view   of  older  geologists   as    to    their 

nature,  84. 
Vein-enrichment :       by      Ascending     Hot 

Waters  (WEED),  xxiii,  403-410. 
Vein-fissure  :  Ontario  mine,  Utah,  61. 
Vein-material :  source,  53,  161. 
Vein-materials:  derivation  from   adjoin- 
ing rocks,  22-24. 

derivation  from  eruptive  rocks,  19-22. 

Leadville,  Colo.:  source,  16. 
Vein -structure:  influence  of  rocks.  217. 
Vein-system  :  Cornwall,  England,  [52]. 

Erzgebirge,  Freiberg,  Saxony,  52. 

Standard  Mine,  Bodie,  Gal.  (BROWN),  833. 
Vein-systems  :  age  and  relations,  290. 
Vein-walls:  structural  features,  54. 

Butte,  Mont.,  55. 

Gunnison  region,  Colo.,  55. 
Vermilion   Creek  Basin,  Wyoming :   dia- 
mond swindle,  [xxxiii]. 
Vermilion  iron  range:  vertical  section,  640. 
Vermilion  Eiver,  Ontario  :   gold-deposits, 

445. 
Vesuvianite :     San      Jose,      Tamaulipas, 

Mexico,  572. 

Victor  mine,  Cripple  Creek,  Colo.,  423. 
Victoria :  gold-quartz  veins,  282. 
Victoria  mine,  Deuison  Township,Sudbury 
district,  Ontario,  505. 

photomicrographs  of  ore,  490. 
Vindicator  mine,  Cripple  Creek,  Colo.,  422. 
Virginia :  .Virgilina  :  copper-veins,  220. 
Vogelsang,    H.:    petrographic    provinces, 

737. 
Vogesite  :  San  Jose,  Tamaulipas,  Mexico, 

567. 
Vogt,  J.  H.  L.:  chromite  in  Norway,  [268]. 

contact-metamorphic  phenomena,  525. 

distribution  of  rare  elements,  745. 

genesis  of  ore-deposits,  [253],  403. 

genesis   of  titaniferous  iron-deposits  of 
Sweden,  xiii. 

geology  of  ore-deposits,  [222]. 

iron-ores  of  Christiania  region,  692. 

nickel  in  basic  rocks,  295. 

origin  of  nickel-ores,  484. 


INDEX. 


953 


Vogt,  J.  H.  L.:  rare  chemical  elements,  737. 

secondary  enrichment,  xxxix. 

source  of  iron,  205. 

titauiferous  iron-ores  of  Norway,  [111]. 
Volcanic  eruptions  :  sequence  in  connec- 
tion   with    sequence    of    metalliferous 

veins,  288. 

Volcanic  gas  :  analysis,  388. 
Vorn  Rath  :  Elha  iron-ores,  8. 
Von  Foullon  :  Sudbury  nickel-ores,  482. 
Vrang,  C.  H.:  iron-ores  of  Sweden,  665. 
Vulcauism  :  expiring:  cause  of  ore  bodies 
721. 

relation  to  ore-deposits,  239. 

vein  forming  by,  704. 


WAGONER.  LUTHER:  The  Detection  and 
Estimation  of  Small  Quantities  of  Gold 
and  Silver  [Trans,  xxxi,  798-810], 
Notice,  829. 

assays  of  California  rocks,  301. 
petroleum  associated  with  quicksilver, 

344. 
Walferdin  :  temperatures  in  earth's  crust, 

714. 
Walhalla,   Victoria,    gold-bearing    rocks: 

analyses,  186. 
gold  in  country-rock  :   curves  showing, 

192,  193. 

vadose  country-rock  :  analyses,  186. 
Walker,  T.  L. :  sperrylite  associated  with 

chalcopyrite,  463. 
Sudbury  nickel-ores,  484. 
Wallace     mine,    near    Whitefish    River,  ! 

Ontario,  508. 

Wall-pyrite :  origin  and  content,  207,  214.  j 
Wall-rocks:  permeability  to  solutions,  207. 
Walls  (see  Vein-walls). 
WASHINGTON,  H.  S.:  The  Distribution  of  j 
the  Elements  in  Igneous  Rocks,  xxviii, 
726-758. 

analysis  of  analcite-tinguaite,  566. 
analysis  of  nephelite-syenite,  562. 
Washoe,  Nev.:  investigations  of  country- 
rocks,  23. 

Water  (see  also  Mine- waters) : 
agency  in  producing  breccia,  47. 
amount  in  magmas,  608. 
analysis,  630. 
compression,  244. 
descending  :  temperature,  245. 
films  :  action  in  joints,  93. 
Geyser      mine,      Silver     Cliff,      Colo.: 

analyses,  150. 
in  igneous  rocks,  262. 
ingredients,  113. 
movement  in  porphyry,  13. 
oxidizing  agents  lost  in  descending,  6. 
quantity  in  crystalline  rocks,  733. 
role  in  magmas,  731. 
stability,  314. 
underground  :  direction  of  flow,  14. 

limiting' depth,  44. 
velocity  moving    through    a    channel, 

450. 

Water-channels:  in  eruptive  rocks,  33. 
locus  at  Leadville,  Colo.,  13. 
natural :  causes,  33. 
Water-courses  :  Geyser  mine,  Silver  Cliff,  j 

Colo.,  147. 
"Water-level"  :  locus,  6. 

60 


Waters,  ascending,  85. 

circulating  in  earth's  crust :    channels 

for,  30. 

deep  -seated,  xiv. 
in  mines:  analyses,  765,  [779]. 
salts  in,  764. 

silver-  and  gold-content,  [800]. 
natural,  chlorine-content,  767. 
vadose,  xiv. 

Water-table  :  definition  and  characteriza- 
tion, 788. 

relation  to  chemical  activity,  788. 
seasonal  variation,  788. 
WATSON,   T.   L.:  Geology   of  the     Virginia 
Barite- Deposits  [Trans.,  xxxviii,  710- 
733],  Notice,  834. 

Lead-  and  Zinc-Deposits  of  the  Virginia- 
Tennessee  Region  [Trans.,  xxxvi,  681- 
737],  Notice,  831-832. 
The    Occurrence   of   Nickel    in    Virginia 
[Trans.,  xxxviii,  683-697],  Notice,  834. 
Yellow  Ocher  Deposits  of  Cartersville  Dis- 
trict,   Bartow     County,     Ga.     [Trans., 
xxxiv,  643-666],  Notice,  830. 
Wells:  temperatures  in,  714. 
Wells,  R.  C.:  reactions  in  dissolving  gold, 

777. 

reactions  of  manganese  compounds,  785. 
services  rendered  by,  764. 
WEED,   W.  H.:  Influence  of  Country-Roclc 

on  Mineral  Veins,  xxi,  216-234. 
Ore- Deposition   and    Vein- Enrichment   by 
•  Ascending  Hot   Waters,  xxiii,  403-410. 
Ore-Deposits  Near  Igneous  Contacts,  xxiii, 

364-402. 
Enrichment  of  Gold  and  Silver  Veins, 

xviii. 

form  of  contact-deposits,  528. 
mineral    vein-formation     at     Boulder 

Hot  Springs,  Montana,  [247]. 
minerals  of  secondary  origin,  [792]. 
secondary      enrichment    of   gold    and 

silver  veins,  [761],  [815]. 
Weed    and     Barrell :    Elkhorn 

Mont.,  ore-deposits,  [239]. 
Weidman,    S.:    origin    of  Baraboo   iron- 
ores,  651,  652. 
White,  David  :  plant-remains  in  Missouri, 

[329]. 
White     Knob     Copper    Deposits,     Mackay, 

Idaho  (KEMP  and  GUNTHER),  833. 
Whitney,    J.    D.:  locus    of  metalliferous 

veins,  280. 
ore-genesis,  [viii]. 
The    Metallic    Wealth    of  the   United 

States,  [110]. 

Williams,  G.  H. :  origin  of  pegmatite,  275. 
Wilson,    A.    D.:  ascent    of  Mt.    Rainier, 

[xxxiii]. 

WINCHELL,  A.  N.:  Discussion  on  A  Consid- 
eration of  Igneous  Rocks  and  their  Segre- 
gation or  Differentiation  as  Related  to  the 
Occurrence  of  Ores,  303-304. 
Winchell,  H.  V.:  genesis   of  chalcocite  at 

Butte,  [761]. 

genesis  of  copper-ores,  402. 
origin  of  iron-deposits  of  Mesabi  range, 

Minn.,  125. 

pyrite  as  a  precipitant,  232. 
synthesis  of  chalcocite,  533. 
Thunder  Bay  silver-veins,  231. 


district, 


954 


INDEX. 


WINSLOW,  ARTHUR  :   Discussion  on  Geolo- 
gical  Distribution  of  Useful   Metals  in 
the  United  States,  86-89. 
Discussion  on    The    Genesis    of    Certain 

Auriferous  Lodes,  208,  211. 
lead-  and  zinc-deposits  of  Missouri, [209], 
Wisconsin  lead-ores,  334. 
Wolf,  T.:  volcanic  gases,  723. 
Wollastouite :  contorted  zones,  Durango, 

Mexico,  578. 

San  Jose,  Tamaulipas,  Mexico,  570. 
Wood  lying  under  sea- water :  examination 

for  gold,  197. 
Worthington     mine,     Drury     township, 

Sudbury  district,  Ontario,  505. 
photographs  of  sections  of  ore,  493. 
Wurtz,    Henry:    solubility    of   gold     in 
ferric  salts,  173. 

Yankee  Girl  mine,  San  Juan  region, 
Colo.,  example  of  chimney-deposits, 
58,  59. 

occurrence  of  ore,  831. 
Yellow      Ocher     Deposits     of     Cartersville 
District,  Bartow  County,    Ga.  (WATSON). 
830. 

Yttrium  :  distribution   in   igneous  rocks, 
749. 


Yukon:    gold-quartz    veins:     formation, 

272. 
Yung  and  McCaffery :  ore-deposits  of  San 

Pedro  district  [577]. 

Zenobia  mine,  Cripple  Creek,  Colo.,  422. 
Zinc:  distribution  in  igneous  rocks,  753. 
Zinc-blende:  effect  of  py  rite  on  solubility, 
[766]. 

in  Geyser  mine,  Silver  Cliff,  Colo.,  146. 
Zinc-deposits :  alteration,  131-132. 
Zinc:  distribution  in  igneous  rocks,  753. 

genesis,  77-79. 

source  of  material,  77. 

Virginia-Tennessee  region,  831. 
Zircon :    crystallization    from      magmas, 

609. 

Zirconium  :  distribution  in  igneous  rocks, 
749. 

quantity  in  igneous  rocks,  733. 
Zirkel,  F.:  contact-metamorphic  phenom- 
ena, 525. 

Zone  of  cementation,  241. 
Zone  of  flowage  :  effect  on  open  channels, 

699. 
Zones  in  ore-deposits,  789. 


/"*V        "  ,          Wv;  .W-    £# 

-^^^^%fc. 


. 


^   i;v'vV 


vW   vwvv 


VwV  «: 


'v'^v*-uv 


u 
v 


YD  07535 


307422 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


' 


